View source for Command-line interface

{{Short description|Computer interface that uses text}}
[[File:Linux command-line. Bash. GNOME Terminal. screenshot.png|thumb|300px|Screenshot of a sample Bash session in GNOME Terminal 3, Fedora 15 ]]
[[File:Windows PowerShell 1.0 PD.png|thumb|300px|Screenshot of [[PowerShell|Windows PowerShell]] 1.0, running on Windows Vista ]]

A '''command-line interface''' ('''CLI''') is a means of interacting with a [[Computer program|computer program]] by inputting lines of text called [[Command (computing)|command-lines]]. Command-line interfaces emerged in the mid-1960s, on [[Computer terminal|computer terminal]]s, as a user-friendly alternative to punched cards. 

Today, most computer users rely on [[Graphical user interface|graphical user interface]]s ("GUIs") instead of CLIs. However, many programs and [[Operating system|operating system]] utilities lack GUIs, and are intended to be used through CLIs. 

Knowledge of CLIs is also useful for writing scripts. Programs that have CLIs are generally easy to automate via scripting, since command-lines, being mere lines of text, are easy to specify in code.

CLIs are made possible by '''command-line interpreters''' or '''command-line processors''', which are programs that read command-lines and carry out the commands.

Alternatives to CLIs include GUIs (most notably [[Desktop metaphor|desktop metaphors]] with a mouse pointer, such as [[Software:Microsoft Windows|Microsoft Windows]]), [[Text-based user interface|text-based user interface]] [[Menu (computing)|menus]] (such as [[Software:DOS Shell|DOS Shell]] and IBM AIX SMIT), and [[Keyboard shortcut|keyboard shortcuts]].

== Comparison to graphical user interfaces ==
[[File:Gem_11_Desktop.png|thumb|250px|A graphical user interface with icons and windows ([[Software:GEM (desktop environment)|GEM 1.1 Desktop]])]]
Compared with a graphical user interface, a command-line interface requires fewer system resources to implement. Since options to commands are given in a few characters in each command line, an experienced user often finds the options easier to access. Automation of repetitive tasks is simplified by line editing and history mechanisms for storing frequently used sequences; this may extend to a [[Scripting language|scripting language]] that can take parameters and variable options. A command-line history can be kept, allowing review or repetition of commands. 
 
A command-line system may require paper or online manuals for the user's reference, although often a "help" option provides a concise review of the options of a command. The command-line environment may not provide graphical enhancements such as different [[Computer font|fonts]] or extended [[Window (computing)|edit windows]] found in a GUI. It may be difficult for a new user to become familiar with all the commands and options available, compared with the [[Icon (computing)|icons]] and drop-down menus of a graphical user interface, without reference to manuals.

==Types==
===Operating system command-line interfaces===
[[File:Apple Unix with Netscape.png|thumb|250px|Apple Computer's CommandShell in A/UX 3.0.1]]
Operating system (OS) command-line interfaces are usually distinct programs supplied with the operating system. A program that implements such a text interface is often called a command-line interpreter, command processor or [[Software:Shell (computing)|shell]].

Examples of command-line interpreters include [[Company:Digital Equipment Corporation|DEC's]] [[DIGITAL Command Language]] (DCL) in [[Software:OpenVMS|OpenVMS]] and [[Software:RSX-11|RSX-11]], the various [[Unix shell]]s ([[Software:Bourne shell|sh]], [[Software:KornShell|ksh]], [[Software:C shell|csh]], [[Software:Tcsh|tcsh]], [[Software:Z shell|zsh]], [[Software:Bash (Unix shell)|Bash]], etc.), CP/M's CCP, [[Engineering:DOS|DOS]]' [[Software:COMMAND.COM|COMMAND.COM]], as well as the OS/2 and the Windows CMD.EXE programs, the latter groups being based heavily on DEC's RSX-11 and RSTS CLIs. Under most operating systems, it is possible to replace the default shell program with alternatives; examples include [[Software:4DOS|4DOS]] for DOS, [[Software:4OS2|4OS2]] for OS/2, and [[Software:Take Command Console|4NT / Take Command]] for Windows.

Although the term 'shell' is often used to describe a command-line interpreter, strictly speaking, a 'shell' can be any program that constitutes the user-interface, including fully graphically oriented ones. For example, the default Windows GUI is a shell program named EXPLORER.EXE, as defined in the SHELL=EXPLORER.EXE line in the WIN.INI configuration file. These programs are shells, but not CLIs.

===Application command-line interfaces===
[[File:GNUOctave430.png|thumb|250px|[[Software:GNU Octave|GNU Octave]]'s GUI with command-line interface]]
Application programs (as opposed to operating systems) may also have command-line interfaces.

An application program may support none, any, or all of these three major types of command-line interface mechanisms:

* ''Parameters'': Most command-line interfaces support a means to pass additional information to a program when it is launched. 
* ''Interactive command-line sessions'': After launch, a program may provide an operator with an independent means to enter commands.
* ''Inter-process communication'': Most operating systems support means of [[Inter-process communication|inter-process communication]] (for example, [[Standard streams|standard streams]] or [[Named pipe|named pipe]]s). Command lines from client processes may be redirected to a CLI program by one of these methods.

Some applications support a CLI, presenting their own prompt to the user and accepting command lines. Other programs support both a CLI and a GUI. In some cases, a GUI is simply a [[Wrapper function|wrapper]] around a separate CLI executable file. In other cases, a program may provide a CLI as an optional alternative to its GUI. CLIs and GUIs often support different functionality. For example, all features of [[Software:MATLAB|MATLAB]], a [[Numerical analysis|numerical analysis]] computer program, are available via the CLI, whereas the MATLAB GUI exposes only a subset of features.

In [[Software:Colossal Cave Adventure|Colossal Cave Adventure]] from 1975, the user uses a CLI to enter one or two words to explore a cave system.

==History==
The command-line interface evolved from a form of communication conducted by people over [[Engineering:Teleprinter|teleprinter]] (TTY) machines. Sometimes these involved sending an order or a confirmation using [[Engineering:Telex|telex]]. Early computer systems often used teleprinter as the means of interaction with an operator. 

The mechanical teleprinter was replaced by a "glass tty", a keyboard and screen emulating the teleprinter. [[Computer terminal#.22Intelligent.22 terminals|"Smart" terminal]]s permitted additional functions, such as cursor movement over the entire screen, or local editing of data on the terminal for transmission to the computer. As the [[Engineering:Microcomputer revolution|microcomputer revolution]] replaced the traditional{{snd}}minicomputer + terminals{{snd}}time sharing architecture, hardware terminals were replaced by [[Terminal emulator|terminal emulator]]s&nbsp;— PC software that interpreted terminal signals sent through the PC's [[Serial port|serial port]]s. These were typically used to interface an organization's new PC's with their existing mini- or mainframe computers, or to connect PC to PC. Some of these PCs were running Bulletin Board System software.

