Execute a system command

From Rosetta Code
Revision as of 22:47, 1 January 2010 by rosettacode>Wmeyer (Added Oz example.)
Task
Execute a system command
You are encouraged to solve this task according to the task description, using any language you may know.

In this task, the goal is to run either the ls (dir on Windows) system command, or the pause system command.

Ada

<lang ada>with Interfaces.C; use Interfaces.C;

procedure Execute_System is

   function Sys (Arg : Char_Array) return Integer;
   pragma Import(C, Sys, "system");
   Ret_Val : Integer;

begin

   Ret_Val := Sys(To_C("ls"));

end Execute_System;</lang>

ALGOL 68

Works with: ALGOL 68G version Any - tested with release mk15-0.8b.fc9 - "system" is not part of the standard's prelude.

<lang algol68>system("ls")</lang>

Or the classic "!" shell escape can be implemented as an "!" operator:

Works with: ALGOL 68G version Any - tested with release mk15-0.8b.fc9 - "system" & "ANDF" are not part of the standard's prelude.

<lang algol68>OP ! = (STRING cmd)BOOL: system(cmd) = 0;

IF ! "touch test.tmp" ANDF ( ! "ls test.tmp" ANDF ! "rm test.tmp" ) THEN

 print (("test.tmp now gone!", new line))

FI</lang>

AppleScript

<lang applescript>do shell script "ls" without altering line endings</lang>

AutoHotkey

<lang autohotkey>Run, %comspec% /k dir & pause</lang>

AWK

<lang awk>BEGIN {

 system("ls")

}</lang>

BASIC

<lang qbasic>SHELL "dir"</lang>

C

ISO C & POSIX:

<lang c>#include <stdlib.h>

int main() {

   system("ls");
   return 0;

}</lang>

C++

Works with: Visual C++ version 2005

<lang cpp>system("pause");</lang>

C#

Using Windows / .NET: <lang csharp>using System.Diagnostics;

namespace Execute {

   class Program
   {
       static void Main(string[] args)
       {
           Process.Start("cmd.exe", "/c dir");
       }
   }

}</lang>

Works with: MCS version 1.2.3.1

<lang csharp>using System;

 class Execute {
    static void Main() {
        System.Diagnostics.Process proc = new System.Diagnostics.Process();
        proc.EnableRaisingEvents=false;
        proc.StartInfo.FileName="ls";
        proc.Start();
   }
}</lang>

Common Lisp

Works with: LispWorks

<lang lisp>(system:call-system "ls")</lang>

Library: trivial-shell

<lang lisp>(trivial-shell:shell-command "ls")</lang>

D

Note that this does not return the output of the command, other than the return value. That functionality can be accomplished via a call to shell(). <lang d>std.process.system("ls");</lang>

dc

<lang dc>! ls</lang>

E

<lang e>def ls := makeCommand("ls") ls("-l")

def [results, _, _] := ls.exec(["-l"]) when (results) -> {

 def [exitCode, out, err] := results
 print(out)

} catch problem {

 print(`failed to execute ls: $problem`)

}</lang>

Erlang

<lang erlang>os:cmd("ls").</lang>

Factor

<lang factor>"ls" run-process wait-for-process</lang>

Forth

Works with: gforth version 0.6.2

<lang forth>s" ls" system</lang>

Fortran

Works with: gfortran

The SYSTEM subroutine (and function) are a GNU extension. <lang fortran>program SystemTest

 call system("ls")

end program SystemTest</lang>

gnuplot

<lang gnuplot>!ls</lang>

Haskell

Works with: GHCi version 6.6

<lang haskell>import System.Cmd

main = system "ls" </lang>

See also: the System.Process module

IDL

<lang idl>$ls</lang>

Will execute "ls" with output to the screen.

