remove absolute paths to rely on $PATH

Relying on full paths is a bad idea, e.g. grep is not always at /usr/bin/grep, sometimes it's just /bin/grep. Same for awk. There are even inconsistencies: one time it's /usr/local/bin/nasm, another time /usr/bin/nasm.
I believe it would be better without full path and instead rely on $PATH to find binaries, as it is normal practice on unix systems.