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Guide to Unix/Commands/Getting Help

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Wikibooks Guide to Unix Computing

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General: Introduction | Explanations | Why Unix-like
Platforms: Linux | BSD
Quick Reference: Commands | Environment Variables | Files | License

man

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Displays the manual page for the specified command

A useful option is: 

$ man -k TEXT

This searches manual page titles and synopsis lines for TEXT

Examples:

To display the manual page for the chown command: 

$ man chown

man has different sections.

  • section 1 is user commands
  • section 2 is system calls (used by programs to communicate with the kernel)
  • section 3 is library reference (for programming in C)
  • section 4 is device drivers
  • section 5 is configuration files and other file formats
  • section 6 is games
  • section 7 is miscellaneous (for example, "ascii" map and C "operator" precedence)
  • section 8 is system commands (like user commands, but mostly for root)

A section number can be specified before the page name. For example, man chmod normally shows the user command "chmod". To see the system call "chmod": 

$ man 2 chmod

To search the man pages for "newsgroups", 

$ man -k newsgroups
actsync              (8)  - synchronize newsgroupsoups
newsgroups           (1)  - a program to list unsubscribed newsgroups
  • If this does not work you may have to run the makewhatis command.

Links:

info

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An advanced man command that is sometimes available. It displays the improved manual pages in Info format for specified command. Seems absent from POSIX.

Examples:

To display the manual page for the grep command: 

$ info grep

To find occurrence of 'grep' in all info manual pages: 

$ info --apropos grep
"(autoconf-2.13)Examining Declarations" -- EGREP_CPP
"(autoconf-2.13)Examining Declarations" -- EGREP_HEADER
"(autoconf-2.13)Old Macro Names" -- HEADER_EGREP
...

To see the physical location of 'grep' info manual page: 

$ info -w grep
/usr/share/info/grep.info.gz

To view a file a info page: 

$ info -f ./some_cmd.info.gz

Links:

apropos

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Searches the manual page short descriptions for a specified keyword. Seems absent from POSIX.

On many systems this is exactly the same as the -k option of the man command.

Examples: 

$ apropos newsgroups
active               (5)  - list of active Usenet newsgroups
newsgroups           (1)  - a program to list unsubscribed newsgroups

Links:

whatis

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Displays short man page descriptions. Seems absent from POSIX.

Examples: 

$ whatis info
info (1)             - read Info documents
info (5)             - readable online documentation

$ whatis chmod
chmod (1) - change file modes
chmod, fchmod (2) - change mode of file

Links:

makewhatis

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Creates the database for the whatis, apropos, and man -k commands. This is commonly run automatically by your system however sometimes you need to run this manually. Seems absent from POSIX.

Examples: 

# makewhatis

$ sudo makewhatis

Links:

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