A git hook to prevent push's if not based on latest in master

pre-push.sh

#!/bin/bash
red='\033[0;31m'
green='\033[0;32m'
yellow='\033[0;33m'
no_color='\033[0m'
BRANCH="$(git symbolic-ref HEAD 2>/dev/null)"
if [ $? != 0 ]
then
    DETATCHED="detached HEAD at $(git rev-parse --short HEAD)"
    echo -e "\n${red} You are currently on ${DETATCHED}. Please make sure you're on a valid branch before pushing. ${no_color}\n"
    exit 1
else
    BRANCH=${BRANCH##refs/heads/}
    if git merge-base --is-ancestor refs/remotes/origin/master ${BRANCH};
    then
        echo -e "\n${green}Pushing \`${BRANCH}\` to remote.${no_color}\n"
    else
        # Write to standard error
        echo -e "\n${red}Error branch \`${BRANCH}\` is not based off the latest commits in master. Please merge in changes from master or rebase branch \`${BRANCH}\` off the changes in master, and then try pushing again.${no_color}\n"
        exit 1
    fi
fi
exit 0