student@ubuntu:~$
unix-foundations Lesson 4 9 min read

Man Pages & Getting Help

Four types of commands, the manual system, and how to answer your own questions

Reading: Shotts, The Linux Command Line: pp. 71–78, 105–112

Quick check before you start: Do you know the difference between cd and /usr/bin/ls? If not, read on. If you can explain which is a builtin and which is an external program, skip to Man Page Structure.

Practice this topic: Man Pages skill drill

After this lesson, you will be able to:

  • Identify the four types of shell commands using type and which
  • Navigate a man page (scroll, search with /, quit with q)
  • Explain man page sections (1 = user commands, 3 = C library functions)
  • Use man -k to search for commands by keyword

Four Types of Commands

Not every command works the same way. The shell recognizes four types:

  1. Executable programs — compiled binaries in /usr/bin, /bin, etc. (ls, cp, gcc)
  2. Shell builtins — built into bash itself (cd, echo, exit)
  3. Shell functions — user-defined mini scripts
  4. Aliases — shortcuts (ll is often aliased to ls -la)

Use type to find out what a command is:

type cd
# cd is a shell builtin

type ls
# ls is /usr/bin/ls

type ll
# ll is aliased to 'ls -la'

Use which to find where an executable lives on disk:

which gcc
# /usr/bin/gcc

which cd
# (no output — cd is a builtin, not a file)

type works on all four kinds. which only finds executables in your PATH. If you need to know what kind of command something is, use type. If you need to know where on disk a program lives, use which.

Man Page Structure

The man command opens the manual page for any documented command:

man ls

Man pages follow a standard structure:

Section Content
NAME Command name and one-line summary
SYNOPSIS Syntax — brackets [ ] mean optional, ... means repeatable
DESCRIPTION What the command does
OPTIONS Every flag explained
EXAMPLES Usage examples (not always present)
SEE ALSO Related commands

Navigating Inside a Man Page

Man pages open in a pager (usually less). The controls:

Key Action
Space / f Page forward
b Page back
/pattern Search forward for pattern
n Next search match
q Quit

Man Page Sections

The manual is divided into numbered sections:

Section Contains Example
1 User commands man 1 ls
2 System calls man 2 open
3 C library functions man 3 printf
5 File formats man 5 passwd
8 Admin commands man 8 mount

Section 3 matters for this course. When you start writing C, man 3 printf shows the C library function, not the shell command. If a name exists in multiple sections, specify the number:

man printf       # shows the shell command (section 1)
man 3 printf     # shows the C library function

Searching for Commands

When you know what you want to do but not which command does it, use man -k:

man -k "copy files"
# cp (1)  — copy files and directories

This searches the one-line descriptions (the NAME section) of every man page. The --help flag is another option — most commands support it:

ls --help

--help gives a shorter summary than the full man page. Use it when you just need a flag reminder.

Check Your Understanding
You want to know whether echo is a shell builtin or an external program. Which command gives you that answer?
Awhich echo
Btype echo
Cman echo
Decho --help
Answer: B. type reports whether a command is a builtin, executable, alias, or function. which only searches PATH for executables — it does not identify builtins. man echo shows documentation for the external /usr/bin/echo, which does not tell you that bash has its own builtin version.

What Comes Next

You can now find help for any command on the system. Next, you will learn how Unix controls who can read, write, and execute files.