Replaces classes in Android Package Files

replace-classes-in-apk.sh

#!/bin/sh

# Replaces classes in Android Package Files
# (c) Sebastian Fischer, CC-BY
# Enhanced by Ben Bek

# Can be used to rebuild an App with a modified version of a used library.

exists()
{
  command -v "$1" >/dev/null 2>&1
}

if !([ -n "$1" ] && [ -n "$2" ] && [ -n "$3" ] && [ -n "$4" ]); then
	echo "Usage: $0 <path to SomeApp.apk> <path to classes.jar> <replaced package path, for example: com/example> <path to private key.jks>"
	exit 1
fi
set -e								# exit on first error

if ! exists d2j-dex2jar; then
        echo "Could not find d2j-dex2jar; please run 'brew install dex2jar'."
        exit 1
elif ! exists dx; then
        echo "Could not find dx executable; please make sure Android Build Tools are in the path."
        exit 1
elif ! exists apksigner; then
        echo "Could not find apksigner executable; please make sure Android Build Tools are in the path."
        exit 1
fi

APK=$1
JAR=$2
PKG=$3

CLASSESJAR_FILE=classes.jar

echo "De-dexing..."
unzip $APK classes*.dex                    			# extract original classes
for dexfile in classes*.dex; do
	filename=${dexfile%.dex}
	d2j-dex2jar -f -o ${filename}.jar ${filename}.dex	# and convert them to .jar
done
filecount=$(ls -1q classes*.dex | wc -l)
if [ $filecount -eq 1 ]; then
	echo "Found one dex file."
else
	echo "Found ${filecount} dex files."
	for j in *.jar; do 
		if jar -tvf "$j" | grep -sq $PKG/; then
			CLASSESJAR_FILE="$j"
		fi
	done
fi
rm classes*.dex
unzip $JAR $PKG/*                               		# extract alternative classes
zip -d $CLASSESJAR_FILE "$PKG/*"
jar uvf $CLASSESJAR_FILE $PKG                        		# and replace originals
rm -rf $PKG
echo "Dexing..."
if [ $filecount -eq 1 ]; then					# not multidex
	d2j-jar2dex -f -o classes.dex $CLASSESJAR_FILE 		# convert back to .dex
else
	dx -JXmx4096M --dex --no-strict --output=temp.zip --multi-dex classes*.jar
	unzip temp.zip classes*.dex
	rm temp.zip
fi
rm classes*.jar
jar uvf $APK classes*.dex                        		# replace .dex in .apk
rm classes*.dex
mv $APK unsigned.apk
echo "Signing, please enter the password for $4..."
apksigner sign --ks $4 --out $APK unsigned.apk  		# sign modified .apk
if [ $APK != "unsigned.apk" ]; then
	rm unsigned.apk
fi
echo "All done. The signed APK has been written to \x1B[4m$APK\x1B[0m."