How to find latest non-merge commit message in Git?

Question

I'd like to find a last (newest) Git commit that is not a merge commit.

(Let's say we just check the commit message, and if it doesn't start with Merge then we assume commit is not a merge - is there some better way BTW?)

I've found this post that could be useful:

https://mislav.net/2010/07/git-tips/

Show the last commit which message matches a regex

$ git show :/fix
# shows the last commit which has the word "fix" in its message

$ git show :/^Merge
# shows the last merge commit

I can mix those attitudes to show last merge commit (this works well):

$ git show --format=%B ':/^(Merge)'

However the syntax for the regular expression here (starting with :/) is pretty obscure, not easy to find documentation for, and I don't understand how to invert it. When I try ?! I get an error:

$ git show --format=%B ':/^(?!Merge)'
fatal: Invalid search pattern: ^(?!Merge)

Can someone guide me how to apply negative match with git show?

Note that the commit messages can be multiline.

Edit:

Let's consider a simple scenario, where all the merges could be fast-forwards (but are not). I want the commit marked in red to be found as "latest".

A script like this seems to do the trick but it's verbose

#!/bin/bash
readCommitMessage () {
    local commit="$1"
    lastCommitMsg=$(git log -1 --pretty=%B $commit)
    #echo "$lastCommitMsg"
}

commit="HEAD"
readCommitMessage
while [[ "$lastCommitMsg" == Merge* ]]; do
    commit="$commit""^2"
    readCommitMessage "$commit"
done

echo "$lastCommitMsg"

Answer 1

git rev-list --no-merges -n 1 HEAD

You can also use log instead of rev-list if you want human readable output rather than just the sha1 which is likely to be more useful when scripting.

(You may want to use --date-order if you want the latest by date rather than just 'a' latest by topological order.)