+ Apt install pacakges provided through 'APT_PACKAGES'

+Update readme

README.md

@@ -1,25 +1,13 @@
-# Rsync - Docker mod for openssh-server
+# APT Install - Universal Docker mod
 
-This mod adds rsync to openssh-server, to be installed/updated during container start.
+Using this mod you can install any package during starup by providing it through the environment variable `APT_PACKAGES`. This is then passed into the installation command as such: `apt install -y --no-install-recommends ${APT_PACKAGES}`.
 
-In openssh-server docker arguments, set an environment variable `DOCKER_MODS=linuxserver/mods:openssh-server-rsync`
+In any docker container arguments, set an environment variable `DOCKER_MODS=linuxserver/mods:universal-apt-install`
 
-If adding multiple mods, enter them in an array separated by `|`, such as `DOCKER_MODS=linuxserver/mods:openssh-server-rsync|linuxserver/mods:openssh-server-mod2`
+If adding multiple mods, enter them in an array separated by `|`, such as `DOCKER_MODS=linuxserver/mods:universal-apt-install|linuxserver/mods:universal-stdout-logs`
 
-# Mod creation instructions
-
-* Fork the repo, create a new branch based on the branch `template`.
-* Edit the `Dockerfile` for the mod. `Dockerfile.complex` is only an example and included for reference; it should be deleted when done.
-* Inspect the `root` folder contents. Edit, add and remove as necessary.
-* Edit this readme with pertinent info, delete these instructions.
-* Finally edit the `.github/workflows/BuildImage.yml`. Customize the build branch, and the vars for `BASEIMAGE` and `MODNAME`.
-* Ask the team to create a new branch named `<baseimagename>-<modname>`. Baseimage should be the name of the image the mod will be applied to. The new branch will be based on the `template` branch.
-* Submit PR against the branch created by the team.
-
-
-## Tips and tricks
-
-* To decrease startup times when multiple mods are used, we have consolidated `apt-get update` down to one file. As seen in the [nodejs mod](https://github.com/linuxserver/docker-mods/tree/code-server-nodejs/root/etc/cont-init.d)
-* Some images has helpers built in, these images are currently:
-    * [Openvscode-server](https://github.com/linuxserver/docker-openvscode-server/pull/10/files)
-    * [Code-server](https://github.com/linuxserver/docker-code-server/pull/95)
+For example, to install `rsync`, `git` and `nginx` add the following lines to your docker compose service:
+```yaml
+- DOCKER_MODS=linuxserver/mods:universal-apt-install
+- APT_PACKAGES=rsync git nginx
+```

root/etc/cont-init.d/95-apt-get

@@ -0,0 +1,5 @@
+#!/usr/bin/with-contenv bash
+
+if [ -f /usr/bin/apt ]; then
+    apt-get update
+fi

root/etc/cont-init.d/97-apt-install

@@ -0,0 +1,13 @@
+#!/usr/bin/with-contenv bash
+
+# Exit if no installable packages are provided
+if [ -z ${APT_PACKAGES+x} ]; then
+    echo "**** No APT packages to install ****"
+    exit 0
+fi
+
+if [ -f /usr/bin/apt ]; then
+    apt install -y --no-install-recommends ${APT_PACKAGES}
+else
+    echo "!!! apt not found !!!"
+fi