use strict;

my %hash = (
	a => 'A',
	b => 'B',
	c => 'C',
	e => 'E',
	d => 'D',
);

for my $s ( qw( a b c d e ) )
{
    my $name = $1 if $s =~ /(c)/;
    $name = $hash{$s}  unless defined $name;
    warn $name || 'undef';
}

Output:
A at 7.pl line 19.
A at 7.pl line 19.
c at 7.pl line 19.
D at 7.pl line 19.
D at 7.pl line 19.