How to send letters plus keyboard combination to adb shell?

Issue

To run my program from Linux command-line I do:

• adb shell
• cd /data/
• ./devprog count

To stop I need to type the letter "T" then hit enter otherwise the devprog keeps running forever. I want to find a way to run the devprog for three seconds and then exit devprog properly by sending the keyboard keys "T + Enter". How can I accomplish this or is it even possible to do with the shell?

I tried the followings:

• timeout 3s adb shell ./data/devprog count
• adb shell ./data/devprog count & timeout 3s | T

I don't know what else to do to run my program for three seconds then exit the command with the keyword combination.

Note: I tried adb shell ./data/devprog count & sleep 3 | xargs adb shell kill. This will stop the program but it will not return any outputs from devporg.

Solution

#!/usr/bin/env bash
adb shell < <(
  printf '%s\n' \
    'cd /data || exit' \
    'exec ./devprog count'
  sleep 3
  printf '%s\n' T
)

Explaining the nonobvious parts of this:

• <(...) is a process substitution; the shell replaces it with a filename that refers to a FIFO from which the output of ... can be read.
• adb shell < <(...) thus runs adb shell, with its input redirected from a process substitution with the embedded code.
• printf '%s\n' "some text" "some more text" writes two lines, first some text, then some more text. We use this to write the commands we want to unconditionally run.
• Using || exit on the cd prevents the script from continuing to run if the cd fails, so we don't invoke commands that might behave unpredictably outside their intended environment.
• Using exec in exec ./devprog count replaces the remote shell with a copy of ./devprog, so we don't need to worry about what happens if ./devprog exits early and puts us back in the shell: with that change made, it's guaranteed that when ./devprog exits, so does the remote shell.

Why did we use a process substitution and not a heredoc? That's because a heredoc is fully evaluated before execution starts, so embedding something like $(sleep 3) in a heredoc would delay adb from starting, but it wouldn't create a delay while adb was running.

Answered By - Charles Duffy