Linux Essentials Preparation · lesson 8 of 23 · 25 min
Getting Help on the Command Line
Linux has extensive built-in documentation. Knowing how to find help is a core skill — you will not memorise every command option, but you will know where to look.
man [command] — manual pages. The primary documentation system. man ls opens the ls manual. Navigate with arrow keys, search with /, quit with q.
Man page sections: 1=user commands, 2=system calls, 3=library functions, 4=device files, 5=file formats, 6=games, 7=miscellaneous, 8=system admin commands. Specify section: man 5 passwd (passwd file format vs man 1 passwd for the command).
[command] –help — quick summary of options. Faster than man pages for a quick reference. Example: ls --help.
info [command] — GNU info system. More detailed than man pages for GNU tools. Hyperlinked. Navigate with n (next), p (previous), q (quit).
apropos [keyword] — searches man page descriptions for a keyword. Useful when you know what you want to do but not the command name. Example: apropos compress.
whatis [command] — one-line description of a command. Example: whatis ls → “ls (1) – list directory contents”.
type [command] — shows whether a command is a shell built-in, alias, or external binary. Example: type cd → “cd is a shell builtin”.
which [command] — shows the full path of an external command. Example: which python3 → /usr/bin/python3.
Exam Tip
apropos searches man page descriptions by keyword. whatis gives a one-line summary. man 5 passwd = file format; man 1 passwd = command. –help is fastest for quick option lookup.
Key Terms
Key Terms
Knowledge Check — 8 Questions
Linux Essentials — Getting Help
Which command opens the manual page for ls?
- help ls
- ls –man
- man ls
- info –ls
Answer: man ls
man [command] opens the manual page. Navigate with arrow keys, search with /, quit with q.
apropos compress will:
- Compress a file
- Search man page descriptions for the word “compress”
- Show the compress manual
- List compressed files
- Answer: Search man page descriptions for the word “compress”
apropos searches the man page database by keyword — useful when you know what you want to do but not the exact command name. man 5 passwd shows:
- The passwd command manual
- The /etc/passwd file format documentation
- Section 5 of all man pages
- Password security guidelines
- Answer: The /etc/passwd file format documentation
Man section 5 = file formats. man 5 passwd describes the /etc/passwd file format. man 1 passwd = the passwd command. The fastest way to see available options for a command is:
- man [command]
- info [command]
- [command] –help
- apropos [command]
- Answer: [command] –help
–help gives a quick summary of options — much faster than reading the full man page when you just need a flag. whatis ls displays:
- All ls options
- A one-line description of ls
- The ls source code
- The ls binary location
- Answer: A one-line description of ls
whatis gives a brief one-line description from the man page database: “ls (1) – list directory contents”. which python3 shows:
- The Python version
- The full path to the python3 binary
- Python3 documentation
- Python3 installed packages
- Answer: The full path to the python3 binary
which shows where a command binary is located: /usr/bin/python3. Useful when multiple versions are installed. type cd reveals that cd is:
- An external binary in /bin
- A shell built-in
- An alias
- A function
- Answer: A shell built-in
cd is a shell built-in — it is part of the shell itself, not an external binary. type distinguishes builtins from external commands.
To quit a man page, press the _____ key.
Answer: q
Man pages use the less pager — press q to quit, / to search, n for next match, arrow keys to scroll.
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