Copying files in ADB shell with run-as

The OP tried to combine the following 3 commands (that he had no problem executing one after another in the interactive shell session) into a single non-interactive command:

adb shell
run-as com.example.app
cat /sdcard/temp_prefs.xml > shared_prefs/com.example.app_preferences.xml

For simplicity let’s start from within an interactive adb shell session. If we just try to combine the last two commands into a single line:

run-as com.example.app cat /sdcard/temp_prefs.xml > shared_prefs/com.example.app_preferences.xml

This would not work because of how shell redirection works – only the cat /sdcard/temp_prefs.xml part of the command would be run with com.example.app UID

Many people “know” to put the part of the command around redirection into quotes:

run-as com.example.app "cat /sdcard/temp_prefs.xml > shared_prefs/com.example.app_preferences.xml"

This does not work because the run-as command is not smart enough to parse the whole command. It expects an executable as the next parameter. The proper way to do it would be to use sh instead:

run-as com.example.app sh -c "cat /sdcard/temp_prefs.xml > shared_prefs/com.example.app_preferences.xml"

So can we just prepend adb shell to the command and be done with it? Not necessarily. By running the command from your PC you also add another local shell and its parser. Specific escape requirements would depend on your OS. In Linux or OSX (if your command does not already contain any ') it is easy to single-quote the whole command like so:

adb shell 'run-as com.example.app sh -c "cat /sdcard/temp_prefs.xml > shared_prefs/com.example.app_preferences.xml"'

But sometimes it is just easier to use an alternative solutions with (-out or less) quotes:

adb shell run-as com.example.app cp /sdcard/temp_prefs.xml shared_prefs/com.example.app_preferences.xml

Or if your device does not have the cp command:

adb shell run-as com.example.app dd if=/sdcard/temp_prefs.xml of=shared_prefs/com.example.app_preferences.xml

Also notice how I used shared_prefs/com.example.app_preferences.xml instead of full /data/data/com.example.app/shared_prefs/com.example.app_preferences.xml – normally inside of run-as command your current directory is the HOME dir of your package.