Special variables: Difference between revisions

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{{task|Basic language learning}}[[Category:Special variables]]
{{task|Basic language learning}}[[Category:Special variables]]


Special variables have a predefined meaning within a computer programming language.
Special variables have a predefined meaning within a computer programming language.




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List the special variables used within the language.
List the special variables used within the language.
<br><br>
<br><br>
=={{header|11l}}==
Refer to [https://11l-lang.org/doc/built-in-global-vars Built-in global variables] for the complete special variables (those variables are global).

=={{header|6502 Assembly}}==
The first 256 bytes of the CPU's address space are collectively known as "zero page RAM" and are common to all 6502 computers (except the custom 6502-based Hu6280 used in the PC Engine/TurboGrafx16.) This section of RAM is faster to load from, as the instructions that use it only take one byte to represent the memory address rather than two. On some implementations, certain zero-page RAM addresses are special, such as address $00 on Commodore 64 (which controls the memory management unit) and address $FF on Easy6502 (which contains the last keyboard input). In addition to loading faster, only the zero page can used indexed indirect addressing modes (the only exception being <code>JMP</code>, which CANNOT jump indirectly using zero page unless you pad it with a high byte of 00.)

The 16-bit 65816 and the Motorola 6809 (which are very similar to the 6502) call the zero page the "direct page" because it can be relocated on those systems. They have a dedicated register which tells the CPU where the direct page actually is. Like on the 6502, it's only 256 bytes in size. This allows the programmer to improve their program's performance by moving the direct page to wherever the majority of the loading will be taking place. Your code may cause problems if you load from the "wrong" direct page, however, so be careful!


=={{header|Ada}}==
=={{header|Ada}}==
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There are far too many attributes to list here, but a standard informative list can be found in Annex K of the documentation if you have it installed.
There are far too many attributes to list here, but a standard informative list can be found in Annex K of the documentation if you have it installed.
Or Here: [http://www2.adacore.com/gap-static/GNAT_Book/html/aarm/AA-K.html Annex K - Language-Defined Attributes]
Or Here: [http://www2.adacore.com/gap-static/GNAT_Book/html/aarm/AA-K.html Annex K - Language-Defined Attributes]

=={{header|AutoHotkey}}==
Refer to [http://www.autohotkey.com/docs/Variables.htm#BuiltIn Built-in Variables] for the complete special variables (those variables are global, except noticed).


=={{header|ALGOL 68}}==
=={{header|ALGOL 68}}==
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{{works with|ALGOL 68G|Any - tested with release [http://sourceforge.net/projects/algol68/files/algol68g/algol68g-1.18.0/algol68g-1.18.0-9h.tiny.el5.centos.fc11.i386.rpm/download 1.18.0-9h.tiny].}}
{{works with|ALGOL 68G|Any - tested with release [http://sourceforge.net/projects/algol68/files/algol68g/algol68g-1.18.0/algol68g-1.18.0-9h.tiny.el5.centos.fc11.i386.rpm/download 1.18.0-9h.tiny].}}
{{wont work with|ELLA ALGOL 68|Any (with appropriate job cards) - tested with release [http://sourceforge.net/projects/algol68/files/algol68toc/algol68toc-1.8.8d/algol68toc-1.8-8d.fc9.i386.rpm/download 1.8-8d] - due to extensive use of '''format'''[ted] ''transput''.}}
{{wont work with|ELLA ALGOL 68|Any (with appropriate job cards) - tested with release [http://sourceforge.net/projects/algol68/files/algol68toc/algol68toc-1.8.8d/algol68toc-1.8-8d.fc9.i386.rpm/download 1.8-8d] - due to extensive use of '''format'''[ted] ''transput''.}}
<lang algol68>#!/usr/local/bin/a68g --script #
<syntaxhighlight lang="algol68">#!/usr/local/bin/a68g --script #


FORMAT f = $g": ["g"]"l$;
FORMAT f = $g": ["g"]"l$;
Line 82: Line 86:
END CO
END CO
));
));
SKIP</lang>
SKIP</syntaxhighlight>
Sample output:
Sample output:
<pre>
<pre>
Line 115: Line 119:
]
]
</pre>
</pre>

===[[ALGOL 68G]]===
===[[ALGOL 68G]]===
{{wont work with|ALGOL 68|Revision 1 - too many extensions to language used, but constants can be defined in a custom prelude.}}
{{wont work with|ALGOL 68|Revision 1 - too many extensions to language used, but constants can be defined in a custom prelude.}}
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{{wont work with|ELLA ALGOL 68|Any (with appropriate job cards) - tested with release [http://sourceforge.net/projects/algol68/files/algol68toc/algol68toc-1.8.8d/algol68toc-1.8-8d.fc9.i386.rpm/download 1.8-8d] - due to extensive use of '''format'''[ted] ''transput''.}}
{{wont work with|ELLA ALGOL 68|Any (with appropriate job cards) - tested with release [http://sourceforge.net/projects/algol68/files/algol68toc/algol68toc-1.8.8d/algol68toc-1.8-8d.fc9.i386.rpm/download 1.8-8d] - due to extensive use of '''format'''[ted] ''transput''.}}
[[ALGOL 68G]] provides some further constants to the scientifically motivated coder:
[[ALGOL 68G]] provides some further constants to the scientifically motivated coder:
<lang algol68>#!/usr/local/bin/a68g --script #
<syntaxhighlight lang="algol68">#!/usr/local/bin/a68g --script #


printf(($g": [", g, "] & [",g,"]"l$,
printf(($g": [", g, "] & [",g,"]"l$,
Line 234: Line 239:
" joule", mksa joule, cgs joule,
" joule", mksa joule, cgs joule,
" erg", mksa erg, cgs erg
" erg", mksa erg, cgs erg
))</lang>
))</syntaxhighlight>
Output:
Output:
<pre>
<pre>
Line 351: Line 356:


=={{header|ALGOL W}}==
=={{header|ALGOL W}}==
<lang algolw>% the Algol W standard environment includes the following standard variables: %
<syntaxhighlight lang="algolw">% the Algol W standard environment includes the following standard variables: %


integer I_W % field width for integer output %
integer I_W % field width for integer output %
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if the relevant EXCEPTION variable is null, the exception is ignored,
if the relevant EXCEPTION variable is null, the exception is ignored,
otherwise it is processed according to the settings of XCPLIMIT etc.
otherwise it is processed according to the settings of XCPLIMIT etc.
%</lang>
%</syntaxhighlight>

=={{header|Arturo}}==

There are no "special" variables in Arturo, as such. There are pre-defined, built-in functions & constants but every symbol can be re-defined at will, even during runtime.

=={{header|AutoHotkey}}==
Refer to [http://www.autohotkey.com/docs/Variables.htm#BuiltIn Built-in Variables] for the complete special variables (those variables are global, except noticed).


=={{header|AWK}}==
=={{header|AWK}}==
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* RSTART - An informative variable that provides the start index of the currently matched substring
* RSTART - An informative variable that provides the start index of the currently matched substring
* SUBSEP - A control variable that specifies the subscript separator for multidimensional arrays
* SUBSEP - A control variable that specifies the subscript separator for multidimensional arrays

=={{header|Batch File}}==
By typing the <code>SET</code> command (without any parameters) in the command prompt, it will display the current environment variables and their current values.<br>
However, there are some special variables that are not listed in the variables displayed by the SET command because their values might change over time. These variables are as follows:<br>
<pre>%CD% - expands to the current directory string.

%DATE% - expands to current date using same format as DATE command.

%TIME% - expands to current time using same format as TIME command.

%RANDOM% - expands to a random decimal number between 0 and 32767.

%ERRORLEVEL% - expands to the current ERRORLEVEL value

%CMDEXTVERSION% - expands to the current Command Processor Extensions
version number.

%CMDCMDLINE% - expands to the original command line that invoked the
Command Processor.

%HIGHESTNUMANODENUMBER% - expands to the highest NUMA node number
on this machine.</pre>
(Source: by typing <code>SET/?</code> command in the command prompt)


=={{header|BBC BASIC}}==
=={{header|BBC BASIC}}==
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@wparam% The WPARAM value (for use with ON MOUSE, ON MOVE and ON SYS)
@wparam% The WPARAM value (for use with ON MOUSE, ON MOVE and ON SYS)
</pre>
</pre>

=={{header|Batch File}}==
By typing the <code>SET</code> command (without any parameters) in the command prompt, it will display the current environment variables and their current values.<br>
However, there are some special variables that are not listed in the variables displayed by the SET command because their values might change over time. These variables are as follows:<br>
<pre>%CD% - expands to the current directory string.

%DATE% - expands to current date using same format as DATE command.

%TIME% - expands to current time using same format as TIME command.

%RANDOM% - expands to a random decimal number between 0 and 32767.

%ERRORLEVEL% - expands to the current ERRORLEVEL value

%CMDEXTVERSION% - expands to the current Command Processor Extensions
version number.

%CMDCMDLINE% - expands to the original command line that invoked the
Command Processor.

%HIGHESTNUMANODENUMBER% - expands to the highest NUMA node number
on this machine.</pre>
(Source: by typing <code>SET/?</code> command in the command prompt)


=={{header|bc}}==
=={{header|bc}}==
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The names of the built-in functions <code>alc, arg, asc, chr, chu, clk, d2x, dbg, den, div, fil, flg, glf, fre, get, low, lst, mem, mod, new, pee, pok, put, ren, rev, rmv, sim, str, swi, sys, tbl, upp, utf, whl, x2d</code> can be used as variable names or names of user defined object member functions, but not as names of user defined functions. Conversely, the name <code>hash</code> can be used for user defined functions, but not for variables. Currentlty, <code>hash</code> is the only predefined object type.
The names of the built-in functions <code>alc, arg, asc, chr, chu, clk, d2x, dbg, den, div, fil, flg, glf, fre, get, low, lst, mem, mod, new, pee, pok, put, ren, rev, rmv, sim, str, swi, sys, tbl, upp, utf, whl, x2d</code> can be used as variable names or names of user defined object member functions, but not as names of user defined functions. Conversely, the name <code>hash</code> can be used for user defined functions, but not for variables. Currentlty, <code>hash</code> is the only predefined object type.


If Bracmat starts in interactive mode, a few more variables are predefined: <code>!v</code> evaluates to a string telling which version of Bracmat you are running. <code>!w</code> and <code>!c</code> evaluate to sections 11 and 12 of the GPL. More vital is the variable <code>main</code>, which is the interpreter's main loop. Setting it to another value changes the behaviour of the interpreter. When running in interactive mode, <code>!</code> or <code>!""</code> evaluates to the last answer, so the empty string is the name of yet another special variable. These variables can be reassigned.
If Bracmat starts in interactive mode, a few more variables are predefined: <code>!v</code> evaluates to a string telling which version of Bracmat you are running. <code>!w</code> and <code>!c</code> evaluate to sections 11 and 12 of the GPL. More vital is the variable <code>main</code>, which is the interpreter's main loop. Setting it to another value changes the behaviour of the interpreter. When running in interactive mode, <code>!</code> or <code>!""</code> evaluates to the last answer, so the empty string is the name of yet another special variable. These variables can be reassigned.


=={{header|C}}==
=={{header|C}}==
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Furthermore one could consider <code>errno</code> from <code><errno.h></code> as a special variable although it actually is a macro which expands to an modifiable lvalue of type <code>int</code>. Many library functions set it to a positive value in case of an error.
Furthermore one could consider <code>errno</code> from <code><errno.h></code> as a special variable although it actually is a macro which expands to an modifiable lvalue of type <code>int</code>. Many library functions set it to a positive value in case of an error.

=={{header|C++}}==

Besides <code>errno</code> like C, C++ has the <code>this</code> pointer so objects can refer to themselves.

<syntaxhighlight lang="cpp">#include <iostream>

struct SpecialVariables
{
int i = 0;

SpecialVariables& operator++()
{
// 'this' is a special variable that is a pointer to the current
// class instance. It can optionally be used to refer to elements
// of the class.
this->i++; // has the same meaning as 'i++'

// returning *this lets the object return a reference to itself
return *this;
}

};

int main()
{
SpecialVariables sv;
auto sv2 = ++sv; // makes a copy of sv after it was incremented
std::cout << " sv :" << sv.i << "\n sv2:" << sv2.i << "\n";
}</syntaxhighlight>
{{out}}
<pre>
sv :1
sv2:1
</pre>


=={{header|Clojure}}==
=={{header|Clojure}}==
The following snippet prints a list of the special variables defined in clojure.core, in *earmuff* form. For further information, consult the [http://clojuredocs.org/quickref/shortdesc/Clojure%20Core documentation].
The following snippet prints a list of the special variables defined in clojure.core, in *earmuff* form. For further information, consult the [http://clojuredocs.org/quickref/shortdesc/Clojure%20Core documentation].
<lang clojure>
<syntaxhighlight lang="clojure">
(apply str (interpose " " (sort (filter #(.startsWith % "*") (map str (keys (ns-publics 'clojure.core)))))))
(apply str (interpose " " (sort (filter #(.startsWith % "*") (map str (keys (ns-publics 'clojure.core)))))))
</syntaxhighlight>
</lang>
{{Out}}
{{Out}}
<pre>*1 *2 *3 *agent* *allow-unresolved-vars* *assert* *clojure-version* *command-line-args* *compile-files* *compile-path*
<pre>*1 *2 *3 *agent* *allow-unresolved-vars* *assert* *clojure-version* *command-line-args* *compile-files* *compile-path*
Line 512: Line 559:


The following code snippet prints a list of all 44 special variables defined by the Common Lisp standard. For further information about each of them consult the [http://www.lispworks.com/documentation/HyperSpec/Front/X_Alph_9.htm online documentation].
The following code snippet prints a list of all 44 special variables defined by the Common Lisp standard. For further information about each of them consult the [http://www.lispworks.com/documentation/HyperSpec/Front/X_Alph_9.htm online documentation].
<lang lisp>(defun special-variables ()
<syntaxhighlight lang="lisp">(defun special-variables ()
(flet ((special-var-p (s)
(flet ((special-var-p (s)
(and (char= (aref s 0) #\*)
(and (char= (aref s 0) #\*)
Line 523: Line 570:
lst)))
lst)))


(format t "~a~%" (sort (special-variables) #'string<))</lang>
(format t "~a~%" (sort (special-variables) #'string<))</syntaxhighlight>


{{Out}}
{{Out}}
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One special boolean variable is __ctfe, that is read-only and it's true inside functions when they are evaluated at compile-time, and false otherwise.
One special boolean variable is __ctfe, that is read-only and it's true inside functions when they are evaluated at compile-time, and false otherwise.
=={{header|Déjà Vu}}==
Calls to some of the standard library functions can be optimized into certain opcodes or sequences of opcodes, namely:
<pre>set setglobal local get getlocal return recurse drop dup swap rot over
[] {} pop-from push-to push-through has get-from set-to raise reraise
call for pass</pre>
In addition, <code>eva</code> is special:
<lang dejavu>!print "hey" #is really short for
eva!print "hey"</lang>
EVA is the part of the standard library that takes care of communication with the outside world. It makes extensive use of the method call syntax, unlike the rest of the standard library, that is why it is special.


=={{header|DWScript}}==
=={{header|DWScript}}==
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Dyalect has a special <code>this</code> which is available inside methods:
Dyalect has a special <code>this</code> which is available inside methods:


<lang dyalect>func Integer.double() {
<syntaxhighlight lang="dyalect">func Integer.Double() {
this + this
this + this
}
}
print(8.double())</lang>
print(8.Double())</syntaxhighlight>

=={{header|Déjà Vu}}==
Calls to some of the standard library functions can be optimized into certain opcodes or sequences of opcodes, namely:
<pre>set setglobal local get getlocal return recurse drop dup swap rot over
[] {} pop-from push-to push-through has get-from set-to raise reraise
call for pass</pre>
In addition, <code>eva</code> is special:
<syntaxhighlight lang="dejavu">!print "hey" #is really short for
eva!print "hey"</syntaxhighlight>
EVA is the part of the standard library that takes care of communication with the outside world. It makes extensive use of the method call syntax, unlike the rest of the standard library, that is why it is special.


=={{header|Erlang}}==
=={{header|Erlang}}==
Erlang has no special variables.
Erlang has no special variables.
What it does have are special functions, module_info/0 and module_info/1. These are added to a module automatically, without being present in the code.
What it does have are special functions, module_info/0 and module_info/1. These are added to a module automatically, without being present in the code.
<syntaxhighlight lang="erlang">
<lang Erlang>
-module( special_variables ).
-module( special_variables ).


Line 613: Line 661:


task() -> ok.
task() -> ok.
</syntaxhighlight>
</lang>
{{out}}
{{out}}
<pre>
<pre>
Line 664: Line 712:
Fortran offers no special variables such as Pi, e, etc. as a part of the language, not even the modern special floating-point "values" such as NaN. Indeed, the syntax has no reserved words generally so that <code>GO TO</code> could be the name of a variable without damage to GO TO statements, though it is generally agreed that calling a variable END is provocative... It does have some ''numbers'' that are special: 5 is the input/output "unit number" for keyboard input and 6 for output to "standard output", the screen on desktop computers; in the past there have been other values that were associated to devices such as the card reader, card punch, lineprinter, paper tape reader, and so on at any given installation. But these constants are not given names as mnemonics for their special values, except by the programmer. There is no equivalent of SYSOUT as in WRITE(SYSOUT,''etc'' without definition by the programmer.
Fortran offers no special variables such as Pi, e, etc. as a part of the language, not even the modern special floating-point "values" such as NaN. Indeed, the syntax has no reserved words generally so that <code>GO TO</code> could be the name of a variable without damage to GO TO statements, though it is generally agreed that calling a variable END is provocative... It does have some ''numbers'' that are special: 5 is the input/output "unit number" for keyboard input and 6 for output to "standard output", the screen on desktop computers; in the past there have been other values that were associated to devices such as the card reader, card punch, lineprinter, paper tape reader, and so on at any given installation. But these constants are not given names as mnemonics for their special values, except by the programmer. There is no equivalent of SYSOUT as in WRITE(SYSOUT,''etc'' without definition by the programmer.


Certain statements involve special names in what appear to be assignments of values to or from a special name that has a value just like a named variable does, but these are ''not'' proper variables at all. For instance, in <lang Fortran> INQUIRE(FILE = FILENAME(1:L),EXIST = EXIST, !Here we go. Does the file exist?
Certain statements involve special names in what appear to be assignments of values to or from a special name that has a value just like a named variable does, but these are ''not'' proper variables at all. For instance, in <syntaxhighlight lang="fortran"> INQUIRE(FILE = FILENAME(1:L),EXIST = EXIST, !Here we go. Does the file exist?
1 ERR = 666,IOSTAT = IOSTAT) !Hopefully, named in good style, etc.
1 ERR = 666,IOSTAT = IOSTAT) !Hopefully, named in good style, etc.
IF (EXIST) THEN !So, does the named file already exist?
IF (EXIST) THEN !So, does the named file already exist?
...etc.</lang>
...etc.</syntaxhighlight>
ERR is a special name, but only inside the context of the INQUIRE (and OPEN, and WRITE, ''etc.'') statement, it is not the name of an existing variable outside that statement whether defined by the language or by the programmer, and if the programmer were to define a variable called ERR it would have no relevance within that INQUIRE statement - though <code>ERR = ERR</code> ''would'' be workable if an ASSIGN statement had assigned statement label 666 to variable ERR. Similarly, the variable named FILENAME is declared by the programmer and because there are no reserved words, could be just FILE. Likewise, EXIST is declared (as LOGICAL) and IOSTAT (as INTEGER) as a mnemonic aid and also to save on the trouble of remembering whether the assignment works left-to-right or right-to-left in each case. It is right-to-left for FILE = ''filename'', input to the INQUIRE statement and left-to-right for EXIST = ''variable'', an output of the INQUIRE statement.
ERR is a special name, but only inside the context of the INQUIRE (and OPEN, and WRITE, ''etc.'') statement, it is not the name of an existing variable outside that statement whether defined by the language or by the programmer, and if the programmer were to define a variable called ERR it would have no relevance within that INQUIRE statement - though <code>ERR = ERR</code> ''would'' be workable if an ASSIGN statement had assigned statement label 666 to variable ERR. Similarly, the variable named FILENAME is declared by the programmer and because there are no reserved words, could be just FILE. Likewise, EXIST is declared (as LOGICAL) and IOSTAT (as INTEGER) as a mnemonic aid and also to save on the trouble of remembering whether the assignment works left-to-right or right-to-left in each case. It is right-to-left for FILE = ''filename'', input to the INQUIRE statement and left-to-right for EXIST = ''variable'', an output of the INQUIRE statement.

=={{header|FreeBASIC}}==
FreeBASIC has no 'special variables'.


=={{header|Go}}==
=={{header|Go}}==
Line 683: Line 734:
=={{header|Icon}} and {{header|Unicon}}==
=={{header|Icon}} and {{header|Unicon}}==
Icon and Unicon have special variables known as keywords which are syntactically are preceded by an &.
Icon and Unicon have special variables known as keywords which are syntactically are preceded by an &.
<syntaxhighlight lang="unicon">
<lang Unicon>
# &keyword # type returned(indicators) - brief description
# &keyword # type returned(indicators) - brief description
# indicators:
# indicators:
Line 760: Line 811:
&y # integer(=G) - pointer vertical position
&y # integer(=G) - pointer vertical position
# keywords may also fail if the corresponding feature is not present.
# keywords may also fail if the corresponding feature is not present.
# Other variants of Icon (e.g. MT-Icon) will have different mixes of keywords.</lang>
# Other variants of Icon (e.g. MT-Icon) will have different mixes of keywords.</syntaxhighlight>


=={{header|IS-BASIC}}==
=={{header|IS-BASIC}}==
<lang IS-BASIC>BLACK - The code of colour black.
<syntaxhighlight lang="is-basic">BLACK - The code of colour black.
BLUE - The code of colour blue.
BLUE - The code of colour blue.
CYAN - The code of colour cyan.
CYAN - The code of colour cyan.
DATE$ - The current date in the standard format.
DATE$ - The current date in the standard format.
EXLINE - The number of the last statement that caused an exception.
EXLINE - The number of the last statement that caused an exception.
EXTYPE - The error code of the last exceotion.
EXTYPE - The error code of the last exception.
FREE - The amount of memory free and avaible to the current program.
FREE - The amount of memory free and avaible to the current program.
GREEN - The code of colour green.
GREEN - The code of colour green.
INF - The largest positive number that the IS-BASIC can candle.
INF - The largest positive number that the IS-BASIC can handle.
MAGENTA - The code of colour magenta.
MAGENTA - The code of colour magenta.
PI - Value of the Pi. This is rounded to 3.141592654
PI - Value of the Pi. This is rounded to 3.141592654
Line 777: Line 828:
TIME$ - The current time in the standard format.
TIME$ - The current time in the standard format.
WHITE - The code of colour white.
WHITE - The code of colour white.
YELLOW - The code of colour yellow.</lang>
YELLOW - The code of colour yellow.
VERNUM - Version number of the BASIC</syntaxhighlight>


=={{header|J}}==
=={{header|J}}==
Line 793: Line 845:


Note that the result of an adverb or conjunction that uses either x or y and one of these other names is always a verb. In this case, x and/or y represent arguments passed to the derived verb.
Note that the result of an adverb or conjunction that uses either x or y and one of these other names is always a verb. In this case, x and/or y represent arguments passed to the derived verb.

