$ perl -le '           
    my $password = "abc$def";
    print $password;
'
abc

##</code><code>##

$ perl -le '
    use warnings;
    my $password = "abc$def";
    print $password;
'
Name "main::def" used only once: possible typo at -e line 3.
Use of uninitialized value $def in concatenation (.) or string at -e line 3.
abc

##</code><code>##

$ perl -le '
    use strict;
    use warnings;
    my $password = "abc$def";
    print $password;
'
Global symbol "$def" requires explicit package name at -e line 4.
Execution of -e aborted due to compilation errors.

##</code><code>##

use strict;
use warnings;