Execute a system command

In this task, the goal is to run either the ls system command, or the pause system command.

AppleScript

do shell script "ls" without altering line endings

C

Compiler: GCC 4.0.1

Platform: BSD

#include <stdlib.h>

int main()
{
    system("ls");
}

C++

Compiler: Visual C++ 2005

system("pause");

Haskell

Interpreter: GHCi 6.6

import System.Cmd

main = system "ls"

IDL

$ls

Will execute "ls" with output to the screen.

 spawn,"ls",result

will execute it and store the result in the string array "result".

 spawn,"ls",unit=unit

will execute it asynchronously and direct any output from it into the LUN "unit" from whence it can be read at any (later) time.

Objective-C

Compiler: GCC 4.0.1 (apple)

NSTask runs an external process with explicit path and arguments.

void runls()
{
    [[NSTask launchedTaskWithLaunchPath:@"/bin/ls"
        arguments:[NSArray array]] waitUntilExit];
}

If you need to run a system command, invoke the shell:

void runSystemCommand(NSString *cmd)
{
    [[NSTask launchedTaskWithLaunchPath:@"/bin/sh"
        arguments:[NSArray arrayWithObjects:@"-c", cmd, nil]]
        waitUntilExit];
}

Or use the C method above.

Perl

Interpreter: Perl

Note the use of grave quotes (or back ticks) instead of "normal" single quotes.

my $results = `ls`;

Back ticks as above returns the results, system as below does not.

system "ls";

Python

Interpreter: Python 2.5

 import os
 code = os.system('ls') # Just execute the command, return a success/fail code
 output = os.popen('ls').read() # If you want to get the output data

or

Interpreter:Python 2.4 (and above)

 import subprocess
 output = subprocess.Popen('ls', shell=True, stdout=subprocess.PIPE).stdout
 print output.read()

Note: The latter is the preferred method for calling external processes, although cumbersome, it gives you finer control over the process.

Tcl

  puts [exec ls]

This page uses "ls" as the primary example. For what it's worth, Tcl has built-in primitives for retrieving lists of files so one would rarely ever directly exec an ls command.

UNIX Shell

UNIX shells are designed to run system commands as a default operation.

ls

If one wants to capture the command's standard output:

CAPTUREDOUTPUT=$(ls)