grep exit status and extra newlines #900

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:

grep() returns 0, even if a string is not found, and the resulting string also contains a newline.

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');

console.log(shell.grep(/^asdfasdf/, 'testfile'))

Output of above:

{ [String: '\n']
  stdout: '\n',
  stderr: null,
  code: 0,
  cat: [Function: bound ],
  exec: [Function: bound ],
  grep: [Function: bound ],
  head: [Function: bound ],
  sed: [Function: bound ],
  sort: [Function: bound ],
  tail: [Function: bound ],
  to: [Function: bound ],
  toEnd: [Function: bound ],
  uniq: [Function: bound ] }

I don't believe you'll have even a newline if you grep for something that isn't found, and you'll definitely get a non-0 status code if the string isn't found.

$ grep -q ^asdfasdf testfile 
$ echo $?
1
$ grep ^asdfasdf testfile > /tmp/asdf
$ cat -v -e /tmp/asdf 
$ file /tmp/asdf 
/tmp/asdf: empty

As best I could tell, the only reliable way to detect the absence of a string to use something like:

shell.grep(/^asdfasdf/, 'testfile').stdout.trim())

Of course, at this point, it might be easier to use regexp on the file directly, but this still seems inconsistent with the behavior of the grep command.