CIS120 Linux Fundamentals by Scott Shaper

The help and man Commands

Think of help and man as your built-in Linux cheat sheets. When you're not sure how to use a command or need to look up its options, these commands are your best friends. They're like having a Linux expert right at your fingertips!

Quick Reference

Command Description Common Use
help Show help for built-in shell commands only Quick reference for commands like cd, echo, pwd
man Show detailed manual pages for non-built-in commands Complete documentation for commands like ls, grep, cat

help Command

The help command is like a quick reference guide for built-in shell commands. It's perfect when you need a fast reminder of how to use commands like cd, echo, or pwd.

When to Use help

Use help when you want to:

How to Tell if a Command is Built-in

To check if a command is built into the shell, you can use:

# Check if cd is a built-in command
type cd
# Output: cd is a shell builtin

# Check if ls is a built-in command
type ls
# Output: ls is /bin/ls  # This means it's not built-in

Remember: If a command is built-in, use help. If it's not built-in, use man.

Common Options

Option What It Does When to Use It
-d Show brief description When you just need a quick summary
-m Show man-page style format When you want more detailed help
-s Show short usage summary When you just need the basic syntax

Practical Examples

Basic Usage
# Get help for cd command
help cd

# Get brief description
help -d echo

# Get usage summary
help -s pwd
Sample Output (for help cd)
# help cd output
cd: cd [-L|[-P [-e]] [-@]] [dir]
    Change the shell working directory.
    
    Options:
      -L  force symbolic links to be followed
      -P  use the physical directory structure
      -e  if the -P option is supplied, and the current working directory
          cannot be determined successfully, exit with a non-zero status
      -@  on systems that support it, present a file with extended attributes
          as a directory containing the attributes

man Command

The man command is like having a complete Linux manual at your fingertips. It provides detailed documentation for almost any command, including examples, options, and related commands.

When to Use man

Use man when you want to:

Common Options

Option What It Does When to Use It
-k Search for keywords When you're not sure which command to use
-f Show brief description When you need a quick summary
-a Show all matching pages When a command has multiple manual pages
-w Show file location When you need to know where the man page is stored
-K Performs a full-text search inside the actual man page contents. When you need to find text across all manuals
-k Runs a keyword search through the man page database. When you need to find a specific keyword
-l List manual pages When you want to see all available man pages
-P Use specific pager When you want to use a different viewer

Understanding Man Page Sections

Man pages are organized into numbered sections, each covering a different type of documentation. Not all commands will have pages in all sections - some might only appear in one section, while others (like passwd) might appear in multiple sections with different meanings.

Section What It Contains Example Notes
1 User commands man 1 ls Most common section for everyday commands
2 System calls man 2 open Functions provided by the kernel
3 Library functions man 3 printf Programming library functions
4 Special files man 4 null Device files in /dev
5 File formats man 5 passwd Configuration file formats
6 Games man 6 fortune Games and amusements
7 Miscellaneous man 7 ascii Various topics and conventions
8 System admin man 8 shutdown Commands for system administration

How to Check Available Sections

To see which sections a command appears in, use the -f option:

# Check all sections for passwd
man -f passwd
# Output might show:
# passwd (1) - change user password
# passwd (5) - password file

Practical Examples

Basic Usage
# View manual for ls command
man ls

# Search for commands about files
man -k file

# View specific section
man 1 passwd

# Search all man pages for a term
man -K "regular expression"

# List all man pages
man -l
Navigation Tips
Key What It Does When to Use It
Space or f Move forward one page When you want to read more
b Move back one page When you want to review previous content
/pattern Search for text When you're looking for specific information
n Find next match When you want to see more search results
N Find previous match When you want to go back to previous search results
q Quit man page When you're done reading
h Show help When you need to see all navigation options
g Go to start When you want to return to the beginning
G Go to end When you want to jump to the end

Tips for Success

Common Mistakes to Avoid

Best Practices