In /usr/bin/freealut-config line 53: -*=*) optarg=`echo "$1" | sed 's/[-_a-zA-Z0-9]*=//'` ;; ^-- SC2006: Use $(...) notation instead of legacy backticked `...`. Did you mean: -*=*) optarg=$(echo "$1" | sed 's/[-_a-zA-Z0-9]*=//') ;; For more information: https://www.shellcheck.net/wiki/SC2006 -- Use $(...) notation instead of le...