Git - How to auto push changes in a directory to another branch

Complete question rewrite

So I thought I was explaining this question very simply and direct but it seems I oversimplified to much, so here is all the extra details. Hopefully this helps everyone see this is also not a duplicate.

I have a repository (project) where I would like to automate the process of pushing commits from one directory in a branch to another branch; something I have not come across yet on SO.

Here is my project with its complete structure:

[PROJECT MASTER BRANCH]
|- gh-pages    (directory)
|- css         (directory)
|- index.html  (file)
|- readme.md   (file)

[PROJECT gh-pages BRANCH]
|- (empty at the moment)

What I am hoping to do is create a hook that will automatically handle changes in my gh-pages directory from the master branch, and copy/ clone/ replace them (whichever term is correct to use) into by gh-pages branch, the projects website branch. Here is an example with all other files left out:

[PROJECT MASTER BRANCH]
|- gh-pages         (directory)   <=== SEE UPDATE BELOW [A]
|  |- css           (directory)
|  |  |- style.css  (file)
|  |- index.html    (file)

[PROJECT gh-pages BRANCH]
|- css           (directory)   <=== SEE UPDATE BELOW [B]
|  |- style.css  (file)
|- index.html    (file)

I am completely new to this level of Git Hub. I normally just stick to the basics and never use the terminal/ shell. So in summary to clarify what I am hoping to do, I would like to:

• Only have to work in the [Master Branch]. All changes I need to make to [gh-pages Branch] I do in the gh-pages directory of [Master Branch]
• Preferable accomplish this by adding a simple file which seems to be a post-receive hook?

Here is some post-receive hook code that I tried using (I made it from studying a few things) but it doesn't work:

#!/bin/bash
while read oldrev newrev refname
do
    branch=$(git rev-parse --symbolic --abbrev-ref $refname)
    if [ "master" == "$branch" ]; then
        git checkout gh-pages
        git checkout master -- gh-pages
        git add gh-pages
        git commit -m "Updating project website from 'master' branch."
    fi
done

NOTE
As mentioned in my comment: This is not a duplicate. This is not asking how to push but rather how to tack on other commands that auto run when I do a normal push. These commands would do the extra work mentioned in my OP.

UPDATE
I have added these arrows to parts of my code I refer to below: <===

[A] What should happen here is that Git should recursively read the master branches gh-pages directory and only copy from that what has updated (or everything if that is easier) into the gh-pages branch.

[B] So if the gh-pages directory in master has an index.html file and a css folder with a style.css file is should only copy over that structure not the gh-pages directory itself. Below is an example of a bad hook that copies the gh-pages directory too:

[PROJECT gh-pages BRANCH]
|- gh-pages         (Directory)   <=== NOT SUPPOSED TO HAPPEN
|  |- css           (directory)
|  |  |- style.css  (file)
|  |- index.html    (file)

Also, the hook should not copy over any other files but what is inside the gh-pages. Even if several other files changed in the master branch only the gh-pages directory files should be copied over.

[C] NEW CODE - This works but causes an error:

#!/bin/bash
branch=$(git rev-parse --abbrev-ref HEAD)
if [ "master" == "$branch" ]; then
    git fetch && git checkout gh-pages
    git checkout master -- gh-pages/*
    git add -A
    git commit -m "Updating project website from 'master' branch."
    git push -u origin gh-pages
fi

This wont work for two reasons. 1) If the repo is behind on commits it cant handle that, it will error out; if a pull is used instead of a fetch the local repo gets wiped like so:

If I leave fetch the local repo stays the way it should:

2) The whole gh-pages directory gets copied over to the gh-pages branch still and not just the files inside it.

Solution 1:

You really don't need this complex approach.

Simply add your own repo as a submodule (of itself!), submodule following the gh-pages branch (since a submodule can follow the latest commit of a branch)!

git checkout master
git rm -r gh-pages # save your data first
git submodule add -b gh-pages -- /remote/url/of/your/own/repo
git commit -m "ADd gh-pages branch as submodule"
git push

That way, you can change files either in your main branch, or in the gh-pages folder (which is actually a submodule)

Whenever you are making changes in gh-pages folder, don't forget to commit there, and in the main folder of your repo in order to record the new gitlink (special entry in the index) reprsenting the new SHA1 of the gh-pages submodule.

cd myrepo/gh-pages
# modify files
git add .
git commit -m "modify gh-pages files"
cd .. # back to myrepo folder
git add gh-pages
git commit -m "record gh-pages new SHA1"
git push

With git 2.7+, you can set:

cd /path/to/main/repo
git config push.recurseSubmodules on-demand

Then a single git push from your main repo will also push the gh-pages submodule to the gh-pages branch.

Later, a single git clone would clone both your main repo and its gh-pages branch (in the gh-pages submodule folder).

That way, you always have both content visible.

And you don't need a complex "synchronization/copy" mechanism.

Update August 2016: Simpler GitHub Pages publishing now allows to keep your page files in a subfolder of the same branch (no more gh-pages needed):

You don't need the submodule approach anymore, since your pagers can be in a subfolder within the same branch.

Solution 2:

What's the problem with the hook script you wrote ? What were the contents of the branch gh-pages when you created it?

I had created an empty branch gh-pages with below command:

git checkout --orphan gh-pages
git rm -rf .
touch README.txt
git add README.txt
git commit -m "Initial commit"
git push -u origin gh-pages

Then I ran below script as a part of post-receive hook and it worked for me.

#!/bin/bash
branch=`git rev-parse --abbrev-ref HEAD` 
if [ "master" == "$branch" ]; then
    git fetch && git checkout gh-pages
    git checkout master -- gh-pages
    git add -A
    git commit -m "Updating project website from 'master' branch."
    git push -u origin gh-pages
fi
done