Some examples:
<syntaxhighlight lang="j"> {{ y }} 1
1
1000 {{ x + y }} 1
1001
100 {{ m + y }} 1
101
(1000) 100 {{ x + m + y }} 1
1101
100 {{ m + n + y }} 10 (1)
111
(1000) 100 {{ x + m + n + y }} 10 (1)
1111
(1000) + {{ x u n u y }} 10 (1)
1011
(1000) 100 {{ x v m v y }} + (1)
1101</syntaxhighlight>


These names may be used as regular names, but that is bad practice except in the context of debugging or illustration.
These names may be used as regular names, but that is bad practice except in the context of debugging or illustration.
Line 946: Line 1,016:
tolist topara ucpboxdraw
tolist topara ucpboxdraw
unboxfkeys unboxskeys winmax </pre>
unboxfkeys unboxskeys winmax </pre>



=={{header|Java}}==
=={{header|Java}}==
Java is heavily object-oriented, and is mostly statically-typed. There aren't many special variables, or aggregates, similar to dynamically-typed languages.<br />


There is ''null'', which is used to represent an object which has no reference assigned.
<syntaxhighlight lang="java">
Object object = null
</syntaxhighlight>

There is ''true'' and ''false'' which are used to denote a ''Boolean'' value.
<syntaxhighlight lang="java">
boolean value = true
</syntaxhighlight>

There is the ''this'' and ''super'' variables, used to reference the current class and parent class, respectively.
<syntaxhighlight lang="java">
this.object
</syntaxhighlight>
<syntaxhighlight lang="java">
super(value)
</syntaxhighlight>

To avoid confusion to anyone unfamiliar with Java, there is the ability to import static, final, variables from other classes.<br />
While these are not 'special variables' they may appear that way to a new user.
<syntaxhighlight lang="java">
import static java.lang.Math.*;
</syntaxhighlight>
<syntaxhighlight lang="java">
double area = PI * (2 * 2);
</syntaxhighlight>

There is the first parameter of the ''main'' method, which is of type ''String[]''.<br />
It is non-null and includes any arguments depicted during execution.
<syntaxhighlight lang="java">
public static void main(String[] args)
</syntaxhighlight>
<br />
Additionally ...<br />
Java has only a few special variables. There is a <code>String</code>-Array for passing command-line-arguments to the program, and there is a <code>Class</code>-Object that can be accessed in a variable-like manner. It is used for reflection, (like examining and modifing class members, their type and modifiers during runtime).
Java has only a few special variables. There is a <code>String</code>-Array for passing command-line-arguments to the program, and there is a <code>Class</code>-Object that can be accessed in a variable-like manner. It is used for reflection, (like examining and modifing class members, their type and modifiers during runtime).
There is the <code>System</code>-"Object" that contains various (mostly static) data about the enviroment the Java VM runs on, and it's cousin <code>Runtime</code> that provides data that is more prone to change during runtime, like available CPU cores and RAM.
There is the <code>System</code>-"Object" that contains various (mostly static) data about the enviroment the Java VM runs on, and it's cousin <code>Runtime</code> that provides data that is more prone to change during runtime, like available CPU cores and RAM.
Line 955: Line 1,059:
Inside an object there is <code>this</code>, a reference that points to the object itself (like 127.0.0.1 in networking) and are used to qualify member access. There is also <code>super</code> that does the same for the base class (actually "the next class in the inheritance tree"). Both are not demonstrated in the example below.
Inside an object there is <code>this</code>, a reference that points to the object itself (like 127.0.0.1 in networking) and are used to qualify member access. There is also <code>super</code> that does the same for the base class (actually "the next class in the inheritance tree"). Both are not demonstrated in the example below.


<lang Java>import java.util.Arrays;
<syntaxhighlight lang="java">import java.util.Arrays;


public class SpecialVariables {
public class SpecialVariables {
Line 986: Line 1,090:
}
}


</syntaxhighlight>
</lang>


=={{header|JavaScript}}==
=={{header|JavaScript}}==
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<code>this</code> evaluates to the object the immediately enclosing function was called on as a method, if it was. If it was not called as a method, <code>this</code> is either the global environment object (usually <code>window</code> in browsers) in non-strict mode, or <code>undefined</code> in strict mode. <code>this</code> is an expression resembling a variable, but not actually a variable; for example, it is a syntax error to assign to it.
<code>this</code> evaluates to the object the immediately enclosing function was called on as a method, if it was. If it was not called as a method, <code>this</code> is either the global environment object (usually <code>window</code> in browsers) in non-strict mode, or <code>undefined</code> in strict mode. <code>this</code> is an expression resembling a variable, but not actually a variable; for example, it is a syntax error to assign to it.


<lang javascript>var obj = {
<syntaxhighlight lang="javascript">var obj = {
foo: 1,
foo: 1,
bar: function () { return this.foo; }
bar: function () { return this.foo; }
};
};
obj.bar(); // returns 1</lang>
obj.bar(); // returns 1</syntaxhighlight>


When a function is entered, the ''variable'' <code>arguments</code> is bound to an “arguments object” which is an array-like object containing the function's arguments, as well as some other information. This how [[varargs]] functions are implemented in JavaScript. If the function's parameters contain “<code>arguments</code>” explicitly, then it is ''not'' overridden and functions as an ordinary parameter.
When a function is entered, the ''variable'' <code>arguments</code> is bound to an “arguments object” which is an array-like object containing the function's arguments, as well as some other information. This how [[varargs]] functions are implemented in JavaScript. If the function's parameters contain “<code>arguments</code>” explicitly, then it is ''not'' overridden and functions as an ordinary parameter.


<lang javascript>function concat() {
<syntaxhighlight lang="javascript">function concat() {
var s = "";
var s = "";
for (var i = 0; i < arguments.length; i++) {
for (var i = 0; i < arguments.length; i++) {
Line 1,007: Line 1,111:
return s;
return s;
}
}
concat("a", "b", "c"); // returns "abc"</lang>
concat("a", "b", "c"); // returns "abc"</syntaxhighlight>


=={{header|jq}}==
=={{header|jq}}==
Variables in jq are identifiers preceded by the sigil "$", e.g. <code>$x</code>. There are no predefined variables, but jq does allow variables to be assigned string values on the command line.
Variables in jq are identifiers preceded by the sigil "$", e.g. <code>$x</code>. There are no predefined variables, but jq does allow variables to be assigned string values on the command line.


For example:<lang sh>$ jq -n -M --arg x 1 '$x|type' # (*)
For example:<syntaxhighlight lang="sh">$ jq -n -M --arg x 1 '$x|type' # (*)
"string"</lang>
"string"</syntaxhighlight>
(*) Windows users would write "$x|type".
(*) Windows users would write "$x|type".


=={{header|Julia}}==
=={{header|Julia}}==
Julia starts with the <code>Base</code> module loaded. Taking "special variables" to mean names in the default global namespace (<code>Base</code>) that aren't functions, types, or modules, then you can obtain them with
Julia starts with the <code>Base</code> module loaded. Taking "special variables" to mean names in the default global namespace (<code>Base</code>) that aren't functions, types, or modules, then you can obtain them with
<lang julia>join(sort(filter(sym -> let n=eval(sym); !(isa(n, Function) || isa(n, Type) || isa(n, Module)); end, names(Base))), ", ")</lang>
<syntaxhighlight lang="julia">join(sort(filter(sym -> let n=eval(sym); !(isa(n, Function) || isa(n, Type) || isa(n, Module)); end, names(Base))), ", ")</syntaxhighlight>
{{out}}
{{out}}
<pre>":, ARGS, CPU_CORES, C_NULL, DL_LOAD_PATH, DevNull, ENDIAN_BOM, ENV, I, Inf, Inf16, Inf32, InsertionSort, JULIA_HOME, LOAD_PATH, MS_ASYNC, MS_INVALIDATE, MS_SYNC, MergeSort, NaN, NaN16, NaN32, OS_NAME, QuickSort, RTLD_DEEPBIND, RTLD_FIRST, RTLD_GLOBAL, RTLD_LAZY, RTLD_LOCAL, RTLD_NODELETE, RTLD_NOLOAD, RTLD_NOW, RoundDown, RoundFromZero, RoundNearest, RoundToZero, RoundUp, STDERR, STDIN, STDOUT, VERSION, WORD_SIZE, catalan, cglobal, e, eu, eulergamma, golden, im, pi, γ, π, φ"</pre>
<pre>":, ARGS, CPU_CORES, C_NULL, DL_LOAD_PATH, DevNull, ENDIAN_BOM, ENV, I, Inf, Inf16, Inf32, InsertionSort, JULIA_HOME, LOAD_PATH, MS_ASYNC, MS_INVALIDATE, MS_SYNC, MergeSort, NaN, NaN16, NaN32, OS_NAME, QuickSort, RTLD_DEEPBIND, RTLD_FIRST, RTLD_GLOBAL, RTLD_LAZY, RTLD_LOCAL, RTLD_NODELETE, RTLD_NOLOAD, RTLD_NOW, RoundDown, RoundFromZero, RoundNearest, RoundToZero, RoundUp, STDERR, STDIN, STDOUT, VERSION, WORD_SIZE, catalan, cglobal, e, eu, eulergamma, golden, im, pi, γ, π, φ"</pre>
Line 1,032: Line 1,136:


The following program illustrates their usage:
The following program illustrates their usage:
<lang scala>// version 1.0.6
<syntaxhighlight lang="scala">// version 1.0.6


class President(val name: String) {
class President(val name: String) {
Line 1,055: Line 1,159:
val pres3 = President("Theodore")
val pres3 = President("Theodore")
pres3.age = 158
pres3.age = 158
}</lang>
}</syntaxhighlight>


{{out}}
{{out}}
Line 1,071: Line 1,175:
In Lasso parameters can be referenced as numerical locals within methods or unbound captures. [http://lassoguide.com/language/variables.html?#parameter-pseudo-locals]
In Lasso parameters can be referenced as numerical locals within methods or unbound captures. [http://lassoguide.com/language/variables.html?#parameter-pseudo-locals]


<lang Lasso>{return #1 + ':'+#2}('a','b') // a:b</lang>
<syntaxhighlight lang="lasso">{return #1 + ':'+#2}('a','b') // a:b</syntaxhighlight>


<lang Lasso>define test(a,b) => #1+':'+#2
<syntaxhighlight lang="lasso">define test(a,b) => #1+':'+#2
test('y','z') // y:z</lang>
test('y','z') // y:z</syntaxhighlight>


=={{header|Lingo}}==
=={{header|Lingo}}==
Line 1,104: Line 1,208:


Further to those, LiveCode comes with a plethora of built-in constants, which are readily listed with the following command:
Further to those, LiveCode comes with a plethora of built-in constants, which are readily listed with the following command:
<lang LiveCode>put the constantNames</lang>It also provides colours as built-ins, accessible through <lang LiveCode>the colornames</lang> You can search the dictionary in the IDE using text "names" to discover more such as the ''propertyNames'' & the ''commandNames'', though are not strictly pertinent to this task.
<syntaxhighlight lang="livecode">put the constantNames</syntaxhighlight>It also provides colours as built-ins, accessible through <syntaxhighlight lang="livecode">the colornames</syntaxhighlight> You can search the dictionary in the IDE using text "names" to discover more such as the ''propertyNames'' & the ''commandNames'', though are not strictly pertinent to this task.



=={{header|Lua}}==
=={{header|Lua}}==
Line 1,115: Line 1,218:
To list all global variables:
To list all global variables:


<lang lua>for n in pairs(_G) do print(n) end</lang>
<syntaxhighlight lang="lua">for n in pairs(_G) do print(n) end</syntaxhighlight>


The list will include built-in global functions, whose availability depends on the implementation and compile time configuration.
The list will include built-in global functions, whose availability depends on the implementation and compile time configuration.

=={{header|M2000 Interpreter}}==
=={{header|M2000 Interpreter}}==
There some read only variables. We can use Help dir$ to get help about dir$.
There some read only variables. We can use Help dir$ to get help about dir$.
Line 1,123: Line 1,227:
All identifiers can be change to be used as variables, using a dot. For modules/functions in a group we have to define these variables using a dot.
All identifiers can be change to be used as variables, using a dot. For modules/functions in a group we have to define these variables using a dot.


<syntaxhighlight lang="m2000 interpreter">
<lang M2000 Interpreter>
Module Checkit {
Module Checkit {
Let inkey$="hello", dir$="Something Else"
Let inkey$="hello", dir$="Something Else"
Line 1,154: Line 1,258:
Check3
Check3


</syntaxhighlight>
</lang>




Line 1,171: Line 1,275:
</pre>
</pre>


=={{header|Mathematica}}/{{header|Wolfram Language}}==

<syntaxhighlight lang="mathematica">Grid[Partition[Names["$*"],4]]

=={{header|Mathematica}}==
<lang Mathematica>Grid[Partition[Names["$*"],4]]
->
->
$Aborted $ActivationGroupID $ActivationKey $ActivationUserRegistered
$Aborted $ActivationGroupID $ActivationKey $ActivationUserRegistered
Line 1,218: Line 1,320:
$TimeZone $TopDirectory $TraceOff $TraceOn
$TimeZone $TopDirectory $TraceOff $TraceOn
$TracePattern $TracePostAction $TracePreAction $Urgent
$TracePattern $TracePostAction $TracePreAction $Urgent
$UserAddOnsDirectory $UserBaseDirectory $UserBasePacletsDirectory $UserDocumentsDirectory</lang>
$UserAddOnsDirectory $UserBaseDirectory $UserBasePacletsDirectory $UserDocumentsDirectory</syntaxhighlight>





=={{header|Maxima}}==
=={{header|Maxima}}==
<lang maxima>/* There are many special variables in Maxima: more than 250 are used for options, for example */
<syntaxhighlight lang="maxima">/* There are many special variables in Maxima: more than 250 are used for options, for example */
fpprec; /* precision for big floats */
fpprec; /* precision for big floats */
obase; /* number base for output */
obase; /* number base for output */
Line 1,230: Line 1,329:
/* Other variables are read-only, and give the list of user-defined variables, functions... */
/* Other variables are read-only, and give the list of user-defined variables, functions... */
infolists; /* give the names of all available lists */
infolists; /* give the names of all available lists */
[labels, values, functions, macros, arrays, myoptions, props, aliases, rules, gradefs, dependencies, let_rule_packages, structures]</lang>
[labels, values, functions, macros, arrays, myoptions, props, aliases, rules, gradefs, dependencies, let_rule_packages, structures]</syntaxhighlight>

=={{header|MIPS Assembly}}==
When multiplying two registers, the product is always stored in the <code>$HI</code> and <code>$LO</code> registers. Their contents can be read into your standard registers with the commands <code>mfhi $reg</code> and <code>mflo $reg</code>.

<syntaxhighlight lang="mips">
li $t0,0x4500
li $t1,0xFFFF
multu $t0,$t1 ;unsigned multiplication of $t0 and $t1
mfhi $t0 ;load the top 32 bits of the product into $t0
mflo $t1 ;load the bottom 32 bits of the product into $t1</syntaxhighlight>

Division is a similar story, except <code>$HI</code> holds the remainder and <code>$LO</code> holds the quotient.

When using <code>JAL functionName</code> to call a function, the <code>$ra</code> register holds the return address.


=={{header|ML/I}}==
=={{header|ML/I}}==
===Input===
===Input===
<lang ML/I>MCSKIP "WITH" NL
<syntaxhighlight lang="ml/i">MCSKIP "WITH" NL
"" Special variables
"" Special variables
"" There are four different kinds of variables in ML/I.
"" There are four different kinds of variables in ML/I.
Line 1,265: Line 1,378:
All other S-variables have implementation defined meanings.
All other S-variables have implementation defined meanings.
>
>
SVARDEMO</lang>
SVARDEMO</syntaxhighlight>


===Output===
===Output===
<lang ML/I>T-variables are local to the current macro call
<syntaxhighlight lang="ml/i">T-variables are local to the current macro call
T1 is the number of arguments to current macro call - value is 2
T1 is the number of arguments to current macro call - value is 2
T2 is the number of macro calls so far - value is 5
T2 is the number of macro calls so far - value is 5
Line 1,282: Line 1,395:
S7, S8 and S9 are currently unused.
S7, S8 and S9 are currently unused.


All other S-variables have implementation defined meanings.</lang>
All other S-variables have implementation defined meanings.</syntaxhighlight>


=={{header|Nanoquery}}==
=={{header|Nanoquery}}==
Nanoquery has a number of immutable special variables which can be listed by executing the following program:
Nanoquery has a number of immutable special variables which can be listed by executing the following program:
<lang nanoquery>println dumpstack()</lang>
<syntaxhighlight lang="nanoquery">println dumpstack()</syntaxhighlight>
{{out}}
{{out}}
<pre>{{dbsize, 0}, {col, 1}, {workingdir, C:\Users\Will\Programs\Nanoquery}, {false, false}, {interactive, false}, {main, true}, {packages, [, Nanoquery.Objects, Nanoquery.Exceptions]}, {libpath, C:\Users\Will\Programs\Nanoquery\nanoquery-2.3_1866}, {args, [-b, rosetta-code/specialvars.nq]}, {rec, 1}, {filename, }, {null, null}, {__file__, C:\Users\Will\Programs\Nanoquery\rosetta-code\specialvars.nq}, {true, true}, {prompt, [\S | rec\R col\C] % }, {cols, 0}, {lockedfiles, []}, {__calls__, [<global>:1]}}</pre>
<pre>{{dbsize, 0}, {col, 1}, {workingdir, C:\Users\Will\Programs\Nanoquery}, {false, false}, {interactive, false}, {main, true}, {packages, [, Nanoquery.Objects, Nanoquery.Exceptions]}, {libpath, C:\Users\Will\Programs\Nanoquery\nanoquery-2.3_1866}, {args, [-b, rosetta-code/specialvars.nq]}, {rec, 1}, {filename, }, {null, null}, {__file__, C:\Users\Will\Programs\Nanoquery\rosetta-code\specialvars.nq}, {true, true}, {prompt, [\S | rec\R col\C] % }, {cols, 0}, {lockedfiles, []}, {__calls__, [<global>:1]}}</pre>
Line 1,320: Line 1,433:
<code>'''ask''', '''class''', '''digits''', '''form''', '''length''', '''null''', '''source''', '''sourceline''', '''super''', '''this''', '''trace''', '''version'''</code>.
<code>'''ask''', '''class''', '''digits''', '''form''', '''length''', '''null''', '''source''', '''sourceline''', '''super''', '''this''', '''trace''', '''version'''</code>.


<lang NetRexx>/* NetRexx */
<syntaxhighlight lang="netrexx">/* NetRexx */
options replace format comments java crossref savelog symbols binary
options replace format comments java crossref savelog symbols binary


Line 1,354: Line 1,467:


return
return
</syntaxhighlight>
</lang>
;Output
;Output
<pre>
<pre>
Line 1,376: Line 1,489:
<ask>answer</ask>
<ask>answer</ask>
</pre>
</pre>

=={{header|Nim}}==

In Nim, there is only one special variable, named <code>result</code>. It is implicitly declared in procedure which returns a result and is initialized with binary zeroes. Statement <code>return value</code> is in fact a shortcut for:
<syntaxhighlight lang="nim">result = value
return</syntaxhighlight>

There are also variables declared in modules and exported. As some modules are implicitly imported, their exported variables are automatically visible. Modules implicitly imported are: “system” (which imports “iterators”, “assertions”, “dollars”, “io” and “widestr”), “threads” and “channels”, the latter two being activated if option <code>--thread:on</code> is used.

These implicit imports add these variables to the list of visible objects:
:– some hooks and handlers used in system programming: <code>globalRaiseHook</code>, <code>localRaiseHook</code>, <code>outOfMemHook</code>, <code>unhandledExceptionHook</code>, <code>errorMessageWriter</code>, <code>onUnhandledException</code>;
:– a read-only variable, <code>nimvm</code> which is true in Nim VM context and false otherwise;
:– the three standard files: <code>stdin</code>, <code>stdout</code>, <code>stderr</code>.


