if ($tally[$i]) {
    printf {$out} "%-20s %30d \n", $regex, $tally[$i] // 0 ;
}

##</code><code>##

use 5.032;
use autodie;
use List::Util qw( max );
use File::Temp qw( tempfile );

my $xml = <<END;
Electric monks believed things for you, thus saving you what was
becoming an increasingly onerous task, that of believing all the
things the world expected you to believe... The new improved Monk Plus
models were twice as powerful, had an entirely new multi-tasking
Negative Capability feature that allowed them to hold up to 16
entirely different and contradictory ideas in memory simultaneously
without generating any irritating system errors.
-- Douglas Adams, Dirk Gently's Holistic Detective Agency
END
my @tally;
my @regexes = (
    qr/\bmonk/,
    qr/\bmonk\b/,
    qr/\bmonk\b/i,
    qr/Douglas Adams, Dirk Gently's Holistic Detective Agency/,
    qr/Douglas Adams, The Hitchhikers Guide To The Galaxy (A trilogy in five)/
);

for my $i (0 .. $#regexes) {
    my $regex = $regexes[$i];
    ++$tally[$i] while $xml =~ /$regex/g;
}

my $max_length = max(map { length "$_" }
                     @regexes[ grep { $tally[$_] } (0 .. $#regexes) ]);

my ($out,$path) = tempfile( CLEANUP => 0);
say "Your output is available at '$path'";

for my $i (0 .. $#regexes) {
    my $regex = $regexes[$i];
    $regex =~ s/^\(\?\^://;
    $regex =~ s/\)$//;
    if ($tally[$i]) {
        printf {$out} "%-${max_length}s %3d\n", $regex, $tally[$i] // 0 ;
    }
}