$ perl -MIPC::System::Simple=system -wle " $ret = system [0,1], q[diff -u t1.txt t2.txt >NUL 2>&1] ; print $ret; print $?"
1
256

$ perl -Mautodie=system -wle " $ret = system [0,1], q[diff -u t1.txt t2.txt >NUL 2>&1] ; print $ret; print $?"
1
256