How to get a list of incoming commits on git push for a new branch in a hook

Question

I'm writing a pre-receive hook to do some validation before accepting commits on the push. It works fine with existing branches since I use following git command to get a list of incoming commits:

git rev-list $old_sha1..$new_sha1

However, above command fails if user pushing a new branch into a shared repository because old_sha1 is all zeros. So the question is how do I get a list of incoming commits for a newly created branch. Doing git rev-list $new_sha1 does not work since it gives all revisions till the beginning of times. Is there a way to specify something like this:

git rev-list $branching_sha1..$new_sha1

Answer 1

Try this:

git rev-list $new_sha1 $(git for-each-ref --format '^%(refname:short)' refs/heads/)

This uses git for-each-ref to print known refs; specifies in --format that the short name be output along with a preceding caret; and says with refs/heads/ to selecting just local heads. You end up running something like this:

git rev-list $new_sha1 ^master ^foo ^bar ^baz

The caret means “exclude commits reachable from here”. So this will give you all commits that are reachable from $new_sha1, but aren’t from any of the existing refs.

To handle the new-ref and existing-ref cases at once, you can use bash’s array support:

if ! [ $old_sha1 = 0000000000000000000000000000000000000000 ] ; then
    excludes=( ^$old_sha1 )
else
    excludes=( $(git for-each-ref --format '^%(refname:short)' refs/heads/) )
fi

git rev-list $new_sha1 "${excludes[@]}"

Answer 2

More simply, you can use this:

git rev-list $new_sha1 --not --all

---

It's quite the same principle as in Aristotle Pagaltzis' answer, but it just uses rev-list's built-in options (which I guess were added after this question was answered...).
The --all parameter is equivalent to the for-each-ref part: it adds all known refs to the command args. The --not parameter, in this particular case, is like adding the ^ prefix to all refs added by --all.
Thus this command will print commits reachable from the new SHA1 except all those reachable from the known (i.e. already pushed) refs.

Answer 3

The following helped in my case. I personally think it's very simple.

OLD_REV=$2
NEW_REV=$3

if [ $OLD_REV == "0000000000000000000000000000000000000000" ]; then
    OLD_REV=$(git merge-base master $NEW_REV)
fi;

git diff --name-only $OLD_REV $NEW_REV