lorien:~$ perl -wle '$SIG{__WARN__}=sub{print"TRAPED"};s///'
TRAPED
TRAPED
lorien:~$  perl -wle '$SIG{__WARN__}=sub{print"TRAPED"};$.,$.=0'
Useless use of a variable in void context at -e line 1.
lorien:~$  perl -wle 'BEGIN{$SIG{__WARN__}=sub{print"TRAPED"};}$.,$.=0'
TRAPED