$ date; perl -wMstrict -le '$a=time;$SIG{ALRM}=sub{$b=time};alarm 2;<>;print $b-$a'; date
Sat Jul 21 05:55:19 AEST 2018

Use of uninitialized value $b in subtraction (-) at -e line 1, <> line 1.
-1532116519
Sat Jul 21 05:55:20 AEST 2018
$