Using ADB Shell with Multiple Devices Connected: Best Practices and Solutions

Introduction to ADB (Android Debug Bridge)

The Android Debug Bridge, commonly known as ADB, is a versatile command-line tool used for communicating with an Android device. It enables developers to perform various tasks such as installing applications, debugging apps, accessing the shell of a connected device, and more. When multiple devices or emulators are connected simultaneously, ADB can encounter issues differentiating which device to target, leading to errors like "more than one device and emulator." This tutorial explores how to effectively use ADB in environments with multiple connected Android devices.

Understanding ADB Commands for Multiple Devices

When you connect multiple Android devices or emulators to your computer, it’s crucial to direct ADB commands specifically to the intended target. Without proper specification, ADB might fail due to ambiguity. Here’s how you can effectively manage and use ADB in such scenarios:

Identifying Connected Devices

Before issuing any command, list all connected devices using:

adb devices

This command returns a list of connected device serial numbers or emulator identifiers.

Example Output:

List of devices attached 
emulator-5554   device
7f1c864e    device

Directing ADB Commands to Specific Devices

Using the `-s` Option

The -s option allows you to specify which device should receive the command. This is particularly useful when multiple devices are connected:

adb -s <device_serial> shell

For example, to open a shell on the device with serial 7f1c864e, use:

adb -s 7f1c864e shell

Targeting Emulators

If you have multiple emulators running and need to target one specifically by its IP address and port, use the following format:

adb -s <emulator_ip>:<port> <command>

For example:

adb -s 192.168.232.2:5555 shell

If there is only a single emulator connected, you can simplify your command with:

adb -e <command>

Using `-d` and `-e` Options

These options target devices based on their connection type:

-d: Directs the command to the only attached USB device. It will return an error if more than one USB device is connected.
```
adb -d shell
```
-e: Directs the command to the only running emulator, returning an error for multiple emulators.
```
adb -e shell
```

Setting Environment Variables

For users on Windows, setting an environment variable can streamline device selection:

Open a Command Prompt and set ANDROID_SERIAL to your desired device’s serial number:
```
set ANDROID_SERIAL=7f1c864e
```
You can now use ADB commands without specifying the -s option:
```
adb shell
```

Handling Offline Devices

Occasionally, devices might appear in an offline state or duplicate due to connection issues. To resolve this:

Restart the ADB server to clear stale connections:
```
adb kill-server
```
Re-run adb devices to refresh the list of connected devices.

Best Practices

Order Matters: When using options like -s, ensure it precedes the command, e.g., adb -s <device_serial> install.
Consistent Naming: Use consistent naming or identifiers for devices/emulators if possible.
Environment Setup: Consider setting environment variables to avoid repetitive specification of device IDs.

Conclusion

Managing multiple Android devices with ADB can initially seem daunting due to command conflicts. However, by understanding how to use the -s, -d, and -e options effectively, along with setting environment variables and refreshing connections, you can streamline your workflow and avoid common pitfalls. These techniques are essential for developers working in multi-device environments.