Rebasing a git history with empty commit messages

Question

I recently converted an svn repository with git svn. Unfortunately the svn history has a number of empty commit messages. This is a problem when I rebase and edit/reword a commit before the most recent commit without a commit message.

$ git rebase -i d01
[detached HEAD ff9839c] asdf
 2 files changed, 9 insertions(+), 0 deletions(-)
Aborting commit due to empty commit message.
Could not apply 054e890... 

$ git branch
* (no branch)
  master

$ git commit --amend
fatal: You are in the middle of a cherry-pick -- cannot amend.

In this example I made a commit message for the second most recent commit with an empty commit message and the rebasing stopped on the most recent commit with an empty commit message.

I would like to edit all of the commits with empty messages at once. Is there a way I can do that? Maybe I can change all commits with a empty commit message to have the commit message "empty" first?

Answer 1

To replace empty commit messages with some template, you can do something like this:

git filter-branch -f --msg-filter '
read msg
if [ -n "$msg" ] ; then
    echo "$msg"
else
    echo "The commit message was empty"
fi'

Answer 2

As I commented before, this totally destroys comments if you happen to have newlines in them. Here's a perl script that does this without being destructive:

#!/usr/bin/perl

my $data = "";    
while(<STDIN>) {
    $data .= $_;
}

if($data =~ /^\s*$/) { $data="[Empty message]\n"; }
print "$data";

Then, just git filter-branch -f --msg-filter /path/to/perlfilter.pl

Answer 3

If you have multiple lines you could also use cat:

git filter-branch -f --msg-filter \
 'msg=$(cat); if [ "$msg" = "" ]; then echo "Here was an empty commit message"; else echo "$msg"; fi'

This handles commit messages with multiple lines as well as messages that contain empty lines for spacing.