$ echo Hello >t1.txt

$ echo World >t2.txt

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

$ perl -Mautodie=system -wle " $ret = system q[diff -u t1.txt t2.txt >NUL 2>&1] ; print $ret; print $?"
"diff -u t1.txt t2.txt >NUL 2>&1" unexpectedly returned exit value 1 at (eval 10) line 13
 at -e line 1

$ perl -MIPC::System::Simple=system -wle " $ret = system q[diff -u t1.txt t2.txt >NUL 2>&1] ; print $ret; print $?"
"diff -u t1.txt t2.txt >NUL 2>&1" unexpectedly returned exit value 1 at -e line 1