Add CLI build instructions (#2515)

Author: je-l

docs/EN/SettingUpAaps/BuildingAaps.md

@@ -24,3 +24,10 @@ You can build the app with your computer using Android Studio.
 
 **[Follow these instructions.](./ComputerBuild.md)**
 
+----
+
+### Build using the command-line
+
+This option is intended for those who prefer to build AAPS in local command-line, without installing Android Studio.
+
+**[Follow these instructions.](./CLIBuild.md)**

docs/EN/SettingUpAaps/CLIBuild.md

@@ -0,0 +1,63 @@
+# Build instructions for the command-line
+
+```{admonition} For users familiar with the command-line and git
+:class: information
+
+The simplest option to build AAPS is the [Browser build](./BrowserBuild.md) alternative.
+```
+
+Tested with Fedora and Debian Linux, other systems should work with minimal adjustments.
+
+## Requirements
+
+Consult the minimum required Java version from [this table](#Building-APK-recommended-specification-of-computer-for-building-apk-file).
+Install the appropriate OpenJDK package using the system package manager.
+For example in Debian, the packages are named like `openjdk-21-jdk`. It should include `javac` and `keytool` binaries.
+
+Download the *Android Command line tools* package from the [Android Studio page](https://developer.android.com/studio#command-line-tools-only).
+Android Studio itself is not required.
+More information about installing this package is found in [sdkmanager docs](https://developer.android.com/tools/sdkmanager).
+After the package is installed, you should manually set two [environment variables](https://developer.android.com/tools/variables): `ANDROID_HOME` and `PATH`.
+Finally, run `sdkmanager --licenses` to finish the installation.
+
+## Building AAPS with Gradle wrapper
+
+### 1. Generate a Java keystore file for signing AAPS
+
+If you already have a keystore file for signing AAPS, reuse that.
+
+```sh
+keytool -genkeypair -v \
+  -keystore aaps-keystore.jks \
+  -alias aaps-key \
+  -keyalg RSA \
+  -keysize 4096 \
+  -validity 20000
+```
+
+You will need the keystore file and passphrase every time you update AAPS.
+
+### 2. Compile the AAPS APK file
+
+Clone the [git repo](https://github.com/nightscout/AndroidAPS) if not already cloned.
+AAPS uses master branch for the latest stable version, ensure you are on the branch/tag you want to build.
+
+Run `./gradlew :app:assembleFullRelease` in the repo. It automatically downloads Gradle, dependencies, and then compiles the code.
+When the build succeeds, you should have an unsigned APK at `app/build/outputs/apk/full/release/app-full-release-unsigned.apk`.
+It should have also installed an `apksigner` binary to `$ANDROID_HOME`. Update your `PATH` again.
+
+### 3. Create a signed APK file from the unsigned one
+
+<!-- Suggest building outside the git repo, to minimize risk of accidental APK commits -->
+
+Change to your home directory and create a signed APK file:
+
+```sh
+apksigner sign \
+  --ks path/to/aaps-keystore.jks \
+  --ks-key-alias aaps-key \
+  --out app-full-release-signed.apk \
+  ./AndroidAPS/app/build/outputs/apk/full/release/app-full-release-unsigned.apk
+```
+
+Now you have `app-full-release-signed.apk` ready for installation or upgrade.

docs/EN/index.md

@@ -94,6 +94,7 @@ Setting up the reporting server <./SettingUpAaps/SettingUpTheReportingServer.md>
 Building AAPS <./SettingUpAaps/BuildingAaps.md>
 - Browser Build <./SettingUpAaps/BrowserBuild.md>
 - Computer Build <./SettingUpAaps/ComputerBuild.md>
+- CLI Build <./SettingUpAaps/CLIBuild.md>
 Transferring and Installing AAPS <./SettingUpAaps/TransferringAndInstallingAaps.md>
 Setup Wizard <./SettingUpAaps/SetupWizard.md>
 Your AAPS Profile <./SettingUpAaps/YourAapsProfile.md>