Early operating system CLIs were implemented as part of [[Software:Resident monitor|resident monitor]] programs, and could not easily be replaced. The first implementation of the shell as a replaceable component was part of the [[Software:Multics|Multics]] [[Time-sharing|time-sharing]] [[Operating system|operating system]].<ref name="Unix_Shells"/> In 1964, MIT Computation Center staff member Louis Pouzin developed the [[Software:RUNCOM|RUNCOM]] tool for executing command scripts while allowing argument substitution.<ref name="multicians"/> Pouzin coined the term "[[Software:Shell (computing)|shell]]" to describe the technique of using commands like a programming language, and wrote a paper about how to implement the idea in the [[Software:Multics|Multics]] operating system.<ref name="Metz_2013"/> Pouzin returned to his native France in 1965, and the first Multics shell was developed by Glenda Schroeder.<ref name="multicians"/>

[[File:Version 7 UNIX SIMH PDP11 Kernels Shell.png|thumb|250px|Bourne shell interaction on Version 7 Unix]]
The first [[Unix shell]], the [[Software:Thompson shell|V6 shell]], was developed by [[Biography:Ken Thompson|Ken Thompson]] in 1971 at [[Organization:Bell Labs|Bell Labs]] and was modeled after Schroeder's Multics shell.<ref name="Mazieres_2004"/><ref name="ibm"/> The [[Software:Bourne shell|Bourne shell]] was introduced in 1977 as a replacement for the V6 shell. Although it is used as an interactive command interpreter, it was also intended as a scripting language and contains most of the features that are commonly considered to produce structured programs. The Bourne shell led to the development of the [[Software:KornShell|KornShell]] (ksh), [[Software:Almquist shell|Almquist shell]] (ash), and the popular Bourne-again shell (or Bash).<ref name="ibm"/>

Early microcomputers themselves were based on a command-line interface such as CP/M, [[Engineering:DOS|DOS]] or AppleSoft BASIC. During the 1980s and 1990s, the introduction of the [[Software:Apple Macintosh|Apple Macintosh]] and of [[Software:Microsoft Windows|Microsoft Windows]] on PCs saw the command line interface as the primary user interface replaced by the Graphical User Interface. The command line remained available as an alternative user interface, often used by [[System administrator|system administrator]]s and other advanced users for system administration, [[Computer programming|computer programming]] and [[Software:Batch processing|batch processing]].

In November 2006, [[Company:Microsoft|Microsoft]] released version 1.0 of Windows PowerShell (formerly codenamed ''Monad''), which combined features of traditional Unix shells with their proprietary object-oriented .NET Framework. [[Software:MinGW|MinGW]] and [[Software:Cygwin|Cygwin]] are [[Open-source software|open-source]] packages for Windows that offer a Unix-like CLI. Microsoft provides MKS Inc.'s [[Software:KornShell|ksh]] implementation ''MKS Korn shell'' for Windows through their [[Software:Windows Services for UNIX|Services for UNIX]] add-on.

Since 2001, the [[Engineering:Macintosh|Macintosh]] operating system [[Software:MacOS|macOS]] has been based on a [[Unix-like]] operating system called [[Software:Darwin (operating system)|Darwin]]. On these computers, users can access a Unix-like command-line interface by running the [[Terminal emulator|terminal emulator]] program called [[Software:Terminal (macOS)|Terminal]], which is found in the Utilities sub-folder of the Applications folder, or by remotely logging into the machine using ssh. [[Software:Z shell|Z shell]] is the default shell for macOS; Bash, [[Software:Tcsh|tcsh]], and the [[Software:KornShell|KornShell]] are also provided. Before [[Software:MacOS Catalina|macOS Catalina]], Bash was the default.

==Usage==
A CLI is used whenever a large vocabulary of commands or queries, coupled with a wide (or arbitrary) range of options, can be entered more rapidly as text than with a pure GUI. This is typically the case with operating system shell<!-- please, see [[talk:Shell (computing) before changing the link back -->|operating system command shell]]s. CLIs are also used by systems with insufficient resources to support a graphical user interface. Some computer language systems (such as [[Python (programming language)|Python]], [[Forth (programming language)|Forth]], LISP, [[Rexx]], and many dialects of [[BASIC]]) provide an interactive command-line mode to allow for rapid evaluation of code.

CLIs are often used by programmers and system administrators, in engineering and scientific environments, and by technically advanced personal computer users. CLIs are also popular among people with visual disabilities since the commands and responses can be displayed using refreshable Braille displays.

==Anatomy of a shell CLI==

The general pattern of a command line interface<ref name="Bash"/><ref name="Microsoft_Windows"/> is:

 Prompt command param1 param2 param3 … paramN

* Prompt — generated by the program to provide context for the user.
* Command&nbsp;— provided by the user. Commands are usually one of three classes:
*# ''Internal'' commands are recognized and processed by the command line interpreter.
*# ''Included'' commands run separate executables.
*# ''External'' commands run executable files that may be included by other parties.{{clarify|date=February 2023}}
* param1 …paramN&nbsp;— parameters provided by the user. The format and meaning of the parameters depends upon the command. In the case of Included or External commands, the values of the parameters are delivered to the program as it is launched by the OS. Parameters may be either Arguments or Options.

In this format, the delimiters between command-line elements are [[Whitespace character|whitespace character]]s and the end-of-line delimiter is the newline delimiter. This is a widely used (but not universal) convention.

<!-- Above is more 'anatomy' and below is a bit more theory and background and higher-level concepts. Maybe separate sections for both? -->
A CLI can generally be considered as consisting of [[Syntax (programming languages)|syntax]] and [[Philosophy:Semantics|semantics]]. The ''syntax'' is the grammar that all commands must follow. In the case of [[Operating system|operating system]]s, [[Engineering:DOS|DOS]] and [[Software:Unix|Unix]] each define their own set of rules that all commands must follow. In the case of embedded systems, each vendor, such as [[Company:Nortel|Nortel]], [[Company:Juniper Networks|Juniper Networks]] or [[Company:Cisco Systems|Cisco Systems]], defines their own proprietary set of rules. These rules also dictate how a user navigates through the system of commands. The ''semantics'' define what sort of operations are possible, on what sort of data these operations can be performed, and how the grammar represents these operations and data—the symbolic meaning in the syntax.

Two different CLIs may agree on either syntax or semantics, but it is only when they agree on both that they can be considered sufficiently similar to allow users to use both CLIs without needing to learn anything, as well as to enable re-use of scripts.

A simple CLI will display a prompt, accept a "command line" typed by the user terminated by the Enter key, then execute the specified command and provide textual display of results or error messages. Advanced CLIs will validate, interpret and parameter-expand the command line before executing the specified command, and optionally capture or redirect its output.

