Running a shell command from Node.js without buffering output

Question

I\'m trying to launch a shell command from Node.js, without redirecting that command\'s input and output -- just like shelling out to a command using a shell script, or

Answer 1

I haven't used it, but I've seen this library: https://github.com/polotek/procstreams

It you'd do this. The .out() automatically pipes to the process's stdin/out.

var $p = require('procstreams');
$p('cat lines.txt').pipe('wc -l').out();

If doesn't support shell syntax, but that's pretty trivial I think.

var command_str = "cat lines.txt | wc -l";
var cmds = command_str.split(/\s?\|\s?/);
var cmd = $p(cmds.shift());
while(cmds.length) cmd = cmd.pipe(cmds.shift());
cmd
  .out()
  .on('exit', function() {
    // Do whatever
  });

Answer 2

There's an example in the node docs for the child_process module:

Example of detaching a long-running process and redirecting its output to a file:

 var fs = require('fs'),
     spawn = require('child_process').spawn,
     out = fs.openSync('./out.log', 'a'),
     err = fs.openSync('./out.log', 'a');

 var child = spawn('prg', [], {
   detached: true,
   stdio: [ 'ignore', out, err ]
 });

 child.unref();

Answer 3

You can inherit stdin/out/error streams via spawn argument so you don't need to pipe them manually:

var spawn = require('child_process').spawn;
spawn('ls', [], { stdio: 'inherit' });

Use shell for shell syntax - for bash it's -c parameter to read script from string:

var spawn = require('child_process').spawn;
var shellSyntaxCommand = 'ls -l | grep test | wc -c';
spawn('sh', ['-c', shellSyntaxCommand], { stdio: 'inherit' });

To summarise:

var spawn = require('child_process').spawn;
function shspawn(command) {
   spawn('sh', ['-c', command], { stdio: 'inherit' });
} 

shspawn('ls -l | grep test | wc -c');

Answer 4

You can replace exec by spawn and use the shell syntax simply with:

const {spawn} = require ('child_process');
const cmd = 'ls -l | grep test | wc -c';
const p = spawn (cmd, [], {shell: true});

p.stdout.on ('data', (data) => {
  console.log (data.toString ());
});

The magic is just {shell: true}.