Checking Commit Ancestry
I have two commit shas and I want to know if the first is an ancestor of the second. Put another way, is this first commit somewhere in the history of this other commit.
Git's merge-base
command combined with the --is-ancestor
flag makes answering this question easy. Furthermore, because it is a plumbing command, it can be used in a script or sequence of commands as a switch based on the answer.
Here is an example of this command in action:
In the first command, head~
is clearly an ancestor of head
, so the echo
command is triggered. In the second, head~
is not an ancestor of head~~
so the return status of 1 short-circuits the rest of the command. Hence, no echo
.
See man git-merge-base
for more details.
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