Unlike a button or menu item in a GUI, a command line is typically self-documenting, stating exactly what the user wants done. In addition, command lines usually include many [[Default (computer science)|default]]s that can be changed to customize the results. Useful command lines can be saved by assigning a character string or [[Software:Alias (command)|alias]] to represent the full command, or several commands can be grouped to perform a more complex sequence&nbsp;– for instance, compile the program, install it, and run it&nbsp;— creating a single entity, called a command procedure or script which itself can be treated as a command. These advantages mean that a user must figure out a complex command or series of commands only once, because they can be saved, to be used again.

The commands given to a CLI shell are often in one of the following forms:

* {{kbd|doSomething how toFiles}}
* {{kbd|doSomething how sourceFile destinationFile}}
* {{kbd|doSomething how < inputFile > outputFile}}
* {{kbd|doSomething how {{!}} doSomething how {{!}} doSomething how > outputFile}}

where ''doSomething'' is, in effect, a verb, ''how'' an adverb (for example, should the command be executed "verbosely" or "quietly") and ''toFiles'' an object or objects (typically one or more files) on which the command should act. The <code>&gt;</code> in the third example is a redirection operator, telling the command-line interpreter to send the output of the command not to its own standard output (the screen) but to the named file. This will overwrite the file. Using <code>&gt;&gt;</code> will redirect the output and append it to the file. Another redirection operator is the [[Vertical bar|vertical bar]] (<code>|</code>), which creates a [[Pipeline (Unix)|pipeline]] where the output of one command becomes the input to the next command.

===CLI and resource protection===
One can modify the set of available commands by modifying which paths appear in the [[PATH (variable)|PATH]] environment variable. Under Unix, commands also need be marked as [[Executable|executable]] files. The directories in the path variable are searched in the order they are given. By re-ordering the path, one can run e.g. \OS2\MDOS\E.EXE instead of \OS2\E.EXE, when the default is the opposite. Renaming of the executables also works: people often rename their favourite editor to EDIT, for example.

The command line allows one to restrict available commands, such as access to advanced internal commands. The Windows CMD.EXE does this. Often, shareware programs will limit the range of commands, including printing a command 'your administrator has disabled running batch files' from the prompt.{{Clarify|reason=The sentence seems ambigious and confuses me. Does "including printing a command 'your administrator has disabled running batch files' from the prompt" describe an act of limiting the range of commands, or does it rather describe a command that a user may (try to) give which is then limited?|date=July 2021}}

Some CLIs, such as those in network routers, have a hierarchy of [[Mode (user interface)|mode]]s, with a different set of commands supported in each mode. The set of commands are grouped by association with security, system, interface, etc. In these systems the user might traverse through a series of sub-modes. For example, if the CLI had two modes called ''interface'' and ''system'', the user might use the command ''interface'' to enter the interface mode. At this point, commands from the system mode may not be accessible until the user exits the interface mode and enters the system mode.

===Command prompt===
[[File:Hard reset BBC Micro 32K Acorn DFS.gif|thumb|Prompt of a BBC Micro after switch-on or hard reset]]
<!-- This section is linked from [[Software:Z shell|Z shell]], Prompt and Abort, Retry, Fail -->
A command prompt (or just ''prompt'') is a sequence of (one or more) characters used in a command-line interface to indicate readiness to accept commands. It literally prompts the user to take action. A prompt usually ends with one of the characters <code>$</code>, <code>%</code>, <code>#</code>,<ref name="DR_1978_SID"/><ref name="DR_1982_SID86"/> <code>:</code>, <code>&gt;</code> or <code>-</code><!-- DOS DEBUG --><ref name="Paul_1997_NWDOSTIP"/> and often includes other information, such as the path of the current working directory and the [[Hostname|hostname]].

On many [[Software:Unix|Unix]] and [[Unix-like|derivative systems]], the prompt commonly ends in <code>$</code> or <code>%</code> if the user is a normal user, but in <code>#</code> if the user is a [[Superuser|superuser]] ("root" in Unix terminology).

End-users can often modify prompts. Depending on the environment, they may include colors, special characters, and other elements (like variables and functions for the current time, user, shell number or working directory) in order, for instance, to make the prompt more informative or visually pleasing, to distinguish sessions on various machines, or to indicate the current level of nesting of commands. On some systems, special tokens in the definition of the prompt can be used to cause external programs to be called by the command-line interpreter while displaying the prompt.

In DOS' COMMAND.COM and in Windows NT's [[Software:Cmd.exe|cmd.exe]] users can modify the prompt by issuing a <code>PROMPT</code> command or by directly changing the value of the corresponding <code>%PROMPT%</code> [[Environment variable|environment variable]]. The default of most modern systems, the <code>C:\></code> style is obtained, for instance, with <code>PROMPT $P$G</code>. The default of older DOS systems, <code>C></code> is obtained by just <code>PROMPT</code>, although on some systems this produces the newer <code>C:\></code> style, unless used on floppy drives A: or B:; on those systems <code>PROMPT $N$G</code> can be used to override the automatic default and explicitly switch to the older style.

Many Unix systems feature the <code>$PS1</code> variable (Prompt String 1),<ref name="Parker_2011"/> although other variables also may affect the prompt (depending on the [[Unix shell|shell]] used). In the Bash shell, a prompt of the form:

<source lang="bash">[time] user@host: work_dir $</source>
could be set by issuing the command
<source lang="bash">export PS1='[\t] \u@\H: \W $'</source>

In zsh the <code>$RPROMPT</code> variable controls an optional "prompt" on the right-hand side of the display. It is not a real prompt in that the location of text entry does not change. It is used to display information on the same line as the prompt, but right-justified.

In [[Software:RISC OS|RISC OS]] the command prompt is a <code>*</code> symbol, and thus (OS) CLI commands are often referred to as "star commands".<ref name="Acorn_1992"/> One can also access the same commands from other command lines (such as the [[BBC BASIC]] command line), by preceding the command with a <code>*</code>.

===Arguments===
{{uncited section|date=October 2023}}
[[File:COMMAND LINE.svg|thumb|right|An MS-DOS command line, illustrating parsing into command and arguments]]
A '''command-line argument''' or '''[[Parameter#Computing|parameter]]''' is an item of information provided to a program when it is started. A program can have many command-line arguments that identify sources or destinations of information, or that alter the operation of the program.

When a command processor is active a program is typically invoked by typing its name followed by command-line arguments (if any). For example, in [[Software:Unix|Unix]] and [[Unix-like]] environments, an example of a command-line argument is:

<source lang="bash">
rm file.s
</source>

"file.s" is a command-line argument which tells the program [[Software:Rm (Unix)|rm]] to remove the file "file.s".

