RFC: specify redirections with JS object parameters #800

I proposed this idea a while ago, but I can't remember where. I'm looking for comments/feedback.

The basic idea is to replace this:

shell.grep('foo', 'file.txt').to('other.txt');

with

shell.grep('foo', 'file.txt', { '>': 'other.txt' });

What does this fix?

It's currently not possible to mute echo() with redirection, which is kind of awkward. With this syntax, we can add support in src/common.js to temporarily add shell.config.silent = true. Then we just need to write echo() to respect that value. Voila.

New features?

This opens the door to some cool new features. Some ideas:

shell.rm('missing-file.txt', { '2>': 'error.log' }); // redirect stderr
shell.cat('first.txt', { '>>': 'second.txt' });
shell.cp('-r', 'src', 'out', { '2>&1': /* not sure what should go here :( */ });
shell.tail('file.txt', { '>': 'stdout.txt', '2>': 'stderr.txt' });

A downside to this design is that we cannot support multiple redirects (e.g. echo foo > file1.txt > file2.txt).

Alternate ideas for syntax

shell.rm('missing-file.txt', { 2: 'error.log' }); // '2' instead of '2>'