Node version (or tell us if you're using electron or some other framework):

v8.11.3

ShellJS version (the most recent version/Github branch you see the bug on):

0.8.2

Operating system:

Mac OS X

Description of the bug:

There doesn't seem to be a way to suppress stdout from echo() even when redirecting to another command / pipe.
Based on the code, it seems like no matter what, the call to sys.stdout.write() will happen.

Example ShellJS command to reproduce the error:

(given a file testfile without the string asdfasdf at the beginning of a line):

const shell = require('shelljs');

if (!shell.grep(/^asdfasdf/, 'testfile').stdout.trim()) {
  shell.echo({silent: true}, 'asdfasdf').toEnd('testfile');
}

In this case, whether {silent: true} (which it seems like it's supposed to be parsed, tho not do anything, based on

const shell = require('shelljs');

if (!shell.grep(/^asdfasdf/, 'testfile').stdout.trim()) {
  shell.config.silent = true;
  shell.echo('asdfasdf').toEnd('testfile');
}

The above code also doesn't suppress stdout.