BISECT_...SING_GIT(1)

✨ BISECT_...SING_GIT ✨

okay bestie, welcome to the bisect_perl_using_git page 💖 this one lives in the User Contributed Perl Documentation corner of your manual, and it's genuinely one of the most useful little tools you'll ever meet, no cap.

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🦋 NAME 🦋

bisect_perl_using_git — literally here to help you bisect Perl 💅

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🌸 DESCRIPTION 🌸

so bisect_perl_using_git helps you bisect Perl. that's the whole vibe. it helps you find at what commit a change happened in Perl 🕵️‍♀️

you can check for file addition and removal — it checks out various commits of Perl and figures out which change was involved. you can also check for a difference in Perl evaluation, in which case it will check out various commits of Perl, compile them, and find out which change was involved. heads up though: that second one is more CPU intensive and you must install ccache 😭 it's giving "worth it but prepare your fans".

first things first, you gotta download the current Git repository of Perl, so run something like this:

mkdir git
cd git
git clone git://perl5.git.perl.org/perl.git perl-git
cd perl-git

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🎀 example one: the autodie origin story

now, I happen to know that the autodie pragma was added sometime in December 2008, but I would like to know which commit. let's find out some commits at the beginning and the end of that month, and see when lib/autodie.pm was added 👑

# git log --before=2008-12-01 -n 1
# 1409bc0658469580630ba458c85fe9cc3cb2d78c
# git log --before=2008-12-31 -n 1
# 675b0f774d374f6951c02c6463c64a746ad46acd
git bisect reset
git bisect start
git bisect good 1409bc0658469580630ba458c85fe9cc3cb2d78c
git bisect bad 675b0f774d374f6951c02c6463c64a746ad46acd
# Bisecting: 114 revisions left to test after this
git bisect run bisect_perl_using_git --action file_added \
  --filename lib/autodie.pm
# ... after checking out 10 trees and about 10 seconds, it says:
# 0b09a93a0cec34bc5d1740400c4ed9500d2f1dbe is first bad commit
# commit 0b09a93a0cec34bc5d1740400c4ed9500d2f1dbe
# Author: Paul Fenwick <pjf@perltraining.com.au>
# Date:   Sat Dec 20 22:21:02 2008 +0900
#
# git-flavoured autodie 1.997 patch
# G'day p5p,
# ...
git bisect reset

ate and left no crumbs 🍓

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🧚 example two: bye bye MANIFEST

sometime after June 2009, ext/Storable/MANIFEST was removed from Perl. let's find out which commit removed it:

# git log --before=2009-06-01 -n 1
# 20f91e418dfa8bdf6cf78614bfebebc28a7613ee
git bisect reset
git bisect start
git bisect good 20f91e418dfa8bdf6cf78614bfebebc28a7613ee
git bisect bad HEAD
# Bisecting: 266 revisions left to test after this
git bisect run bisect_perl_using_git --action file_removed \
  --filename ext/Storable/MANIFEST
# ... after checking out 11 trees and about 10 seconds, it says:
# 2868e48536e3f471e5ba483466cc1bc53caff5a is first bad commit
# commit e2868e48536e3f471e5ba483466cc1bc53caff5a
# Author: David Mitchell <davem@iabyn.com>
# Date:   Fri Jun 12 17:24:43 2009 +0100
#
#    remove ext/Storable/MANIFEST; its out of date related to CPAN
#    and for most dual-life modules we don't bother including it in blead
# ...
git bisect reset

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🔥 example three: the real bug report moment

now for a real bug report, where some code that works in Perl 5.8.8 and should work in Perl 5.10.0 but does not 😭 the main character energy of a genuine regression:

http://rt.perl.org/rt3/Public/Bug/Display.html?id=62056

we create a ~/testcase.pl which contains the following:

#!perl
use strict;
use warnings;
use charnames ':full';
my $x;
m/$x\N{START OF HEADING}/

and then run:

git bisect reset
git bisect start
git bisect good perl-5.8.8
git bisect bad perl-5.10.0
# Bisecting: 4041 revisions left to test after this
git bisect run bisect_perl_using_git --action perl_fails \
  --filename ~/testcase.pl
# ... after checking out 16 trees and about one hour, it says:
# fc8cd66c26827f6c2ee1aa00ab2d3b3c320a4a28 is first bad commit
# commit fc8cd66c26827f6c2ee1aa00ab2d3b3c320a4a28
# Author: Yves Orton <demerphq@gmail.com>
# Date:   Tue Sep 19 03:37:19 2006 +0200
#
#    Re: \N{...} in regular expression [PATCH]
# ...
git bisect reset

ngl, "checking out 16 trees and about one hour" is the moment where you go make a snack and let the computer cook 🫶

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💜 AUTHOR 💜

Leon Brocard, "<acme@astray.com>"

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🎀 COPYRIGHT 🎀

Copyright (C) 2009, Leon Brocard

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🌈 LICENSE 🌈

This module is free software; you can redistribute it or modify it under the same terms as Perl itself.

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and that's the whole page, bestie ✨ this was perl v5.42.0, dated 2025-07-25, filed under BISECT_...SING_GIT(1) — go bisect something iconic 👑💅