headerless ps options result in spurious output

[treyharris]

I forked and was about to write a fix to send you a pull request, but then in reading the code I noticed the -n option, which up till now I'd missed. Still, this seems to qualify as a bug, so I thought I'd mention it.

On MacOS If you give options such that the ps header is suppressed completely, you get the PID 1 line from psgrep as the first line of output:

% psgrep -o 'pid=,ppid=,comm=' mosh
    1     0 /sbin/launchd
60243     1 mosh-server
83177  1277 /usr/local/Cellar/mobile-shell/1.2.6/bin/mosh-client my-mbp |
55353  5322 /usr/local/Cellar/mobile-shell/1.2.6/bin/mosh-client trey-mbp-my.local |

clearly it's just interpreting the top line as the header, because giving -n suppresses that:

% psgrep -n -o 'pid=,ppid=,comm=' mosh
60243     1 mosh-server
83177  1277 /usr/local/Cellar/mobile-shell/1.2.6/bin/mosh-client my-mbp |
55353  5322 /usr/local/Cellar/mobile-shell/1.2.6/bin/mosh-client trey-mbp-my.local |

Since the only reason I can see to care about this is when you're trying to suppress the output, and there's an easier way in -n, this is pretty low-priority, but again I thought I'd let you know.

(I don't think this bug can arise on Linux because the only way to create a headerless ps output using options requires passing -o multiple times, which psgrep doesn't support. I haven't tried any other operating systems.)