Script checkouts each submodule on a given branch if latter exists (or fallback branch is used) and pulls if behind

git_sm_co.sh

#!/usr/bin/env bash

fetch=$(git fetch);

if [ "$(git show-ref refs/remotes/origin/$1)" ]; then # Checking branch for existence on remote
    co=$(git checkout "$1"); # Checkouting branch that we checked for existence above
else
    defaultFb="master"; # Default fallback
    fb=${2:-$defaultFb} # Resulting fallback
    echo "- Branch $1 does not exist. Switching to ${fb}";
    co=$(git checkout $fb); # Checkouting fallback branch
fi

echo "$co"; # Showing output for consistency

if [[ $co == *"can be fast-forwarded"* ]]; then # Checking if we are behind the checkouted branch
    echo "$(git pull)"; # Performing `pull`
fi

    exit 0;

Installation

Wherever you are execute

cd ~ && \
curl -O https://gist.githubusercontent.com/wilensky/aafe1c09ae0edb2897bd74f051553f4a/raw/5de7216d8444b7faa255c4fe4764f7c5c14f9240/git_sm_co.sh && \
chmod a+x git_sm_co.sh && \
cd -

Usage

cd ~/some/project-with-submodules
git submodule foreach '~/git_sm_co.sh my-branch' # Default fallback branch is `master`
git submodule foreach '~/git_sm_co.sh my-branch some/fallback-branch' # Fallback branch is defined as `some/fallback-branch` and will be used if `my-branch` is not on repository