=={{header|OASYS}}==
=={{header|OASYS}}==
Line 1,387: Line 1,513:
Some predefined variables from the <code>[http://caml.inria.fr/pub/docs/manual-ocaml/libref/Sys.html Sys]</code> module:
Some predefined variables from the <code>[http://caml.inria.fr/pub/docs/manual-ocaml/libref/Sys.html Sys]</code> module:


<lang ocaml>val argv : string array
<syntaxhighlight lang="ocaml">val argv : string array
(** The command line arguments given to the process.
(** The command line arguments given to the process.
The first element is the command name used to invoke the program.
The first element is the command name used to invoke the program.
Line 1,424: Line 1,550:
where [major], [minor], and [patchlevel] are integers, and
where [major], [minor], and [patchlevel] are integers, and
[additional-info] is an arbitrary string. The [[.patchlevel]] and
[additional-info] is an arbitrary string. The [[.patchlevel]] and
[[+additional-info]] parts may be absent. *)</lang>
[[+additional-info]] parts may be absent. *)</syntaxhighlight>


Some predefined variables from the <code>[http://caml.inria.fr/pub/docs/manual-ocaml/libref/Pervasives.html Pervasives]</code> module:
Some predefined variables from the <code>[http://caml.inria.fr/pub/docs/manual-ocaml/libref/Pervasives.html Pervasives]</code> module:


<lang ocaml>val max_int : int
<syntaxhighlight lang="ocaml">val max_int : int
(** The greatest representable integer. *)
(** The greatest representable integer. *)


Line 1,442: Line 1,568:
val epsilon_float : float
val epsilon_float : float
(** The difference between [1.0] and the smallest exactly representable
(** The difference between [1.0] and the smallest exactly representable
floating-point number greater than [1.0]. *)</lang>
floating-point number greater than [1.0]. *)</syntaxhighlight>


=={{header|Oforth}}==
=={{header|Oforth}}==
Line 1,466: Line 1,592:
System.ISLUNIX
System.ISLUNIX
</pre>
</pre>

=={{header|Pascal}}==
Pascal does not have any predefined special variables.
However, two identifiers ''can'' become “special”:
If you list in the <tt>program</tt> parameter list the identifiers of the spelling <tt>input</tt> and/or <tt>output</tt>, they will identify <tt>text</tt> variables referring to an implementation-defined input and output facility.
<syntaxhighlight lang="pascal">program foo(input, output);
begin
{ In this program, `input` and `output` have special meaning. }
end.</syntaxhighlight>
Neverthless, these identifiers are in no way ''reserved''.
<syntaxhighlight lang="pascal">program foo(output);
var
input: integer;
begin
{ In this program only `output` has special meaning. }
end.</syntaxhighlight>
Note that some run-time libraries of compilers usually ship a variety of predefined variables, but these are not part of the programming language itself.


=={{header|PARI/GP}}==
=={{header|PARI/GP}}==
Line 1,509: Line 1,652:
%ENV # associative container holding the environment variables
%ENV # associative container holding the environment variables
%SIG # associative container holding signal handlers</pre>
%SIG # associative container holding signal handlers</pre>

=={{header|Perl 6}}==

It is probably useful to briefly explain normal variables in Perl 6 before tackling special variables.

Variables in Perl 6 have a prefix sigil to distinguish them from named subroutines, functions, classes, and so on. There is a system of sigils to mark the fundamental structural type of the variable:
<lang perl6> $foo scalar (object)
@foo ordered array
%foo unordered hash (associative array)
&foo code/rule/token/regex
::foo package/module/class/role/subset/enum/type/grammar</lang>
Sigils indicate overall interface, not the exact type of the bound object. Different sigils imply different minimal abilities. Ordinary sigils indicate normally scoped variables, either lexical or package scoped. Oddly scoped variables include a secondary sigil (a twigil) that indicates what kind of strange scoping the variable is subject to:
<lang perl6> $foo # ordinary scoping
$.foo # object attribute public accessor
$^foo # self-declared formal positional parameter
$:foo # self-declared formal named parameter
$*foo # dynamically overridable global variable
$?foo # compiler hint variable
$=foo # Pod variable
$<foo> # match variable, short for $/{'foo'}
$!foo # object attribute private storage
$~foo # the foo sublanguage seen by the parser at this lexical spot</lang>

Special Variables:

Perl 6 has deprecated most of the "line-noise" variables from Perl 5 in favor of named variables.

<lang perl6> $_ # The implicit variable lexically scoped to the current block
@_ # Implicit array of parameters to the current block. Still available but rarely used or needed with the improved sub signatures
$! # Current Exception object
$/ # Last match
$0, $1, $2... # Captured values from match: $/[0], $/[1], $/[2] ...
$?ARCH # Host architecture
$?XARCH # Target architecture
@*ARGS # command-line arguments
$*ARGFILES # The magic command-line input handle
&?BLOCK # current block (itself)
::?CLASS # current class (as package or type name)
$?CLASS # current class
@=COMMENT # All the comment blocks in the file
%?CONFIG # configuration hash
$*CWD # current working directory
$=DATA # data block handle (=begin DATA ... =end)
@=DATA # Same as above, but array
%?DEEPMAGIC # Controls the mappings of magical names to sub definitions
$?DISTRO # Which OS distribution am I compiling under
$*DISTRO # Which OS distribution am I running under
$*EGID # effective group id
%*ENV # system environment variables
$*ERR # Standard error handle
$*EUID # effective user id
$*EXECUTABLE_NAME # executable name
$?FILE # current filename of source file
$?GRAMMAR # current grammar
$*GID # group id
$*IN # Standard input handle; is an IO object
@*INC # where to search for user modules (but not std lib!)
$?KERNEL # operating system compiled for
$*KERNEL # operating system running under
%?LANG # What is the current set of interwoven languages?
$*LANG # LANG variable from %*ENV that defines what human language is used
$?LINE # current line number in source file
%*META-ARGS # Meta-arguments
$?MODULE # current module
%*OPTS # Options from command line
%*OPT... # Options from command line to be passed down
$*OUT # Standard output handle
$?PACKAGE # current package
$?PERL # Which Perl am I compiled for?
$*PERL # perl version running under
$*PID # system process id
%=POD # POD
$*PROGRAM_NAME # name of the Perl program being executed
%*PROTOCOLS # Stores the methods needed for the uri() function
::?ROLE # current role (as package or type name)
$?ROLE # current role
&?ROUTINE # current sub or method (itself)
$?SCOPE # Current "my" scope
$*TZ # Local time zone
$*UID # system user id
$?USAGE # Default usage message generated at compile time
$?VM # Which virtual machine am I compiling under
$?XVM # Which virtual machine am I cross-compiling for</lang>

Also, not really a variable but...
<lang perl6> * # A standalone term that has no fixed value, instead it captures the notion of "Whatever",
# the meaning of which is decided lazily by whatever it is an argument to.
# See the "*" section of http://perlcabal.org/syn/S02.html#Built-In_Data_Types</lang>


=={{header|Phix}}==
=={{header|Phix}}==
{{libheader|Phix/basics}}
Phix has no special variables.
Phix has no special variables.


Line 1,615: Line 1,671:


=={{header|PL/I}}==
=={{header|PL/I}}==
<syntaxhighlight lang="pl/i">
<lang PL/I>
Special variables in PL/I are termed "Pseudo-variables".
Special variables in PL/I are termed "Pseudo-variables".
They are used only on the LHS of an assignment statement.
They are used only on the LHS of an assignment statement.
Line 1,637: Line 1,693:
and may be used when a re-try of the conversion is to be
and may be used when a re-try of the conversion is to be
attempted with modified data).
attempted with modified data).
</syntaxhighlight>
</lang>


=={{header|PowerShell}}==
=={{header|PowerShell}}==
This is the list:
This is the list:
<syntaxhighlight lang="powershell">
<lang PowerShell>
<#
<#
$$
$$
Line 1,682: Line 1,738:
$True
$True
#>
#>
</syntaxhighlight>
</lang>
For descriptions:
For descriptions:
<syntaxhighlight lang="powershell">
<lang PowerShell>
help about_automatic_variables
help about_automatic_variables
</syntaxhighlight>
</lang>


=={{header|PureBasic}}==
=={{header|PureBasic}}==
Line 1,693: Line 1,749:
=={{header|Python}}==
=={{header|Python}}==
By default, Python starts execution in a namespace which has direct access to names defined in the globals() dict and the __builtins__ dict. The members of which can be found by the following code:
By default, Python starts execution in a namespace which has direct access to names defined in the globals() dict and the __builtins__ dict. The members of which can be found by the following code:
<lang Python>names = sorted((set(globals().keys()) | set(__builtins__.__dict__.keys())) - set('_ names i'.split()))
<syntaxhighlight lang="python">names = sorted((set(globals().keys()) | set(__builtins__.__dict__.keys())) - set('_ names i'.split()))
print( '\n'.join(' '.join(names[i:i+8]) for i in range(0, len(names), 8)) )</lang>
print( '\n'.join(' '.join(names[i:i+8]) for i in range(0, len(names), 8)) )</syntaxhighlight>
;Output
;Output
<pre>ArithmeticError AssertionError AttributeError BaseException BufferError BytesWarning DeprecationWarning EOFError
<pre>ArithmeticError AssertionError AttributeError BaseException BufferError BytesWarning DeprecationWarning EOFError
Line 1,713: Line 1,769:
round set setattr slice sorted staticmethod str sum
round set setattr slice sorted staticmethod str sum
super tuple type vars zip</pre>
super tuple type vars zip</pre>

=={{header|Quackery}}==

The trite answer would be that Quackery has no variables.

It does, however, have Ancillary Stacks which stand in for variables, in that they are places where values can reside. Their behaviour is to place a pointer to themselves on the stack (''the stack'' refers to the Quackery Data Stack, the place from which words take arguments and return results), so that they can have values moved to and from them.

Ancillary Stacks might also, arguably, be considered slightly outside the language proper. To use a metaphor, if Quackery is a workshop, and Quackery words are tools for working on data, then the stack is the workbench that data resides on while it is being worked upon, and Ancillary Stacks are the storage spaces where one can put things to keep the workbench tidy. If asked to list the tools in a workshop, would you necessarily list shelves and cupboards as tools?

If predefined system constants are to be included, (i.e. words that take no arguments and always return the same value, a category which includes Ancillary Stacks) then there are several, including but not limited to <code>space</code> which returns 32, <code>carriage</code> which returns 13 (and is taken to mean whatever the host system regards as a carriage return/line feed), <code>[]</code>, which returns the empty nest <code>[ ]</code>, <code>true</code> which returns 1 and <code>false</code> which returns 0.

However, I suspect the most useful answer is "those things which need to be taken into consideration whilst coding in Quackery, because they give words side-effects rather than the words being purely functional in their behaviour."

With this definition there is only one word that requires mention; <code>base</code>. <code>base</code> is a system ancillary stack that holds the current base for numerical i/o and converting numerical strings to and from numbers and so forth. It has a default value of 10 — i.e. Quackery regards numbers as decimal unless that assumption is overridden by putting a different value on the top of the ancillary stack called <code>base</code>.


=={{header|Racket}}==
=={{header|Racket}}==
Line 1,727: Line 1,797:
names that are bound to these parameters are not special, and can be
names that are bound to these parameters are not special, and can be
changed or hidden.)
changed or hidden.)

=={{header|Raku}}==
(formerly Perl 6)

It is probably useful to briefly explain normal variables in Raku before tackling special variables.

Variables in Raku have a prefix sigil to distinguish them from named subroutines, functions, classes, and so on. There is a system of sigils to mark the fundamental structural type of the variable:
<syntaxhighlight lang="raku" line> $foo scalar (object)
@foo ordered array
%foo unordered hash (associative array)
&foo code/rule/token/regex
::foo package/module/class/role/subset/enum/type/grammar</syntaxhighlight>
Sigils indicate overall interface, not the exact type of the bound object. Different sigils imply different minimal abilities. Ordinary sigils indicate normally scoped variables, either lexical or package scoped. Oddly scoped variables include a secondary sigil (a twigil) that indicates what kind of strange scoping the variable is subject to:
<syntaxhighlight lang="raku" line> $foo # ordinary scoping
$.foo # object attribute public accessor
$^foo # self-declared formal positional parameter
$:foo # self-declared formal named parameter
$*foo # dynamically overridable global variable
$?foo # compiler hint variable
$=foo # POD variable
$<foo> # match variable, short for $/{'foo'}
$!foo # object attribute private storage
$~foo # the foo sublanguage seen by the parser at this lexical spot</syntaxhighlight>

A selection (not comprehensive) of Raku's automatically set and/or pre-defined compile-time and run-time variables.

<syntaxhighlight lang="raku" line># Lexical variables

$_ # implicit variable lexically scoped to the current block
$! # current Exception object
$/ # last match
$0, $1, $2... # captured values from match: $/[0], $/[1], $/[2] ...

# Compile-time variables

$?PACKAGE # current package
$?CLASS # current class
$?MODULE # current module
$?ROLE # current role
$?DISTRIBUTION # which OS distribution am I compiling under
$?FILE # current filename of source file
$?LINE # current line number in source file
&?ROUTINE # current sub or method (itself)
&?BLOCK # current block (itself)

# Dynamic variables

$*USAGE # value of the auto-generated USAGE message
$*PROGRAM-NAME # path to the current executable
$*PROGRAM # location (in the form of an IO::Path object) of the Raku program being executed
@*ARGS # command-line arguments
$*ARGFILES # the magic command-line input handle
$*CWD # current working directory
$*DISTRO # which OS distribution am I running under
%*ENV # system environment variables
$*ERR # standard error handle
$*EXECUTABLE-NAME # name of the Raku executable that is currently running
$*EXECUTABLE # IO::Path absolute path of the Raku executable that is currently running
$*IN # standard input handle; is an IO object
$*KERNEL # operating system running under
$*OUT # standard output handle
$*RAKU # Raku version running under
$*PID # system process id
$*TZ # local time zone
$*USER # system user id

# Run-time variables

$*COLLATION # object that can be used to configure Unicode collation levels
$*TOLERANCE # used by the =~= operator to decide if two values are approximately equal
$*DEFAULT-READ-ELEMS # affects the number of bytes read by default by IO::Handle.read</syntaxhighlight>

Also, not really a variable but...
<syntaxhighlight lang="raku" line> * # A standalone term that has no fixed value, instead it captures the notion of "Whatever",
# the meaning of which is decided lazily by whatever it is an argument to.
# See the docs on Whatever: https://docs.raku.org/type/Whatever</syntaxhighlight>


=={{header|REXX}}==
=={{header|REXX}}==
Line 1,751: Line 1,897:
In each case, the three special variable names &nbsp; ('''RC''', &nbsp; '''RESULT''', &nbsp; and &nbsp; '''SIGL''') &nbsp; may be in lower/upper/mixed case.
In each case, the three special variable names &nbsp; ('''RC''', &nbsp; '''RESULT''', &nbsp; and &nbsp; '''SIGL''') &nbsp; may be in lower/upper/mixed case.
<br><br>The scope of the special variables is &nbsp; LOCAL.
<br><br>The scope of the special variables is &nbsp; LOCAL.
<lang rexx>/*REXX program demonstrates REXX special variables: RC, RESULT, SIGL */
<syntaxhighlight lang="rexx">/*REXX program demonstrates REXX special variables: RC, RESULT, SIGL */
/*line two. */
/*line two. */
/*line three.*/ say copies('═',79)
/*line three.*/ say copies('═',79)
Line 1,779: Line 1,925:
exit /*stick a fork in it, we're done.*/
exit /*stick a fork in it, we're done.*/
/*──────────────────────────────────HALVE subroutine────────────────────*/
/*──────────────────────────────────HALVE subroutine────────────────────*/
halve: return arg(1) / 2 /*a simple halving function. */</lang>
halve: return arg(1) / 2 /*a simple halving function. */</syntaxhighlight>
'''output''' using:
'''output''' using:
:::* Regina REXX
:::* Regina REXX
Line 1,847: Line 1,993:
Note that RETURN transfers control but does not set SIGL.
Note that RETURN transfers control but does not set SIGL.


<lang rexx>'dir a2.txt'
<syntaxhighlight lang="rexx">'dir a2.txt'
Say 'rc='rc
Say 'rc='rc
'dir 33.*'
'dir 33.*'
Line 1,869: Line 2,015:
Novalue:
Novalue:
Say 'NOVALUE encountered in line' sigl':' sourceline(sigl)
Say 'NOVALUE encountered in line' sigl':' sourceline(sigl)
Exit </lang>
Exit </syntaxhighlight>
{{out}}
{{out}}
<pre> Datentr„ger in Laufwerk E: ist E_DESKTOP
<pre> Datentr„ger in Laufwerk E: ist E_DESKTOP
Line 1,919: Line 2,065:
for (_ <- 1 to 10) doIt() // Discarded val
for (_ <- 1 to 10) doIt() // Discarded val
def f: T; def f_=(t: T) // Combo for creating mutable f member.</pre>
def f: T; def f_=(t: T) // Combo for creating mutable f member.</pre>

=={{header|Smalltalk}}==
=={{header|Smalltalk}}==
Talking about special (reserved) names, there are:
Talking about special (reserved) names, there are:
Line 1,931: Line 2,078:
* nil
* nil
Technically, these could be redefined, but the system would not work if any of them was. Therefore most compilers refuse code which obviously attempts to do so, and we can think of them as being reserved names as well.
Technically, these could be redefined, but the system would not work if any of them was. Therefore most compilers refuse code which obviously attempts to do so, and we can think of them as being reserved names as well.
Global binding names are returned by <lang smalltalk>Smalltalk keys</lang>
Global binding names are returned by <syntaxhighlight lang="smalltalk">Smalltalk keys</syntaxhighlight>
Things like the shell environment, command line argument, version numbers etc. are usually not exposed via globals, but instead held in private class variables (static variables), which can be accessed via getter messages (which, by the way, makes it easier to insert a dialect compatibility layer). An example for this would be: <lang smalltalk>Float precision</lang> or <lang smalltalk>Smalltalk version</lang>
Things like the shell environment, command line argument, version numbers etc. are usually not exposed via globals, but instead held in private class variables (static variables), which can be accessed via getter messages (which, by the way, makes it easier to insert a dialect compatibility layer). An example for this would be: <syntaxhighlight lang="smalltalk">Float precision</syntaxhighlight> or <syntaxhighlight lang="smalltalk">Smalltalk version</syntaxhighlight>


Name conventions:
Name conventions:
Line 1,992: Line 2,139:
:This local variable holds the Tcl list of arguments supplied to the current procedure after all the other formal arguments have been satisfied. Note that it needs to be explicitly listed in the formal arguments ''and'' be last in the list of formal arguments to have this behavior.
:This local variable holds the Tcl list of arguments supplied to the current procedure after all the other formal arguments have been satisfied. Note that it needs to be explicitly listed in the formal arguments ''and'' be last in the list of formal arguments to have this behavior.


== {{header|UNIX Shell}}==
=={{header|UNIX Shell}}==


The following variables are reserved for special purposes within the Bourne shell:
The following variables are reserved for special purposes within the Bourne shell:
Line 2,045: Line 2,192:


=={{header|Ursa}}==
=={{header|Ursa}}==
<lang ursa># contains arguments passed to the ursa
<syntaxhighlight lang="ursa"># contains arguments passed to the ursa
# interpreter on the command line
# interpreter on the command line
string<> args
string<> args
Line 2,059: Line 2,206:


# represents true
# represents true
boolean true</lang>
boolean true</syntaxhighlight>


=={{header|VBA}}==
=={{header|VBA}}==
VBA does not have special variables.
VBA does not have special variables.

=={{header|XLISP}}==
=={{header|XLISP}}==
XLISP provides the following built-in variables:
XLISP provides the following built-in variables:
Line 2,083: Line 2,231:
CLASS</pre>
CLASS</pre>


== {{header|zkl}} ==
=={{header|Wren}}==
Wren has two special variables ''this'' and ''super''. When used in a constructor or instance method of a class. ''this'' refers to the current instance and ''super'' refers to a super-class whose constructor or (typically overridden) method you wish to invoke. Here's an example.
<lang zkl>__DATE__, __DEBUG__, __FILE__, __LINE__, __NAME__, __TIME__</lang>
<syntaxhighlight lang="wren">class Parent {
construct new(name) {
_name = name
}

name { _name }
}

class Child is Parent {
construct new(name, parentName) {
_name = name
super(parentName) // call parent's constructor
}

name { _name } // overrides Parent's name method

printNames() {
System.print("My name is %(this.name) and my parent's name is %(super.name).")
}
}

var c = Child.new("John", "Fred")
c.printNames()</syntaxhighlight>

{{out}}
<pre>
My name is John and my parent's name is Fred.
</pre>

=={{header|Z80 Assembly}}==
It's somewhat debatable whether processor registers count as "variables," since they don't have a location in the address space but their contents can change. Excluding those for now, there are a few memory locations that have special meaning:

The following memory locations can be called as functions using the <code>RST</code> instructions. Each appears to take a byte as an operand, but in fact there are only 8 different "operands" and each is hardcoded in, which means that only one byte is needed to describe both the <code>RST</code> and the destination byte. Unfortunately, there is very little room for code in these areas, since each is only '''8 bytes long!''' Most of the time you'll put a jump to the actual routine you want to execute in these areas. The last one, <code>RST 38</code>, may allow more room for code depending on the system.

* &0000 - called with RST 00
* &0008 - called with RST 08
* &0010 - called with RST 10
* &0018 - called with RST 18
* &0020 - called with RST 20
* &0028 - called with RST 28
* &0030 - called with RST 30
* &0038 - called with RST 38

The memory location &0066 is special because it contains the NMI routine. NMI stands for "Non-Maskable Interrupt" and is a hardware interrupt that can't be stopped by a <code>DI</code> command. When an NMI occurs, the CPU will save the program counter on the stack and jump to &0066, and execute from there. The <code>RETN</code> instruction is used to return back to the main program. Usually an <code>ORG </code> directive is the easiest way to guarantee that your code will begin at the correct address for NMI. Since you can't predict exactly what state your program will be in when an NMI happens, it's important that the NMI routine uses either the stack or the exchange commands to preserve the register state at the start and restores it before returning. Otherwise, your NMI could ruin whatever your program was doing at the time.

Depending on the hardware, programming the NMI routine may not actually be your responsibility. It's usually only required when programming for a ROM-cartridge game console like the Sega Master System. On home computers, the NMI routine at &0066 is typically built into the firmware by the manufacturer and cannot be changed; however that routine will often contain a jump to another memory location that you can change indirectly using system calls and parameter passing.


<syntaxhighlight lang="z80">org &0066

NMI_HANDLER: ;this label is optional, the CPU doesn't need it to know how to jump here.
retn ;in this example, the NMI routine will immediately return without doing anything.</syntaxhighlight>

The <code>I</code> register handles the interrupt operation in <code>IM 2</code> mode. The Game Boy does not have this register, as it handles interrupts differently.

