$ perl -e " $x = shift; /$x/" "(?{ die 666 })"
Eval-group not allowed at runtime, use re 'eval' in regex m/(?{ die 666 })/ at -e line 1.

$ perl -Mre=eval -e " $x = shift; /$x/" "(?{ die 666 })"
666 at (re_eval 1) line 1.

$ perl -Mre=eval -Te " $x = shift; /$x/" "(?{ die 666 })"
Eval-group in insecure regular expression in regex m/(?{ die 666 })/ at -e line 1.