<lang idl>spawn,"ls",result</lang>

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

<lang idl>spawn,"ls",unit=unit</lang>

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

Io

<lang io>SystemCall with("ls") run</lang>

J

The system command interface in J is provided by the standard "task" script: <lang j>load'task'

NB. Execute a command and wait for it to complete shell 'dir'

NB. Execute a command but don't wait for it to complete fork 'notepad'

NB. Execute a command and capture its stdout stdout =: shell 'dir'

NB. Execute a command, provide it with stdin, NB. and capture its stdout stdin =: 'blahblahblah' stdout =: stdin spawn 'grep blah'</lang>


Java

Works with: Java version 1.5+

<lang java5>import java.util.Scanner; import java.io.*;

public class Program {

   public static void main(String[] args) {    	
   	try {
   		Process p = Runtime.getRuntime().exec("cmd /C dir");//Windows command, use "ls -oa" for UNIX
   		Scanner sc = new Scanner(p.getInputStream());    		
   		while (sc.hasNext()) System.out.println(sc.nextLine());
   	}
   	catch (IOException e) {
   		System.out.println(e.getMessage());
   	}
   }

}</lang>

Works with: Java version 1.4+

There are two ways to run system commands. The simple way, which will hang the JVM (I would be interested in some kind of reason). -- this happens because the the inputStream buffer fills up and blocks until it gets read. Moving your .waitFor after reading the InputStream would fix your issue (as long as your error stream doesn't fill up) <lang java>import java.io.IOException; import java.io.InputStream;

public class MainEntry {

   public static void main(String[] args) {
       executeCmd("ls -oa");
   }
   private static void executeCmd(String string) {
       InputStream pipedOut = null;
       try {
           Process aProcess = Runtime.getRuntime().exec(string);
           aProcess.waitFor();
           pipedOut = aProcess.getInputStream();
           byte buffer[] = new byte[2048];
           int read = pipedOut.read(buffer);
           // Replace following code with your intends processing tools
           while(read >= 0) {
               System.out.write(buffer, 0, read);
               
               read = pipedOut.read(buffer);
           }
       } catch (IOException e) {
           e.printStackTrace();
       } catch (InterruptedException ie) {
           ie.printStackTrace();
       } finally {
           if(pipedOut != null) {
               try {
                   pipedOut.close();
               } catch (IOException e) {
               }
           }
       }
   }
   
   

}</lang>

And the right way, which uses threading to read the InputStream given by the process. <lang java>import java.io.IOException; import java.io.InputStream;

public class MainEntry {

   public static void main(String[] args) {
       // the command to execute
       executeCmd("ls -oa");
   }
   private static void executeCmd(String string) {
       InputStream pipedOut = null;
       try {
           Process aProcess = Runtime.getRuntime().exec(string);
           // These two thread shall stop by themself when the process end
           Thread pipeThread = new Thread(new StreamGobber(aProcess.getInputStream()));
           Thread errorThread = new Thread(new StreamGobber(aProcess.getErrorStream()));
           
           pipeThread.start();
           errorThread.start();
           
           aProcess.waitFor();
       } catch (IOException e) {
           e.printStackTrace();
       } catch (InterruptedException ie) {
           ie.printStackTrace();
       }
   }

}

//Replace the following thread with your intends reader class StreamGobber implements Runnable {

   private InputStream Pipe;
   public StreamGobber(InputStream pipe) {
       if(pipe == null) {
           throw new NullPointerException("bad pipe");
       }
       Pipe = pipe;
   }
   public void run() {
       try {
           byte buffer[] = new byte[2048];
           int read = Pipe.read(buffer);
           while(read >= 0) {
               System.out.write(buffer, 0, read);
               read = Pipe.read(buffer);
           }
       } catch (IOException e) {
           e.printStackTrace();
       } finally {
           if(Pipe != null) {
               try {
                   Pipe.close();
               } catch (IOException e) {
               }
           }
       }
   }

}</lang>

JavaScript

JavaScript does not have any facilities to interact with the OS. However, host environments can provide this ability.

