Execute a system command
In this task, the goal is to run either the ls system command, or the pause system command.
You are encouraged to solve this task according to the task description, using any language you may know.
Ada
<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;
</Ada>
AppleScript
do shell script "ls" without altering line endings
C
Platform: BSD
#include <stdlib.h>
int main()
{
system("ls");
}
C++
system("pause");
C#
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
s" ls" system
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
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)
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 uses 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) {
}
}
}
}
}
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
Objective-C
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.
OCaml
<ocaml>Sys.command "ls"</ocaml>
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 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');
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
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
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
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
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