Glossary

Shell

The program that reads your commands and runs them.

The shell is the program sitting between you and the operating system: it prints the prompt, reads what you type, interprets it, and asks the kernel to run the resulting programs. Bash is the most common on Linux; zsh, fish and dash are alternatives with the same job.

Crucially, the shell does real work before any command runs — it expands variables, replaces $(command) with its output, interprets quotes and expands wildcards like *.txt against the filesystem. The command you type is not what the command receives. Understanding that order of operations explains most "why did it do that?" moments in the terminal.

See it in practice

$ echo *.txt

The shell expands the wildcard and hands the resulting file names to echo — echo never sees an asterisk. Prefix any command with echo to preview what it will actually receive.

Where you'll meet it

Terminal

The window that displays a shell session.

Bash

The default shell on most Linux distributions.

echo

Print text and variables, and write or append to files with > and >>.

Bash scripting for beginners

In-depth guide

Learn these concepts by typing them: the interactive course builds them up lesson by lesson in a real simulated shell.