#!/usr/bin/perl
use strict;
use warnings;

my @lines = qw(<tag>A</tag> <TAG>B</TAG> <tag>C</tag>);

for my $expr (
    'lc',
    'lc($_), 1',
    '$_=lc($_); s/<tag>//; s/<\/tag>//; $_ => 2'
    ) {
    my @values = eval "map {$expr} \@lines";

    print join("\n   ", "map {$expr} =>", @values), "\n";
}