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

Answer 1

More simply, you can use this:

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

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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.