Remove lines from a file: Difference between revisions
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Empty lines are considered and should still be counted, and if the specified line is empty, it should still be removed. However, an appropriate message should appear, if an attempt is made to remove lines beyond the end of the file. |
Empty lines are considered and should still be counted, and if the specified line is empty, it should still be removed. However, an appropriate message should appear, if an attempt is made to remove lines beyond the end of the file. |
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=={{header|Icon}} and {{header|Unicon}}== |
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<lang Icon>procedure main() # remove lines |
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removelines("foo.bar",3,2) | stop("Failed to remove lines.") |
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end |
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procedure removelines(fn,start,skip) |
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f := open(fn,"r") | fail # open to read |
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every put(F := [],|read(f)) # file to list |
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close(f) |
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if *F < start-1+skip then fail |
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every F[start - 1 + (1 to skip)] := &null # mark delete |
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f := open(fn,"w") | fail # open to rewrite |
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every write(\!F) # write non-nulls |
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close(f) |
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return # done |
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end</lang> |
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=={{header|J}}== |
=={{header|J}}== |
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Revision as of 03:25, 25 July 2011
The task is to demonstrate how to remove a specific line or a number of lines from a file. This should be implemented as a routine that takes three parameters (filename, starting line, and the number of lines to be removed). For the purpose of this task, line numbers and the number of lines start at one, so to remove the first two lines from the file foobar.txt, the parameters should be: foobar.txt, 1, 2
Empty lines are considered and should still be counted, and if the specified line is empty, it should still be removed. However, an appropriate message should appear, if an attempt is made to remove lines beyond the end of the file.
Icon and Unicon
<lang Icon>procedure main() # remove lines
removelines("foo.bar",3,2) | stop("Failed to remove lines.")
end
procedure removelines(fn,start,skip)
f := open(fn,"r") | fail # open to read every put(F := [],|read(f)) # file to list close(f)
if *F < start-1+skip then fail every F[start - 1 + (1 to skip)] := &null # mark delete f := open(fn,"w") | fail # open to rewrite every write(\!F) # write non-nulls close(f) return # done
end</lang>
J
<lang j>removeLines=:4 :0
'count start'=. x
file=. boxxopen y
lines=. <;.2]1!:1 file
(;lines {~ <<< (start-1)+i.count) 1!:2 file
)</lang>
Thus: <lang bash>$ cal >cal.txt $ cat cal.txt
July 2011
Su Mo Tu We Th Fr Sa
1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31</lang>
<lang j> 2 1 removeLines 'cal.txt'</lang>
<lang bash>$ cat cal.txt
1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31</lang>
Note that this code assumes that the last character in the file is the line end character.
Lua
<lang lua>function remove( filename, starting_line, num_lines )
local fp = io.open( filename, "r" ) if fp == nil then return nil end
content = {}
i = 1;
for line in fp:lines() do
if i < starting_line or i >= starting_line + num_lines then
content[#content+1] = line end i = i + 1
end
if i > starting_line and i < starting_line + num_lines then
print( "Warning: Tried to remove lines after EOF." )
end
fp:close() fp = io.open( filename, "w+" )
for i = 1, #content do
fp:write( string.format( "%s\n", content[i] ) )
end
fp:close()
end</lang>
Tcl
<lang tcl>proc removeLines {fileName startLine count} {
# Work out range to remove
set from [expr {$startLine - 1}]
set to [expr {$startLine + $count - 2}]
# Read the lines
set f [open $fileName]
set lines [split [read $f] "\n"]
close $f
# Write the lines back out, without removed range
set f [open $fileName w]
puts -nonewline $f [join [lreplace $lines $from $to] "\n"]
close $f
}</lang>