Check if git branch contains commit with given subject

Given an exact subject line of a commit I want to know if a branch contains a commit with that subject.

What I have right now is: git log --format="%s" -F --grep="$msg" "$branch" | grep -Fq --max-count=1 -- "$msg"

I.e. search the log with a fixed-string grep and print the subject. Then search that subject with the same fixed-string and stop at the first match.

The 2nd grep is required because git log --grep may find the pattern anywhere in the commit message (e.g Fixes "$msg")

However this has the downside that it seemingly always walks the entire history of that branch which takes quite long.

As a test I ran git log --format="%s" -F --grep="$msg" "$branch" | grep -Fq --max-count=1 -- "$msg" and git log --format="%s" -F --grep="$msg" "$branch" and they both took the same time although the commit to grep for is found/printed very fast (for the 2nd)

So is there a way to directly find a commit in a branch by a given subject (using fixed strings as $msg comes from another command and may contain regex-like characters) faster or at least make my log-grep-pipe exit faster (on success)?

Try this:

git log --format="%s" "$branch" | grep -Fqx --max-count=1 -- "$msg"

Here x will match the entire line.. and max-count will return the first match.