Release APK builder that asks for your key passwords interactively, so you don't have to store them in your build script or VCS. For use with the Gradle build system. CC0 license.

build.gradle

// additional required configuration to hook into the build script
android {
	signingConfigs {
		release
	}

	buildTypes {
		release {
			signingConfig signingConfigs.release
		}
	}
}

// specify signing properties on the command line
if (hasProperty('storeFile')) {
	println 'Generating a signed package.'
	android.signingConfigs.release.storeFile = file(storeFile)
	android.signingConfigs.release.storePassword = storePassword
	android.signingConfigs.release.keyAlias = keyAlias
	android.signingConfigs.release.keyPassword = keyPassword
} else {
	android.buildTypes.release.signingConfig = null
}

release.sh

#!/bin/bash

if [[ $# -ne 1 ]]; then
	echo "Usage: $0 keystore"
	exit 1
fi

if [[ ! -f $1 ]]; then
	echo "$1 doesn't exist or isn't a keystore"
	exit 1
fi

read -s -p "Keystore Password: " STORE_PASS
echo
read -p "Key Alias: " KEY_ALIAS
read -s -p "Key Password: " KEY_PASS
echo

export ORG_GRADLE_PROJECT_storeFile="$1"
export ORG_GRADLE_PROJECT_storePassword="$STORE_PASS"
export ORG_GRADLE_PROJECT_keyAlias="$KEY_ALIAS"
export ORG_GRADLE_PROJECT_keyPassword="$KEY_PASS"

./gradlew signingReport

read -p "Is this correct? [y/n] " -n 1 -r
echo
if [[ $REPLY =~ ^[Yy]$ ]]; then
	./gradlew build
fi

Just a note:

In my case it only worked if i used project.hasproperty() instead of only hasproperty()