Works with: JScript

<lang javascript>var shell = new ActiveXObject("WScript.Shell"); shell.run("cmd /c dir & pause");</lang>

Works with: Rhino

<lang javascript>runCommand("cmd", "/c", "dir", "d:\\"); print("==="); var options = {

   // can specify arguments here in the options object
   args: ["/c", "dir", "d:\\"],
   // capture stdout to the options.output property
   output: 

}; runCommand("cmd", options); print(options.output);</lang>

Joy

<lang joy>"ls" system.</lang>

Works with: UCB Logo

The lines of output of the SHELL command are returned as a list. <lang logo>print first butfirst shell [ls -a]  ; ..</lang>

Lua

<lang lua>-- just executing the command os.execute("ls")

-- to execute and capture the output, use io.popen local f = io.popen("ls") -- store the output in a "file" print( f:read("*a") ) -- print out the "file"'s content</lang>

M4

<lang M4>syscmd(ifdef(`__windows__',`dir',`ls'))</lang>

MAXScript

<lang maxscript>dosCommand "pause"</lang>

Make

make can use system command in either definition of variables or in the targets

in definition

<lang make>contents=$(shell cat foo) curdir=`pwd`</lang>

in target

<lang make>mytarget:

  cat foo | grep mytext</lang>

Modula-3

This code requires the UNSAFE keyword because M3toC deals with C strings (which are pointers), and are implemented in Modula-3 as UNTRACED, meaning they are not garbage collected, which is why the code calls FreeCopiedS().

Also note the EVAL keyword, which ignores the return value of a function. <lang modula3>UNSAFE MODULE Exec EXPORTS Main;

IMPORT Unix, M3toC;

VAR command := M3toC.CopyTtoS("ls");

BEGIN

 EVAL Unix.system(command);
 M3toC.FreeCopiedS(command);

END Exec.</lang>

Objective-C

Works with: GCC


NSTask runs an external process with explicit path and arguments. <lang objc>void runls() {

   [[NSTask launchedTaskWithLaunchPath:@"/bin/ls"
       arguments:[NSArray array]] waitUntilExit];

}</lang> If you need to run a system command, invoke the shell: <lang objc>void runSystemCommand(NSString *cmd) {

   [[NSTask launchedTaskWithLaunchPath:@"/bin/sh"
       arguments:[NSArray arrayWithObjects:@"-c", cmd, nil]]
       waitUntilExit];

}</lang> Complete usage example:

Works with: Cocoa


Works with: GNUstep

<lang objc>#import <Foundation/Foundation.h>

void runSystemCommand(NSString *cmd) {

   [[NSTask launchedTaskWithLaunchPath:@"/bin/sh"
       arguments:[NSArray arrayWithObjects:@"-c", cmd, nil]]
       waitUntilExit];

}

int main(int argc, const char **argv) {

   NSAutoreleasePool *pool;
   pool = [NSAutoreleasePool new];
   runSystemCommand(@"ls");
   [pool release];
   return 0;

}</lang> Or use the C method above.

OCaml

Just run the command:

<lang ocaml>Sys.command "ls"</lang>

To capture the output of the command:

<lang ocaml>#load "unix.cma";; let syscall cmd =

 let inc, outc = Unix.open_process cmd in  
 let buf = Buffer.create 16 in                       
 (try
    while true do
      Buffer.add_channel buf inc 1
    done
  with End_of_file -> ());
 let _status = Unix.close_process (inc, outc) in
 Buffer.contents buf;;

let listing = syscall "ls";;</lang>

Octave

<lang octave>system("ls");</lang>

Oz

<lang oz>{OS.system "ls" _}</lang>

A more sophisticated example can be found here.

Perl

<lang perl>my @results = qx(ls);

  1. runs command and returns its STDOUT as a string

my @results = `ls`;

  1. ditto, alternative syntax

system "ls";

  1. runs command and returns its exit status; its STDOUT gets output to our STDOUT

print `ls`;

  1. The same, but with back quotes

exec "ls";

  1. replace current process with another</lang>

Also see: http://perldoc.perl.org/perlipc.html#Using-open()-for-IPC http://perldoc.perl.org/IPC/Open3.html

PHP

The first line execute the command and the second line display the output: <lang php>@exec($command,$output); echo nl2br($output);</lang> Note:The '@' is here to prevent error messages to be displayed, 'nl2br' translate '\n' chars to 'br' in HTML.

