retag.pl

#!/usr/bin/env perl
use 5.010;
use strict;
use warnings;
use File::Slurp 'read_file';

my ($commitlist, $taglist) = @ARGV;
die "usage: $0 <commit-list> <tag-list>\n"
  unless -f $commitlist && -f $taglist;

my @commits = map { chomp; $_ } read_file($commitlist);
my %tags = map { chomp; $_ => 1 } read_file($taglist);

COMMIT:
for my $c ( @commits ) {
  for my $t ( reverse sort keys %tags ) {
    system "git diff --quiet -b $c $t";
    if ( $? == 0 ) {
      system "git co $c";
      system "git tag -d $t";
      system "git tag $t";
      delete $tags{$t};
      next COMMIT;
    }
  }
}