tests: use grep -F instead of obsolescent fgrep Testing on Fedora 38 failed with: fgrep: warning: fgrep is obsolescent; using grep -F The warning comes from https://git.savannah.gnu.org/cgit/grep.git/commit/?id=a9515624709865d480e3142fd959bccd1c9372d1 . For further anecdotal evidence of the change, see https://www.phoronix.com/news/GNU-Grep-3.8-Stop-egrep-fgrep . grep -F is POSIX, but there is a risk that it doesn't work the same on all platforms - especially older Unix versions. It should however always be possible to put a GNU grep in $PATH before running the tests.