write $GH_CNAME to CNAME before commiting

closes #12

README.md

@@ -15,7 +15,7 @@ Remember that you may also have to adjust your [repository settings](https://hel
 
 Because this action deploys to separate, "deploy-only" branches, you can not use it if you want to deploy from a repo subdirectory such as `docs/`.
 In those cases you really don't need a GitHub Action, because you would be committing the build artifacts yourself.
-For details see the [GitHub Pages Documentation](https://help.github.com/articles/configuring-a-publishing-source-for-github-pages/). 
+For details see the [GitHub Pages Documentation](https://help.github.com/articles/configuring-a-publishing-source-for-github-pages/).
 
 There are already great GitHub actions to use static site generators *and* then deploy to GitHub Pages (for [jekyll](https://github.com/helaili/jekyll-action), [jekyll](https://github.com/BryanSchuetz/jekyll-deploy-gh-pages), [zola](https://github.com/shalzz/zola-deploy-action) and surely many more to come).
 This action isn't that, though I've borrowed much of the git action from these works.
@@ -40,9 +40,10 @@ The discussion is documented [here](https://github.com/maxheld83/ghaction-ghpage
 
 ## Environment Variables
 
-Just `BUILD_DIR`, the build directory relative to your repository root.
-You can also pass `.` if you want to push your repository root.
-
+|Variable|Meaning|
+|-----|-----|
+|`BUILD_DIR`|The build directory relative to your repository root. You can also pass `.` if you want to push your repository root.|
+|`GH_CNAME`|Your custom domain name. Will be written to the `CNAME` file in your `BUILD_DIR`.|
 
 ## Arguments
 

entrypoint.sh

@@ -17,6 +17,12 @@ if [[ "$REPONAME" == "$GHIO" ]]; then
 else
   REMOTE_BRANCH="gh-pages"
 fi && \
+if [[ -z "$GH_CNAME" ]]; then
+  echo "No CNAME is set"
+else
+  echo "Setting CNAME"
+  echo $GH_CNAME > CNAME
+fi && \
 git init && \
 git config user.name "${GITHUB_ACTOR}" && \
 git config user.email "${GITHUB_ACTOR}@users.noreply.github.com" && \