Some programming languages, such as [[C (programming language)|C]], [[C++]] and [[Java (programming language)|Java]], allow a program to interpret the command-line arguments by handling them as string parameters in the main function. Other languages, such as [[Python (programming language)|Python]], expose operating system specific [[Application programming interface|API]] (functionality) through <code>sys</code> [[Modular programming|module]], and in particular <code>sys.argv</code> for "command-line arguments".

In Unix-like operating systems, a single hyphen used in place of a file name is a special value specifying that a program should handle data coming from the standard input or send data to the standard output.

====Command-line option====
<!-- This section is linked from several places inside or outside this article, preferable by "#SwitChar". Do not remove or rename this section heading without also updating the links. -->
A '''command-line option''' or simply '''option''' (also known as a '''flag''' or '''switch''') modifies the operation of a command; the effect is determined by the command's program. Options follow the command name on the command line, separated by spaces. A space before the first option is not always required, such as <code>Dir/?</code> and <code style="white-space:nowrap">DIR /?</code> in DOS, which have the same effect<ref name="Paul_1997_NWDOSTIP"/> of listing the DIR command's available options, whereas <code>dir --help</code> (in many versions of Unix) ''does'' require the option to be preceded by at least one space (and is case-sensitive).

The format of options varies widely between operating systems. In most cases the syntax is by convention rather than an operating system requirement; the entire command line is simply a string passed to a program, which can process it in any way the programmer wants, so long as the interpreter can tell where the command name ends and its arguments and options begin.

A few representative samples of command-line options, all relating to listing files in a directory, to illustrate some conventions:
{| class="wikitable"
|-
! Operating system !! Command !! Valid alternative !! Notes
|-
| [[Software:OpenVMS|OpenVMS]] || <code>directory/owner</code> || <code>Dir /Owner</code> || instruct the ''directory'' command to also display the ownership of the files.<br><small>''Note the Directory command name is not case sensitive, and can be abbreviated to as few letters as required to remain unique.''</small>
|-
| Windows || <code>DIR/Q/O:S d*</code> || <code>dir /q d* /o:s</code> || display ownership of files whose names begin with "D", sorted by size, smallest first.<br><small>''Note spaces around argument d* are required.''</small>
|-
| [[Unix-like]] systems || <code>ls -lS D*</code> || <code>ls -S -l D*</code> || display in long format files and directories beginning with "D" (but not "d"), sorted by size (largest first).<br><small>''Note spaces are required around all arguments and options, but some can be run together, e.g. '''-lS''' is the same as '''-l -S'''.''</small>
|-
| [[Software:Data General RDOS|Data General RDOS]] [[Software:Data General RDOS#RDOS CLI|CLI]]|| {{nowrap|<code>list/e/s 04-26-80/b</code>}} || {{nowrap|<code>List /S/E 4-26-80/B</code>}} || list every attribute for files created before 26 April 1980.<br><small>''Note the /B at the end of the date argument is a '''local switch''', that modifies the meaning of that argument, while /S and /E are '''global switches''', i.e. apply to the whole command.''</small>
|}

=====Abbreviating commands=====
In [[Software:Multics|Multics]], command-line options and subsystem keywords may be abbreviated. This idea appears to derive from the PL/I programming language, with its shortened keywords (e.g., STRG for STRINGRANGE and DCL for DECLARE). For example, in the Multics "forum" subsystem, the ''-long_subject'' parameter can be abbreviated ''-lgsj''. It is also common for Multics commands to be abbreviated, typically corresponding to the initial letters of the words that are strung together with underscores to form command names, such as the use of ''did'' for ''delete_iacl_dir''.

In some other systems abbreviations are automatic, such as permitting enough of the first characters of a command name to uniquely identify it (such as <code>SU</code> as an abbreviation for <code>SUPERUSER</code>) while others may have some specific abbreviations pre-programmed (e.g. <code>MD</code> for <code>MKDIR</code> in COMMAND.COM) or user-defined via batch scripts and aliases (e.g. <code>alias md mkdir</code> in [[Software:Tcsh|tcsh]]).

====={{anchor|SwitChar}}Option conventions in DOS, Windows, OS/2=====
On DOS, OS/2 and Windows, different programs called from their COMMAND.COM or CMD.EXE (or internal their commands) may use different syntax within the same operating system. For example:

* Options may be indicated by either of the "switch characters": <code>/</code>, <code>-</code>, or either may be allowed. See below.
* They may or may not be case-sensitive.
* Sometimes options and their arguments are run together, sometimes separated by whitespace, and sometimes by a character, typically <code>:</code> or <code>=</code>; thus <code>Prog -fFilename</code>, <code>Prog -f Filename</code>, <code>Prog -f:Filename</code>, <code>Prog -f=Filename</code>.
* Some programs allow single-character options to be combined;<ref name="Paul_1997_NWDOSTIP"/> others do not. The switch <code>-fA</code> may mean the same as <code>-f -A</code>,<ref name="Paul_1997_NWDOSTIP"/> or it may be incorrect, or it may even be a valid but different parameter.

In [[Engineering:DOS|DOS]], OS/2 and [[Software:Windows|Windows]], the forward slash (<code>/</code>) is most prevalent, although the hyphen-minus is also sometimes used. In many versions of DOS (MS-DOS/PC&nbsp;DOS 2.xx and higher, all versions of [[Software:DR-DOS|DR-DOS]] since 5.0, as well as [[Software:PTS-DOS|PTS-DOS]], [[Software:Embedded DOS|Embedded DOS]], [[Software:FreeDOS|FreeDOS]] and RxDOS) the '''switch character''' (sometimes abbreviated '''switchar''' or '''switchchar''') to be used is defined by a value returned from a [[System call|system call]] (INT&nbsp;21h/AX=3700h). The default character returned by this API is <code>/</code>, but can be changed to a hyphen-minus on the above-mentioned systems, except for under Datalight ROM-DOS and MS-DOS/PC&nbsp;DOS 5.0 and higher, which always return <code>/</code> from this call (unless one of many available [[Terminate-and-stay-resident program|TSRs]] to reenable the SwitChar feature is loaded). In some of these systems (MS-DOS/PC&nbsp;DOS 2.xx, DOS Plus 2.1, DR-DOS 7.02 and higher, PTS-DOS, Embedded DOS, FreeDOS and RxDOS), the setting can also be pre-configured by a SWITCHAR directive in CONFIG.SYS. General Software's Embedded DOS provides a SWITCH command for the same purpose, whereas [[Software:4DOS|4DOS]] allows the setting to be changed via <code>SETDOS /W:n</code>.<ref name="4DOS_8.00_HELP"/> Under DR-DOS, if the setting has been changed from <code>/</code>, the first directory separator <code>\</code> in the display of the [[Software:PROMPT (DOS command)|PROMPT]] parameter <code>$G</code> will change to a forward slash <code>/</code> (which is also a valid directory separator in DOS, FlexOS, 4680 OS, 4690 OS, OS/2 and Windows) thereby serving as a visual clue to indicate the change.<ref name="Paul_1997_NWDOSTIP"/> Also, the current setting is reflected also in the built-in help screens.<ref name="Paul_1997_NWDOSTIP"/> Some versions of DR-DOS [[Software:COMMAND.COM|COMMAND.COM]]<!-- 7.07 --> also support a PROMPT token <code>$/</code> to display the current setting. COMMAND.COM since DR-DOS 7.02 also provides a pseudo-environment variable named <code>%/%</code> to allow portable batchjobs to be written.<ref name="Caldera_1998_DELTREE101"/><ref name="Caldera_1998_NEW703"/> Several external DR-DOS commands<!-- f.e. SYS in DR-DOS 7.07 --> additionally support an [[Environment variable|environment variable]] <code>%SWITCHAR%</code> to override the system setting.