The <code>r</code> register handles memory refresh. You should '''not''' write to this register, as doing so can damage your hardware. But reading from this register is safe. It basically contains a pseudo-random value, and while its randomness isn't sufficient to reliably seed a PRNG, it can be used to add a little "salt" to a random value. (It should be noted that the Game Boy doesn't have this register, so don't bother trying.)
<syntaxhighlight lang="z80"> ld a,r ;read from the refresh register.</syntaxhighlight>

=={{header|zkl}}==
<syntaxhighlight lang="zkl">__DATE__, __DEBUG__, __FILE__, __LINE__, __NAME__, __TIME__</syntaxhighlight>
As in the C preprocessor. Some (like __DEBUG__) can be changed, others (like __LINE__, __TIME__) are constants.
As in the C preprocessor. Some (like __DEBUG__) can be changed, others (like __LINE__, __TIME__) are constants.



== {{header|ZX Spectrum Basic}} ==
=={{header|ZX Spectrum Basic}}==


The ZX Spectrum does Not make a difference between capital or lower character variable names. A normal variable can be severall letters long, any DEF FN, FOR/NEXT, DIM (STRING or DATA) array name is a single letter variable name. None of these are special variables. for 128k zx spectrum matters that In REVERSED SENSE some variable names are IMposible becouse of the tokenized form in the 48k basic eg 'not' will be NOT !!!!
The ZX Spectrum does Not make a difference between capital or lower character variable names. A normal variable can be severall letters long, any DEF FN, FOR/NEXT, DIM (STRING or DATA) array name is a single letter variable name. None of these are special variables. for 128k zx spectrum matters that In REVERSED SENSE some variable names are IMposible becouse of the tokenized form in the 48k basic eg 'not' will be NOT !!!!
Line 2,161: Line 2,370:
* 23732 P-RAMT - Address of last byte of physical RAM.
* 23732 P-RAMT - Address of last byte of physical RAM.


<lang zxbasic>10 PRINT "The border colour is "; PEEK (23624): REM bordcr
<syntaxhighlight lang="zxbasic">10 PRINT "The border colour is "; PEEK (23624): REM bordcr
20 PRINT "The ramtop address is "; PEEK (23730) + 256 * PEEK (23731): REM ramtop
20 PRINT "The ramtop address is "; PEEK (23730) + 256 * PEEK (23731): REM ramtop
30 POKE 23609,50: REM set keyboard pip to 50</lang>
30 POKE 23609,50: REM set keyboard pip to 50</syntaxhighlight>


{{omit from|GUISS|Does not have any variables at all}}
{{omit from|GUISS|Does not have any variables at all}}
{{omit from|68000 Assembly|Existence of special variables depends entirely on the implementation}}

{{omit from|8086 Assembly|Existence of special variables depends entirely on the implementation}}
{{omit from|x86 Assembly|Existence of special variables depends entirely on the implementation}}
{{omit from|ARM Assembly|Existence of special variables depends entirely on the implementation}}

Latest revision as of 15:31, 9 February 2024

Task
Special variables
You are encouraged to solve this task according to the task description, using any language you may know.

Special variables have a predefined meaning within a computer programming language.


Task

List the special variables used within the language.

11l

Refer to Built-in global variables for the complete special variables (those variables are global).

6502 Assembly

The first 256 bytes of the CPU's address space are collectively known as "zero page RAM" and are common to all 6502 computers (except the custom 6502-based Hu6280 used in the PC Engine/TurboGrafx16.) This section of RAM is faster to load from, as the instructions that use it only take one byte to represent the memory address rather than two. On some implementations, certain zero-page RAM addresses are special, such as address $00 on Commodore 64 (which controls the memory management unit) and address $FF on Easy6502 (which contains the last keyboard input). In addition to loading faster, only the zero page can used indexed indirect addressing modes (the only exception being JMP, which CANNOT jump indirectly using zero page unless you pad it with a high byte of 00.)

The 16-bit 65816 and the Motorola 6809 (which are very similar to the 6502) call the zero page the "direct page" because it can be relocated on those systems. They have a dedicated register which tells the CPU where the direct page actually is. Like on the 6502, it's only 256 bytes in size. This allows the programmer to improve their program's performance by moving the direct page to wherever the majority of the loading will be taking place. Your code may cause problems if you load from the "wrong" direct page, however, so be careful!

Ada

Ada has no special variables in the standard namespace, nor are any such variables commonplace in packages, almost all are constants or private variables changed through functions. The closest thing Ada has to special variables are attributes, which are of an object oriented nature dependant on their prefix. Examples:

  • When X is of an array type, X'First denotes the first index of the array (Ada arrays are not limited to starting at 0 or 1).
  • When X is of a scalar type, X'First denotes the lower bound of that type.
  • X'Size gives the number of bits of memory type X is stored as, but can also be assigned to, to force the program to store the type in that number of bits. (Provided its more than the minimum)
  • For example, a 2 bit record (structure) X might be stored as a byte by default as a speed optimization, but X'Size := 2; would force it to be stored as two bits.

There are far too many attributes to list here, but a standard informative list can be found in Annex K of the documentation if you have it installed. Or Here: Annex K - Language-Defined Attributes

ALGOL 68

Works with: ALGOL 68 version Revision 1 - no extensions to language used.
Works with: ALGOL 68G version Any - tested with release 1.18.0-9h.tiny.
#!/usr/local/bin/a68g --script #

FORMAT f = $g": ["g"]"l$;

printf((f,
  "pi", pi,
  "random", random, # actually a procedure #

  "flip", flip,
  "flop", flop,
  "TRUE", TRUE,
  "FALSE", FALSE,

  "error char", error char,
  "null character", null character,
CO   "NIL", NIL, NIL is not printable END CO

# "lengths" details how many distinctive precisions are permitted. #
# e.g. int length = 3 suggests 3 distincts types: #
#      INT, LONG INT, and LONG LONG INT #
  "bits shorths", bits shorths,
  "bits lengths", bits lengths,
  "bytes shorths", bytes shorths,
  "bytes lengths", bytes lengths,
  "int shorths", int shorths,
  "int lengths", int lengths,
  "real shorths", real shorths,
  "real lengths", real lengths,

  "max abs char", max abs char,
# short/long int/real also possible #
  "max int", max int,
  "small real", small real,
  "max real", max real,

# "width" indicates how many characters are require to prepresent the value #
# short/long bits/bytes/int/real also possible #
  "bits width", bits width,
  "bytes width", bytes width,
  "int width", int width,
  "real width", real width,
  "exp width", exp width
));

# ALL the following are actually procedures #
print((
  "space: [", space, "]", new line,
  "new line: [", new line, "]", new line,
  "new page: [", new page, "]", new line
CO the following are standard, but not implemented in algol68g
  "char number: [", char number, "]", new line,
  "line number: [", line number, "]", new line,
  "page number: [", page number, "]", new line
END CO
));
SKIP

Sample output: 

pi: [+3.14159265358979e  +0]
random: [+6.08495516447216e  -2]
flip: [T]
flop: [F]
TRUE: [T]
FALSE: [F]
error char: [*]
null character: [bits shorths: [         +1]
bits lengths: [         +3]
bytes shorths: [         +1]
bytes lengths: [         +2]
int shorths: [         +1]
int lengths: [         +3]
real shorths: [         +1]
real lengths: [         +3]
max abs char: [       +255]
max int: [+2147483647]
small real: [+2.22044604925031e -16]
max real: [+1.79769313486235e+308]
bits width: [        +32]
bytes width: [        +32]
int width: [        +10]
real width: [        +15]
exp width: [         +3]
space: [ ]
new line: [
]
new page: [
           ]

ALGOL 68G

Works with: ALGOL 68G version Any - tested with release 1.18.0-9h.tiny.

ALGOL 68G provides some further constants to the scientifically motivated coder: 

#!/usr/local/bin/a68g --script #

printf(($g": [", g, "] & [",g,"]"l$,
  "Math constants", "long","long long",
    "pi", long pi, long long pi,
  "Physical Constants", "mksa","cgs",
  "Fundamental constants", "mksa","cgs",
  "  speed of light", mksa speed of light, cgs speed of light,
  "  vacuum permeability", mksa vacuum permeability, "~", # cgs vacuum permeability,#
  "  vacuum permittivity", mksa vacuum permittivity, "~", # cgs vacuum permittivity,#
  "  num avogadro", num avogadro,"~",
  "  faraday", mksa faraday, cgs faraday,
  "  boltzmann", mksa boltzmann, cgs boltzmann,
  "  molar gas", mksa molar gas, cgs molar gas,
  "  standard gas volume", mksa standard gas volume, cgs standard gas volume,
  "  planck constant", mksa planck constant, cgs planck constant,
  "  planck constant bar", mksa planck constant bar, cgs planck constant bar,
  "  gauss", mksa gauss, cgs gauss,
  "  micron", mksa micron, cgs micron,
  "  hectare", mksa hectare, cgs hectare,
  "  miles per hour", mksa miles per hour, cgs miles per hour, 
  "  kilometers per hour", mksa kilometers per hour, cgs kilometers per hour,
  "Astronomy and astrophysics", "mksa","cgs",
  "  astronomical unit", mksa astronomical unit, cgs astronomical unit,
  "  gravitational constant", mksa gravitational constant, cgs gravitational constant,
  "  light year", mksa light year, cgs light year,
  "  parsec", mksa parsec, cgs parsec,
  "  grav accel", mksa grav accel, cgs grav accel,
  "  solar mass", mksa solar mass, cgs solar mass,
  "Atomic and nuclear physics", "mksa","cgs",
  "  electron charge", mksa electron charge, cgs electron charge,
  "  electron volt", mksa electron volt, cgs electron volt,
  "  unified atomic mass", mksa unified atomic mass, cgs unified atomic mass,
  "  mass electron", mksa mass electron, cgs mass electron,
  "  mass muon", mksa mass muon, cgs mass muon,
  "  mass proton", mksa mass proton, cgs mass proton,
  "  mass neutron", mksa mass neutron, cgs mass neutron,
  "  num fine structure", num fine structure,"~",
  "  rydberg", mksa rydberg, cgs rydberg,
  "  bohr radius", mksa bohr radius, cgs bohr radius,
  "  angstrom", mksa angstrom, cgs angstrom,
  "  barn", mksa barn, cgs barn,
  "  bohr magneton", mksa bohr magneton, cgs bohr magneton,
  "  nuclear magneton", mksa nuclear magneton, cgs nuclear magneton,
  "  electron magnetic moment", mksa electron magnetic moment, cgs electron magnetic moment,
  "  proton magnetic moment", mksa proton magnetic moment, cgs proton magnetic moment,
  "Time", "mksa","cgs",
  "  minute", mksa minute, cgs minute,
  "  hour", mksa hour, cgs hour,
  "  day", mksa day, cgs day,
  "  week", mksa week, cgs week,
  "Imperial units", "mksa","cgs",
  "  inch", mksa inch, cgs inch,
  "  foot", mksa foot, cgs foot,
  "  yard", mksa yard, cgs yard,
  "  mile", mksa mile, cgs mile,
  "  mil", mksa mil, cgs mil,
  "Nautical units", "mksa","cgs",
  "  nautical mile", mksa nautical mile, cgs nautical mile,
  "  fathom", mksa fathom, cgs fathom,
  "  knot", mksa knot, cgs knot,
  "Volume", "mksa","cgs",
  "  acre", mksa acre, cgs acre,
  "  liter", mksa liter, cgs liter,
  "  us gallon", mksa us gallon, cgs us gallon,
  "  canadian gallon", mksa canadian gallon, cgs canadian gallon,
  "  uk gallon", mksa uk gallon, cgs uk gallon,
  "  quart", mksa quart, cgs quart,
  "  pint", mksa pint, cgs pint,
  "Mass and weight", "mksa","cgs",
  "  pound mass", mksa pound mass, cgs pound mass,
  "  ounce mass", mksa ounce mass, cgs ounce mass,
  "  ton", mksa ton, cgs ton,
  "  metric ton", mksa metric ton, cgs metric ton,
  "  uk ton", mksa uk ton, cgs uk ton,
  "  troy ounce", mksa troy ounce, cgs troy ounce,
  "  carat", mksa carat, cgs carat,
  "  gram force", mksa gram force, cgs gram force,
  "  pound force", mksa pound force, cgs pound force,
  "  kilopound force", mksa kilopound force, cgs kilopound force,
  "  poundal", mksa poundal, cgs poundal,
  "Thermal energy and power", "mksa","cgs",
  "  calorie", mksa calorie, cgs calorie,
  "  btu", mksa btu, cgs btu,
  "  therm", mksa therm, cgs therm,
  "  horsepower", mksa horsepower, cgs horsepower,
  "Pressure", "mksa","cgs",
  "  bar", mksa bar, cgs bar,
  "  std atmosphere", mksa std atmosphere, cgs std atmosphere,
  "  torr", mksa torr, cgs torr,
  "  meter of mercury", mksa meter of mercury, cgs meter of mercury,
  "  inch of mercury", mksa inch of mercury, cgs inch of mercury,
  "  inch of water", mksa inch of water, cgs inch of water,
  "  psi", mksa psi, cgs psi,
  "Viscosity", "mksa","cgs",
  "  poise", mksa poise, cgs poise,
  "  stokes", mksa stokes, cgs stokes,
  "Light and illumination", "mksa","cgs",
  "  stilb", mksa stilb, cgs stilb,
  "  lumen", mksa lumen, cgs lumen,
  "  lux", mksa lux, cgs lux,
  "  phot", mksa phot, cgs phot,
  "  footcandle", mksa footcandle, cgs footcandle,
  "  lambert", mksa lambert, cgs lambert,
  "  footlambert", mksa footlambert, cgs footlambert,
  "Radioactivity", "mksa","cgs",
  "  curie", mksa curie, cgs curie,
  "  roentgen", mksa roentgen, cgs roentgen,
  "  rad", mksa rad, cgs rad,
  "Force and energy", "mksa","cgs",
  "  newton", mksa newton, cgs newton,
  "  dyne", mksa dyne, cgs dyne,
  "  joule", mksa joule, cgs joule,
  "  erg", mksa erg, cgs erg
))

Output: 

Math constants: [long] & [long long]
pi: [+3.141592653589793238462643383e  +0] & [+3.14159265358979323846264338327950288419716939937510582097494459e  +0]
Physical Constants: [mksa] & [cgs]
Fundamental constants: [mksa] & [cgs]
  speed of light: [+2.99792458000000e  +8] & [+2.99792458000000e +10]
  vacuum permeability: [+1.25663706144000e  -6] & [~]
  vacuum permittivity: [+8.85418781700000e -12] & [~]
  num avogadro: [+6.02214199000001e +23] & [~]
  faraday: [+9.64853429775000e  +4] & [+9.64853429775000e  +3]
  boltzmann: [+1.38065040000000e -23] & [+1.38065040000000e -16]
  molar gas: [+8.31447200000000e  +0] & [+8.31447200000000e  +7]
  standard gas volume: [+2.27109810000000e  -2] & [+2.27109810000000e  +4]
  planck constant: [+6.62606930000000e -34] & [+6.62606930000000e -27]
  planck constant bar: [+1.05457168236445e -34] & [+1.05457168236445e -27]
  gauss: [+1.00000000000000e  -4] & [+1.00000000000000e  +0]
  micron: [+1.00000000000000e  -6] & [+1.00000000000000e  -4]
  hectare: [+1.00000000000000e  +4] & [+1.00000000000000e  +8]
  miles per hour: [+4.47040000000000e  -1] & [+4.47040000000000e  +1]
  kilometers per hour: [+2.77777777778000e  -1] & [+2.77777777778000e  +1]
Astronomy and astrophysics: [mksa] & [cgs]
  astronomical unit: [+1.49597870691000e +11] & [+1.49597870691000e +13]
  gravitational constant: [+6.67300000000000e -11] & [+6.67300000000000e  -8]
  light year: [+9.46053620707001e +15] & [+9.46053620707001e +17]
  parsec: [+3.08567758135000e +16] & [+3.08567758135000e +18]
  grav accel: [+9.80665000000000e  +0] & [+9.80665000000000e  +2]
  solar mass: [+1.98892000000000e +30] & [+1.98892000000000e +33]
Atomic and nuclear physics: [mksa] & [cgs]
  electron charge: [+1.60217648700000e -19] & [+1.60217648700000e -20]
  electron volt: [+1.60217648700000e -19] & [+1.60217648700000e -12]
  unified atomic mass: [+1.66053878200000e -27] & [+1.66053878200000e -24]
  mass electron: [+9.10938188000000e -31] & [+9.10938188000000e -28]
  mass muon: [+1.88353109000000e -28] & [+1.88353109000000e -25]
  mass proton: [+1.67262158000000e -27] & [+1.67262158000000e -24]
  mass neutron: [+1.67492716000000e -27] & [+1.67492716000000e -24]
  num fine structure: [+7.29735253300000e  -3] & [~]
  rydberg: [+2.17987196968000e -18] & [+2.17987196968000e -11]
  bohr radius: [+5.29177208300000e -11] & [+5.29177208300000e  -9]
  angstrom: [+1.00000000000000e -10] & [+1.00000000000000e  -8]
  barn: [+1.00000000000000e -28] & [+1.00000000000000e -24]
  bohr magneton: [+9.27400899000000e -24] & [+9.27400899000000e -21]
  nuclear magneton: [+5.05078317000000e -27] & [+5.05078317000000e -24]
  electron magnetic moment: [+9.28476362000000e -24] & [+9.28476362000000e -21]
  proton magnetic moment: [+1.41060663300000e -26] & [+1.41060663300000e -23]
Time: [mksa] & [cgs]
  minute: [+6.00000000000000e  +1] & [+6.00000000000000e  +1]
  hour: [+3.60000000000000e  +3] & [+3.60000000000000e  +3]
  day: [+8.64000000000000e  +4] & [+8.64000000000000e  +4]
  week: [+6.04800000000000e  +5] & [+6.04800000000000e  +5]
Imperial units: [mksa] & [cgs]
  inch: [+2.54000000000000e  -2] & [+2.54000000000000e  +0]
  foot: [+3.04800000000000e  -1] & [+3.04800000000000e  +1]
  yard: [+9.14400000000000e  -1] & [+9.14400000000000e  +1]
  mile: [+1.60934400000000e  +3] & [+1.60934400000000e  +5]
  mil: [+2.54000000000000e  -5] & [+2.54000000000000e  -3]
Nautical units: [mksa] & [cgs]
  nautical mile: [+1.85200000000000e  +3] & [+1.85200000000000e  +5]
  fathom: [+1.82880000000000e  +0] & [+1.82880000000000e  +2]
  knot: [+5.14444444444000e  -1] & [+5.14444444444000e  +1]
Volume: [mksa] & [cgs]
  acre: [+4.04685642241000e  +3] & [+4.04685642241000e  +7]
  liter: [+1.00000000000000e  -3] & [+1.00000000000000e  +3]
  us gallon: [+3.78541178402000e  -3] & [+3.78541178402000e  +3]
  canadian gallon: [+4.54609000000000e  -3] & [+4.54609000000000e  +3]
  uk gallon: [+4.54609200000000e  -3] & [+4.54609200000000e  +3]
  quart: [+9.46352946004000e  -4] & [+9.46352946004000e  +2]
  pint: [+4.73176473002000e  -4] & [+4.73176473002000e  +2]
Mass and weight: [mksa] & [cgs]
  pound mass: [+4.53592370000000e  -1] & [+4.53592370000000e  +2]
  ounce mass: [+2.83495231250000e  -2] & [+2.83495231250000e  +1]
  ton: [+9.07184740000000e  +2] & [+9.07184740000000e  +5]
  metric ton: [+1.00000000000000e  +3] & [+1.00000000000000e  +6]
  uk ton: [+1.01604690880000e  +3] & [+1.01604690880000e  +6]
  troy ounce: [+3.11034750000000e  -2] & [+3.11034750000000e  +1]
  carat: [+2.00000000000000e  -4] & [+2.00000000000000e  -1]
  gram force: [+9.80665000000000e  -3] & [+9.80665000000000e  +2]
  pound force: [+4.44822161526000e  +0] & [+4.44822161526000e  +5]
  kilopound force: [+4.44822161526000e  +3] & [+4.44822161526000e  +8]
  poundal: [+1.38255000000000e  -1] & [+1.38255000000000e  +4]
Thermal energy and power: [mksa] & [cgs]
  calorie: [+4.18680000000000e  +0] & [+4.18680000000000e  +7]
  btu: [+1.05505585262000e  +3] & [+1.05505585262000e +10]
  therm: [+1.05506000000000e  +8] & [+1.05506000000000e +15]
  horsepower: [+7.45700000000000e  +2] & [+7.45700000000000e  +9]
Pressure: [mksa] & [cgs]
  bar: [+1.00000000000000e  +5] & [+1.00000000000000e  +6]
  std atmosphere: [+1.01325000000000e  +5] & [+1.01325000000000e  +6]
  torr: [+1.33322368421000e  +2] & [+1.33322368421000e  +3]
  meter of mercury: [+1.33322368421000e  +5] & [+1.33322368421000e  +6]
  inch of mercury: [+3.38638815789000e  +3] & [+3.38638815789000e  +4]
  inch of water: [+2.49088900000000e  +2] & [+2.49088900000000e  +3]
  psi: [+6.89475729317000e  +3] & [+6.89475729317000e  +4]
Viscosity: [mksa] & [cgs]
  poise: [+1.00000000000000e  -1] & [+1.00000000000000e  +0]
  stokes: [+1.00000000000000e  -4] & [+1.00000000000000e  +0]
Light and illumination: [mksa] & [cgs]
  stilb: [+1.00000000000000e  +4] & [+1.00000000000000e  +0]
  lumen: [+1.00000000000000e  +0] & [+1.00000000000000e  +0]
  lux: [+1.00000000000000e  +0] & [+1.00000000000000e  -4]
  phot: [+1.00000000000000e  +4] & [+1.00000000000000e  +0]
  footcandle: [+1.07600000000000e  +1] & [+1.07600000000000e  -3]
  lambert: [+1.00000000000000e  +4] & [+1.00000000000000e  +0]
  footlambert: [+1.07639104000000e  +1] & [+1.07639104000000e  -3]
Radioactivity: [mksa] & [cgs]
  curie: [+3.70000000000000e +10] & [+3.70000000000000e +10]
  roentgen: [+2.58000000000000e  -4] & [+2.58000000000000e  -8]
  rad: [+1.00000000000000e  -2] & [+1.00000000000000e  +2]
Force and energy: [mksa] & [cgs]
  newton: [+1.00000000000000e  +0] & [+1.00000000000000e  +5]
  dyne: [+1.00000000000000e  -5] & [+1.00000000000000e  +0]
  joule: [+1.00000000000000e  +0] & [+1.00000000000000e  +7]
  erg: [+1.00000000000000e  -7] & [+1.00000000000000e  +0]

ALGOL W

% the Algol W standard environment includes the following standard variables: %

integer                I_W          % field width for integer output %
integer                R_W          % field width for real output %
integer                R_D          % number of decimal places for real output %
string(1)              R_FORMAT     % format for real output:
                                          S - "scaled" normalised mantissa with exponent
                                          A - "aligned" fixed point format
                                          F - "free" either scaled or aligned as appropriate
                                                     for the value and field width
                                    %
integer                S_W          % separator width - number of spaces following non-string output items %
integer                MAXINTEGER   % largest integer value %
real                   EPSILON      % largest positive real number such that 1 + epsilon = 1 %
long real              LONGEPSILON  % largest positive long real number such that 1 + longepsilon = 1 %
long real              MAXREAL      % largest real number %
long real              PI           % approximation to pi %

% the following reference(EXCEPTION) variables control how errors are handled:
    ENDFILE                         - end-of-file
    OVFL                            - overflow
    UNFL                            - underflow
    DIVZERO                         - division by zero
    INTOVFL                         - integer overflow
    INTDIVZERO                      - integer division by zero or modulo 0
    SQRTERR                         - invalid SQRT parameter
    EXPERR                          - invalid EXP parameter
    LNLOGERR                        - invalid LN or LOG parameter
    SINCOSERR                       - invalid SIN or COS parameter

The EXCEPTION record is defined as follows:

record    EXCEPTION( logical    XCPNOTED      - true if the exception has occurred
                   ; integer    XCPLIMIT      - number of times the exception can occur
                                                before the program terminates
                              , XCPACTION     - if the program continues, controls how to
                                                replace the erroneous value
                   ; logical    XCPMARK       - true if an error message should be printed
                                                even if the program continues
                   ; string(64) XCPMSG        - message to describe the exception
                   )
 
if the relevant EXCEPTION variable is null, the exception is ignored,
otherwise it is processed according to the settings of XCPLIMIT etc.
%

Arturo

There are no "special" variables in Arturo, as such. There are pre-defined, built-in functions & constants but every symbol can be re-defined at will, even during runtime.

