If you want to write an awk script, which portable to any awk implementations and versions (gawk/nawk/mawk...) it is really hard, even if with --posix (gawk)

nowadays many people work with docker containers. Most default docker images do not have bash and something like [[ $string == *foo* ]] will not work.

It's not so much a criticism as the preference of a more universal solution over a more limited one. Please consider that, years later, people (like me) will stop by to look for this answer and may be pleased to find one that's useful in a wider scope than the original question. As they say in the Open Source world: "choice is good!"

readlink is not part of the standard. A portable script could be implemented with only POSIX shell features.

the following seems to do it without the bashism