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Is there a Git command that can be used to determine if a merge is in-process (i.e. uncommitted)? I know I can simply check for .git/MERGE_HEAD, but is this proper and/or future-proof for command-line scripts?
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To see the beginning of the merge conflict in your file, search the file for the conflict marker <<<<<<< . When you open the file in your text editor, you'll see the changes from the HEAD or base branch after the line <<<<<<< HEAD .
Since MERGE_HEAD is only available during a merge and is also future-proof, we can simply use git rev-list -1 MERGE_HEAD (conveniently, a plumbing command) which will exit with code 128 if MERGE_HEAD is not found.
For simple text files, Git uses an approach known as the longest common subsequence algorithm to perform merges and to detect merge conflicts. In its simplest form, Git find the longest set of lines in common between your changed file and the common ancestor.
One trick is to use a Git command that will fail if a merge is in progress. You can then check the return code of the command. You'll also want to make sure that the command will not affect your working copy or index in the event that it succeeds. While there are many commands that fall into this category, one that seems appropriate is
git merge HEAD which returns a 128 code if a merge is in progress, but 0 otherwise. Note that when a merge is not in-process, this command will simply print Already up-to-date since you are just merging with yourself. So, for scripting purposes, you can do this (in BASH)
git merge HEAD &> /dev/null result=$? if [ $result -ne 0 ] then echo "Merge in progress." else echo "Merge not in progress." fi Note that even with the --quiet flag of git merge, an in-process merge will still cause this command to print to the error stream. This is why I redirect its output to /dev/null.
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