Example creating a git repo with a long lived feature branch and pruning a set of changes out

repo_prune.pl

#!/usr/bin/perl

use strict;
use warnings;

system("rm -rf repo");

mkdir "repo";

chdir "repo";

mkdir "a";
mkdir "b";

system("touch a/a.txt");
system("touch b/b.txt");

system("git init .");
system("git add a b");
system("git commit -m 'base'");

# create a set of original history
for (my $i = 0; $i < 10; $i++) {
    open A, ">>a/a.txt" or die "terribly";
    open B, ">>b/b.txt" or die "terribly";

    print A "orig.$i\n";
    print B "orig.$i\n";

    close A or die "terribly";
    close B or die "terribly";

    system("git add -u");
    system("git commit -m 'commit orig.$i'");
}

# create a feature branch
system("git checkout -b other");

# create a bunch of history on master and the feature branch
for (my $i = 0; $i < 10; $i++) {
    system("git checkout other");

    for (my $j = 0; $j < 3; $j++) {
        open A, ">>a/a.txt" or die "terribly";
        open B, ">>b/b.txt" or die "terribly";

        print A "other.$i.$j\n";
        print B "other.$i.$j\n";

        close A or die "terribly";
        close B or die "terribly";

        system("git add -u");
        system("git commit -m 'commit other.$i.$j'");
    }

    system("git checkout master");
    for (my $j = 0; $j < 3; $j++) {
        open A, ">>a/a.txt" or die "terribly";
        open B, ">>b/b.txt" or die "terribly";

        print A "master.$i.$j\n";
        print B "master.$i.$j\n";

        close A or die "terribly";
        close B or die "terribly";

        system("git add -u");
        system("git commit -m 'commit master.$i.$j'");
    }
}

system("git checkout other");
system("git checkout -b other_rewritten");

# find the common merge base
my $merge_base = `git merge-base master other`;
chomp($merge_base);

# filter out all changes in the a dir for all commits on the feature branch
system("git filter-branch --tree-filter 'git checkout $merge_base -- a' ${merge_base}..HEAD");