Introduction to the Linux Command Line

Linux systems provide multiple ways to view documentation for commands—whether through brief usage instructions or extensive manuals. Knowing how to access command help ensures efficient learning, troubleshooting, and effective use of the CLI environment.

Using help for Shell Builtins

The help command displays documentation for shell builtins in Bash.

help cd

This shows usage details for cd, including options and exit status codes.

Using --help for Executable Programs

Most external commands support a --help option to display basic usage and flags.

mkdir --help

Output typically includes syntax, available options, and brief instructions.

Using man for Manual Pages

Manual pages provide detailed documentation for commands and system interfaces.

man ls

This opens the man page for ls, which includes a full description, syntax, option list, and exit status explanation.

Man Page Sections

Section	Contents
1	User commands
2	System calls (kernel)
3	C library functions
4	Device files
5	File formats
6	Games
7	Miscellaneous
8	Admin commands

Specifying Section Numbers

man 5 passwd

Opens the file format documentation for /etc/passwd, rather than the user command.

Using apropos for Keyword Searches

Search for commands matching a keyword across all man page descriptions.

apropos partition

Returns related tools such as fdisk or cfdisk.

Using whatis for Brief Descriptions

Get a one-line summary of a command’s purpose.

whatis ls

Returns: ls (1) - list directory contents, indicating section 1.

Using info for Structured Documentation

Info pages are hyperlinked documents offering detailed GNU references.

info coreutils

Info Navigation Commands

Command	Action
?	Show help menu
Page Up	Previous page
Page Down	Next page
n	Next section
p	Previous section
Q	Exit

Conclusion

Linux provides layered access to command documentation suited to different needs:

• Use help for shell builtins
• Use --help for quick summaries
• Use man for complete manuals
• Use apropos to find related commands
• Use whatis for brief explanations
• Use info for structured, cross-referenced guides

By mastering these tools, users can quickly find accurate information and enhance their command-line skills.