Sometimes Perl is not the right tool for the job. You are starting an entire instance of perl just for a regex match, when sed will do:

echo "$XXX" | sed -e 's/;arg=.*$//' -e 's!^.*/!!'
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On my box, simply running perl -e 1 takes longer than the above sed command. For a shell script, these differences matter.

Perl oneliners are great at the prompt, but if you are putting them into a shell script, you should probably move the entire script to Perl.