AutoHotkey

Refer to Built-in Variables for the complete special variables (those variables are global, except noticed).

AWK

There are two types of special variables within AWK: Control variables and Informative variables.

  • dollarint variables - The dollarint special variables represent fields within a record
  • ARGC - An informative variable that provides command line parameter information
  • ARGV - An informative array that provides command line parameter information
  • CONVFMT - A control variable that specifies the conversion format of numerical strings
  • ENVIRON - An informative array that contains the environment strings
  • FILENAME - An informative variable that provides the current input [filename]
  • FNR - An informative variable that provides the record number within the current file
  • FS - A control variable that specifies the input field separator
  • NF - An informative variable that provides the number of fields within the current record
  • NR - An informative variable that provides the total number of records processed
  • OFMT - A control variable that specifies the output format of numerical values
  • OFS - A control variable that specifies the output field separator
  • ORS - A control variable that specifies the output record separator
  • RLENGTH - An informative variable that provides the length of the currently matched substring
  • RS - A control variable that specifies the input record separator
  • RSTART - An informative variable that provides the start index of the currently matched substring
  • SUBSEP - A control variable that specifies the subscript separator for multidimensional arrays

Batch File

By typing the SET command (without any parameters) in the command prompt, it will display the current environment variables and their current values.
However, there are some special variables that are not listed in the variables displayed by the SET command because their values might change over time. These variables are as follows:

%CD% - expands to the current directory string.

%DATE% - expands to current date using same format as DATE command.

%TIME% - expands to current time using same format as TIME command.

%RANDOM% - expands to a random decimal number between 0 and 32767.

%ERRORLEVEL% - expands to the current ERRORLEVEL value

%CMDEXTVERSION% - expands to the current Command Processor Extensions
    version number.

%CMDCMDLINE% - expands to the original command line that invoked the
    Command Processor.

%HIGHESTNUMANODENUMBER% - expands to the highest NUMA node number
    on this machine.

(Source: by typing SET/? command in the command prompt)

BBC BASIC

Works with: BBC BASIC for Windows

The special (system) variables are as follows: 

@%        The number output format control variable 
@cmd$     The command line of a 'compiled' program 
@dir$     The directory (folder) from which the program was loaded 
@flags%   An integer incorporating BBC BASIC's control flags 
@hcsr%    The handle of the mouse pointer (cursor) 
@haccel%  The handle of the keyboard accelerator, if used 
@hevent%  The handle of the event used to prevent blocking in serial I/O 
@hfile%() An array of file handles indexed by channel number 
@hmdi%    The Multiple Document Interface window handle (if any) 
@hwacc%   The window handle to which keyboard accelerator commands should be sent 
@hwnd%    The 'window handle' for the main (output) window 
@hwo%     The handle of the WAVEOUTPUT device 
@hpal%    The handle for the colour palette 
@ispal%   A Boolean which is non-zero if the display is paletted 
@lib$     The directory (folder) containing the library files 
@lparam%  The LPARAM value (for use with ON MOUSE, ON MOVE and ON SYS) 
@memhdc%  The 'device context' for the main (output) window
@midi%    The MIDI device ID (non-zero if a MIDI file is playing) 
@msg%     The MSG value (for use with ON MOUSE, ON MOVE and ON SYS) 
@ox%      The horizontal offset (in pixels) between the output bitmap and the window contents 
@oy%      The vertical offset (in pixels) between the output bitmap and the window contents 
@prthdc%  The 'device context' for the current printer (if any) 
@tmp$     The temporary directory (folder) 
@usr$     The user's Documents directory (folder) 
@vdu%     A pointer to the text and graphics parameters 
@vdu{}    A structure containing the main text and graphics variables 
@wparam%  The WPARAM value (for use with ON MOUSE, ON MOVE and ON SYS)

bc

There are three special variables:

  • scale: determines how many digits after the decimal point a result of an expression will have (possible integer values from 0 to BC_SCALE_MAX, i.e. an implementation-specific maximum; initial value is 0)
  • ibase: the input radix (possible integer values from 2 to 16; initial value is 10)
  • obase: the output radix (possible integer values from 2 to BC_BASE_MAX; initial value is 10)
Works with: GNU bc

The GNU implementation adds another special variable, last, that contains the value of the last printed number.

Bracmat

Every function has a local variable arg. It is the function's actual argument. Pattern matching is used to dissect the argument, if needed. Functions in a pattern have an additional argument, sjt, which is bound to (part of) the subject of the pattern match operation. It is the part of the subject that the function, in the role of a pattern, attempts to match. These variables can be reassigned.

The names of the built-in functions alc, arg, asc, chr, chu, clk, d2x, dbg, den, div, fil, flg, glf, fre, get, low, lst, mem, mod, new, pee, pok, put, ren, rev, rmv, sim, str, swi, sys, tbl, upp, utf, whl, x2d can be used as variable names or names of user defined object member functions, but not as names of user defined functions. Conversely, the name hash can be used for user defined functions, but not for variables. Currentlty, hash is the only predefined object type.

If Bracmat starts in interactive mode, a few more variables are predefined: !v evaluates to a string telling which version of Bracmat you are running. !w and !c evaluate to sections 11 and 12 of the GPL. More vital is the variable main, which is the interpreter's main loop. Setting it to another value changes the behaviour of the interpreter. When running in interactive mode, ! or !"" evaluates to the last answer, so the empty string is the name of yet another special variable. These variables can be reassigned.

C

C99 introduced the (read-only) special variable __func__ (of type static const char[]) which holds the name of the current function.

Furthermore one could consider errno from <errno.h> as a special variable although it actually is a macro which expands to an modifiable lvalue of type int. Many library functions set it to a positive value in case of an error.

C++

Besides errno like C, C++ has the this pointer so objects can refer to themselves. 

#include <iostream>

struct SpecialVariables
{
    int i = 0;

    SpecialVariables& operator++()
    {
        // 'this' is a special variable that is a pointer to the current
        // class instance.  It can optionally be used to refer to elements
        // of the class.
        this->i++;  // has the same meaning as 'i++'

        // returning *this lets the object return a reference to itself
        return *this;
    }

};

int main()
{
    SpecialVariables sv;
    auto sv2 = ++sv;     // makes a copy of sv after it was incremented
    std::cout << " sv :" << sv.i << "\n sv2:" << sv2.i << "\n";
}
Output:
 sv :1
 sv2:1

Clojure

The following snippet prints a list of the special variables defined in clojure.core, in *earmuff* form. For further information, consult the documentation. 

(apply str (interpose " " (sort (filter #(.startsWith % "*") (map str (keys (ns-publics 'clojure.core)))))))
Output:
*1 *2 *3 *agent* *allow-unresolved-vars* *assert* *clojure-version* *command-line-args* *compile-files* *compile-path*
*compiler-options* *data-readers* *default-data-reader-fn* *e *err* *file* *flush-on-newline* *fn-loader* *in* *math-context*
*ns* *out* *print-dup* *print-length* *print-level* *print-meta* *print-readably* *read-eval* *source-path* *unchecked-math*
*use-context-classloader* *verbose-defrecords* *warn-on-reflection*

Common Lisp

Note: the term "special variable" has a meaning in Common Lisp and related dialects, different from the way it is being used here. It is a jargon which denotes a dynamically scoped variable. ANSI Common Lisp's standard-defined variables are special variables in both senses of the term.

The following code snippet prints a list of all 44 special variables defined by the Common Lisp standard. For further information about each of them consult the online documentation. 

(defun special-variables ()
  (flet ((special-var-p (s)
           (and (char= (aref s 0) #\*)
                (find-if-not (lambda (x) (char= x #\*)) s)
                (char= (aref s (1- (length s))) #\*))))
    (let ((lst '()))
      (do-symbols (s (find-package 'cl))
        (when (special-var-p (symbol-name s))
          (push s lst)))
      lst)))

(format t "~a~%" (sort (special-variables) #'string<))
Output:
(*BREAK-ON-SIGNALS* *COMPILE-FILE-PATHNAME* *COMPILE-FILE-TRUENAME* *COMPILE-PRINT* *COMPILE-VERBOSE* *DEBUG-IO*
 *DEBUGGER-HOOK* *DEFAULT-PATHNAME-DEFAULTS* *ERROR-OUTPUT* *FEATURES* *GENSYM-COUNTER* *LOAD-PATHNAME*
 *LOAD-PRINT* *LOAD-TRUENAME* *LOAD-VERBOSE* *MACROEXPAND-HOOK* *MODULES* *PACKAGE* *PRINT-ARRAY* *PRINT-BASE*
 *PRINT-CASE* *PRINT-CIRCLE* *PRINT-ESCAPE* *PRINT-GENSYM* *PRINT-LENGTH* *PRINT-LEVEL* *PRINT-LINES*
 *PRINT-MISER-WIDTH* *PRINT-PPRINT-DISPATCH* *PRINT-PRETTY* *PRINT-RADIX* *PRINT-READABLY* *PRINT-RIGHT-MARGIN*
 *QUERY-IO* *RANDOM-STATE* *READ-BASE* *READ-DEFAULT-FLOAT-FORMAT* *READ-EVAL* *READ-SUPPRESS* *READTABLE*
 *STANDARD-INPUT* *STANDARD-OUTPUT* *TERMINAL-IO* *TRACE-OUTPUT*)

Inside the REPL, there are more special variables available:

  • -: Contains the form that is currently evaluated.
> (format t "~a" -)
(FORMAT T ~a -)
NIL
  • *, **, ***: Contain the last, penultimate, antepenultimate primary values that were printed.
> (+ 1 2)
3
> (values 1 2)
1 ;
2
> (* 4 5)
20
> (list * ** ***)
(20 1 3)
  • +, ++, +++: Contain the last, penultimate, antepenultimate forms that were evaluated.
> (+ 1 2)
3
> (values 1 2)
1 ;
2
> (* 4 5)
20
> (list + ++ +++)
((* 4 5) (VALUES 1 2) (+ 1 2))
  • /, //, ///: Contain a list of the last, penultimate, antepenultimate values that were printed.
> (floor 10 2)
5 ;
0
> (values 1 'a "foo")
1 ;
A ;
"foo"
> (+ 1 2)
3
> (list / // ///)
((3) (1 A "foo") (5 0))

D

In D there are not many special variables, beside a string[] argument of the main function. Variables like the C "errno" are usually not used, despite the C library is available.

One special boolean variable is __ctfe, that is read-only and it's true inside functions when they are evaluated at compile-time, and false otherwise.

DWScript

DWScript has no special variables in the base language.

Hosts can however define any number of contextual or environmental variables.

Dyalect

Dyalect has a special this which is available inside methods: 

func Integer.Double() {
    this + this
}
print(8.Double())

Déjà Vu

Calls to some of the standard library functions can be optimized into certain opcodes or sequences of opcodes, namely: 

set setglobal local get getlocal return recurse drop dup swap rot over
[] {} pop-from push-to push-through has get-from set-to raise reraise
call for pass

In addition, eva is special: 

!print "hey" #is really short for
eva!print "hey"

EVA is the part of the standard library that takes care of communication with the outside world. It makes extensive use of the method call syntax, unlike the rest of the standard library, that is why it is special.

Erlang

Erlang has no special variables. What it does have are special functions, module_info/0 and module_info/1. These are added to a module automatically, without being present in the code. 

-module( special_variables ).

-export( [task/0] ).

task() -> ok.
Output:
2> special_variables:module_info().
[{exports,[{task,0},{module_info,0},{module_info,1}]},
 {imports,[]},
 {attributes,[{vsn,[11317586745549911665324094732832680475]}]},
 {compile,[{options,[]},
           {version,"4.8"},
           {time,{2013,10,28,20,2,58}},
           {source,"/Users/bengt/rosetta/special_variables.erl"}]}]
3> special_variables:module_info(exports).
[{task,0},{module_info,0},{module_info,1}]

Forth

In a standard system, there are a handful of predefined variables, such as:

  • BASE contains the current input/output numeric base (default 10 for decimal).
  • STATE is a flag telling whether the system is in interpret or compile mode.

The DO-LOOP construct also has accessors I and J (and sometimes K) for obtaining the loop indices of the inner and outer nested loops.

Common Practice

Although not mandated in the Forth language specification, traditionally the language implements system variables as what are called USER variables. The name dates back to the a time when FORTH was used as a multi-user O/S and therefore each user needed a set of variables to control the state of their instance of the system. The user variables exist in a memory block called the USER AREA and are replicated for each task. When used for embedded systems, Forth is commonly implemented as a multi-tasking system, so this architecture is still relevant today. On a context switch the system assigns a system VARIABLE called 'UP' (user pointer) to point to the new task's USER AREA. Using UP, the task's local stack pointers can be read into the machine and a fast context switch can be completed. UP is commonly held in a CPU register on machines that have larger register sets.

This following list is an example of a set of USER variables in a small system. Consult the implementation documents for details on the USER variables in a specific FORTH system. 

Name      Type          Description
---------------------------------------------
TIB      integer    Terminal Input Buffer address
U0       integer    current user area address
>IN      integer    holds offset into TIB, used for parsing
BASE     integer    holds number conversion radix
STATE    integer    holds compiler state (true=compiling, false=interpreting)
DP       integer    holds dictionary memory pointer
'SOURCE  integer[2] contains length and address of input source
LATEST   integer    address of last word added to dictionary
HP       integer    HOLD pointer, used for number formatting routines
LP       integer    leave-stack pointer, used by do loops
S0       integer    end of parameter stack
PAD      chars[80]  Generic buffer. (size is implementation dependent)
L0       integer    bottom of leave stack
R0       integer    end of return stack

It is worth noting that any of these variable names could be used in a program. The result would be that the original variable would be hidden from the compiler as the new variable with the same name would be found first. In other words the function of the original variable would NOT change in system. Forth has a "hyper-static" name space.

Fortran

Fortran offers no special variables such as Pi, e, etc. as a part of the language, not even the modern special floating-point "values" such as NaN. Indeed, the syntax has no reserved words generally so that GO TO could be the name of a variable without damage to GO TO statements, though it is generally agreed that calling a variable END is provocative... It does have some numbers that are special: 5 is the input/output "unit number" for keyboard input and 6 for output to "standard output", the screen on desktop computers; in the past there have been other values that were associated to devices such as the card reader, card punch, lineprinter, paper tape reader, and so on at any given installation. But these constants are not given names as mnemonics for their special values, except by the programmer. There is no equivalent of SYSOUT as in WRITE(SYSOUT,etc without definition by the programmer.

Certain statements involve special names in what appear to be assignments of values to or from a special name that has a value just like a named variable does, but these are not proper variables at all. For instance, in 

           INQUIRE(FILE = FILENAME(1:L),EXIST = EXIST,	!Here we go. Does the file exist?
     1      ERR = 666,IOSTAT = IOSTAT) 		!Hopefully, named in good style, etc.
           IF (EXIST) THEN	!So, does the named file already exist?
           ...etc.

ERR is a special name, but only inside the context of the INQUIRE (and OPEN, and WRITE, etc.) statement, it is not the name of an existing variable outside that statement whether defined by the language or by the programmer, and if the programmer were to define a variable called ERR it would have no relevance within that INQUIRE statement - though ERR = ERR would be workable if an ASSIGN statement had assigned statement label 666 to variable ERR. Similarly, the variable named FILENAME is declared by the programmer and because there are no reserved words, could be just FILE. Likewise, EXIST is declared (as LOGICAL) and IOSTAT (as INTEGER) as a mnemonic aid and also to save on the trouble of remembering whether the assignment works left-to-right or right-to-left in each case. It is right-to-left for FILE = filename, input to the INQUIRE statement and left-to-right for EXIST = variable, an output of the INQUIRE statement.

FreeBASIC

FreeBASIC has no 'special variables'.

Go

Go has no special variables in the base language.

A number of the standard packages however, define special variables or constants. Standard error values are common, as are enumeration-like constants for controling functions. Examples of some more frequently used package variables might be io.EOF, os.Args, and os.Stdout.

See also Topic variable#Go for an example of '.' of the template package.

Haskell

Like C, there are practically no special variables. The program entry point, main, is the one exception.

Icon and Unicon

Icon and Unicon have special variables known as keywords which are syntactically are preceded by an &. 

# &keyword # type returned(indicators) - brief description
# indicators:
#    * - generates multiple values
#    = - modifiable
#    ? - may fail (e.g. status inquiry)
#    U - Unicon
#    G - Icon or Unicon with Graphics
#
&allocated   # integer(*) - report memory allocated in total and by storage regions
&ascii       # cset -  ASCII character set
&clock       # string - time of day
&col         # integer(=G) - column location of pointer
&collections # integer(*) - garbage collection activity in total and by storage region
&column      # integer(U) - source code column
&control     # null(?G) - control key state
&cset        # cset - universal character set
&current     # co-expression - current co-expression
&date        # string - today's date
&dateline    # string - time stamp
&digits      # cset - digit characters
&dump        # integer(=) - termination dump
&e           # real - natural log e
&error       # integer(=) - enable/disable error conversion/fail on error
&errno       # integer(?) - variable containing error number from previous posix command
&errornumber # integer(?) - error number of last error converted to failure
&errortext   # string(?) - error message of last error converted to failure
&errorvalue  # any(?) - erroneous value of last error converted to failure
&errout      # file - standard error file
&eventcode   # integer(=U) - program execution event in monitored program
&eventsource # co-expression(=U) - source of events in monitoring program
&eventvalue  # any(=U) - value from event in monitored program
&fail        # none - always fails
&features    # string(*) - identifying features in this version of Icon/Unicon
&file        # string -  current source file
&host        # string - host machine name
&input       # file - standard input file
&interval    # integer(G) - time between input events
&lcase       # cset - lowercase letters
&ldrag       # integer(G) - left button drag
&letters     # cset - letters
&level       # integer - call depth
&line        # integer - current source line number
&lpress      # integer(G) - left button press
&lrelease    # integer(G) - left button release
&main        # co-expression - main task
&mdrag       # integer(G) - middle button drag
&meta        # null(?G) - meta key state
&mpress      # integer(G) - middle button press
&mrelease    # integer(G) - middle button release
&now         # integer(U) - current time
&null        # null - null value
&output      # file - standard output file
&pick        # string (U) - variable containing the result of 3D selection
&phi         # real - golden ratio
&pos         # integer(=) - string scanning position
&progname    # string(=) - program name
&random      # integer(=) - random number seed
&rdrag       # integer(G) - right button drag
&regions     # integer(*) - region sizes
&resize      # integer(G) - window resize
&row         # integer(=G) - row location of pointer
&rpress      # integer(G) - right button press
&rrelease    # integer(G) - right button release
&shift       # null(?G) - shift key state
&source      # co-expression - invoking co-expression
&storage     # integer(*) - memory in use in each region
&subject     # string - string scanning subject
&syserr      # integer - halt on system error
&time        # integer(=) - elapsed time in milliseconds
&trace       # integer(=) - trace program
&ucase       # cset - upper case letters
&version     # string - version
&window      # window(=G) - the current graphics rendering window
&x           # integer(=G) - pointer horizontal position
&y           # integer(=G) - pointer vertical position
# keywords may also fail if the corresponding feature is not present.
# Other variants of Icon (e.g. MT-Icon) will have different mixes of keywords.

