Why is git prompting me for a post-pull merge commit message?

In git 1.7.10, the git developers decided merge commits could be made too easily. As explained in this blog post, forcing the interactive commit message behavior should make those commit messages more detailed and could reduce the overall frequency of unnecessary merges.

You can use the --no-edit flag to avoid this behavior, but, well, don't. Merge commits, like any commits to history, should be well constructed. Your history should be nothing but useful.

To create a shortcut for future use, either:-

Edit your ~/.gitconfig with the following:

[core]
    mergeoptions = --no-edit

Or execute the following in Terminal

git config --global core.mergeoptions --no-edit

First, take heed of the warnings in Christopher's answer above.

Then, if you still want to disable automatic merge commit message editing, set this environment variable:

    GIT_MERGE_AUTOEDIT=no

This environment variable and its "no" setting are documented on the git merge doc page. It is recommended to use it only in scripts that need to merge non-interactively, but of course it can be set as part of your shell environment to make its effects more permanent.