Other:

$results = `ls`;
# runs command and returns its STDOUT as a string

system("ls");
# runs command and returns its exit status; its STDOUT gets output to our STDOUT

echo `ls`;
#The same, but with back quotes

See also: proc_open()

Pike

<lang pike>import Process;

int main(){

  // This appears to only work in Pike >= 7.8 :(
  string response = run("ls");
  // response is now a map containing 3 fields
  // stderr, stdout, and exitcode. We want stdout.
  write(response["stdout"] + "\n");

}</lang>

Pop11

The sysobey function runs commands using a shell:

<lang pop11>sysobey('ls');</lang>

PowerShell

Since PowerShell is a shell, running commands is the default operation. <lang powershell>dir ls Get-ChildItem</lang> are all equivalent (the first two are aliases for the third) but they are PowerShell-native commands. If one really needs to execute dir (which is no program but rather a built-in command in cmd.exe) this can be achieved by <lang powershell>cmd /c dir</lang>

Prolog

Works with: SWI Prolog
Works with: GNU Prolog

<lang prolog>shell('ls').</lang>

Python

Works with: Python version 2.5

<lang python>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. Deprecated.</lang>

or

Works with: Python version 2.4 (and above)

<lang python>from subprocess import PIPE, Popen, STDOUT p = Popen('ls', stdout=PIPE, stderr=STDOUT) print p.communicate()[0]</lang>

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

or

Works with: Python version 2.2 (and above)

<lang python>import commands stat, out = commands.getstatusoutput('ls') if not stat:

   print out</lang>

R

<lang R>system("ls")</lang>

Raven

Back tick string is auto executed:

<lang raven>`ls -la` as listing</lang>

Or specifically on any string:

<lang raven>'ls -la' shell as listing</lang>

REBOL

<lang REBOL>; Capture output to string variable:

x: "" call/output "dir" x print x

The 'console' refinement displays the command output on the REBOL command line.

call/console "dir *.r" call/console "ls *.r"

call/console "pause"

The 'shell' refinement may be necessary to launch some programs.

call/shell "notepad.exe"</lang>

Ruby

<lang ruby>string = `ls`

  1. runs command and returns its STDOUT as a string

string = %x{ls}

  1. ditto, alternative syntax

system "ls"

  1. runs command and returns its exit status; its STDOUT gets output to our STDOUT

print `ls`

  1. The same, but with back quotes

exec "ls"

  1. replace current process with another
  1. call system command and read output asynchronously

io = IO.popen('ls')

  1. ... later

io.each {|line| puts line}</lang>

Slate

Run a command normally through the shell:

<lang slate>Platform run: 'ls'.</lang>

Run a command (this way takes advantage of the 'does not understand' message for the shell object and calls the Platform run: command above with a specific command):

<lang slate>shell ls: '*.slate'.</lang>

Smalltalk

<lang smalltalk>Smalltalk system: 'ls'.</lang>

Standard ML

Just run the command:

<lang sml>OS.Process.system "ls"</lang>

Tcl

<lang tcl>puts [exec ls]</lang>

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.

It is also possible to execute a system command by "open"ing it through a pipe from whence any output of the command can be read at any (later) time. For example:

<lang tcl>set io [open "|ls" r]</lang>

would execute "ls" and pipe the result into the unit "io". From there one could receive it either line by line like this:

<lang tcl>set nextline [gets $io]</lang>

or read the whole shebang in a fell swoop:

<lang tcl>set lsoutput [read $io]</lang>

If the command is opened "rw", it is even possible to send it user input through the same handle, though care must be taken with buffering in that case.

