Fix pytest for mac by replacing grep with perl

[tanujkhattar]

grep -P does not work on mac anymore. Replace it with perl -nle instead.

[vtomole]

mac anymore

Since when? What version of Mac? This is not the only place we call grep.

[tanujkhattar]

This is the only place we call grep -P i.e. use perl regex with grep.

It looks it's been quite a while, so I guess for this project it might have never worked on a mac by default, unless people have a GNU grep version installed. I can dig in more to find relevant information on the difference if that's necessary.

[vtomole]

@tanujkhattar

The macOS that we are running on Github Workflow doesn't seem to be running into this problem. What version of mac gives this error? The version we are running must be different.

[tanujkhattar]

$> grep --version
grep (BSD grep) 2.5.1-FreeBSD

[viathor]

Checked on my Mac and indeed, -P is missing:

usage: grep [-abcDEFGHhIiJLlmnOoqRSsUVvwxZ] [-A num] [-B num] [-C[num]]
	[-e pattern] [-f file] [--binary-files=value] [--color=when]
	[--context[=num]] [--directories=action] [--label] [--line-buffered]
	[--null] [pattern] [file ...]

Also, checked that the perl command works on my Mac and Linux.