Don't use exec
. Use spawn
which is an EventEmmiter
object. Then you can listen to stdout
/stderr
events (spawn.stdout.on('data',callback..)
) as they happen.
From NodeJS documentation:
var spawn = require('child_process').spawn,
ls = spawn('ls', ['-lh', '/usr']);
ls.stdout.on('data', function (data) {
console.log('stdout: ' + data.toString());
});
ls.stderr.on('data', function (data) {
console.log('stderr: ' + data.toString());
});
ls.on('exit', function (code) {
console.log('child process exited with code ' + code.toString());
});
exec
buffers the output and usually returns it when the command has finished executing.
exec
will also return a ChildProcess object that is an EventEmitter.
var exec = require('child_process').exec;
var coffeeProcess = exec('coffee -cw my_file.coffee');
coffeeProcess.stdout.on('data', function(data) {
console.log(data);
});
OR pipe
the child process's stdout to the main stdout.
coffeeProcess.stdout.pipe(process.stdout);
OR inherit stdio using spawn
spawn('coffee -cw my_file.coffee', { stdio: 'inherit' });
There are already several answers however none of them mention the best (and easiest) way to do this, which is using spawn
and the { stdio: 'inherit' }
option. It seems to produce the most accurate output, for example when displaying the progress information from a git clone
.
Simply do this:
var spawn = require('child_process').spawn;
spawn('coffee', ['-cw', 'my_file.coffee'], { stdio: 'inherit' });
Credit to @MorganTouvereyQuilling for pointing this out in this comment.
Inspired by Nathanael Smith's answer and Eric Freese's comment, it could be as simple as:
var exec = require('child_process').exec;
exec('coffee -cw my_file.coffee').stdout.pipe(process.stdout);
I'd just like to add that one small issue with outputting the buffer strings from a spawned process with console.log()
is that it adds newlines, which can spread your spawned process output over additional lines. If you output stdout
or stderr
with process.stdout.write()
instead of console.log()
, then you'll get the console output from the spawned process 'as is'.
I saw that solution here: Node.js: printing to console without a trailing newline?
Hope that helps someone using the solution above (which is a great one for live output, even if it is from the documentation).
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