Command line help and documentation

This lesson will cover how to use built-in help commands and command documentation. You will discover how to qucikly access help pages to learn about a command, or refresh your knowledge of how to use it.

Built-in Help Systems

The help command

The help command is used to list all availble commands, or find out about a specific command:

# Show all available commands
help

# Get help for a specific command
help command_name

Output:

C:\Users\name>help
For more information on a specific command, type HELP command-name
ASSOC          Displays or modifies file extension associations.
ATTRIB         Displays or changes file attributes.
BREAK          Sets or clears extended CTRL+C checking.
BCDEDIT        Sets properties in boot database to control boot loading.
CACLS          Displays or modifies access control lists (ACLs) of files.
CALL           Calls one batch program from another.
CD             Displays the name of or changes the current directory.
...

The man command (command manual)

# View manual page for a command
man command_name

# Search manual pages
man -k search_term

Here is the shortened result of man mkdir:

MKDIR(1)                    General Commands Manual                    MKDIR(1)

NAME
     mkdir – make directories

SYNOPSIS
     mkdir [-pv] [-m mode] directory_name ...

DESCRIPTION
     The mkdir utility creates the directories named as operands, in the order
     specified, using mode “rwxrwxrwx” (0777) as modified by the current
     umask(2).

     The options are as follows:

     -m mode        Set the file permission bits of the final created directory
                    to the specified mode.  The mode argument can be in any of
                    the formats specified to the chmod(1) command.  If a
                    symbolic mode is specified, the operation characters ‘+’
                    and ‘-’ are interpreted relative to an initial mode of
                    “a=rwx”.

     -p             Create intermediate directories as required.  If this
                    option is not specified, the full path prefix of each
                    operand must already exist.
                    ...

💡 Tip: Use the q key to exit the manual.

Understanding the command manual

Manual sections

As you will see in the above example, the man command is broken down into sections such as:

1. NAME: Command name and brief example.
2. SYNOPSIS: The syntax and options.
3. DESCRIPTION: Detailed description.
4. OPTIONS: Available command options.
5. EXIT STATUS: Exit status values returned..
6. EXAMPLES: How to use.
7. SEE ALSO: Related commands.
8. HISTORY: Command history and versions.

Navigating the manual

• Space: Next page.
• b: Previous page
• e: Scroll down by one line.
• y: Scroll down by one line.
• z: Forward by one window.
• w: Backward by one window.
• /: Search (/term_to_search)
• q: Quit/exit.

While viewing the manual, you can also use h to list a full range of keyboard commands:

Commands marked with * may be preceded by a number, N.
      Notes in parentheses indicate the behavior if N is given.
      A key preceded by a caret indicates the Ctrl key; thus ^K is ctrl-K.

  h  H                 Display this help.
  q  :q  Q  :Q  ZZ     Exit.
 ---------------------------------------------------------------------------

                           MOVING

  e  ^E  j  ^N  CR  *  Forward  one line   (or N lines).
  y  ^Y  k  ^K  ^P  *  Backward one line   (or N lines).
  f  ^F  ^V  SPACE  *  Forward  one window (or N lines).
  b  ^B  ESC-v      *  Backward one window (or N lines).
  z                 *  Forward  one window (and set window to N).
  w                 *  Backward one window (and set window to N).
  ESC-SPACE         *  Forward  one window, but don't stop at end-of-file.
  d  ^D             *  Forward  one half-window (and set half-window to N).
  u  ^U             *  Backward one half-window (and set half-window to N).
  ESC-)  RightArrow *  Right one half screen width (or N positions).
  ESC-(  LeftArrow  *  Left  one half screen width (or N positions).
  ESC-}  ^RightArrow   Right to last column displayed.
  ESC-{  ^LeftArrow    Left  to first column.
  F                    Forward forever; like "tail -f".
  ESC-F                Like F but stop when search pattern is found.
HELP -- Press RETURN for more, or q when done

Extending command syntax

Various commands can be extended using options/arguments:

command [options] [arguments]

For example, the ls command is used to list files in a directory. This can be modified to show more/less detail:

# List all files
ls -a

# List all files with details
ls -l

# Combine options
ls -la

Finding commands

The which command is used to locate the executable file to be run for a command:

The which Command

# Find command location
which command_name

This will return a path such as /bin/mkdir.

The type Command

This is used to discover how commands will be interpereted by the shell. Fibd out if a command is an alias, shell built-in, file, keyword, or function:

# Show command type
type command_name

# Option to list the type and executable path if available
type -a command_name

Here are some examples (terminal output may differ):