As always, with these ads it may be putting too much stock into the accuracy of the ad to eliminate that employer out of hand. It's possible that the ad was written by a recruiter who thought they knew what the requirements were for the job -- or it could be that the job is 90% Perl and the other 10% is zsh / bash. Or they could be trying to screen out the developers who don't want to *any* shell scripting -- just Perl only.

I was hired at my current job as a Perl developer, but I have ended up using and creating shell scripts (preinst and postinst scripts for Debian's dpkg are the most recent examples) as part of my job. No biggie.