Check whether git is in a special state

git_check_status.sh

#!/bin/bash
#
# git_check_status.sh: check whether git is in a special state
#
# Ben Cohen, July 2021
#
# This script returns failure if the current directory is a git worktree
# that is in a special state - merge, rebase, bisect or detached HEAD - or
# returns success if the worktree is in a normal state, or the current
# directory is not a git worktree.
#
# If invoked with the option "-v" then a description will be printed if
# git is in a special state.
#
# The following can be used to provide a warning in your bash prompt,
# instead of discovering that you have been working with a detached HEAD
# for the last three days...
#
#   PS1="\[\033[7;36m\]\$(git_check_status.sh -v)\[\033[00m\]$PS1"
#

usage() {
    echo "Usage: $0 [-v]" 1>&2
    exit 1
}

while getopts "v" o; do
    case "${o}" in
        v) verbose=1
           ;;
        *) usage
           ;;
    esac
done

if ! git rev-parse --is-inside-work-tree >& /dev/null
then
    # The current directory is not inside a git repo
    exit 0
fi

GITDIR=$(git rev-parse --git-dir)

if [ -e "$GITDIR/MERGE_HEAD" ]
then
    # Doing a merge
    [ -n "$verbose" ] && echo -n "MERGING"
    exit 2
fi

if [ -e "$GITDIR/BISECT_START" ]
then
    # Doing git bisect
    [ -n "$verbose" ] && echo -n "BISECTING"
    exit 3
fi

if [ -e "$GITDIR/rebase-merge" -o -e "$GITDIR/rebase-apply" ]
then
    # Doing git rebase
    [ -n "$verbose" ] && echo -n "REBASING"
    exit 4
fi

if [ "$(git rev-parse --abbrev-ref --symbolic-full-name HEAD)" = "HEAD" ]
then
    # HEAD is detached
    [ -n "$verbose" ] && echo -n "OFF-BRANCH"
    exit 1
fi

# The current directory is in a git repo but not in a special state
exit 0