However, many programs are hardwired to use <code>/</code> only, rather than retrieving the switch setting before parsing command-line arguments. A very small number, mainly ports from Unix-like systems, are programmed to accept "-" even if the switch character is not set to it (for example <code>[[Software:Netstat|netstat]]</code> and <code>[[Software:Ping (networking utility)|ping]]</code>, supplied with [[Software:Microsoft Windows|Microsoft Windows]], will accept the /? option to list available options, and yet the list will specify the "-" convention).

=====Option conventions in Unix-like systems=====
In [[Unix-like]] systems, the ASCII hyphen-minus begins options; the new (and [[Software:GNU|GNU]]) convention is to use ''two'' hyphens then a word (e.g. <code>--create</code>) to identify the option's use while the old convention (and still available as an option for frequently-used options) is to use one hyphen then one letter (e.g., <code>-c</code>); if one hyphen is followed by two or more letters it may mean two options are being specified, or it may mean the second and subsequent letters are a parameter (such as filename or date) for the first option.<ref>{{Cite web|title=Argument Syntax (The GNU C Library)|url=https://www.gnu.org/software/libc/manual/html_node/Argument-Syntax.html|access-date=2021-07-09|website=gnu.org|archive-date=2021-06-18 |archive-url=https://web.archive.org/web/20210618184837/https://www.gnu.org/software/libc/manual/html_node/Argument-Syntax.html|url-status=live}}</ref>

Two hyphen-minus characters without following letters (<code>--</code>) may indicate that the remaining arguments should not be treated as options, which is useful for example if a file name itself begins with a hyphen, or if further arguments are meant for an inner command (e.g., [[Software:Sudo|sudo]]). Double hyphen-minuses are also sometimes used to prefix "long options" where more descriptive option names are used. This is a common feature of [[Software:GNU|GNU]] software. The ''[[Software:Getopt|getopt]]'' function and program, and the ''getopts'' command are usually used for parsing command-line options.

Unix command names, arguments and options are case-sensitive (except in a few examples, mainly where popular commands from other operating systems have been ported to Unix).

=====Option conventions in other systems=====
[[Software:FlexOS|FlexOS]], [[Finance:IBM 4680 OS|4680 OS]] and [[Finance:IBM 4690 OS|4690 OS]] use <code>-</code>.

CP/M typically used <code><nowiki>[</nowiki></code>.

[[Software:Conversational Monitor System|Conversational Monitor System]] (CMS) uses a single [[Bracket#Parentheses|left parenthesis]] to separate options at the end of the command from the other arguments. For example, in the following command the options indicate that the target file should be replaced if it exists, and the date and time of the source file should be retained on the copy:
<code>COPY source file a target file b (REPLACE OLDDATE)</code>

[[Company:Data General|Data General]]'s CLI under their [[Software:Data General RDOS|RDOS]], [[Software:Data General AOS|AOS]], etc. operating systems, as well as the version of CLI that came with their [[Business Basic]], uses only <code>/</code> as the switch character, is case-insensitive, and allows "local switches" on some arguments to control the way they are interpreted, such as {{nowrap|<code>MAC/U LIB/S A B C $LPT/L</code>}} has the global option "U" to the macro assembler command to append user symbols, but two local switches, one to specify LIB should be skipped on pass 2 and the other to direct listing to the printer, $LPT.

===Built-in usage help===
One of the criticisms of a CLI is the lack of cues to the user as to the available actions.{{citation needed|date=April 2015}} In contrast, GUIs usually inform the user of available actions with menus, icons, or other visual cues.{{citation needed|date=April 2015}} To overcome this limitation, many CLI programs display a usage message, typically when invoked with no arguments or one of <code>?</code>, <code>-?</code>, <code>-h</code>, <code>-H</code>, <code>/?</code>, <code>/h</code>, <code>/H</code>, <code>/Help</code>, <code>-help</code>, or <code>--help</code>.<ref name="Paul_1997_NWDOSTIP"/><ref name="Paul_2002_CPI"/><ref name="Paul_2002_DEBUG"/>

However, entering a program name without parameters in the hope that it will display usage help can be hazardous, as programs and scripts for which command line arguments are optional will execute without further notice.

Although desirable at least for the help parameter, programs may not support all option lead-in characters exemplified above.
Under DOS, where the default command-line option character can be changed from <code>/</code> to <code>-</code>, programs may query the SwitChar API in order to determine the current setting. So, if a program is not hardwired to support them all, a user may need to know the current setting even to be able to reliably request help.
If the SwitChar has been changed to <code>-</code> and therefore the <code>/</code> character is accepted as alternative path delimiter also at the DOS command line, programs may misinterpret options like <code>/h</code> or <code>/H</code> as paths rather than help parameters.<ref name="Paul_1997_NWDOSTIP"/> However, if given as first or only parameter, most DOS programs will, by convention<!-- at least in all versions of DR-DOS as well as under 4DOS and NDOS -->, accept it as request for help regardless of the current SwitChar setting.<ref name="Paul_1997_NWDOSTIP"/><ref name="4DOS_8.00_HELP"/>

In some cases, different levels of help can be selected for a program. Some programs supporting this allow to give a verbosity level as an optional argument to the help parameter (as in <code>/H:1</code>, <code>/H:2</code>, etc.) or they give just a short help on help parameters with question mark and a longer help screen for the other help options.<ref name="Paul_2006_FreeKEYB"/>

Depending on the program, additional or more specific help on accepted parameters is sometimes available by either providing the parameter in question as an argument to the help parameter or vice versa (as in <code>/H:W</code> or in <code>/W:?</code> (assuming <code>/W</code> would be another parameter supported by the program)).<ref name="CCI_1997_HELP"/><ref name="Paul_1997_DRDOSTIP"/><ref name="Paul_2002_DEBUG"/><ref name="Paul_2002_CPI"/><ref name="Paul_2006_FreeKEYB"/><ref group="nb" name="NB1"/>

In a similar fashion to the help parameter, but much less common, some programs provide additional information about themselves (like mode, status, version, author, license or contact information) when invoked with an "about" parameter like <code>-!</code>, <code>/!</code>, <code>-about</code>, or <code>--about</code>.<ref name="Paul_2002_CPI"/>

Since the <code>?</code> and <code>!</code> characters typically also serve other purposes at the command line, they may not be available in all scenarios, therefore, they should not be the only options to access the corresponding help information.

