My git pre-commit hook

pre-commit

#!/usr/bin/env perl
use strict;
use warnings;
use MIME::Base64;

my $AGAINST = "HEAD";
`git rev-parse --verify HEAD >/dev/null 2>&1`;
$? and $AGAINST = "4b825dc642cb6eb9a060e54bf8d69288fbee4904"; # Initial commit

my $filename_regex    = qr{^\+\+\+ b(.+)};
my $regex_string      = MIME::Base64::decode('KD9pKShmdWNrfHNoaXR8YmFsbHN8Y3VudHxjb2NrfHNoZWl0fHNsdXR8d2hvcmV8c3RydW1wZXR8Ym9uZ3xib2xsb2Nrc3xib25lcnxza2VlemV8Z3V6emx8c2thbmt8aG9yc2V8amVzdXN8amV6dXN8Y2hyaXN0fHRpdHMp');
my $four_letter_regex = qr{$regex_string};

my %bad_words;
my %trailing_whitespace;

my $current_file;
open(my $diff, "-|", "git diff --cached --diff-filter=AM -z $AGAINST")
    or die "Cant get diff output";
while ( <$diff> ) {
    chomp;
    /$filename_regex/;
    $1 and do { $current_file = $1; next };
    next unless /^\+/;
    while ( my $match = $_ =~ /$four_letter_regex/g ) {
        $bad_words{$current_file}++;
    }
    /\s+$/ and $trailing_whitespace{$current_file}++;
}
close $diff;

my $file_is_bad;

if ( my @keys = keys %bad_words ) {
    printf STDERR "%s has %d naughty words!\n"
        , $_
        , $bad_words{$_}
        foreach @keys;
    $file_is_bad++;
}

if ( my @keys = keys %trailing_whitespace ) {
    printf STDERR "%s has %d lines with trailing whitepace!\n"
        , $_
        , $trailing_whitespace{$_}
        foreach @keys;
    $file_is_bad++;
}

$file_is_bad and die "Blocking commit";

`git diff-index --check --cached $AGAINST --`