Sujith's Library

Bash - 03 - help pages

Linux provides several forms of support, with the most commonly used being the man (manual) pages.

--help : Pass this option to any command to see the available options.

cd --help
ls --help
mkdir --help

help : Provides help for built-in shell commands.

help cd
help echo  
# Works for built-in commands only

For commands with both long (--option) and short (-o) versions, use the short version in the terminal and the long version in scripts for clarity.

man Pages

man is the manual for a command (if it exists). It expects the name of the command as its argument and displays the corresponding man page.

man ls
man mkdir

In the manual:

  • Space or B to scroll down.
  • N to navigate between search hits.
  • Shift + N to navigate backwards.

Note: man cd doesn’t exist because cd is a built-in shell function. Use --help instead.

The man page is displayed within the vi editor (view/search mode only).

A man page typically contains sections like:

  • Name
  • Synopsis
  • Description
  • Options
  • Configuration Files
  • Exit Codes
  • Files
  • Other man pages to consult

Other Command Line Help

whatis

whatis : Provides a brief description of a command.

sujith@sujith-Latitude-7490:~$ whatis ls pwd rm rmdir mkdir touch echo
ls (1)               - list directory contents
pwd (1)              - print name of current/working directory
rm (1)               - remove files or directories
rmdir (1)            - remove empty directories
rmdir (2)            - delete a directory
mkdir (1)            - make directories
mkdir (2)            - create a directory
touch (1)            - change file timestamps
echo (1)             - display a line of text

whatis also supports the -w option for wildcards.

sujith@sujith-Latitude-7490:~$ whatis -w mkd*
mkdir (1)            - make directories
mkdir (2)            - create a directory
mkdirat (2)          - create a directory
mkdosfs (8)          - create an MS-DOS FAT filesystem
mkdtemp (3)          - create a unique temporary directory

Searching in /usr/bin To see all available commands which are present in contents of /usr/bin.

Using apropos

apropos allows finding commands using a description.
It takes a string and searches for commands that has description that match the string provided as an argument.

apropos delete
apropos delete directory

Using " " can help narrow down the search to specific phrases:

apropos "remove directory"

Using regular expressions (e.g., .*) to match anything between words:

apropos "remove .* directory"
apropos "delete .* directory"
sujith@sujith-Latitude-7490:~$ apropos "virtual memory"
mremap (2)           - remap a virtual memory address
proc_sys_vm (5)      - virtual memory subsystem
proc_vmstat (5)      - virtual memory statistics
tmpfs (5)            - a virtual memory filesystem
vmstat (8)           - Report virtual memory statistics
rmdir (2)            - delete a directory
sujith@sujith-Latitude-7490:~$ apropos "user account"
userdel (8)          - delete a user account and related files
usermod (8)          - modify a user account
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Bash - 04 - Variables and Aliases