Help command :

On Unix-like operating system shells, the help command displays information about builtin commands.

Help displays brief summaries of shell built-in commands. If PATTERN is specified, gives detailed help on all commands matching PATTERN, otherwise the list of help topics is printed.

Syntax

help [-dms] [PATTERN …]

Options

• d – Output short description for each topic.

Example : $help -d help
help - Display information about builtin commands.

• m – Display usage in pseudo-manpage format.

// using help with -m

$help -m help
NAME
    help - Display information about builtin commands.
SYNOPSIS
    help [-dms] [pattern ...]
DESCRIPTION
    Display information about built-in commands.

• s – Output only a short usage synopsis for each topic matching.
  

// using help with -s 

$help -s help
help: help [-dms] [pattern ...]