my %langTags=(
    perl => {
        HEAD => [
            '#!/usr/bin/perl',
        ],
        DEFAULT => [
            'use strict;',
            'use warnings;',
        ],
        cgi => [
            'use CGI::Carp qw( fatalsToBrowser );',
            'use CGI qw( -nosticky -compile -no_debug -private_tempfiles -newstyle_urls );',
        ],
        moose => [
            'use Moose;'
        ],
        # ...
    },
    bash => {
        HEAD => [
            '#!/bin/bash',
        ],
        cgi => [
            'source /usr/local/lib/bash/bashcgi-lib.bash',
        ],
        csv => [
            'source /usr/local/lib/bash/csv-lib.bash',
        ],
        ourlibs => [
            'source /usr/local/lib/bash/foo-lib.bash',
            'source /usr/local/lib/bash/bar-lib.bash',
        ],
        # ...
    },
    c => {
        DEFAULT => [
            '#include <stdio.h>',
            '#include <stdlib.h>',
            '#include <string.h>',
        ],
        # ...
    },
    # ...
);
##</code><code>##

my %extToLang=(
    pl => 'perl',
    pm => 'perl',
    c => 'c',
    h => 'c',
    sh => 'bash',
    bash => 'bash',
);
my $filename;
my $lang;

# setup $filename and perhaps also $lang

if (!$lang and ($filename=~/\.([^.]+)$/) {
    $lang=$extToLang{$1};
}
$lang or die "Missing language parameter";
##</code><code>##

use List::MoreUtils qw ( uniq );
my @allTags=uniq map { keys %$_ } values %langTags;