Display the difference of two git hash

git-hashdiff.sh

#!/bin/bash
# coding: utf-8

# git-hashdiff
#     Display the difference of two git hash.
#     Args: $1 -- git reference (HEAD, origin/master etc.)
#           $2 -- another reference

check_ref() {
    local ref=$1

    git rev-parse "$ref" > /dev/null 2>&1

    if [ ! "$?" = "0" ];then
        echo "fatal: the invalid reference:"$ref"" 1>&2
        exit 1
    fi
}

if [ ! "$#" = "2" ];then
    echo "usage: git hashdiff [ref_a] [ref_b]" 1>&2
    exit 1
fi

declare ref_one=$1 # git reference (HEAD, origin/master etc.)
declare ref_two=$2 # git reference

check_ref "$ref_one"
check_ref "$ref_two"

declare hash_one="$(git rev-parse $ref_one)"
declare hash_two="$(git rev-parse $ref_two)"

printf "a: %s\n" $hash_one
printf "b: %s\n" $hash_two

if [ "$hash_one" = "$hash_two" ];then
    exit 0
else
    exit 1
fi