What Is the Bourne Shell?

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∟What Is the Bourne Shell?

This section provides a quick introduction of the Bourne shell which is the default shell on the Android system, which is based on the Linux system, which is based on Unix system.

The Bourne shell is a Unix shell introduced by Stephen Bourne in 1977. The Bourne shell replaced the Thompson shell and became the default shell of Unix systems. Bourne shell is also the default shell for the Android system, which is based on the Linux system, which is based on the Unix system.

The Bourne shell is a command-line interpreter that provides a traditional user interface for the Unix-based operating systems. Users direct the operation of the computer by entering commands as text for a command line interpreter to execute or by creating text scripts of one or more such commands.

The Bourne shell has the following main features:

Built-in Commands - The ability to use a few useful commands built into the shell.
Command Path Variable - The ability to define a list of paths where the shell can search for external program to execute.
Command Substitution - The ability to execute extra commands in sub shells and uses their output in the command line.
Filename Substitution - The ability to expand filename wildcard characters with real file names.
Input and Output Redirection - The ability to change standard input and/or output from terminal console to files.
Job Control - The ability to suspend an interactive job and resume it at a later time, or send it into the "background".
Execution Control Commands - The ability to execute commands conditionally and repeatedly.
Execution Pipes - The ability to pipe output of one command into another command as input.
Quotation and Escape Sequences - The ability to protect special characters with single quotes and backslashes.
Shell Scripts - The ability to write shell scripts with execution flow control and variables.
Signal Handling - The ability to trap interruption signals (errors).
Variable Substitution - The ability to reference values of built-in and user defined shell variables.

The Bourne shell is the default shell supported on Android systems. You can invoke it remotely using the Android Debugging Bridge (abd) tool your connected desktop computer as descripted in "Android Debug Bridge (adb) Tool" chapter.

If you have "adb" installed as part of the Android SDK Platform Tools of Android Studio package, the "adb" program file is located in the "platform-tools" sub-directory. You can include "platform-tools" in the PATH environment variable, so you can run the "adb" command without specifying the path name. For example, this is what I did on macOS computer:

herong$ export PATH=$PATH:~/Applications/platform-tools/

herong$ adb devices
List of devices attached
10.0.0.150:5555	device

herong$ adb shell

milan:/ $ uname -a
Linux 4.19.191+ #1 SMP PREEMPT Tue Apr 25 04:32:44 CDT 2023 aarch64

milan:/ $ exit

If you are using a Windows computer, setting up the PATH environment variable is slightly different:

herong> set PATH=%PATH%;\local\platform-tools

herong> adb devices
List of devices attached
emulator-5554   offline

herong> adb shell df

Filesystem         Size     Used     Free   Blksize
/dev             242.9M    24.0K   242.8M      4096
/sys/fs/cgroup   242.9M    12.0K   242.9M      4096
/mnt/asec        242.9M     0.0K   242.9M      4096
/mnt/obb         242.9M     0.0K   242.9M      4096