Recompile just the assets in an Android APK. Faster than `gradle installDebug` if you're just modifying HTML/CSS/JS.

recompile_assets.sh

#!/bin/bash
#
# Recompile Android assets into a -debug.apk. Assumes you have apktool
# installed and it's globally accessible as "apktool".
#
# Usage: ./recompile_assets.sh [path/to/debug.apk] [path/to/assets]
#
# If you don't include any arguments, it will try to determine the 
# location of your assets/apk using the current working directory.
#
# This script currently doesn't do any merging of assets, so hopefully
# you have them all in src/main/assets.
#
# On Gist at https://gist.github.com/nolanlawson/4f63c0fccb49498bb2ca
#

APK_FILE=$1
ASSETS=$2

if [[ -z $APK_FILE ]]; then
  APK_FILE=`find . | grep '\-debug\.apk$' | head -n 1`
fi

if [[ -z $ASSETS ]]; then
  ASSETS=`find . | grep src/main/assets$`
fi

if [[ -z $APK_FILE ]]; then
  echo -e "\nCouldn't find the debug.apk file"
  exit 1
fi

if [[ -z $ASSETS ]]; then
  echo -e "\nCouldn't find the assets file"
  exit 1
fi

if [[ ! -x `which apktool` ]]; then
  echo -e "\nCouldn't find apktool. Install it and make it globally accessible as 'apktool' please!"
  echo "https://code.google.com/p/android-apktool/downloads/list"
  exit 1
fi

echo -e "\nUsing apk file: $APK_FILE"
echo "Using assets dir: $ASSETS"

echo -e "\nDecompiling..."

RANDO=$RANDOM
TMPDIR=/tmp/apktool-$RANDO

apktool d $APK_FILE $TMPDIR


echo -e "\nCopying over assets..."

rm -fr $TMPDIR/assets
cp -r $ASSETS $TMPDIR/assets

echo -e "\nRecompiling..."

apktool b $TMPDIR $APK_FILE

echo -e "\nSigning..."

jarsigner $APK_FILE androiddebugkey -digestalg SHA1 -sigalg MD5withRSA -keystore ~/.android/debug.keystore -keypass android -storepass android

echo -e "\nDone!\n"