Git : Determine if branch is in a merge conflict state

Use git ls-files -u. It prints unmerged files. If it prints nothing, there are no unmerged files.

However, while that's a direct answer for the question you asked "as asked", using git pull in a script is a bit dicey: pull is a convenience script that runs fetch for you, and then (depending on how you direct it and/or have configured your repo) runs either merge or rebase for you. Given that you are writing a script that has a particular goal in mind, you should most likely be using lower-level commands that do more-specific things. For instance, you might use git fetch followed by (as Etan Reisner suggested in a comment) git merge --ff-only so as to never attempt a merge.

Based on the answer given by torek, here is a ready-to-use snippet:

CONFLICTS=$(git ls-files -u | wc -l)
if [ "$CONFLICTS" -gt 0 ] ; then
   echo "There is a merge conflict. Aborting"
   git merge --abort
   exit 1
fi