[[File:RT-11 help.jpg|thumb|The end of the {{mono|HELP}} command output from RT-11SJ displayed on a VT100]]
If more detailed help is necessary than provided by a program's built-in internal help, many systems support a dedicated external "<code>[[Software:Help (command)|help]] ''command''</code>" command (or similar), which accepts a command name as calling parameter and will invoke an external help system.

In the DR-DOS family, typing <code>/?</code> or <code>/H</code> at the [[Software:COMMAND.COM|COMMAND.COM]] prompt instead of a command itself will display a dynamically generated list of available internal commands;<ref name="Paul_1997_NWDOSTIP"/> [[Software:4DOS|4DOS]] and NDOS support the same feature by typing <code>?</code> at the prompt<ref name="4DOS_8.00_HELP"/> (which is also accepted by newer versions<!-- only 7.02 and higher --> of DR-DOS COMMAND.COM); internal commands can be individually disabled or reenabled via <code>SETDOS /I</code>.<ref name="4DOS_8.00_HELP"/> In addition to this, some newer versions of DR-DOS COMMAND.COM<!-- 7.07 --> also accept a <code>?%</code> command to display a list of available built-in pseudo-environment variables. Besides their purpose as quick help reference this can be used in batchjobs to query the facilities of the underlying command-line processor.<ref name="Paul_1997_NWDOSTIP"/>

===Command description syntax===
Built-in usage help and [[Man page|man page]]s commonly employ a small syntax to describe the valid command form:<ref name="OpenGroup_2008"/><ref name="Microsoft_2005_Shell"/><ref name="Microsoft_2010_Syntax"/><ref group="nb" name="NB2"/>

* angle brackets for ''required'' parameters: <code>ping <hostname></code>
* square brackets for ''optional'' parameters: <code>mkdir [-p] <dirname></code>
* ellipses for ''repeated'' items: <code>cp <source1> [source2…] <dest></code>
* vertical bars for ''choice'' of items: <code>netstat {-t|-u}</code>

Notice that these characters have different meanings than when used directly in the shell. Angle brackets may be omitted when confusing the parameter name with a literal string is not likely.

===The space character===
<!-- this is a file-system feature, nothing to do with the command line -->
In many areas of computing, but particularly in the command line, the space character can cause problems as it has two distinct and incompatible functions: as part of a command or parameter, or as a parameter or name [[Delimiter|separator]]. Ambiguity can be prevented either by prohibiting embedded spaces in file and directory names in the first place (for example, by substituting them with underscores <code>_</code>), or by enclosing a name with embedded spaces between quote characters or using an [[Escape character|escape character]] before the space, usually a backslash (<code>\</code>). For example
:<code>Long path/Long program name Parameter one Parameter two</code> …
is ambiguous (is "program name" part of the program name, or two parameters?); however
:<code>Long_path/Long_program_name Parameter_one Parameter_two</code> …,
:<code>LongPath/LongProgramName ParameterOne ParameterTwo</code> …,
:<code>"Long path/Long program name" "Parameter one" "Parameter two"</code> …
and
:<code>Long\ path/Long\ program\ name Parameter\ one Parameter\ two</code> …
are not ambiguous. [[Software:Unix|Unix]]-based operating systems minimize the use of embedded spaces to minimize the need for quotes. In [[Software:Microsoft Windows|Microsoft Windows]], one often has to use quotes because embedded spaces (such as in directory names) are common.

== Command-line interpreter ==
{{Quote|Although most users think of the shell as an interactive command interpreter, it is really a programming language in which each statement runs a command. Because it must satisfy both the interactive and programming aspects of command execution, it is a strange language, shaped as much by history as by design.|Brian W. Kernighan & Rob Pike<ref name="Kerninghan_1984"/>|style=}}

The term '''command-line interpreter''' ('''CLI''') is applied to [[Computer program|computer program]]s designed to [[Interpreter (computing)|interpret]] a sequence of lines of text which may be entered by a user, read from a [[Computer file|file]] or another kind of [[Data stream|data stream]]. The context of interpretation is usually one of a given [[Operating system|operating system]] or [[Programming language|programming language]].

Command-line interpreters allow users to issue various commands in a very efficient (and often terse) way. This requires the user to know the names of the commands and their parameters, and the syntax of the [[Programming language|language]] that is interpreted.

The Unix [[Shebang (Unix)|<code>#!</code>]] mechanism and OS/2 EXTPROC command facilitate the passing of batch files to external processors. One can use these mechanisms to write specific command processors for dedicated uses, and process external data files which reside in batch files.

Many graphical interfaces, such as the OS/2 [[Presentation Manager]] and early versions of Microsoft Windows use command-lines to call helper programs to open documents and programs. The commands are stored in the graphical shell{{clarify|date=May 2012}} or in files like the registry or the OS/2 <code>OS2USER.INI</code> file.

===Early history===
[[File:TTY33ASR.jpg|thumb|A Teletype Model 33 ASR teleprinter keyboard with punched tape reader and punch]]
[[File:Terminal-dec-vt52.jpg|thumb|[[Company:Digital Equipment Corporation|DEC]] VT52 terminal]]
The earliest computers did not support interactive input/output devices, often relying on sense switches and lights to communicate with the [[Computer operator|computer operator]]. This was adequate for [[Software:Batch processing|batch]] systems that ran one program at a time, often with the programmer acting as operator. This also had the advantage of low overhead, since lights and switches could be tested and set with one machine instruction. Later a single [[System console|system console]] was added to allow the operator to communicate with the system.

From the 1960s onwards, user interaction with computers was primarily by means of command-line interfaces, initially on machines like the [[Engineering:Teletype Model 33|Teletype Model 33]] ASR, but then on early [[Engineering:Cathode ray tube|CRT]]-based computer terminals such as the [[Engineering:VT52|VT52]].

All of these devices were purely text based, with no ability to display graphic or pictures.<ref group="nb" name="NB3"/> For business application programs, text-based [[Menu (computing)|menus]] were used, but for more general interaction the command line was the interface.

Around 1964 Louis Pouzin introduced the concept and the name ''shell'' in [[Software:Multics|Multics]], building on earlier, simpler facilities in the [[Software:Compatible Time-Sharing System|Compatible Time-Sharing System]] (CTSS).<ref name="Pouzin"/>{{better source needed|reason=introduced the concept (sic)|date=September 2013}}

From the early 1970s the [[Software:Unix|Unix]] operating system adapted the concept of a powerful command-line environment, and introduced the ability to ''[[Pipeline (Unix)|pipe]]'' the output of one command in as input to another. Unix also had the capability to save and re-run strings of commands as "shell scripts" which acted like custom commands.