IS-BASIC

BLACK   - The code of colour black.
BLUE    - The code of colour blue.
CYAN    - The code of colour cyan.
DATE$   - The current date in the standard format.
EXLINE  - The number of the last statement that caused an exception.
EXTYPE  - The error code of the last exception.
FREE    - The amount of memory free and avaible to the current program.
GREEN   - The code of colour green.
INF     - The largest positive number that the IS-BASIC can handle.
MAGENTA - The code of colour magenta.
PI      - Value of the Pi. This is rounded to 3.141592654
RED     - The code of colour red.
TIME$   - The current time in the standard format.
WHITE   - The code of colour white.
YELLOW  - The code of colour yellow.
VERNUM  - Version number of the BASIC

J

special local variables

The names x y u v m n are used as parameters in explicit J definitions: 

  y:  right argument
  x:  (optional) left argument
  u:  left argument to an adverb or conjunction
  v:  right argument to a conjunction
  m:  left noun argument to an adverb or conjunction (value error if verb provided)
  n:  right noun argument to a conjunction (value error if verb provided)

Note that the result of an adverb or conjunction that uses either x or y and one of these other names is always a verb. In this case, x and/or y represent arguments passed to the derived verb.

Some examples: 

   {{ y }} 1
1
   1000 {{ x + y }} 1
1001
   100 {{ m + y }} 1
101
   (1000) 100 {{ x + m + y }} 1
1101
   100 {{ m + n + y }} 10 (1)
111
   (1000) 100 {{ x + m + n + y }} 10 (1)
1111
   (1000) + {{ x u n u y }} 10 (1)
1011
   (1000) 100 {{ x v m v y }} + (1)
1101

These names may be used as regular names, but that is bad practice except in the context of debugging or illustration.

special global variables

In J 602: Names in locale z are in the path for all locales, including the default locale (base) -- these provide "language features": 

   names_z_''
ARGV           BINPATH        CR             CRLF           DEL            Debug          
EAV            EMPTY          FF             FIXFONT        FIXFONTWH      IF64           
IFCONSOLE      IFGTK          IFJ6           IFJAVA         IFJHS          IFUNIX         
IFWIN          IFWIN32        IFWINCE        IFWINE         IFWINNT        JVERSION       
LF             LF2            Note           PROFONT        SYSPPC         TAB            
UNAME          adverb         apply          assert         bind           boxopen        
boxxopen       break          bx             clear          coclass        cocreate       
cocurrent      codestroy      coerase        cofullname     coinsert       coname         
conames        conew          conjunction    conl           copath         coreset        
cutopen        datatype       def            define         do             drop           
dyad           each           edit           empty          erase          every          
exit           expand         fetch          inv            inverse        items          
jcwdpath       jhostpath      jpath          jpathsep       jsystemdefs    leaf           
list           load           loadd          loadp          mbopen         mbsave         
monad          nameclass      namelist       names          nc             nl             
noun           on             open           pick           require        rows           
script         scriptd        scripts        setbreak       sign           sminfo         
smoutput       sort           split          startupconsole startupide     table          
take           tmoutput       toCRLF         toHOST         toJ            tolower        
toupper        type           ucp            ucpcount       utf8           uucp           
verb           wcsize         wd             wdbox          wdcenter       wdclipread     
wdclipwrite    wde            wdfit          wdforms        wdget          wdhandler      
wdinfo         wdishandle     wdisparent     wdmove         wdpclose       wdqshow        
wdquery        wdreset        wdselect       wdstatus       winpathsep

Names in the locales j and jijs are available by explicity referencing those locales and are used to provide "system features" and "ide features": 

   names_j_''
BOXES              BROWSER            CONFIRMCLOSE       DIRTREEX           DISPLAYLOAD        
EPSREADER          FORMAT             FORMSIZES          GetSystemMetrics   IFJIJX             
INPUTLOG           INPUTLOGFILE       LOADED             P2UPFONT           PATHJSEP           
PATHSEP            PDFREADER          PRINTERFONT        PRINTOPT           PUBLIC             
READONLY           SCRIPTS            SHOWSIP            SMPRINT            SM_CMONITORS       
SM_CXVIRTUALSCREEN SM_CYVIRTUALSCREEN SM_XVIRTUALSCREEN  SM_YVIRTUALSCREEN  STARTUP            
SYSTEMFOLDERS      TARGET             USERFOLDERS        WINPOS             XDIFF              
addfname           boxdraw            buildpublic        classwizard        cleantable         
config             cutnames           deb                debug              demos              
dirmatch           dltb               edit               editfind           editinputlog       
editinputprompt    exist              extijs             fexist             fif                
filenewform        fileprint          fileprintsetup     filex              fixWINPOS          
formedit           formeditrun        forms              fullname           getinputlog        
getpath            getscripts         gettarget          gettargetlocale    globaldefs         
gridwizard         help               htmlhelp           jpath              lab                
lastactive         loadp              open               openfiles          origin             
pacman             printfiles         prints             projectmanager     save               
saveuserfolders    scriptmake         scripts            wpreset            wpsave             
wpset                                                                                          
   names_jijs_''
EMPTY                      FIXFONTDEF                 FKEYS                      
FTYPES                     IFIOX                      IFMAX                      
IFREADONLY                 IFSAVED                    IFSHOW                     
JIJS                       JIJSMAC                    JRECENT                    
NEWUSER                    PPSCRIPT                   QFORMX                     
RECENT                     RECENTFILE                 RECENTLOC                  
RECENTMAX                  SCMP                       SMBLK                      
SMDESK                     SMHWNDP                    SMINIT                     
SMNAME                     SMPATH                     SMSEL                      
SMSIZE                     SMSTYLE                    SMTEXT                     
SMTORG                     aboutj                     boxfkeys                   
boxskeys                   checkreadonly              cleartemp                  
close                      closeijs                   closeijx                   
closewindows               comparesvn                 create                     
cutpara                    deb                        destroy                    
exitijs                    filecase                   fkeycase                   
fkeylist                   fkeyrun                    fkeyselect                 
fkeyselect1                flerase                    flexist                    
flopen                     flread                     flwrite                    
foldpara                   foldtext                   getSMSEL                   
getactsize                 getcascade                 getcascade1                
getcascades                getfile                    getformx                   
getline                    getsaveas                  getscrollpos               
getselection               getskey                    id2loc                     
id2name                    id2names                   id2type                    
ide_maximize               ide_minimize               ide_restore                
ifshiftkey                 iftempscript               info                       
intn                       jijs_aboutj_button         jijs_actrl_fkey            
jijs_bctrl_fkey            jijs_bctrlshift_fkey       jijs_cancel                
jijs_close                 jijs_close_button          jijs_dctrl_fkey            
jijs_default               jijs_demos_button          jijs_ectrl_fkey            
jijs_ectrlshift_fkey       jijs_editconfigure_button  jijs_editcopy_button       
jijs_editcut_button        jijs_editdirmatch_button   jijs_editexport_button     
jijs_editfif_button        jijs_editfind_button       jijs_editformedit_button   
jijs_editinputlog_button   jijs_editlint_button       jijs_editpaste_button      
jijs_editreadonly_button   jijs_editredo_button       jijs_editselectall_button  
jijs_editundo_button       jijs_f1_fkey               jijs_f1ctrl_fkey           
jijs_f1shift_fkey          jijs_fctrl_fkey            jijs_fctrlshift_fkey       
jijs_filecleartemp_button  jijs_fileexit_button       jijs_filenewclass_button   
jijs_filenewijs_button     jijs_fileopen_button       jijs_fileopensystem_button 
jijs_fileopenuser_button   jijs_fileprint_button      jijs_fileprintsetup_button 
jijs_filerecent_button     jijs_fkeys_button          jijs_forms_button          
jijs_gctrl_fkey            jijs_hctrl_fkey            jijs_helpconstants_button  
jijs_helpcontext_button    jijs_helpcontrols_button   jijs_helpdictionary_button 
jijs_helpforeigns_button   jijs_helpgeneral_button    jijs_helpgl2cmd_button     
jijs_helphelp_button       jijs_helpindex_button      jijs_helpphrases_button    
jijs_helpprimer_button     jijs_helprelease_button    jijs_helprelnotes_button   
jijs_helpuser_button       jijs_helpvocab_button      jijs_helpwdcmd_button      
jijs_helpwdover_button     jijs_ictrl_fkey            jijs_jctrl_fkey            
jijs_kctrl_fkey            jijs_kctrlshift_fkey       jijs_labadvance_button     
jijs_labauthor_button      jijs_labchapters_button    jijs_labs_button           
jijs_lctrl_fkey            jijs_lctrlshift_fkey       jijs_max_button            
jijs_mctrl_fkey            jijs_nctrl_fkey            jijs_nctrlshift_fkey       
jijs_octrl_fkey            jijs_pctrl_fkey            jijs_qctrl_fkey            
jijs_rctrl_fkey            jijs_rctrlshift_fkey       jijs_rundebug_button       
jijs_runfile_button        jijs_runfiled_button       jijs_runline_button        
jijs_runpacman_button      jijs_runprojman_button     jijs_runselection_button   
jijs_runwindow_button      jijs_runwindowd_button     jijs_save_button           
jijs_saveas_button         jijs_sctrl_fkey            jijs_sellower_button       
jijs_selminus_button       jijs_selplus_button        jijs_selplusline1_button   
jijs_selplusline2_button   jijs_selsort_button        jijs_seltoggle_button      
jijs_selupper_button       jijs_selwrap_button        jijs_tctrl_fkey            
jijs_tile_button           jijs_tileacross_button     jijs_tilecascade_button    
jijs_togglebox_button      jijs_wctrl_fkey            jijs_wctrlshift_fkey       
jrecent_cancel             jrecent_close              jrecent_enter              
jrecent_lb_button          jrecent_open_button        jrecent_run                
jrecent_run_button         jrecent_rund_button        jrecent_view_button        
lint                       marksavedid                name2id                    
new                        newijs                     newijx                     
nounrep                    openijs                    parentname                 
pathname                   pmovex                     qsmact                     
qsmall                     qsmallforms                qsmallijs                  
qsmlastijs                 qsmlastxs                  qsmout                     
qsmsize                    query                      quote                      
rdist                      readid                     readid16                   
readonlydefault            recent_open                recent_put                 
recent_read                recent_run                 recent_save                
resizefont                 restorefont                roundint                   
runcompare                 runexport                  runfile                    
runimmx0                   runimmx1                   runline                    
runselection               runwindow                  save                       
saveas                     saveopenwindows            scmp_cancel                
scmp_close                 scmp_close_button          scmp_current_button        
scmp_original_button       scmp_revert_button         scmp_run                   
scmp_show                  select_line                select_text                
set_fkeys                  set_skey1                  set_skeys                  
setfontall                 setpnall                   setreadonly                
sh                         smappend                   smclose                    
smfocus                    smfocusact                 smfocusout                 
smgetsel                   smmove                     smopen                     
smprompt                   smread                     smreplace                  
smsave                     smscroll                   smsel                      
smselact                   smselout                   smsetcmd                   
smsetsaved                 smsetselect                smwrite                    
sysmodifiers               tile                       tile2fit                   
tile2fit1                  tileacross                 tilecascade                
tileget                    todelim                    tofoldername               
togglebox                  togglereadonly             togglexs                   
tolist                     topara                     ucpboxdraw                 
unboxfkeys                 unboxskeys                 winmax

Java

Java is heavily object-oriented, and is mostly statically-typed. There aren't many special variables, or aggregates, similar to dynamically-typed languages.

There is null, which is used to represent an object which has no reference assigned. 

Object object = null

There is true and false which are used to denote a Boolean value. 

boolean value = true

There is the this and super variables, used to reference the current class and parent class, respectively. 

this.object

super(value)

To avoid confusion to anyone unfamiliar with Java, there is the ability to import static, final, variables from other classes.
While these are not 'special variables' they may appear that way to a new user. 

import static java.lang.Math.*;

double area = PI * (2 * 2);

There is the first parameter of the main method, which is of type String[].
It is non-null and includes any arguments depicted during execution. 

public static void main(String[] args)


Additionally ...
Java has only a few special variables. There is a String-Array for passing command-line-arguments to the program, and there is a Class-Object that can be accessed in a variable-like manner. It is used for reflection, (like examining and modifing class members, their type and modifiers during runtime). There is the System-"Object" that contains various (mostly static) data about the enviroment the Java VM runs on, and it's cousin Runtime that provides data that is more prone to change during runtime, like available CPU cores and RAM.

Inside an object there is this, a reference that points to the object itself (like 127.0.0.1 in networking) and are used to qualify member access. There is also super that does the same for the base class (actually "the next class in the inheritance tree"). Both are not demonstrated in the example below. 

import java.util.Arrays;

public class SpecialVariables {

    public static void main(String[] args) {

        //String-Array args contains the command line parameters passed to the program
        //Note that the "Arrays.toString()"-call is just used for pretty-printing
        System.out.println(Arrays.toString(args));

        //<Classname>.class might qualify as a special variable, since it always contains a Class<T>-object that
        //is used in Reflection
        System.out.println(SpecialVariables.class);


        //The following are not really "variables", since they are properly encapsulated:

        //System.getenv() returns a String-String-Map of environment-variables
        System.out.println(System.getenv());

        //System.getProperties() returns a Map of "things somebody might want to know", including OS and architecture
        // the Java VM runs on, various paths like home direcoty of the user that runs the program, class (library) paths,
        System.out.println(System.getProperties());

        //Runtime.getRuntime() returns a Runtime-Object that contains "changing" data about the running Java VM's 
        // environment, like available processor cores or available RAM 
        System.out.println(Runtime.getRuntime().availableProcessors());

    }
}

JavaScript

this evaluates to the object the immediately enclosing function was called on as a method, if it was. If it was not called as a method, this is either the global environment object (usually window in browsers) in non-strict mode, or undefined in strict mode. this is an expression resembling a variable, but not actually a variable; for example, it is a syntax error to assign to it. 

var obj = {
  foo: 1,
  bar: function () { return this.foo; }
};
obj.bar(); // returns 1

When a function is entered, the variable arguments is bound to an “arguments object” which is an array-like object containing the function's arguments, as well as some other information. This how varargs functions are implemented in JavaScript. If the function's parameters contain “arguments” explicitly, then it is not overridden and functions as an ordinary parameter. 

function concat() {
  var s = "";
  for (var i = 0; i < arguments.length; i++) {
    s += arguments[i];
  }
  return s;
}
concat("a", "b", "c"); // returns "abc"

jq

Variables in jq are identifiers preceded by the sigil "$", e.g. $x. There are no predefined variables, but jq does allow variables to be assigned string values on the command line.

For example:

$ jq -n -M --arg x 1 '$x|type'   # (*)   
"string"

(*) Windows users would write "$x|type".

Julia

Julia starts with the Base module loaded. Taking "special variables" to mean names in the default global namespace (Base) that aren't functions, types, or modules, then you can obtain them with 

join(sort(filter(sym -> let n=eval(sym); !(isa(n, Function) || isa(n, Type) || isa(n, Module)); end, names(Base))), ", ")
Output:
":, ARGS, CPU_CORES, C_NULL, DL_LOAD_PATH, DevNull, ENDIAN_BOM, ENV, I, Inf, Inf16, Inf32, InsertionSort, JULIA_HOME, LOAD_PATH, MS_ASYNC, MS_INVALIDATE, MS_SYNC, MergeSort, NaN, NaN16, NaN32, OS_NAME, QuickSort, RTLD_DEEPBIND, RTLD_FIRST, RTLD_GLOBAL, RTLD_LAZY, RTLD_LOCAL, RTLD_NODELETE, RTLD_NOLOAD, RTLD_NOW, RoundDown, RoundFromZero, RoundNearest, RoundToZero, RoundUp, STDERR, STDIN, STDOUT, VERSION, WORD_SIZE, catalan, cglobal, e, eu, eulergamma, golden, im, pi, γ, π, φ"

(Because of Julia's multiple dispatch that allows a single function to have multiple definitions for different argument types, combined with the ability of functions in modules or variables in the local scope to safely shadow names in the global namespace, having a large global namespace is seen as a convenience rather than a problem.)

Kotlin

There are two 'special variables' that I can think of in Kotlin:

  • 'it' which implicitly refers to the parameter of a lambda expression where it only has one.
  • 'field' which implicitly refers to the backing field of a property within its get/set accessors.


The following program illustrates their usage: 

// version 1.0.6

class President(val name: String) {
    var age: Int = 0
        set(value) {
           if (value in 0..125) field = value  // assigning to backing field here
           else throw IllegalArgumentException("$name's age must be between 0 and 125")
        }   
}

fun main(args: Array<String>) {   
    val pres = President("Donald")
    pres.age = 69
    val pres2 = President("Jimmy")
    pres2.age = 91
    val presidents = mutableListOf(pres, pres2)
    presidents.forEach {
        it.age++  // 'it' is implicit sole parameter of lambda expression
        println("President ${it.name}'s age is currently ${it.age}")
    }
    println()
    val pres3 = President("Theodore")
    pres3.age = 158
}
Output:
President Donald's age is currently 70
President Jimmy's age is currently 92

Exception in thread "main" java.lang.IllegalArgumentException: Theodore's age must be between 0 and 125
        at President.setAge(test10.kt:5)
        at Test10Kt.main(test10.kt:21)

Lasso

In Lasso parameters can be referenced as numerical locals within methods or unbound captures. [1] 

{return #1 + ':'+#2}('a','b') // a:b

define test(a,b) => #1+':'+#2
test('y','z') // y:z

Lingo

In terms of statement "put <varName>" showing some meaningful output, the following can be rated as "special variables" in Lingo:

-- constants

  • BACKSPACE
  • EMPTY
  • ENTER
  • FALSE
  • PI
  • QUOTE
  • RETURN
  • SPACE
  • TAB
  • TRUE
  • VOID


-- core objects

  • _global
  • _key
  • _mouse
  • _movie
  • _player
  • _system

LiveCode

The most important special variable is known as it. The LC Dictionary says "A special local variable that is used with commands such as get, read from file, convert, ask, and answer. Use the it keyword to get the result of certain commands, or as a handy temporary storage place." It's use is closely followed by a special function called result that is similarly mentioned in the dictionary as well "Is a global property returning the last value returned by return from a handler, from an engine function, or from an engine command which sets the result."

Further to those, LiveCode comes with a plethora of built-in constants, which are readily listed with the following command: 

put the constantNames

It also provides colours as built-ins, accessible through 

the colornames

You can search the dictionary in the IDE using text "names" to discover more such as the propertyNames & the commandNames, though are not strictly pertinent to this task.

Lua

arg
global table containing command line parameters with the name of the program at index 0. Not available in interactive mode
_G
the table with the global environment, i.e. all global variables, including itself and the other variables listed here
_VERSION
string with the name of the interpreter and the major and minor version, e.g. "Lua 5.2"

To list all global variables: 

for n in pairs(_G) do print(n) end

The list will include built-in global functions, whose availability depends on the implementation and compile time configuration.

M2000 Interpreter

There some read only variables. We can use Help dir$ to get help about dir$.

All identifiers can be change to be used as variables, using a dot. For modules/functions in a group we have to define these variables using a dot. 

Module Checkit {
      Let inkey$="hello", dir$="Something Else"
      \\ using a dot we tell to interpreter to skip internal identifiers,
      \\ and look for user variables
      Print .inkey$="hello", .dir$="Something Else"
      
      Print dir$   ' return current path
      do
            Print "wait to press space"
      Until inkey$=" "
}
Checkit
Module check2 {
      Global inkey$="ok"
      Print .inkey$="ok"
}
check2

Module Check3 {
      Group A {
            Module Check3 {
                  \\ using a dot before the name
                  .inkey$="ok"
                  Print .inkey$="ok"
            }
      }
      A.Check3
}
Check3


about$, appdir$, browser$, clipboard$, clipboard.image$, codepage, colors,
command$, computer$, control$, dir$, duration, empty, error$, field,
fontname$, grabframe$, height, hwnd, inkey$, islet, isnum, key$, lan$,
letter$, memory, menu.visible, menu, menuitems, mode, module$, monitor.stack,
monitor.stack.size, motion.wx, motion.wy, motion.x, motion.xw, motion.y, motion.yw,
mouse, mouse.key, mouse.x, mouse.y, mousea.x, mousea.y, movie.counter, movie.device$,
movie.error$, movie.status$, movie, music.counter, now, number, os$, osbit, parameters$,
pen, platform$, point, pos, pos.x, pos.y, printername$, properties$, reportlines, rnd,
row, scale.x, scale.y, speech, sprite$, stack.size, tab, tempname$, temporary$,
this, threads$, tick, timecount, today, twipsx, twipsy, user.name$, volume,
width, x.twips, y.twips

Mathematica/Wolfram Language

Grid[Partition[Names["$*"],4]]
->
$Aborted                       $ActivationGroupID             $ActivationKey                 $ActivationUserRegistered     
$AddOnsDirectory               $AllowDataUpdates              $AllowDocumentationUpdates     $AllowInternet                
$AssertFunction                $Assumptions                   $BaseDirectory                 $BatchInput                   
$BatchOutput                   $BoxForms                      $ByteOrdering                  $Canceled                     
$CharacterEncoding             $CharacterEncodings            $CommandLine                   $CompilationTarget            
$ConditionHold                 $ConfiguredKernels             $Context                       $ContextPath                  
$ControlActiveSetting          $CreationDate                  $CurrentLink                   $DateStringFormat             
$DefaultFont                   $DefaultFrontEnd               $DefaultImagingDevice          $DefaultPath                  
$Display                       $DisplayFunction               $DistributedContexts           $DynamicEvaluation            
$Echo                          $Epilog                        $ExportFormats                 $Failed                       
$FinancialDataSource           $FormatType                    $FrontEnd                      $FrontEndSession              
$GeoLocation                   $HistoryLength                 $HomeDirectory                 $IgnoreEOF                    
$ImagingDevices                $ImportFormats                 $InitialDirectory              $Input                        
$InputFileName                 $Inspector                     $InstallationDate              $InstallationDirectory        
$InstalledServices             $InterfaceEnvironment          $InternetProxyRules            $IterationLimit               
$KernelCount                   $KernelID                      $Language                      $LaunchDirectory              
$LibraryPath                   $LicenseExpirationDate         $LicenseID                     $LicenseProcesses             
$LicenseServer                 $LicenseSubprocesses           $LicenseType                   $Line                         
$Linked                        $LinkSupported                 $LoadedFiles                   $MachineAddresses             
$MachineDomain                 $MachineDomains                $MachineEpsilon                $MachineID                    
$MachineName                   $MachinePrecision              $MachineType                   $MaxExtraPrecision            
$MaxLicenseProcesses           $MaxLicenseSubprocesses        $MaxMachineNumber              $MaxNumber                    
$MaxPiecewiseCases             $MaxPrecision                  $MaxRootDegree                 $MessageGroups                
$MessageList                   $MessagePrePrint               $Messages                      $MinMachineNumber             
$MinNumber                     $MinorReleaseNumber            $MinPrecision                  $ModuleNumber                 
$NetworkLicense                $NewMessage                    $NewSymbol                     $Notebooks                    
$NumberMarks                   $Off                           $OperatingSystem               $Output                       
$OutputForms                   $OutputSizeLimit               $Packages                      $PacletSite                   
$ParentLink                    $ParentProcessID               $PasswordFile                  $PatchLevelID                 
$Path                          $PathnameSeparator             $PerformanceGoal               $PipeSupported                
$Post                          $Pre                           $PreferencesDirectory          $PrePrint                     
$PreRead                       $PrintForms                    $PrintLiteral                  $PrintServiceRequest          
$PrintServiceResponse          $PrintShortErrorMessages       $PrintWSDLDebug                $ProcessID                    
$ProcessorCount                $ProcessorType                 $ProductInformation            $ProgramName                  
$RandomState                   $RecursionLimit                $ReleaseNumber                 $RootDirectory                
$ScheduledTask                 $ScriptCommandLine             $SessionID                     $SetParentLink                
$SharedFunctions               $SharedVariables               $SoundDisplay                  $SoundDisplayFunction         
$SuppressInputFormHeads        $SynchronousEvaluation         $SyntaxHandler                 $System                       
$SystemCharacterEncoding       $SystemID                      $SystemWordLength              $TemporaryDirectory           
$TemporaryPrefix               $TextStyle                     $TimedOut                      $TimeUnit                     
$TimeZone                      $TopDirectory                  $TraceOff                      $TraceOn                      
$TracePattern                  $TracePostAction               $TracePreAction                $Urgent                       
$UserAddOnsDirectory           $UserBaseDirectory             $UserBasePacletsDirectory      $UserDocumentsDirectory

Maxima

/* There are many special variables in Maxima: more than 250 are used for options, for example */
fpprec;  /* precision for big floats */
obase;   /* number base for output */

/* Other variables are read-only, and give the list of user-defined variables, functions... */
infolists; /* give the names of all available lists */
[labels, values, functions, macros, arrays, myoptions, props, aliases, rules, gradefs, dependencies, let_rule_packages, structures]

MIPS Assembly

When multiplying two registers, the product is always stored in the $HI and $LO registers. Their contents can be read into your standard registers with the commands mfhi $reg and mflo $reg. 

li $t0,0x4500
li $t1,0xFFFF
multu $t0,$t1  ;unsigned multiplication of $t0 and $t1
mfhi $t0       ;load the top 32 bits of the product into $t0
mflo $t1       ;load the bottom 32 bits of the product into $t1

Division is a similar story, except $HI holds the remainder and $LO holds the quotient.

