Actually use the log file, fixed bad update grep (UNIX)

[chris-blackburn]

For many projects, I have tag files already generated, so I'd like to just update those. However, I noticed that gutentags would only update tag files it generated. The regex pattern used to find the changed file wasn't working for some reason, so I updated it.

I also updated the script to use the log file it wasn't previously using.

[ludovicchabant]

Hi and thanks for the PR!

I didn't know about those special bracketed names for grep's regex engine, that's nice, thanks. I'm not sure what your regex changes though -- before, it was skipping over any non-tab character up to the first tab, and now you're matching any alpha-numeric character up to the first whitespace. So AFAICT it will fail if a symbol has non-alpha-numeric characters (unlikely, but worth noting) but will also match if the whitespace after it isn't a tab (unlikely, I think that's part of the ctags standard?).

I don't understand what you're doing with the redirections, too. Looking it up, I think this use of exec only works in bash and ksh?