use strict;  # mustn't forget that

open(LIST, "wordlist.txt");
open(MSTR, "master.txt");

# get the wordlist
my @wordlist = map { chomp; $_ } <LIST>;

# get the master list, sorted by word length, longest words first
my @master = sort { length($b) <=> length($a) } map { chomp; $_ } <MSTR>;

# declare a hash to hold the findings:
my %report;

foreach my $lookfor ( @master ) {
    foreach my $lookat ( @wordlist ) {
        if ( $lookat =~ /$lookfor/ ) {
            $report{$lookfor} .= ",$lookat";
            $lookat = "";  # erases this word from @wordlist
        }
    }
}

foreach my $word ( sort keys %report ) {
    $report{$word} =~ s/,/ /;  # change initial comma to space
    print "$word:$report{$word}$/";
}