When using JAL functionName to call a function, the $ra register holds the return address.

ML/I

Input

MCSKIP "WITH" NL
"" Special variables
"" There are four different kinds of variables in ML/I.
"" Permanent (P) variables - these have no special predefined values.
"" Character (C) variables - these have no special predefined values.
"" Temporary (T) variables - a macro has at least three of these, and
""    those have predefined values.
"" System (S) variables - these are for control and status. The number
""    of these is implementation dependent.
MCSKIP MT,<>
MCINS %.
MCDEF TVARDEMO , NL
AS <T-variables are local to the current macro call
T1 is the number of arguments to current macro call - value is %T1.
T2 is the number of macro calls so far - value is %T2.
T3 is the current depth of nesting - value is %T3.
>
TVARDEMO xxx,yyy

MCDEF SVARDEMO WITHS NL
AS <The first nine S-variables are implementation independent
S1 controls startline insertion - value is %S1.
S2 is the current source text line number - value is %S2.
S3 controls error messages related to warning markers - value is %S3.
S4 controls context printout after a <MCNOTE> - value is %S4.
S5 is the count of processing errors - value is %S5.
S6 enables the definition of an atom to be changed - value is %S6.
S7, S8 and S9 are currently unused.

All other S-variables have implementation defined meanings.
>
SVARDEMO

Output

T-variables are local to the current macro call
T1 is the number of arguments to current macro call - value is 2
T2 is the number of macro calls so far - value is 5
T3 is the current depth of nesting - value is 1

The first nine S-variables are implementation independent
S1 controls startline insertion - value is 0
S2 is the current source text line number - value is 32
S3 controls error messages related to warning markers - value is 0
S4 controls context printout after a MCNOTE - value is 0
S5 is the count of processing errors - value is 0
S6 enables the definition of an atom to be changed - value is -1
S7, S8 and S9 are currently unused.

All other S-variables have implementation defined meanings.

Nanoquery

Nanoquery has a number of immutable special variables which can be listed by executing the following program: 

println dumpstack()
Output:
{{dbsize, 0}, {col, 1}, {workingdir, C:\Users\Will\Programs\Nanoquery}, {false, false}, {interactive, false}, {main, true}, {packages, [, Nanoquery.Objects, Nanoquery.Exceptions]}, {libpath, C:\Users\Will\Programs\Nanoquery\nanoquery-2.3_1866}, {args, [-b, rosetta-code/specialvars.nq]}, {rec, 1}, {filename, }, {null, null}, {__file__, C:\Users\Will\Programs\Nanoquery\rosetta-code\specialvars.nq}, {true, true}, {prompt, [\S | rec\R col\C] % }, {cols, 0}, {lockedfiles, []}, {__calls__, [<global>:1]}}

These variables are: 

dbsize:      the amount of rows in the currently referenced database object
col:         the index of the currently referenced database column
workingdir:  the current working directory as a string
false:       the boolean value false
interactive: a boolean that represents if this program is being run from the
             interpreter interactively
main:        boolean that represents if this code is in the global portion
             of the current program
packages:    list of strings holding the built-in packages that have been imported
libpath:     string representing the path where the standard library is expected to be
args:        list of string containing the args that the current program was
             started with
rec:         the index of the currently referenced database row
filename:    the path of the currently open database file
null:        represents the null object
__file__:    absolute path of the current running program
true:        the boolean value true
prompt:      contains the current interpreter prompt string
cols:        the amount of columns in the currently referenced database object
lockedfiles: list of strings containing the paths of files that have been locked
             for writing by the 'lock' command
__calls__:   stack containing the current Nanoquery call stack

NetRexx

For convenience, NetRexx provides some special names for naming commonly-used concepts within terms. These are only recognized if there is no variable of the same name previously seen in the current scope.

The current set of special names includes: ask, class, digits, form, length, null, source, sourceline, super, this, trace, version. 

/* NetRexx */
options replace format comments java crossref savelog symbols binary

class RCSpecialVariables

method RCSpecialVariables()
  x = super.toString
  y = this.toString
  say '<super>'x'</super>'
  say '<this>'y'</this>'
  say '<class>'RCSpecialVariables.class'</class>'
  say '<digits>'digits'</digits>'
  say '<form>'form'</form>'
  say '<[1, 2, 3].length>'
  say [1, 2, 3].length
  say '</[1, 2, 3].length>'
  say '<null>'
  say null
  say '</null>'
  say '<source>'source'</source>'
  say '<sourceline>'sourceline'</sourceline>'
  say '<trace>'trace'</trace>'
  say '<version>'version'</version>'

  say 'Type an answer:'
  say '<ask>'ask'</ask>'

  return

method main(args = String[]) public static

  RCSpecialVariables()

  return
Output
<super>RCSpecialVariables@3487a5cc</super>
<this>RCSpecialVariables@3487a5cc</this>
<class>class RCSpecialVariables</class>
<digits>9</digits>
<form>scientific</form>
<[1, 2, 3].length>
3
</[1, 2, 3].length>
<null>

</null>
<source>Java method RCSpecialVariables.nrx</source>
<sourceline>21</sourceline>
<trace>off</trace>
<version>NetRexx 3.00 11 Jun 2011</version>
Type an answer:
answer
<ask>answer</ask>

Nim

In Nim, there is only one special variable, named result. It is implicitly declared in procedure which returns a result and is initialized with binary zeroes. Statement return value is in fact a shortcut for: 

result = value
return

There are also variables declared in modules and exported. As some modules are implicitly imported, their exported variables are automatically visible. Modules implicitly imported are: “system” (which imports “iterators”, “assertions”, “dollars”, “io” and “widestr”), “threads” and “channels”, the latter two being activated if option --thread:on is used.

These implicit imports add these variables to the list of visible objects:

– some hooks and handlers used in system programming: globalRaiseHook, localRaiseHook, outOfMemHook, unhandledExceptionHook, errorMessageWriter, onUnhandledException;
– a read-only variable, nimvm which is true in Nim VM context and false otherwise;
– the three standard files: stdin, stdout, stderr.

OASYS

The only special variable is player (of type object) which specifies which object the player invokes methods on by default.

OASYS Assembler

The only special variable is %@ which specifies which object the player invokes methods on by default.

OCaml

Some predefined variables from the Sys module: 

val argv : string array
(** The command line arguments given to the process.
   The first element is the command name used to invoke the program.
   The following elements are the command-line arguments
   given to the program. *)

val executable_name : string
(** The name of the file containing the executable currently running. *)

val interactive : bool ref
(** This reference is initially set to [false] in standalone
   programs and to [true] if the code is being executed under
   the interactive toplevel system [ocaml]. *)

val os_type : string
(** Operating system currently executing the Caml program. One of
-  ["Unix"] (for all Unix versions, including Linux and Mac OS X),
-  ["Win32"] (for MS-Windows, OCaml compiled with MSVC++ or Mingw),
-  ["Cygwin"] (for MS-Windows, OCaml compiled with Cygwin). *)

val word_size : int
(** Size of one word on the machine currently executing the Caml
   program, in bits: 32 or 64. *)

val max_string_length : int
(** Maximum length of a string. *)

val max_array_length : int
(** Maximum length of a normal array.  The maximum length of a float
    array is [max_array_length/2] on 32-bit machines and
    [max_array_length] on 64-bit machines. *)

val ocaml_version : string
(** [ocaml_version] is the version of Objective Caml.
    It is a string of the form ["major.minor[.patchlevel][+additional-info]"],
    where [major], [minor], and [patchlevel] are integers, and
    [additional-info] is an arbitrary string. The [[.patchlevel]] and
    [[+additional-info]] parts may be absent. *)

Some predefined variables from the Pervasives module: 

val max_int : int
(** The greatest representable integer. *)

val min_int : int
(** The smallest representable integer. *)

val max_float : float
(** The largest positive finite value of type [float]. *)

val min_float : float
(** The smallest positive, non-zero, non-denormalized value of type [float]. *)

val epsilon_float : float
(** The difference between [1.0] and the smallest exactly representable
    floating-point number greater than [1.0]. *)

Oforth

Oforth special variables are read-only :

Output:
true
false
null
System.Out
System.In
System.Err
System.Console
System.Args
Systel.NbCores
System.CELLSIZE
System.VERSION
SYstem.MAXTHREADS
System.ASSERTMODE
System.ISWIN
System.ISLUNIX

Pascal

Pascal does not have any predefined special variables. However, two identifiers can become “special”: If you list in the program parameter list the identifiers of the spelling input and/or output, they will identify text variables referring to an implementation-defined input and output facility. 

program foo(input, output);
begin
	{ In this program, `input` and `output` have special meaning. }
end.

Neverthless, these identifiers are in no way reserved. 

program foo(output);
var
	input: integer;
begin
	{ In this program only `output` has special meaning. }
end.

Note that some run-time libraries of compilers usually ship a variety of predefined variables, but these are not part of the programming language itself.

PARI/GP

There are three special variables in GP: Pi (3.14...), Euler (Euler's gamma), and I (the imaginary unit).

PARI has many special variables. Probably the most important is avma, the current stack pointer, and the related top and bot; see section 4.3 of the User's Guide to the PARI Library.

Other important special variables are:

  • Universal objects gen_0, gen_1, gen_2, gen_m1, gen_m2, ghalf, and gnil. (The manual erroneously omits the last on this list.) These can be identified with is_universal_constant(). Note that gen_I is not a universal object but a function.
  • Defaults: DEBUGLEVEL and DEBUGMEM
  • Prime-related variables _maxprime (traditionally accessed via maxprime()) and diffptr
  • Others: precdl, overflow, hiremainder, ...

The PARI developer's guide lists two more:

  • PARI_SIGINT_block: When this is nonzero, SIGINT is blocked.
  • PARI_SIGINT_pending: When this is nonzero, a SIGINT has been blocked but not yet handled.

Perl

Works with: Perl 5.28

A selection of the variables with special meaning to Perl. If you find it hard to remember the 'punctuation' names, longer 'English' names are available via a core module. 

use English;                     # enables use of long variable names

$.     $INPUT_LINE_NUMBER        # sequence number
$,     $OUTPUT_FIELD_SEPARATOR   # output field separator
$;     $SUBSCRIPT_SEPARATOR      # subscript separator for multidimensional array emulation
$_     $ARG                      # topic/current/default variable
$"     $LIST_SEPARATOR           # alternative output field separator
$+     $LAST_PAREN_MATCH         # last substring matched to a regular expression subpattern
$0     $PROGRAM_NAME             # name of the program being executed
$!     $ERRNO                    # error number from host operating system
$@     $EVAL_ERROR               # error from the last "eval" operator
$/     $INPUT_RECORD_SEPARATOR   # input record separator
$\     $OUTPUT_RECORD_SEPARATOR  # output record separator for 'print'
$|     $OUTPUT_AUTOFLUSH         # controls output buffering
$&     $MATCH                    # string matched by last regular expression
$'     $POSTMATCH                # substring following last matched regular expression
$`     $PREMATCH                 # substring preceding last matched regular expression

@ARGV                            # array containing the command line parameters
@F                               # array of fields of each line read in when auto-split is on
@INC                             # array of library search paths

%ENV                             # associative container holding the environment variables
%SIG                             # associative container holding signal handlers

Phix

Library: Phix/basics

Phix has no special variables.

PicoLisp

PicoLisp has no special variables, but some naming conventions concerning the "meaning" of a variable's (i.e. symbol's) value: 

- Global variables start with an asterisk '*'
- Functions and other global symbols start with a lower case letter
- Locally bound symbols start with an upper case letter
- Local functions start with an underscore '_'
- Classes start with a plus-sign '+', where the first letter
   - is in lower case for abstract classes
   - and in upper case for normal classes
- Methods end with a right arrow '>'
- Class variables may be indicated by an upper case letter

For historical reasons, the global constant symbols 'T' and 'NIL' do not obey these rules, and are written in upper case.

PL/I

Special variables in PL/I are termed "Pseudo-variables".
They are used only on the LHS of an assignment statement.

They include:
   REAL to assign the real part of a COMPLEX variable;
   IMAG to assign the imaginary part of a COMPLEX variable;
   SUBSTR is used to assign part of a string (used on the LHS of an assignment);
   STRING when used on the left-hand of an assignment;
   UNSPEC used to assign a bit pattern to a variable;
   ENTRYADDR is used to assign an address to an ENTRY variable that is
             to be invoked;
   ONCHAR resets the current value of the CHAR built-in function (when
          a data conversion error occurs, and it is desired to re-attempt
          the conversion);
   ONSOURCE assigns a new value to the ONSOURCE built-in function
            (may be used when a data conversion error occurs,
             and a re-try of the conversion is to be attempted with modified data);
   ONGSOURCE assigns a new value to the ONGSOURCE built-in function
            (may be used when a data conversion error occurs,
             and may be used when a re-try of the conversion is to be
             attempted with modified data).

PowerShell

This is the list: 

<#
    $$
    $?
    $^
    $_
    $Args
    $ConsoleFileName
    $Error
    $Event
    $EventSubscriber
    $ExecutionContext
    $False
    $ForEach
    $Home
    $Host
    $Input
    $LastExitCode
    $Matches
    $MyInvocation
    $NestedPromptLevel
    $NULL
    $PID
    $Profile
    $PSBoundParameters
    $PsCmdlet
    $PsCulture
    $PSDebugContext
    $PsHome
    $PSitem
    $PSScriptRoot
    $PsUICulture
    $PsVersionTable
    $Pwd
    $Sender
    $ShellID
    $SourceArgs
    $SourceEventArgs
    $This
    $True
#>

For descriptions: 

help about_automatic_variables

PureBasic

PureBasic has no 'special variables'. It does define constants that reflect compiler settings that can be tested and used as a part of compiling. All other non-explicitly declared values that vary during runtime are returned by functions.

Python

By default, Python starts execution in a namespace which has direct access to names defined in the globals() dict and the __builtins__ dict. The members of which can be found by the following code: 

names = sorted((set(globals().keys()) | set(__builtins__.__dict__.keys())) - set('_ names i'.split()))
print( '\n'.join(' '.join(names[i:i+8]) for i in range(0, len(names), 8)) )
Output
ArithmeticError AssertionError AttributeError BaseException BufferError BytesWarning DeprecationWarning EOFError
Ellipsis EnvironmentError Exception False FloatingPointError FutureWarning GeneratorExit IOError
ImportError ImportWarning IndentationError IndexError KeyError KeyboardInterrupt LookupError MemoryError
NameError None NotImplemented NotImplementedError OSError OverflowError PendingDeprecationWarning ReferenceError
ResourceWarning RuntimeError RuntimeWarning StopIteration SyntaxError SyntaxWarning SystemError SystemExit
TabError True TypeError UnboundLocalError UnicodeDecodeError UnicodeEncodeError UnicodeError UnicodeTranslateError
UnicodeWarning UserWarning ValueError Warning WindowsError ZeroDivisionError __build_class__ __builtins__
__debug__ __doc__ __import__ __name__ __package__ abs all any
ascii bin bool bytearray bytes callable chr classmethod
compile complex copyright credits delattr dict dir divmod
enumerate eval exec exit filter float format frozenset
getattr globals hasattr hash help hex id input
int isinstance issubclass iter len license list locals
map max memoryview min next object oct open
ord pow print property quit range repr reversed
round set setattr slice sorted staticmethod str sum
super tuple type vars zip

Quackery

The trite answer would be that Quackery has no variables.

It does, however, have Ancillary Stacks which stand in for variables, in that they are places where values can reside. Their behaviour is to place a pointer to themselves on the stack (the stack refers to the Quackery Data Stack, the place from which words take arguments and return results), so that they can have values moved to and from them.

Ancillary Stacks might also, arguably, be considered slightly outside the language proper. To use a metaphor, if Quackery is a workshop, and Quackery words are tools for working on data, then the stack is the workbench that data resides on while it is being worked upon, and Ancillary Stacks are the storage spaces where one can put things to keep the workbench tidy. If asked to list the tools in a workshop, would you necessarily list shelves and cupboards as tools?

If predefined system constants are to be included, (i.e. words that take no arguments and always return the same value, a category which includes Ancillary Stacks) then there are several, including but not limited to space which returns 32, carriage which returns 13 (and is taken to mean whatever the host system regards as a carriage return/line feed), [], which returns the empty nest [ ], true which returns 1 and false which returns 0.

However, I suspect the most useful answer is "those things which need to be taken into consideration whilst coding in Quackery, because they give words side-effects rather than the words being purely functional in their behaviour."

With this definition there is only one word that requires mention; base. base is a system ancillary stack that holds the current base for numerical i/o and converting numerical strings to and from numbers and so forth. It has a default value of 10 — i.e. Quackery regards numbers as decimal unless that assumption is overridden by putting a different value on the top of the ancillary stack called base.

Racket

Racket does not have special variables in the usual sense. In fact, being a language that specializes in making up langugaes it has no special anything hard-wired in.

But it does have "parameters" -- a kind of mutable values that can be set for a specific dynamic runtime extent: either around some piece of code, or globally, or in some thread. These parameters are used to configure many aspects of the runtime system, for example "current-directory" has the obvious meaning. (But again, the names that are bound to these parameters are not special, and can be changed or hidden.)

Raku

(formerly Perl 6)

It is probably useful to briefly explain normal variables in Raku before tackling special variables.

Variables in Raku have a prefix sigil to distinguish them from named subroutines, functions, classes, and so on. There is a system of sigils to mark the fundamental structural type of the variable: 

 $foo   scalar (object)
 @foo   ordered array
 %foo   unordered hash (associative array)
 &foo   code/rule/token/regex
 ::foo  package/module/class/role/subset/enum/type/grammar

Sigils indicate overall interface, not the exact type of the bound object. Different sigils imply different minimal abilities. Ordinary sigils indicate normally scoped variables, either lexical or package scoped. Oddly scoped variables include a secondary sigil (a twigil) that indicates what kind of strange scoping the variable is subject to: 

 $foo                # ordinary scoping
 $.foo               # object attribute public accessor
 $^foo               # self-declared formal positional parameter
 $:foo               # self-declared formal named parameter
 $*foo               # dynamically overridable global variable
 $?foo               # compiler hint variable
 $=foo               # POD variable
 $<foo>              # match variable, short for $/{'foo'}
 $!foo               # object attribute private storage
 $~foo               # the foo sublanguage seen by the parser at this lexical spot

A selection (not comprehensive) of Raku's automatically set and/or pre-defined compile-time and run-time variables. 

# Lexical variables

 $_                  # implicit variable lexically scoped to the current block
 $!                  # current Exception object
 $/                  # last match
 $0, $1, $2...       # captured values from match: $/[0], $/[1], $/[2] ...

