Making a system call that returns the stdout outpu

Question

Perl and PHP do this with backticks. For example,

$output = `ls`;

Returns a directory listing. A similar function, system("foo"), returns the operating system return code for the given command foo. I'm talking about a variant that returns whatever foo prints to stdout.

How do other languages do this? Is there a canonical name for this function? (I'm going with "backtick"; though maybe I could coin "syslurp".)

Answer 1

Python

from subprocess import check_output as qx

output = qx(['ls', '-lt'])

Python <2.7 or <3.1

Extract subprocess.check_output() from subprocess.py or adapt something similar to:

import subprocess

def cmd_output(args, **kwds):
  kwds.setdefault("stdout", subprocess.PIPE)
  kwds.setdefault("stderr", subprocess.STDOUT)
  p = subprocess.Popen(args, **kwds)
  return p.communicate()[0]

print cmd_output("ls -lt".split())

The subprocess module has been in the stdlib since 2.4.

Answer 2

Why there is still no c# guy here :)

This is how to do it in C#. The built-in way.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;

namespace TestConsole
{
    class Program
    {
        static void Main(string[] args)
        {
            Process p = new Process();

            p.StartInfo.UseShellExecute = false;
            p.StartInfo.CreateNoWindow = true;
            p.StartInfo.RedirectStandardOutput = true;
            p.StartInfo.RedirectStandardError = true;
            p.StartInfo.FileName = "cmd";
            p.StartInfo.Arguments = "/c dir";
            p.Start();

            string res = p.StandardOutput.ReadToEnd();
            Console.WriteLine(res);
        }

    }
}

Answer 3

Ruby: either backticks or the '%x' builtin syntax.

puts `ls`;
puts %x{ls};

Answer 4

Don't forget Tcl:

set result [exec ls]

Answer 5

Clozure Common Lisp:

(with-output-to-string (stream)
   (run-program "ls" '("-l") :output stream))

LispWorks

(with-output-to-string (*standard-output*)
  (sys:call-system-showing-output "ls -l" :prefix "" :show-cmd nil))

Answer 6

Python:

import os
output = os.popen("foo").read()