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
system command, or the pause
system command.
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;
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");
C#
Compiler: MCS 1.2.3.1
using System; class Execute { static void Main() { System.Diagnostics.Process proc = new System.Diagnostics.Process(); proc.EnableRaisingEvents=false; proc.StartInfo.FileName="ls"; proc.Start(); } }
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`) }
Forth
Interpreter: gforth 0.6.2
s" ls" system
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.
Java
Compiler: JDK 1.4 and up There is two way to run system commands. The simple way, which have the inconvenience to hang the JVM (I would be interested in some kind of reason).
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) { } } } } }
And the right way, which use threading to read the inputstream given by the process.
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) { } } } } }
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
my @results = qx(ls); # runs command and returns its STDOUT my @results = `ls`; # dito, alternative syntax system "ls"; # runs command and returns its exit status 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 commans using a shell:
sysobey('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.
or
Interpreter:Python 2.2 (and above)
import commands stat, out = commands.getstatusoutput('ls') if not stat: print out
Ruby
string = `ls`
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.
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:
set io [open "|ls" r]
would execute "ls" and pipe the result into the unit "io". From there one could receive it either line by line like this:
set nextline [gets $io]
or read the whole shebang in a fell swoop:
set lsoutput [read $io]
If the command is opened "rw", it is even possible to send it user input through the same handle.
Toka
needs shell " ls" system
UNIX Shell
UNIX shells are designed to run system commands as a default operation.
ls
If one wants to capture the command's standard output:
CAPTUREDOUTPUT=$(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