# Compile-time variables

$?PACKAGE            # current package
$?CLASS              # current class
$?MODULE             # current module
$?ROLE               # current role
$?DISTRIBUTION       # which OS distribution am I compiling under
$?FILE               # current filename of source file
$?LINE               # current line number in source file
&?ROUTINE            # current sub or method (itself)
&?BLOCK              # current block (itself)

# Dynamic variables

$*USAGE              # value of the auto-generated USAGE message
$*PROGRAM-NAME       # path to the current executable
$*PROGRAM            # location (in the form of an IO::Path object) of the Raku program being executed
@*ARGS               # command-line arguments
$*ARGFILES           # the magic command-line input handle
$*CWD                # current working directory
$*DISTRO             # which OS distribution am I running under
%*ENV                # system environment variables
$*ERR                # standard error handle
$*EXECUTABLE-NAME    # name of the Raku executable that is currently running
$*EXECUTABLE         # IO::Path absolute path of the Raku executable that is currently running
$*IN                 # standard input handle; is an IO object
$*KERNEL             # operating system running under
$*OUT                # standard output handle
$*RAKU               # Raku version running under
$*PID                # system process id
$*TZ                 # local time zone
$*USER               # system user id

# Run-time variables

$*COLLATION          # object that can be used to configure Unicode collation levels
$*TOLERANCE          # used by the =~= operator to decide if two values are approximately equal
$*DEFAULT-READ-ELEMS # affects the number of bytes read by default by IO::Handle.read

Also, not really a variable but... 

 *  # A standalone term that has no fixed value, instead it captures the notion of "Whatever",
    # the meaning of which is decided lazily by whatever it is an argument to.
    # See the docs on Whatever: https://docs.raku.org/type/Whatever

REXX

version 1

The REXX language has three special variables:

  •   RC             [the return code from commands issued to the host]
  •   RESULT     [the result RETURNed from a subroutine or function]
  •   SIGL         [the source line number that did the transfer of control]

Each of the above may be used as a regular REXX variable;   they aren't reserved keywords or reserved variable names.
Because REXX may define (or re-define) any of these variables during execution of the REXX program, its recommended that they be not be used as regular REXX variables.

Initially, the above three special variables aren't defined   (until the appropriate action for their use has been performed).

If no commands have been issued to the host, then the   RC   special variable isn't defined.
If no subroutines have been invoked, then the   RESULT   special variable isn't defined.
If no SIGNAL or CALL (or subroutine invocation) has been used, then the   SIGL   special variable isn't defined.
(This excludes the use of:
  •   SIGNAL ON   ααα
  •   SIGNAL OFF ααα
which don't actually transfer control.)

In each case, the three special variable names   (RC,   RESULT,   and   SIGL)   may be in lower/upper/mixed case.

The scope of the special variables is   LOCAL. 

/*REXX program demonstrates REXX special variables:  RC,  RESULT,  SIGL */
                           /*line two.  */
                           /*line three.*/             say copies('═',79)
rc=1/3                     /*line four. */
signal youWho              /*line five. */
myLoo='this got skipped'   /*line six.  */
youwho:                    /*line seven.*/
sep=copies('─', 9)         /*line eight.*/
say sep  'SIGL=' sigl      /*line nine. */
say sep  'REXX source statement' SIGL '=' sourceline(sigl)
                                                       say copies('═',79)
g=44
call halve  g
say sep  'rc='     rc
say sep  'result=' result
                                                       say copies('═',79)
h=66
hh=halve(h)
say sep  'rc='     rc
say sep  'result=' result
say sep  'hh='     hh
                                                       say copies('═',79)
'DIR  /ad  /b'                         /*display the directories (Bare).*/
say sep  'rc='     rc
say sep  'result=' result
                                                       say copies('═',79)
exit                                   /*stick a fork in it, we're done.*/
/*──────────────────────────────────HALVE subroutine────────────────────*/
halve: return arg(1) / 2               /*a simple halving function.     */

output using:

  • Regina REXX
═══════════════════════════════════════════════════════════════════════════════
───────── SIGL= 5
───────── REXX source statement 5 = signal youWho              /*line five. */
═══════════════════════════════════════════════════════════════════════════════
───────── rc= 0.333333333
───────── result= 22
═══════════════════════════════════════════════════════════════════════════════
───────── rc= 0.333333333
───────── result= 22
───────── hh= 33
═══════════════════════════════════════════════════════════════════════════════
Documents and Settings
Program Files
Recycled
System Volume Information
TEMP
WINDOWS
───────── rc= 0
───────── result= 22
═══════════════════════════════════════════════════════════════════════════════

output using:

  • PC/REXX
  • Personal REXX
  • R4 REXX
  • ROO
═══════════════════════════════════════════════════════════════════════════════
───────── SIGL= 5
───────── REXX source statement 5 = signal youWho              /*line five. */
═══════════════════════════════════════════════════════════════════════════════
───────── rc= 0.333333333
───────── result= 22
═══════════════════════════════════════════════════════════════════════════════
───────── rc= 0.333333333
───────── result= 33
───────── hh= 33
═══════════════════════════════════════════════════════════════════════════════
Documents and Settings
Program Files
Recycled
System Volume Information
TEMP
WINDOWS
───────── rc= 0
───────── result= 33
═══════════════════════════════════════════════════════════════════════════════

version 2

The REXX language has three special variables:

RC is set upon return from a command

RESULT is set or dropped after a CALL to a subroutine: It is assigned the value given in the RETURN statement or it is dropped when there was a RETURN without expression. (some REXX implementations set RESULT also upon return from a function invocation - see version 1 and the Discussion)

SIGL is set when control is tranferred within the REXX program. (i.e. when a subroutine is called, a function is invoked, or a SIGNAL instruction was used explicitly or as a result of a raised condition) Note that RETURN transfers control but does not set SIGL. 

'dir a2.txt'
Say 'rc='rc
'dir 33.*'
Say 'rc='rc

Call square 5
Say 'RESULT='result
Say 'SIGL='sigl

x2=square(3) /* just a simle example */
Say '3**2='||x2

Signal On Novalue
x=y   /* y was not yet assigned a value */

Exit
square: Procedure Expose sigl
Say 'square was invoked from line' sigl':' sourceline(sigl)
Return arg(1)**2

Novalue:
Say 'NOVALUE encountered in line' sigl':' sourceline(sigl)
Exit
Output:
 Datentr„ger in Laufwerk E: ist E_DESKTOP
 Volumeseriennummer: 66C1-0469

 Verzeichnis von E:\

28.07.2014  11:53            19.219 A2.txt
               1 Datei(en),         19.219 Bytes
               0 Verzeichnis(se), 198.658.433.024 Bytes frei
rc=0
 Datentr„ger in Laufwerk E: ist E_DESKTOP
 Volumeseriennummer: 66C1-0469

 Verzeichnis von E:\

rc=1
square was invoked from line 6: Call square 5
RESULT=25
SIGL=6
square was invoked from line 10: x2=square(3) /* just a simle example */
3**2=9
NOVALUE encountered in line 14: x=y   /* y was not yet assigned a value */

Ruby

A list and description of Ruby's Special Variables

Scala

Scala has only a few special variables. Inside an object there is this, a reference that points to the object itself (like 127.0.0.1 in networking) and are used to qualify member access. There is also super that does the same for the base class (actually "the next class in the inheritance tree").

Depending on the context, underscore has the following meaning: 

import scala._    // Wild card -- all of scala is imported
import scala.{ Predef => _, _ } // Exception, everything except Predef
def f[M[_]]       // Higher kinded type parameter
def f(m: M[_])    // Existential type
_ + _             // Anonymous function placeholder parameter
m _               // Eta expansion of method into method value
m(_)              // Partial function application
_ => 5            // Discarded parameter
case _ =>         // Wild card pattern -- matches anything
val (a, _) = (1, 2) // same thing
for (_ <- 1 to 10)  // same thing
f(xs: _*)         // Sequence xs is passed as multiple parameters to f(ys: T*)
case Seq(xs @ _*) // Identifier xs is bound to the whole matched sequence
var i: Int = _    // Initialization to the default value
def abc_<>!       // An underscore must separate alphanumerics from symbols on identifiers
t._2              // Part of a method name, such as tuple getters
var i: Int = _    // Initialization with a default value
for (_ <- 1 to 10) doIt() // Discarded val
def f: T; def f_=(t: T) // Combo for creating mutable f member.

Smalltalk

Talking about special (reserved) names, there are:

  • self - the current method's receiver
  • super - ditto, but different message send lookup
  • thisContext - the current stackframe/aka active continuation

Everything else is found via the lexical scope ending in bindings in a namespace. The global default namespace is called "Smalltalk" and contains (beside bindings for all classes by name) the singletons:

  • true
  • false
  • nil

Technically, these could be redefined, but the system would not work if any of them was. Therefore most compilers refuse code which obviously attempts to do so, and we can think of them as being reserved names as well.

Global binding names are returned by 

Smalltalk keys

Things like the shell environment, command line argument, version numbers etc. are usually not exposed via globals, but instead held in private class variables (static variables), which can be accessed via getter messages (which, by the way, makes it easier to insert a dialect compatibility layer). An example for this would be: 

Float precision

or 

Smalltalk version

Name conventions:

  • class names - upperCase first
  • class variables (statics) - ditto
  • shared pool variables - ditto
  • all other variables (incl. instance variables) - lowercase first
  • method names - lowercase first; except for constant/parameter getters, which are sometimes uc-first

Tcl

There are three major categories of special variables in Tcl: global variables special to the Tcl language, global variables set by Tcl-based interpreters, and local variables with special interpretations.

Language Globals

These variables are defined by the standard implementation of Tcl, and are present in all Tcl interpreters by default.

env
This global array is Tcl's interface to the process's environment variables.
errorCode
This global scalar holds a machine-readable description of the last error to occur. (Note that prior to Tcl 8.6, internally-generated exceptions often used NONE for this value.)
errorInfo
This global scalar holds a stack trace from the last error to occur.
tcl_library
This global scalar holds the location of Tcl's own internal library.
tcl_version, tcl_patchLevel
This global scalar holds the version of Tcl in use. From Tcl 8.5 onwards, these hold the same (detailed) value.
tcl_pkgPath
This global scalar holds a Tcl list of directories where Tcl looks for packages by default. This is used to initialize the auto_path global variable.
auto_path
This global scalar holds a Tcl list of directories where Tcl looks for packages (and auto-loaded scripts, though this facility is deprecated).
tcl_platform
This global array holds a description of the platform on which Tcl is executing.
tcl_precision
This global scalar holds the number of significant figures to use when converting a floating-point value to a string by default. From Tcl 8.5 onwards it should not be changed. (If you are thinking of using this, consider using the format command instead.)
tcl_rcFileName
This global scalar holds the name of a file to source when the interpreter starts in interactive mode.
tcl_rcRsrcName
This global scalar is only used on classic Mac OS (now deprecated); consult the documentation for more information.
tcl_traceCompile
If enabled at library configuration time, this global scalar allows tracing of the compilation of bytecode in the interpreter.
tcl_traceExec
If enabled at library configuration time, this global scalar allows tracing of the execution of bytecode in the interpreter.
tcl_wordchars, tcl_nonwordchars
These global scalars hold regular expression fragments that describe the current platform's interpretation of what is and isn't a word.

Interpreter Globals

These global variables are only features of the most common Tcl-based shells, tclsh and wish.

argc
This global scalar holds the number of arguments (after the script) passed to the Tcl interpreter.
argv
This global scalar holds a Tcl list of the arguments (after the script) passed to the Tcl interpreter.
argv0
This global scalar holds the name of the main script to execute that was passed to the Tcl interpreter, or the name of the interpreter itself in interactive mode.
tcl_interactive
This global scalar holds whether this interpreter is working in interactive mode (i.e., needs to print command prompts, run a REPL, etc.)
tcl_prompt1, tcl_prompt2
These global scalars allow customization of the prompt strings in interactive mode.
geometry

This global scalar holds the user-supplied preferred dimensions of the initial window. Only used by interpreters that load the Tk library.

Local Special Variables

This is a language feature of procedures.

args
This local variable holds the Tcl list of arguments supplied to the current procedure after all the other formal arguments have been satisfied. Note that it needs to be explicitly listed in the formal arguments and be last in the list of formal arguments to have this behavior.

UNIX Shell

The following variables are reserved for special purposes within the Bourne shell:

  • $0 the invoked command positional variable
  • $1 the first positional variable
  • $2 the second positional variable
  • $3 the third positional variable
  • $4 the fourth positional variable
  • $5 the fifth positional variable
  • $6 the sixth positional variable
  • $7 the seventh positional variable
  • $8 the eighth positional variable
  • $9 the nineth positional variable
  • $* the dollarstar expands to all command line arguments
  • $@ the dollarsnail expands to all command line arguments
  • $# the dollarhash expands to the number of command line arguments given
  • $? the dollarhook expands to the exit status of the last command executed
  • $- a list of all options used to invoke the shell
  • $$ the pid of the currentprocess
  • $! the pid of the last command executed as a background process
  • CDPATH Additional locations to be searched by the cd command
  • HOME The default working directory of the current user
  • HUSHLOGIN
  • IFS Internal field separator. This contains space,tab and newline characters
  • LANG Determines the default locale in the absence of other locale related environment variables
  • LC_ALL High precedence override for locale specific behaviour
  • LC_CTYPE Determines locale specific character classification
  • LOGNAME The login name of the user
  • LS_COLORS
  • MAIL The full pathname of the users mail file
  • MAILCHECK The time limit that the shell timer uses before checking for new mail
  • MAILPATH
  • OPTARG
  • OPTIND
  • PATH The shell search path
  • PPID
  • PS1 Primary system prompt
  • PS2 Secondary system prompt
  • PS3 Ternary system prompt
  • PS4 Forth system prompt
  • PWD Current working directory
  • SHACCT
  • SHELL The name of the current shell
  • SHLVL
  • TERM The current terminal type
  • TIMEOUT
  • TZ The current timezone
  • USER The current username
  • underscore

Ursa

# contains arguments passed to the ursa
# interpreter on the command line
string<> args

# iodevice that points to the console by default
iodevice console

# contains "\n"
string endl

# represents false
boolean false

# represents true
boolean true

VBA

VBA does not have special variables.

XLISP

XLISP provides the following built-in variables: 

*PACKAGE*
*READTABLE*
*ERROR-HANDLER*
*UNBOUND-HANDLER*
*LOAD-PATH*
*STANDARD-INPUT*
*STANDARD-OUTPUT*
*ERROR-OUTPUT*
*FIXNUM-FORMAT*
*HEXNUM-FORMAT*
*FLONUM-FORMAT*
*PRINT-CASE*
*SOFTWARE-TYPE*
T                ; bound to #T
NIL              ; bound to '()
OBJECT
CLASS

Wren

Wren has two special variables this and super. When used in a constructor or instance method of a class. this refers to the current instance and super refers to a super-class whose constructor or (typically overridden) method you wish to invoke. Here's an example. 

class Parent {
    construct new(name) {
        _name = name
    }

    name { _name }
}

class Child is Parent {
    construct new(name, parentName) {
        _name = name
        super(parentName)  // call parent's constructor
    }

    name { _name } // overrides Parent's name method

    printNames() {
        System.print("My name is %(this.name) and my parent's name is %(super.name).")
    }
}

var c = Child.new("John", "Fred")
c.printNames()
Output:
My name is John and my parent's name is Fred.

Z80 Assembly

It's somewhat debatable whether processor registers count as "variables," since they don't have a location in the address space but their contents can change. Excluding those for now, there are a few memory locations that have special meaning:

The following memory locations can be called as functions using the RST instructions. Each appears to take a byte as an operand, but in fact there are only 8 different "operands" and each is hardcoded in, which means that only one byte is needed to describe both the RST and the destination byte. Unfortunately, there is very little room for code in these areas, since each is only 8 bytes long! Most of the time you'll put a jump to the actual routine you want to execute in these areas. The last one, RST 38, may allow more room for code depending on the system.

  • &0000 - called with RST 00
  • &0008 - called with RST 08
  • &0010 - called with RST 10
  • &0018 - called with RST 18
  • &0020 - called with RST 20
  • &0028 - called with RST 28
  • &0030 - called with RST 30
  • &0038 - called with RST 38

The memory location &0066 is special because it contains the NMI routine. NMI stands for "Non-Maskable Interrupt" and is a hardware interrupt that can't be stopped by a DI command. When an NMI occurs, the CPU will save the program counter on the stack and jump to &0066, and execute from there. The RETN instruction is used to return back to the main program. Usually an ORG directive is the easiest way to guarantee that your code will begin at the correct address for NMI. Since you can't predict exactly what state your program will be in when an NMI happens, it's important that the NMI routine uses either the stack or the exchange commands to preserve the register state at the start and restores it before returning. Otherwise, your NMI could ruin whatever your program was doing at the time.

Depending on the hardware, programming the NMI routine may not actually be your responsibility. It's usually only required when programming for a ROM-cartridge game console like the Sega Master System. On home computers, the NMI routine at &0066 is typically built into the firmware by the manufacturer and cannot be changed; however that routine will often contain a jump to another memory location that you can change indirectly using system calls and parameter passing. 


org &0066

NMI_HANDLER:   ;this label is optional, the CPU doesn't need it to know how to jump here.
retn           ;in this example, the NMI routine will immediately return without doing anything.

The I register handles the interrupt operation in IM 2 mode. The Game Boy does not have this register, as it handles interrupts differently.

The r register handles memory refresh. You should not write to this register, as doing so can damage your hardware. But reading from this register is safe. It basically contains a pseudo-random value, and while its randomness isn't sufficient to reliably seed a PRNG, it can be used to add a little "salt" to a random value. (It should be noted that the Game Boy doesn't have this register, so don't bother trying.) 

 ld a,r ;read from the refresh register.

zkl

__DATE__, __DEBUG__, __FILE__, __LINE__, __NAME__, __TIME__

As in the C preprocessor. Some (like __DEBUG__) can be changed, others (like __LINE__, __TIME__) are constants.


ZX Spectrum Basic

The ZX Spectrum does Not make a difference between capital or lower character variable names. A normal variable can be severall letters long, any DEF FN, FOR/NEXT, DIM (STRING or DATA) array name is a single letter variable name. None of these are special variables. for 128k zx spectrum matters that In REVERSED SENSE some variable names are IMposible becouse of the tokenized form in the 48k basic eg 'not' will be NOT !!!! There are a set of system variables held at a fixed memory addresses, which can be accessed via PEEK and POKE functions. The system variables and addresses are:

  • 23552 KSTATE - Keyboard state.
  • 23560 LAST K - Newly pressed key.
  • 23561 REPDEL - Delay (in 50ths of a second) before keyboard starts repeating.
  • 23562 REPPER - Delay (in 50ths of a second) between keyboard repetions.
  • 23563 DEFADD - Address of arguments for a user defined function.
  • 23565 K DATA - Second byte of colour controls sequences from keyboard.
  • 23566 TVDATA - Colour and location information for television set.
  • 23568 STRMS - Addresses of channels attached to streams.
  • 23606 CHARS - 256 less than the address of the current character set
  • 23608 RASP - Length of the warning buzz.
  • 23609 PIP - Length of the keyboard click.
  • 23610 ERR NR One less than the error code and starts at 255 (for -1)
  • 23611 FLAGS - Various flags to control the BASIC system.
  • 23612 TV FLAG - Flags associated with the television output.
  • 23613 ERR SP - Address of item on machine stack to be used as error return.
  • 23615 LIST SP - Return address from automatic listing.
  • 23617 MODE - Cursor type
  • 23618 NEWPPC - Line number to be jumped to.
  • 23620 NSPPC - Statement number in line to be jumped to
  • 23621 PPC - Line number of statement currently being executed.
  • 23623 SUBPPC - Statement number within the line that is currently being executed.
  • 23624 BORDCR - Colour of the border (overscan area) and input area (times 8)
  • 23625 E PPC - Current line number (for list editing)
  • 23627 VARS - Address of the variables.
  • 23629 DEST - Address of variable in assignment.
  • 23631 CHANS - Address of channel data.
  • 23633 CURCHL - Address of information being used for input and output.
  • 23635 PROG - Address of the BASIC program.
  • 23637 NXTLIN - Address of the next line in the program.
  • 23639 DATADD - Address of terminator of the last DATA item.
  • 23641 E LINE - Address of command being typed in.
  • 23643 K CUR - Address of the cursor.
  • 23645 CH ADD - Address of the next character to be interpreted
  • 23647 X PTR - Address of the character after the syntax error marker.
  • 23649 WORKSP - Address of temporary work space.
  • 23651 STKBOT - Address of bottom of calculator stack.
  • 23653 STKEND - Address of start of free space.
  • 23655 BREG - The B register of the calculator.
  • 23656 MEM - Address of area used for calculator memory.
  • 23658 FLAGS2 - Miscellaneous flags.
  • 23659 DF SZ - The number of lines in the input area.
  • 23660 S TOP - The number of the top program line in automatic listings.
  • 23662 OLDPPC - Line number to which CONTINUE jumps.
  • 23664 OSPPC - Number within line of statement to which CONTINUE jumps.
  • 23665 FLAGX - Various flags.
  • 23666 STRLEN - Length of string type destination in assignment.
  • 23668 T ADDR - Address of next item in the syntax table.
  • 23670 SEED - The random number seed.
  • 23672 FRAMES - A 3 byte frame counter incremented every 20ms.
  • 23675 UDG - Address of the user defined graphics
  • 23677 COORDS Coordinates of the last point plotted.
  • 23679 P POSN - Column number for the position of the printer carriage.
  • 23680 PR CC - Address of next free position in the printer buffer.
  • 23682 ECHO E - Column and line number positions in the input buffer.
  • 23684 DF CC - Display address for the current print position.
  • 23686 DFCCL - Display address in the input area.
  • 23688 S POSN - Column and row number of the print position.
  • 23690 SPOSNL - Column and row number for the print position in the input area.
  • 23692 SCR CT - Scroll counter - Number of lines left before stopping with Scroll?
  • 23693 ATTR P - Permanent current colours attributes
  • 23694 MASK P - Permanent current colour attribute mask
  • 23695 ATTR T - Temporary current colour attributes
  • 23696 MASK T - Temporary current colour attribute mask
  • 23697 P FLAG - More flags.
  • 23698 MEMBOT - Memory area address used by the calculator
  • 23728 NMIADD - The address of the users Non Maskable Interrupt service routine.
  • 23730 RAMTOP - Address of last byte of BASIC system area.
  • 23732 P-RAMT - Address of last byte of physical RAM.
10 PRINT "The border colour is "; PEEK (23624): REM bordcr
20 PRINT "The ramtop address is "; PEEK (23730) + 256 * PEEK (23731): REM ramtop
30 POKE 23609,50: REM set keyboard pip to 50
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