spawn-error-forwarder

Emit errors on stdout stream for a spawned child process. Useful for capturing errors from a spawned process when you want the output from stdout.

Setup

$ npm install spawn-error-forwarder

API

fwd(child [, errFactory] -> child

Buffers child.stderr output. If the spawned process exits with a code > 0, the buffered output of child.stderr is used to generate an error which is emitted on child.stdout. By default, the error message is the output of child.stderr. If you provide an errFactory function, it will be called with code, stderr where code is the child's exit code and stderr is a string that contains the output of child.stderr. errFactory should return an Error to be emitted on child.stdout.

Example

var fwd   = require('spawn-error-forwarder');
var spawn = require('child_process').spawn;
var child = spawn('git', ['log', 'non-existent-path']);

fwd(child, function (code, stderr) {
  return new Error('git log exited with ' + code + ':\n\n' + stderr);
});

child.stdout
  .on('error', console.error.bind(console))
  .pipe(process.stdout);

We want to pipe the output of git log to process.stdout but since we're providing a path that doesn't exist git will exit with a non-zero code and we'll log its output with console.error.