Toka

<lang toka>needs shell " ls" system</lang>

UNIX Shell

UNIX shells are designed to run system commands as a default operation. <lang bash>ls</lang> If one wants to capture the command's standard output: <lang bash>CAPTUREDOUTPUT=$(ls)</lang>

In C-Shell this can be achieved by <lang bash>set MYCMDOUTPUT = `ls` echo $MYCMDOUTPUT</lang>

Where as in Korn Shell it becomes: <lang bash>MYCMDOUTPUT=`ls` echo $MYCMDOUTPUT</lang>

Note: in these last cases, C-Shell and Korn Shell, these are "backticks" rather than quotes or apostrophes. These "backticks" can also be used in Bourne compatible shells, though the $(...) form is preferred when discussing such things in e-mail, on USENET, or in other online forums (such as this wiki). Also the $(...) form of command substitution is nestable.

If one wishes to replace the shell process with some other command (chain into some command with no return) one can use the exec shell built-in command in any of the common UNIX shells (C-Shell, and all of the Bourne-compatible shells).

<lang bash>exec ls</lang>

Ursala

The library function, ask, parameterized by a shell descriptor, such as bash, spawns a process that interacts with that shell by feeding it a list of commands, and returns a transcript of the interaction.

Note that the output from the spawned process is captured and returned only, not sent to the standard output stream of the parent.

Here is a self-contained command line application providing a limited replacement for the ls command. <lang Ursala>#import std

  1. import cli
  1. executable ('parameterized',)

myls = <.file$[contents: --<>]>@hm+ (ask bash)/0+ -[ls --color=no]-!</lang> The color option is needed to suppress terminal escape sequences.

Visual Basic

Shelling out a sub task in Visual Basic is rather a pain if you need to wait for the task to complete, which is probably the usual case. But it is possible. <lang vb>Attribute VB_Name = "mdlShellAndWait" Option Explicit

Private Declare Function OpenProcess Lib "kernel32" _

   (ByVal dwDesiredAccess As Long, ByVal bInheritHandle As Long, _
   ByVal dwProcessId As Long) As Long

Private Declare Function GetExitCodeProcess Lib "kernel32" _

   (ByVal hProcess As Long, lpExitCode As Long) As Long

Private Const STATUS_PENDING = &H103& Private Const PROCESS_QUERY_INFORMATION = &H400

' ' Little function go get exit code given processId ' Function ProcessIsRunning( processId as Long ) as Boolean

   Dim exitCode as Long
   Call GetExitCodeProcess(lProcessId, exitCode)
   ProcessIsRunning = (exitCode = STATUS_PENDING)

End Function

' Spawn subprocess and wait for it to complete. ' I believe that the command in the command line must be an exe or a bat file. ' Maybe, however, it can reference any file the system knows how to "Open" ' ' commandLine is an executable. ' expectedDuration - is for poping up a dialog for whatever ' infoText - text for progressDialog dialog

Public Function ShellAndWait( commandLine As String, _

   expectedDuration As Integer ) As Boolean
   
   Dim inst As Long
   Dim startTime As Long
   Dim expirationTime As Long
   Dim pid As Long
   Dim expiresSameDay As Boolean
   
   On Error GoTo HandleError
   'Deal with timeout being reset at Midnight ($hitForBrains VB folks)
   startTime = CLng(Timer)
   expirationTime = startTime + expectedDuration
   expiresSameDay = expirationTime < 86400
   If Not expiresSameDay Then
       expirationTime = expirationTime - 86400
   End If
   inst = Shell(commandLine, vbMinimizedNoFocus)
   
   If inst <> 0 Then
       pid = OpenProcess(PROCESS_QUERY_INFORMATION, False, inst)
       Do While ProcessIsRunning( pid)
           DoEvents
           If Timer > expirationTime And (expiresSameDay Or Timer < startTime) Then
               Exit Do
           End If
       Loop 
       ShellAndWait = True
   Else
       MsgBox ("Couldn't execute command: " & commandLine)
       ShellAndWait = False
   End If
       
   Exit Function
  

HandleError:

   MsgBox ("Couldn't execute command: " & commandLine)
   ShellAndWait = False

End Function

Sub SpawnDir()

  ShellAndWait("dir", 10)

End Sub</lang>