What is Bash and why is it important?

Bash is the GNU "Bourne-Again Shell," the default command interpreter on most Linux systems — and because it's nearly everywhere, learning it once pays off on almost any machine.

The name is a pun. The original Unix shell was the Bourne Shell (sh), written by Stephen Bourne. When the GNU project wrote a free, improved replacement, they called it "Bourne-Again" — a play on "born again." So Bash is sh reborn, staying compatible with old sh scripts while adding modern conveniences.

What "modern conveniences" buys you day to day:

• Tab completion — half-type a command or filename, press Tab, let the shell finish it (fewer typos, faster typing).
• Command history — Up/Down to recall past commands, history to list them, Ctrl+R to search.
• Variables and environment — store and pass values, e.g. $HOME`, `$PATH.
• Pipes and redirection — wire one command's output into the next (a | b) or into a file (> out.txt).
• A full scripting language — loops, conditionals, functions, so a sequence of commands becomes a reusable program.

echo $SHELL    # prints your login shell, usually /bin/bash

Gotcha: $SHELL shows your configured login shell, not necessarily the one running right now. To see the actually-running shell, check echo $0 or ps -p $$.