Moving maildir-deduplicate.py to its own repository was tricky, as I wanted to keep the commit history.

I followed my old notes from a previous article and started the migration process: 

$ git clone [email protected]:kdeldycke/scripts.git
$ cd ./scripts

But I didn’t went very far. As soon as I tried to remove all content but the script from the revision tree, I stumble upon a puzzling error: 

$ git filter-branch --prune-empty --tree-filter 'find ./ -maxdepth 1 -not -name "maildir-deduplicate.py" -and -not -path "./.git*" -and -not -path "./" -print -exec rm -rf "{}" \;' -- --all
Rewrite 8fe2934d1552c97246836987f0ea08e10ba749ae (1/174)fatal: invalid date format: 0 +0000
could not write rewritten commit

The bad commit the message refers to is the first one. It’s a special commit I create everytime I initialize a Git repository  .

From the error message, I suspected a wrong date format. So I reset it: 

$ export GIT_TMP_INIT_HASH=`git show-ref init | cut -d ' ' -f 1`
$ git filter-branch --env-filter '
    if [ $GIT_COMMIT = $GIT_TMP_INIT_HASH ]
        then
            export GIT_AUTHOR_DATE="Thu, 01 Jan 1970 00:00:00 +0000"
            export GIT_COMMITTER_DATE="Thu, 01 Jan 1970 00:00:00 +0000"
    fi' -- --all
$ unset GIT_TMP_INIT_HASH

Then I called my previous git filter-branch command but failed the same way.

I tried another date scheme: 

$ export GIT_TMP_INIT_HASH=`git show-ref init | cut -d ' ' -f 1`
$ git filter-branch --env-filter '
    if [ $GIT_COMMIT = $GIT_TMP_INIT_HASH ]
        then
            export GIT_AUTHOR_DATE="1970-01-01 00:00:00 +0000"
            export GIT_COMMITTER_DATE="1970-01-01 00:00:00 +0000"
    fi' -- --all
$ unset GIT_TMP_INIT_HASH

Same error again.

Finally, the command below fixed this issue once and for all: 

$ export GIT_TMP_INIT_HASH=`git show-ref init | cut -d ' ' -f 1`
$ git filter-branch --env-filter '
    if [ $GIT_COMMIT = $GIT_TMP_INIT_HASH ]
        then
            export GIT_AUTHOR_DATE="$(TZ=UTC date -d@100000000 -R)"
            export GIT_COMMITTER_DATE="$(TZ=UTC date -d@100000000 -R)"
    fi' -- --all
$ unset GIT_TMP_INIT_HASH

As you can see it sets the dates further in time (100000000 seconds after epoch).

And you know why this works? Because recent version of Git don’t allow dates with less than 9 digits  .

That was not excepted, but it allowed me to proceed in my repository migration.