$ cat /tmp/test.pl 
#!/usr/bin/perl -w
$x = $y + 1; # sollte eine Warnung werfen

$ /tmp/test.pl
Name "main::y" used only once: possible typo at /tmp/test.pl line 2.
Name "main::x" used only once: possible typo at /tmp/test.pl line 2.
Use of uninitialized value in addition (+) at /tmp/test.pl line 2.

$ /usr/bin/perl /tmp/test.pl
Name "main::y" used only once: possible typo at /tmp/test.pl line 2.
Name "main::x" used only once: possible typo at /tmp/test.pl line 2.
Use of uninitialized value in addition (+) at /tmp/test.pl line 2.