Re: [PATCH] test-lib-functions: avoid non POSIX ERE in test_dir_is_empty()

Carlo Arenas [off-list ref] writes:

egrep (and also fgrep, which we intentionally support because it is
missing from some ancient AIX system[1]) will be removed in the
next[2] release of GNU grep.

It is not a reason not to nudge us to prepare for the eventual
removal of these two commands, but we need to keep the facts
straight in our log messages.  

The way I read [2], they will only start giving a warning message
nudging the users to use "grep -[EF]", and for them to be able to
warn, I would imagine they have to stay in the release without
getting removed.

[1] 87539416fd (tests: grep portability fixes, 2008-09-30)
[2] https://git.savannah.gnu.org/cgit/grep.git/commit/?id=a9515624709865d480e3142fd959bccd1c9372d1

There are about 35 places in t/ we call egrep or fgrep; if we can
add a pair of replacement shell functions in t/test-lib.sh for them
to use whatever command GIT_TEST_EGREP and GIT_TEST_FGREP
environment variables specify and fall back on "grep -E/-F"
otherwise, we can prepare for the change without too much code
churning.

Something along the lines of

	# in test-lib-functions.sh
        : ${GIT_TEST_EGREP:=grep -E} ${GIT_TEST_FGREP:=grep -F}
        egrep () { $GIT_TEST_EGREP "$@" }
        fgrep () { $GIT_TEST_FGREP "$@" }

where people could do something silly like

	GIT_TEST_FGREP='command fgrep' \
	GIT_TEST_EGREP='command egrep' \
	make test

perhaps?