git-get-mainbranch

#!/usr/bin/env bash

set -e

#
# This script takes the name of a remote and prints a symbolic name for its
# HEAD; typically that is the name of its `master` or `main` branch; but I've
# also seen different values, such as `gh-pages`, `trunk`, etc.
#
if test $# -eq 0 ; then
    remote=origin
elif test $# -eq 1 ; then
    remote=$1
else
    echo "Error, usage: $(basename $0) <REMOTE>"
    exit 1
fi

# ensure the given remote name is valid
git remote get-url "${remote}" > /dev/null

# check if the HEAD is present and if not, fetch it
if ! git symbolic-ref "refs/remotes/${remote}/HEAD" > /dev/null 2> /dev/null 
then
    git fetch "${remote}" > /dev/null 2> /dev/null 
    git remote set-head "${remote}" --auto > /dev/null
fi
git symbolic-ref "refs/remotes/${remote}/HEAD" | sed "s@^refs/remotes/${remote}/@@"