The command-line was also the main interface for the early home computers such as the Commodore PET, Apple II and [[Engineering:BBC Micro|BBC Micro]]&nbsp;– almost always in the form of a [[BASIC]] interpreter. When more powerful business oriented microcomputers arrived with CP/M and later [[Engineering:DOS|DOS]] computers such as the IBM PC, the command-line began to borrow some of the syntax and features of the Unix shells such as globbing and [[Pipeline (Unix)|piping]] of output.

The command-line was first seriously challenged by the [[Company:PARC|PARC]] GUI approach used in the 1983 [[Engineering:Apple Lisa|Apple Lisa]] and the 1984 [[Software:Apple Macintosh|Apple Macintosh]]. A few computer users used GUIs such as [[Software:GEOS (16-bit operating system)|GEOS]] and [[Software:Windows 3.1|Windows 3.1]] but the majority of IBM PC users did not replace their [[Software:COMMAND.COM|COMMAND.COM]] shell with a GUI until [[Software:Windows 95|Windows 95]] was released in 1995.<ref name="Betanews"/><ref name="Microsoft_History"/>

===Modern usage as an operating system shell===
While most non-expert computer users now use a GUI almost exclusively, more advanced users have access to powerful command-line environments:

* The default VAX/VMS command shell, using the [[DIGITAL Command Language|DCL]] language, has been ported to Windows systems at least three times, including PC-DCL and Acceler8 DCL Lite. Unix command shells have been ported to VMS and DOS/Windows 95 and Windows NT types of operating systems.
* [[Software:COMMAND.COM|COMMAND.COM]] is the command-line interpreter of [[Software:MS-DOS|MS-DOS]], [[Software:IBM PC DOS|IBM PC DOS]], and clones such as [[Software:DR-DOS|DR-DOS]], [[Software:SISNE plus|SISNE plus]], [[Software:PTS-DOS|PTS-DOS]], [[ROM-DOS]], and [[Software:FreeDOS|FreeDOS]].
* Windows [[Software:Resource Kit|Resource Kit]] and [[Software:Windows Services for UNIX|Windows Services for UNIX]] include Korn and the Bourne shells along with a Perl interpreter (Services for UNIX contains ActiveState [[Software:ActivePerl|ActivePerl]] in later versions and [[Interix]] for versions 1 and 2 and a shell compiled by Microsoft)
* IBM OS/2 (and derivatives such as [[Software:EComStation|eComStation]] and [[Software:ArcaOS|ArcaOS]]) has the [[Software:Cmd.exe|cmd.exe]] processor. This copies the [[Software:COMMAND.COM|COMMAND.COM]] commands, with extensions to REXX.
* cmd.exe is part of the [[Software:Windows NT|Windows NT]] stream of operating systems.
* Yet another cmd.exe is a stripped-down shell for [[Software:Windows CE|Windows CE]] 3.0.
* An MS-DOS type interpreter called PocketDOS has been ported to Windows CE machines; the most recent release is almost identical to MS-DOS 6.22 and can also run Windows 1, 2, and 3.0, [[QBasic]] and other development tools, 4NT and 4DOS. The latest release includes several shells, namely MS-DOS 6.22, PC&nbsp;DOS 7, DR&nbsp;DOS 3.xx, and others.
* Windows users might use the [[Software:CScript|CScript]] interface to alternate programs, from command-line. [[PowerShell]] provides a command-line interface, but its applets are not written in [[Shell script]]. Implementations of the [[Unix shell]] are also available as part of the [[Software:Microsoft POSIX subsystem|POSIX sub-system]],<ref name="Microsoft_POSIX"/> [[Software:Cygwin|Cygwin]], [[MKS Toolkit]], [[UWIN]], [[Software:Hamilton C shell|Hamilton C shell]] and other software packages. Available shells for these interoperability tools include [[Software:C shell|csh]], [[Software:KornShell|ksh]], [[Software:Bourne shell|sh]], Bash, [[Software:Restricted shell|rsh]], tclsh and less commonly zsh, psh
* Implementations of [[Organization:PHP|PHP]] have a shell for interactive use called php-cli.
* Standard Tcl/Tk has two interactive shells, Tclsh and Wish, the latter being the GUI version.
* [[Python (programming language)|Python]], [[Ruby (programming language)|Ruby]], [[Lua (programming language)|Lua]],<!-- [[Julia (programming language)|Julia]], --> [[XLNT]], and other interpreters also have command shells for interactive use.
* [[Software:FreeBSD|FreeBSD]] uses [[Software:Tcsh|tcsh]] as its default interactive shell for the [[Superuser|superuser]], and [[Software:Almquist shell|ash]] as default scripting shell.
* Many [[Software:Linux distribution|Linux distribution]]s have the Bash implementation of the [[Unix shell]]. 
*Apple [[Software:MacOS|macOS]] and some Linux distributions use [[Software:Z shell|zsh]]. Previously, macOS used [[Software:Tcsh|tcsh]] and Bash.
* Embedded Linux (and other embedded [[Unix-like]]) devices often use the [[Software:Almquist shell|Ash]] implementation of the Unix shell, as part of Busybox.
* [[Software:Android (operating system)|Android]] uses the [[Software:KornShell|mksh]] shell,<ref name="Android_mksh"/><ref name="Android_adb"/> which replaces a shell derived from [[Software:Almquist shell|ash]]<ref name="Android_sh"/> that was used in older Android versions<!-- Not clear if switch was in Gengerbread, or before-->, supplemented with commands from the separate ''toolbox''<ref name="Android_Toolbox"/> binary.
* Routers with [[Software:Cisco IOS|Cisco IOS]],<ref name="Cisco_IOS"/> Junos<ref name="Juniper"/> and many others are commonly configured from the command line.
* The [[Software:Plan 9 from Bell Labs|Plan 9]] operating system uses the rc shell which is similar in design to the [[Unix shell#Bourne shell|Bourne]] shell.

==Scripting==
Most command-line interpreters support scripting, to various extents. (They are, after all, interpreters of an interpreted programming language, albeit in many cases the language is unique to the particular command-line interpreter.) They will interpret scripts (variously termed [[Shell script|shell script]]s or [[Batch file|batch file]]s) written in the [[Programming language|language]] that they interpret. Some command-line interpreters also incorporate the interpreter engines of other languages, such as REXX, in addition to their own, allowing the executing of scripts, in those languages, directly within the command-line interpreter itself.

Conversely, scripting programming languages, in particular those with an [[Eval|eval]] function (such as REXX, [[Perl]], [[Python (programming language)|Python]], [[Ruby (programming language)|Ruby]] or [[Software:Jython|Jython]]), can be used to implement command-line interpreters and filters. For a few [[Operating system|operating system]]s, most notably [[Engineering:DOS|DOS]], such a command interpreter provides a more flexible command-line interface than the one supplied. In other cases, such a command interpreter can present a highly customised user interface employing the user interface and input/output facilities of the language.

