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
<lang>system("ls")</lang>
Or the classic "!" shell escape can be implemented as an "!" operator:
<lang>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
do shell script "ls" without altering line endings
AWK
<lang awk>BEGIN {
system("ls")
}</lang>
C
<lang c> #include <stdlib.h>
int main() { system("ls"); }</lang>
C++
system("pause");
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>
<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>
dc
! ls
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`) }
Erlang
os:cmd("ls").
Forth
s" ls" system
Fortran
The SYSTEM subroutine (and function) are a GNU extension. <lang fortran>program SystemTest
call system("ls")
end program SystemTest</lang>
Haskell
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.
Io
SystemCall with("ls") run
J
The system command interface in J is provided by the standard "task" script:
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'
Java
<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>
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>
Logo
The lines of output of the SHELL command are returned as a list.
print first butfirst shell [ls -a] ; ..
MAXScript
dosCommand "pause"
Make
make can use system command in either definition of variables or in the targets
in definition
contents=$(shell cat foo) curdir=`pwd`
in target
mytarget: cat foo | grep mytext
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
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:
<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>
Perl
my @results = qx(ls); # runs command and returns its STDOUT as a string my @results = `ls`; # ditto, alternative syntax system "ls"; # runs command and returns its exit status; its STDOUT gets output to our STDOUT print `ls`; #The same, but with back quotes exec "ls"; # replace current process with another
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:
@exec($command,$output); echo nl2br($output);
Note:The '@' is here to prevent error messages to be displayed, 'nl2br' translate '\n' chars to 'br' in HTML.
Pop11
The sysobey function runs commands using a shell:
sysobey('ls');
Prolog
<lang prolog>shell('ls').</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
or
from subprocess import PIPE, Popen, STDOUT p = Popen('ls', stdout=PIPE, stderr=STDOUT) print p.communicate()[0]
Note: The latter is the preferred method for calling external processes, although cumbersome, it gives you finer control over the process.
or
import commands stat, out = commands.getstatusoutput('ls') if not stat: print out
Raven
Back tick string is auto executed:
`ls -la` as listing
Or specifically on any string:
'ls -la' shell as listing
Ruby
<lang ruby> string = `ls`
# runs command and returns its STDOUT as a string string = %x{ls} # ditto, alternative syntax system "ls" # runs command and returns its exit status; its STDOUT gets output to our STDOUT print `ls` #The same, but with back quotes exec "ls" # replace current process with another</lang>
Smalltalk
<lang smalltalk>Smalltalk system: 'ls'.</lang>
Standard ML
Just run the command:
<lang ocaml>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 $io]</lang>
If the command is opened "rw", it is even possible to send it user input through the same handle, though care must be taken with buffering in that case.
Toka
needs shell " ls" system
UNIX Shell
UNIX shells are designed to run system commands as a default operation.
ls
If one wants to capture the command's standard output:
CAPTUREDOUTPUT=$(ls)
In C-Shell this can be achieved by
set MYCMDOUTPUT = `ls` echo $MYCMDOUTPUT
Where as in Korn Shell it becomes:
MYCMDOUTPUT=`ls` echo $MYCMDOUTPUT
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 $(...) form of command substitution is nestable.
If one wishes to replace the shell process with some other command (chain into some command with no return) one can use the exec shell built-in command in any of the common UNIX shells (C-Shell, and all of the Bourne-compatible shells).
exec ls
Visual Basic
Shelling out a sub task in Visual Basic is rather a pain if you need to wait for the task to complete, which is probably the usual case. But it is possible. <lang vb>Attribute VB_Name = "mdlShellAndWait" Option Explicit
Private Declare Function OpenProcess Lib "kernel32" _
(ByVal dwDesiredAccess As Long, ByVal bInheritHandle As Long, _ ByVal dwProcessId As Long) As Long
Private Declare Function GetExitCodeProcess Lib "kernel32" _
(ByVal hProcess As Long, lpExitCode As Long) As Long
Private Const STATUS_PENDING = &H103& Private Const PROCESS_QUERY_INFORMATION = &H400
' ' Little function go get exit code given processId ' Function ProcessIsRunning( processId as Long ) as Boolean
Dim exitCode as Long Call GetExitCodeProcess(lProcessId, exitCode) ProcessIsRunning = (exitCode = STATUS_PENDING)
End Function
' Spawn subprocess and wait for it to complete. ' I believe that the command in the command line must be an exe or a bat file. ' Maybe, however, it can reference any file the system knows how to "Open" ' ' commandLine is an executable. ' expectedDuration - is for poping up a dialog for whatever ' infoText - text for progressDialog dialog
Public Function ShellAndWait( commandLine As String, _
expectedDuration As Integer ) As Boolean Dim inst As Long Dim startTime As Long Dim expirationTime As Long Dim pid As Long Dim expiresSameDay As Boolean On Error GoTo HandleError
'Deal with timeout being reset at Midnight ($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>