foo.pl:

#!/usr/bin/perl -w 

$x = $y . $z;




$ ./foo.pl 
Name "main::y" used only once: possible typo at ./foo.pl line 3.
Name "main::z" used only once: possible typo at ./foo.pl line 3.
Name "main::x" used only once: possible typo at ./foo.pl line 3.
Use of uninitialized value in concatenation (.) or string at ./foo.pl line 3.
Use of uninitialized value in concatenation (.) or string at ./foo.pl line 3.

$ perl foo.pl 
Name "main::y" used only once: possible typo at foo.pl line 3.
Name "main::z" used only once: possible typo at foo.pl line 3.
Name "main::x" used only once: possible typo at foo.pl line 3.
Use of uninitialized value in concatenation (.) or string at foo.pl line 3.
Use of uninitialized value in concatenation (.) or string at foo.pl line 3.