Dating back to the 1960s, a Command Line Interface is a computer language interpreter with which users are able to communicate with computer systems via a statement or command.
Though less widely used nowadays, it is still a useful tool for many software developers due to the efficient nature.
A shell is a user interface that used to access the services of an operating system. These shells can either be text-based in the form of a CLI or graphically with a graphical user interface (GUI).
Examples of such command-lines interfaces are:
- Bash and GitBash
- Powershell
- Interactive Ruby Shell
However, there are differences between the different shells and their available commands.
The basic structure of a Cli is:
- Prompt: the program provides this to help give the user context
- Command: the user provides a command for the interface
- Parameter(s): one or more optional parameters are provided from the user depending on the command given
Whitespace acts as a delimiter.
Newline acts as the end-of-line delimiter
One of a beginner CLI users most helpful commands. It can allow the user to see the list of available commands, subcommands and options.
The syntax of a command commonly follows:
| Syntax | Symbol |
|---|---|
| As written items are without braces or brackets | Type as shown |
| Required parameters are enclosed in angle brackets | <Placeholder> |
| Optional parameters are enclosed in square brackets | [Placeholder] |
| Sets of required parameters are enclosed in square brackets | {Placeholder} |
| Mutually exclusive options are differenciated via a vertical bar | ` |
| Optionally repeated items are shown using ellipses | ... |
For example:
$ git help -a
usage: git [--version] [--help] [-C <path>] [-c <name>=<value>]
[--exec-path[=<path>]] [--html-path] [--man-path] [--info-path]
[-p | --paginate | -P | --no-pager] [--no-replace-objects] [--bare]
[--git-dir=<path>] [--work-tree=<path>] [--namespace=<name>]
<command> [<args>]
The hypen indicates the beginning of a new option. Conventionally two hyphens are used followed by a word, for example:
--help, however some languages allow the abbreviation by using a single hyphen follwed by a character
-h and even combination of commands when more than one character follows, while other languages may not allow this.
$ rm -rf [FILE]
In Bash can be the same command to remove the file(s) as:
$ rm -r -f [FILE]
$ rm -R -f [FILE]
$ rm --recursive --force
A comprehensive list of Microsoft commands with explanations, abbreviations, options and examples of their useage can be found here.
Code Academy's breakdown of some basic cli commands
Learn about basic Shell