c:\test>perl -wE"my $a, $b or die;"
Name "main::b" used only once: possible typo at -e line 1.
Died at -e line 1.

##</code><code>##

c:\test>perl -wE"my $a, $b;"
Parentheses missing around "my" list at -e line 1.
Useless use of a variable in void context at -e line 1.
Name "main::b" used only once: possible typo at -e line 1.

##</code><code>##

c:\test>perl -wE"my $a, qq[$b];"
Useless use of string in void context at -e line 1.
Name "main::b" used only once: possible typo at -e line 1.
Use of uninitialized value $b in string at -e line 1.

##</code><code>##

c:\test>perl -wE"open my $a, qq[> $b];"
Name "main::b" used only once: possible typo at -e line 1.
Use of uninitialized value $b in concatenation (.) or string at -e line 1.

##</code><code>##

c:\test>perl -wE"open my $a, +$b;"
Name "main::b" used only once: possible typo at -e line 1.
Use of uninitialized value $b in open at -e line 1.

c:\test>perl -wE"open my $a, ''.$b;"
Name "main::b" used only once: possible typo at -e line 1.
Use of uninitialized value $b in concatenation (.) or string at -e line 1.