When I do git diff COMMIT I see the changes between that commit and HEAD (as far as I know), but I would like to see the changes that were made by that single commit.
I haven't found any obvious options on diff / log that will give me that output.
To see the changes between two commits use
git diff COMMIT~ COMMIT
This will show you the changes between its previous commit and this commit.
For details go through- https://gitirc.eu/git-diff.html
git show COMMIT
Will show you commit’s data, including diff - but not merge commits.