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

my $file1Content = <<CONTENT;
red green blue red orange
CONTENT

my $file2Content = <<CONTENT;
yellow orange
red grey purple
CONTENT

my %group1;

open my $file1, '<', \$file1Content;
while (my $line = <$file1>) {
    my @words = map {lc} grep {$_} split /[\W\d]+/, $line;
    
    $group1{$_} = $_ for @words;
}


my %common;

open my $file2, '<', \$file2Content;

while (my $line = <$file2>) {
    my @words = map {lc} grep {/\S/} split /[\W\d]+/, $line;
    
    $common{$_} = $_ for grep {exists $group1{$_}} @words;
}

print "$_\n\n" for sort values %common;
printf "Found %1.0f words in common\n", scalar keys %common;