Command-line arguments

Command-line arguments
You are encouraged to solve this task according to the task description, using any language you may know.

Retrieve the list of command-line arguments given to the program.

Example command line:

myprogram -c "alpha beta" -h "gamma"

Ada

Command line arguments are available through the pre-defined package Ada.Command_Line.

with Ada.Command_line; use Ada.Command_Line;
with Ada.Text_IO; use Ada.Text_IO

procedure Print_Commands is
begin
   -- The number of command line arguments is retrieved from the function Argument_Count
   -- The actual arguments are retrieved from the function Argument
   -- The program name is retrieved from the function Command_Name
   Put(Command_Name & " ");
   for Arg in 1..Argument_Count loop
      Put(Argument(Arg) & " ");
   end loop;
   New_Line;
end Print_Commands;

C

Command line arguments are passed to main. Since the program name is also passed as "argument", the provided count is actually one more than the number of program arguments. Traditionally the argument count is named argc and the array of argument strings is called argv, but that's not mandatory; any (non-reserved) name will work just as well. It is, however, a good idea to stick to the conventional names.

Be careful on systems that use Unicode or other multibyte character sets. You may need to use a type of _wchar* and multi-byte-character-set-aware versions of printf.

 #include <stdio.h>
 
 int main(int argc, char* argv[])
 {
   int i;
   printf("This program is named %s.\n", argv[0]);
   for (i = 1; i < argc; ++i)
     printf("the argument #%d is %s\n", i, argv[i]);
 }

C++

Command line arguments are passed the same way as in C.

This example uses iostream. Traditional C I/O also works.

#include <iostream>

int main(int argc, char* argv[])
{
  std::cout << "This program is named " << argv[0] << "\n";
  std::cout << "There are " << argc-1 << " arguments given.\n";
  for (int i = 1; i < argc; ++i)
    std::cout << "the argument #" << i << " is " << argv[i] << "\n";
}

Clean

getCommandLine from the module ArgEnv returns an array of command-line arguments (the first element is the name of the program).

import ArgEnv

Start = getCommandLine

E

interp.getArgs()

Forth

Access to command line arguments is not a standard feature of Forth, since it is designed to be used without an operating system. The popular GNU implementation gforth runs from a shell and can access command line arguments similar to C: variable argc contains the count (including the command itself) and arg is a function that returns the nth argument as a string.

Interpreter: gforth 0.6.2

\ args.f: print each command line argument on a separate line
: main
  argc @ 0 do i arg type cr loop ;

main bye

Here is output from a sample run.

$ gforth args.f alpha "beta gamma" delta
gforth
args.f
alpha
beta gamma
delta
$

Haskell

Defined by the System module, getArgs :: IO [String] provides the command-line arguments in a list.

myprog.hs:

import System
main = getArgs >>= print

myprog a -h b c
=> ["a","-h","b","c"]

Java

public class Arguments {
  public static void main(String[] args) {
     System.out.println("There are " + args.length + " arguments given.");
     for(int i = 0; i < args.length; i++) 
        System.out.println("The argument #" + (i+1) + " is " + args[i] + "and is at index " + i);
  }
}

LSE64

argc , nl  # number of arguments (including command itself)
0         # argument
dup arg dup 0 = || ,t  1 + repeat
drop

Perl

Interpreter: Perl v5.x

@ARGV is the array containing all command line parameters

my @params = @ARGV;
my $second = $ARGV[1];
my $fifth = $ARGV[4];

Pop11

variable poparglist contains list of command line arguments (as strings). One can use iteration over list to process then (for example print).

lvars arg;
for arg in poparglist do
   printf(arg, '->%s<-\n');
endfor;

Python

argv in the sys module is a list containing all command line arguments, including the program name. The standard built-in len() function gives the total number of arguments. A slice of sys.argv[1:] is normally used to exclude the program's (executable) name.

import sys
program_name = sys.argv[0]   # gets the program name
all_arguments = sys.argv[1:] # arguments, excluding the program name
argc = len(sys.argv[1:])     # number of "normal" arguments

Notes: Invoking the interactive interpreter with command line arguments will not work correctly; the arguments will be modified in odd ways by the interpreter. (This includes commands like: python -i -c "x=123; print x" --- which executes the command line code and leaves on in the interpreter, as intended, but leaves the sys.argv list containing only the "-c" and no program executable nor other flags or arguments). One can modify the sys.argv but this change will not affect your process' "command tail" as seen by the UNIX/Linux ps command, for example. In other words sys.argv is only a copy of your system arguments it is not a reference to your command tail).

Ruby

Command line arguments are available in the constant Object::ARGV.

myprog:

 #! /usr/bin/env ruby
 p ARGV

 myprog a -h b c
 => ["a","-h","b","c"]

Tcl

The pre-defined variable argc contains the number of arguments passed to the routine, argv contains the arguments as a list. Retrieving the second argument might look something like this:

 if { $argc > 1 } { puts [lindex $argv 1] }

(Tcl counts from zero, thus [lindex $list 1] retrieves the second item in the list)

Toka

Arguments are stored into an array. The first element in the array is the name of the program, the rest are the arguments in order. The number of arguments is provided by #args.

 [ arglist array.get type cr ] is show-arg
 [ dup . char: = emit space ] is #= 
 1 #args [ i #= show-arg ] countedLoop

UNIX Shell

Bourne Shell

To retrieve the entire list of arguments:

WHOLELIST="$@"

To retrieve the second and fifth arguments:

SECOND=$2
FIFTH=$5