What is Bash?

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Bash is a vital tool for managing Linux machines. The name is short for "Bourne Again Shell."

A shell is a program that commands the operating system to perform actions. You enter commands in a console on your computer and run the commands directly, or you can use scripts to run batches of commands. Shells like PowerShell and Bash give system administrators the power and precision they need for fine-tuned control of the computers they're responsible for.

There are other Linux shells, including csh and zsh, but Bash has become the de facto Linux standard. That's because Bash is compatible with Unix's first serious shell, the Bourne shell, also known as sh. Bash incorporates the best features of its predecessors. But Bash also has some fine features of its own, including built-in commands and the ability to invoke external programs.

One reason for Bash's success is its simplicity. Bash, like the rest of Linux, is based on the Unix design philosophy. As Peter Salus summarized in his book A Quarter Century of Unix, three of the "big ideas" embodied in Unix are:

• Programs do one thing and do it well.
• Programs work together.
• Programs use text streams as the universal interface.

The last part is key to understanding how Bash works. In Unix and Linux, everything is a file. That means you can use the same commands without worrying about whether the I/O stream—the input and output—comes from a keyboard, a disk file, a socket, a pipe, or another I/O abstraction.

Let's learn the basics of Bash, starting with the syntax and commonly used commands, like ls and cat.