I want to start using GitHub Pages for my project's website. This simply requires a branch (subtree) named gh-pages in the repo, and serves up its content. The problem is that part of the website (manual, changelog, download page...) is auto-generated by the build system, so I want to find the best way to commit these changes to the gh-pages branch while the main repo remains on master (or wherever).

To commit to the gh-pages branch, I could write a script that clones the repo into a temporary directory, makes the modifications, commits them, and then pushes them back to the main repo. But this sounds like an error-prone process, so I'm hoping there is an easier way.

A friend suggested that I might add the gh-pages branch as a submodule to the main repository. I ran a little experiment, but it doesn't quite work:

$ git init main
Initialized empty Git repository in /tmp/main/.git/
$ cd main
$ touch main.txt
$ git add .
$ git commit -m'Initial commit in main branch.'
[master (root-commit) 1c52a4e] Initial commit in main branch.
 0 files changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 main.txt
$ git symbolic-ref HEAD refs/heads/gh-pages
$ rm .git/index
$ git clean -fdx
Removing main.txt
$ touch index.html
$ git add .
$ git commit -m'Initial commit in website branch.'
[gh-pages (root-commit) 94b10f2] Initial commit in website branch.
 0 files changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 index.html
$ git checkout master
Switched to branch 'master'
$ git submodule add -b gh-pages . gh-pages
repo URL: '.' must be absolute or begin with ./|../
$ git submodule add -b gh-pages ./ gh-pages
remote (origin) does not have a url defined in .git/config

I'm new to submodules; have done some reading, of course, but I don't understand this behaviour. Why does it need an origin

git github git-submodules
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