Very cool. VERY cool. But some people may prefer changing the command to this...

(read-from-minibuffer "Replace region command: " '("perl -ple \'\'" . 
+12 ))
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1. without the -l, you lose any newlines in your buffer
2. shell-command-on-region seems to use a normal shell, which means the double quotes won't going to protect any variables in your region.