In Centos 6/RHEL and other Linux distros, command line programs come with their
own documentation called manual pages or man pages. These are generally written by the developer of the corresponding program and are divided into
number of sections.

Below is the list of
available man sections. Every section has a unique number and
contains only a specific type of man pages.

  • 1 – Executable programs or
    commands
  • 2 – System calls ( functions
    provided by the kernel )
  • 3 – Library calls ( functions
    provided by the library )
  • 4 – Special files
  • 5 – File formats and conventions
    ( configuration files )
  • 6 – Games
  • 7 – Miscellaneous
  • 8 – System administration commands

Syntax:

$ man <topicname>

View the Man Page of a command

To read the man page of an Linux command, pass the command name as
the argument to the man. The following will display the man page for
passwd command.

$ man passwd
PASSWD(1) User utilities  PASSWD(1)
NAME
    passwd – change user password

Some topics may even have man pages in more than one section. In such
a case, man command will display the page which has lower section
number.

In this example, the passwd command has manual pages in multiple
sections. But, by default, it displays the man page from the section
1.

The
“PASSWD(1)” shown in the 1st line of the man command output
indicates that it is displaying the man page from section 1. The man
page output displays the command name, syntax of the commands,
description of what the command does, options provided by the
command, etc…

View Man Page from a Specific Section

To read the man page from a particular section, provide the
section number as follows. The passwd command has man page in both
section 1 and section 5. By default, if you don’t specify the
section number, it will display man page from section 1.

To display man page from section 5, specify the section number as
shown below.

$ man 5 passwd

Now it will display the manual page for /etc/passwd configuration
file, since the section number 5 is for File Formats and Conversions.

List Available Man Sections for a Command

You can also list all the available sections on a particular topic
using -aw option.

$ man -aw printf
/usr/share/man/man1/printf.1.gz

View All Man Pages for a Command – Display All Sections

To view all the man pages for a particular topic, use the “-a”
option. You’ll see the lowest-number man page first. When you exit
that page, and press “Enter” the next man page will appear.

$ man -a printf

Change the Default Pager used by Man Command

By default man command will use the $PAGER environment variable to
identify which pager to use for showing output. User can change the
pager in which they prefer to see the man page using ‘-P’ option.

The following command will display the man page using more command
pager.

$ man -P more printf

Search Man Page against NAME Section

To search the man page against NAME section, use “-f” option
as shown below.

$ man -f printf

printf (3) – formatted output conversion

This is equivalent to using whatis
shell command
.

The above command, searches the manual page names, and displays
the description for the given topic if the manual page names, matches
with the given topic. You can also pass multiple topics in the same
command line.

Search Man Page against NAME and DESCRIPTION Section

To search the man page against NAME & DESCRIPTION section, use
“-k” option. It is equivalent to using “apropos” shell
command.

$ man -k printf

printf               (1)  – format and print data
printf [builtins]    (1)  – bash built-in commands, see bash(1)
printftest           (6)  – tests the vgagl gl_printf function
set_matchpathcon_printf [set_matchpathcon_flags] (3)  – set flags controlling the operation of matchpathcon or matchpathcon_index and configure the behaviour of validity checking and error displaying

The above command will search for the keyword “printf” as regular
expression and display the man pages that match the keyword.

Author: Paul Anthony McGowan

Web Technology & Linux Enthusiast, Javascript Afficiado, General Observer Of World Corruption. Builder Of A Variety Of Web Properties And Campaigner Against Serious Government Criminality. Founder of Vorteasy

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