I needed simple and portable way to generate a random v4 UUID in Perl, so I ripped out various pieces of UUID::Tiny and came up with this.

sub gen_uuid {
    my $uuid = '';
    for ( 1 .. 4 ) {
        $uuid .= pack 'I', int(rand(2 ** 32));
    }

    substr $uuid, 6, 1, chr( ord( substr( $uuid, 6, 1 ) ) & 0x0f | 0x40 );

    return join '-',
        map { unpack 'H*', $_ }
        map { substr $uuid, 0, $_, '' }
        ( 4, 2, 2, 2, 6 );
}