Is it possible to write task taking stdin using `gulp-run`

[kompot]

Hi, is it possible to write a task taking stdin as input and forwarding it further? Something like

gulp.task('task-taking-stdin', function() {
  var run = require('gulp-run');
  run.exec().pipe(someOtherTask())
});

Could you please guide me if that's something possible to be achieved with gulp-run.

[cbarrick]

The run function is actually a constructor, where the new keyword is optional. The constructed object is a stream, which, when written to, spawns a new process with the written data as the stdin. The .exec method is simply an alias for .write. So run('my-command').exec('my-stdin') is how you run a command with a specific stdin. .exec can take whatever is most convenient (strings, buffers, or Vinyl files) to use as stdin, but note that every call to .exec/.write spawns a separate process.

I'm not entirely clear as to what you are asking, so forgive me if the following examples don't cover your use case.

---

Trying to use process.stdin (i.e. tty input) as the stdin of your command?

In general, I don't recommend doing that. If you have cases where you need different inputs to your command, I would write separate tasks and hard-code the input:

gulp.task('task-A', function () {
  run('my-command').exec('some input');
}
gulp.task('task-B', function () {
  run('my-command').exec('different input');
}

If you absolutely must use process.stdin as the stdin of the command, try creating a Vinyl file from process.stdin and passing that to .exec.

---

Creating a command pipeline like you would in a shell/make?

A command that looks like this in a shell:

command1 | command2 | command3

could look like this with gulp-run:

run('command1').exec()
  .pipe(run('command2'))
  .pipe(run('command3'));

or, even better, like this:

run('command1 | command2 | command3').exec();

---

Using the output of a command as the input to another plugin?

Like other gulp plugins, you can pipe the output to another plugin

run('command1 | command2 | command3').exec()
  .pipe(some_other_plugin);

---

Using the output of another plugin as the stdin of a command?

The other plugin probably has a pipe method that's compatible with gulp-run

some_other_plugin()
  .pipe(run('command1'));

[kompot]

Thank you for your effort for such a detailed explanation. Really cleared things up.

What I'm trying to achieve is that I run external (to gulp) command like

cat file.txt | gulp taskThatTakesStdin

I guess this is the way to go "try creating a Vinyl file from process.stdin and passing that to .exec"?

[cbarrick]

Could you run that external command from within your gulp task instead?

You can't pipe out to another task, but you can wrap your existing task. Something like:

gulp.task('new-task', function () {
    run('cat file.txt').exec()
        .pipe(foo())
        .pipe(bar());
})

where the old task was

gulp.task('old-task', function () {
    foo()
        .pipe(bar());
})

[kompot]

Actually I think I can. The task was to check whether git staged content passes eslint/jscs tests.

So I'll try to run git cat-file -p /path/to/staged/file within gulp and not in a pre-commit hook.

Thanks for your participation!