Like many other Version Control Systems, Git has a way to fire off custom scripts when certain important actions occur. There are two groups of these hooks: client-side and server-side. Client-side hooks are triggered by operations such as committing and merging, while server-side hooks run on network operations such as receiving pushed commits. You can use these hooks for all sorts of reasons. (source https://git-scm.com/book/en/v2/Customizing-Git-Git-Hooks)

#!/bin/bash

#path to root directory of your project
TARGET="/home/project/dev"

#path to git bare repository
GIT_DIR="/home/project/project.bare"


BRANCH="develop"

while read oldrev newrev ref
do
    if [ "$ref" = "refs/heads/$BRANCH" ];
    then
        echo "Ref $ref received. Deploying ${BRANCH} branch..."
        #git --work-tree=$TARGET --git-dir=$GIT_DIR checkout -f $BRANCH
        cd $TARGET
        unset GIT_DIR
        git pull
    else
        echo "Ref $ref received. Doing nothing: only the ${BRANCH} branch may be deployed on this server."
    fi
done