Specify GNU grep, find, etc.

[anirvan]

I ran the script on MacOS, which uses BSD-derived versions of find, grep, and mktemp, and don't support the same command line options used in the code. I had to change three things to get it to run on a Mac.

Would it be possible to specifically state that this requires GNU tools — or alternatively, to change the code so uses only basic POSIX options?

FYI, here's are the three things I needed to manually change to get this to work on a Mac:

• grep --perl-regexp
• find -printf
• mktemp --directory

[fluks]

I can change the code so it uses only POSIX options. Can you send your changes as a PR?

[fluks]

I made changes myself in f7b41e6. Can you test does that work on Mac?