The Linux Command Line
linuxcommand.org
William Shotts' free comprehensive book on the Linux command line — covering navigation, file operations, permissions, shell scripting, processes, and system administration — available to read online in full.
Why it is useful
The most readable and complete free resource for learning the Unix command line. Goes well beyond 'here are some commands' to explain how the shell works, how processes interact, and how to write real shell scripts. The full text is available free online; a print edition exists for those who prefer it. Essential reading for anyone who wants to be truly comfortable at the command line.
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