Not here to help just here to say I was never able to get perl working either.

What version of unRAID are you on? I'm on 6.8.3, just tried to install perl and got the following:

Processing Packages...

json-c-0.15.20200726 package up to date, checksum ok.
krb5-1.18.3 package up to date, checksum ok.
libmediainfo-19.09 package up to date, checksum ok.
libzen-0.4.37 package up to date, checksum ok.
lmdb-0.9.24 package up to date, checksum ok.
mediainfo-19.09 package up to date, checksum ok.
moreutils-0.63 package up to date, checksum ok.
ncurses-terminfo-6.1.20191130 package up to date, checksum ok.
par2cmdline-0.8.0 package up to date, checksum ok.
Downloading perl-5.32.0-x86_64-1.txz package...
perl-5.32.0-x86_64-1.txz package download sucessful!
Installing perl-5.32.0 package...
screen-4.7.0 package up to date, checksum ok.
unrar-5.8.5 package up to date, checksum ok.
utempter-1.1.6.20191231 package up to date, checksum ok.
Cleaning up packages...
All packages processed...

same issue, did you resolve the problem?

Realise this is a bit late for you but for the benefit of Google...

If the Nerdpack GUI fails to work

Download Perl from here:

https://slackware.pkgs.org/14.2/slackware-x86_64/perl-5.22.2-x86_64-1.txz.html

copy the txz binary package onto the Unraid server.

Then in terminal navigate to the directory with the share and run the install command. i.e.
upgradepkg --install-new perl-5.22.2-x86_64-1.txz