==Other command-line interfaces==
The command line provides an interface between programs as well as the user. In this sense, a command line is an alternative to a [[Dialog box|dialog box]]. Editors and databases present a command line, in which alternate command processors might run. On the other hand, one might have options on the command line, which opens a dialog box. The latest version of 'Take Command' has this feature. DBase used a dialog box to construct command lines, which could be further edited before use.

Programs like BASIC, [[Software:Diskpart|diskpart]], [[Software:Edlin|Edlin]], and QBASIC all provide command-line interfaces, some of which use the system shell. Basic is modeled on the default interface for 8-bit Intel computers. Calculators can be run as command-line or dialog interfaces.

[[Software:Emacs|Emacs]] provides a command-line interface in the form of its minibuffer. Commands and arguments can be entered using Emacs standard text editing support, and output is displayed in another buffer.

There are a number of text mode games, like ''[[Software:Colossal Cave Adventure|Adventure]]'' or ''King's Quest 1-3'', which relied on the user typing commands at the bottom of the screen. One controls the character by typing commands like 'get ring' or 'look'. The program returns a text which describes how the character sees it, or makes the action happen. The text adventure ''The Hitchhiker's Guide to the Galaxy'', a piece of [[Interactive fiction|interactive fiction]] based on [[Biography:Douglas Adams|Douglas Adam's]] book of the same name, is a teletype-style command-line game.

The most notable of these interfaces is the [[Standard streams|standard streams]] interface, which allows the output of one command to be passed to the input of another. Text files can serve either purpose as well. This provides the interfaces of piping, filters and redirection. Under Unix, [[Everything is a file|devices are files]] too, so the normal type of file for the shell used for stdin,stdout and stderr is a [[Engineering:Teleprinter#Teleprinters in computing|tty]] device file.

Another command-line interface allows a shell program to launch helper programs, either to launch documents or start a program. The command is processed internally by the shell, and then passed on to another program to launch the document. The graphical interface of Windows and OS/2 rely heavily on command-lines passed through to other programs&nbsp;– console or graphical, which then usually process the command line without presenting a user-console.

Programs like the OS/2 [[Software:E (PC DOS)|E editor]] and some other IBM [[Software:Text editor|editors]], can process command-lines normally meant for the shell, the output being placed directly in the document window.

A web browser's URL input field can be used as a command line. It can be used to "launch" web apps, access browser configuration, as well as perform a search. [[Company:Google|Google]], which has been called "the command line of the internet" will perform a domain-specific search when it detects search parameters in a known format.<ref name="Google"/> This functionality is present whether the search is triggered from a browser field or on Google's website.

There are [[JavaScript]] libraries that allow to write command line applications in browser as standalone Web apps or as part of bigger application.<ref>{{Cite web |url=https://terminal.jcubic.pl/ |title=jQuery Terminal Emulator |access-date=2021-04-20  |archive-date=2021-04-20  |archive-url=https://web.archive.org/web/20210420221405/https://terminal.jcubic.pl/ |url-status=live }}</ref> An example of such a website is the CLI interface to [[Software:DuckDuckGo|DuckDuckGo]].<ref>{{Cite web |url=https://duckduckgo.com/tty/ |title=DuckDuckGo TTY |access-date=2021-04-20  |archive-date=2021-05-07  |archive-url=https://web.archive.org/web/20210507211818/https://duckduckgo.com/tty/ |url-status=live }}</ref> There are also [[Web-based SSH]] applications, that allow to give access to server command line interface from a browser.

Many PC video games feature a command line interface often referred to as a console. It is typically used by the game developers during development and by mod developers for debugging purposes as well as for cheating or skipping parts of the game.

==See also==
* [[Software:Comparison of command shells|Comparison of command shells]]
* [[List of command-line interpreters]]
* [[Console application]]
* [[Interpreter directive]]
* Read-eval-print loop
* [[Shell script]]
* [[Software:Run command|Run command]]
* {{Section link|Graphical user interface|Comparison to other interfaces}}
* ''[[In the Beginning... Was the Command Line]]''

==Notes==
{{Reflist|group="nb"|refs=
<ref group="nb" name="NB1">An example is the comprehensive internal help system of the DR-DOS 7.03 DEBUG command, which can be invoked via <code>??</code> at the debug prompt (rather than only the default <code>?</code> overview). Specific help pages can be selected via <code>?n</code> (where <code>n</code> is the number of the page). Additionally, help for specific commands can be displayed by specifying the command name after <code>?</code>, f.e. <code>?D</code> will invoke help for the various dump commands (like <code>D</code> etc.). Some of these features were already supported by the DR DOS 3.41 SID86 and GEMSID.</ref>
<ref group="nb" name="NB2">Notable difference for describing the command syntax of [[Engineering:DOS|DOS]]-like operating systems: Windows Server 2003 R2 documentation uses italic letters for “information that the user must supply", but Windows Server 2008 documentation uses angle brackets. Italics can not be displayed by the internal "help” command, while there is no problem with angle brackets.</ref>
<ref group="nb" name="NB3">With the exception of ASCII art.</ref>
}}

==References==
{{Reflist|refs=
<ref name="Unix_Shells">{{cite web |title=Unix Shells |url=http://linuxfinances.info/info/unixshells.html |quote=the notion of having a replaceable "command shell" rather than a "monitor" tightly integrated with the OS kernel tends to be attributed to Multics. |archive-url=https://web.archive.org/web/20071108064620/http://www.linuxfinances.info/info/unixshells.html |archive-date=November 8, 2007}}</ref>
<ref name="multicians">{{cite web |title=The Origin of the Shell |website=www.multicians.org |url=http://www.multicians.org/shell.html |access-date=2017-04-12 |archive-date=2017-12-21  |archive-url=https://web.archive.org/web/20171221142542/http://www.multicians.org/shell.html |url-status=live }}</ref>
<ref name="Metz_2013">{{cite magazine |author-last=Metz |author-first=Cade |title=Say Bonjour to the Internet's Long-Lost French Uncle |magazine=Wired |date=2013-01-03 |url=https://www.wired.com/2013/01/louis_pouzin_internet_hall/ |access-date=2017-07-31}}</ref>
<ref name="Mazieres_2004">{{cite web |author-last=Mazières |author-first=David |title=MULTICS - The First Seven Years |website=Advanced Operating Systems |publisher=Stanford Computer Science Department |date=Fall 2004 |url=http://www.scs.stanford.edu/nyu/04fa/notes/l4d.txt |access-date=2017-08-01 |archive-date=2014-11-23  |archive-url=https://web.archive.org/web/20141123000315/http://www.scs.stanford.edu/nyu/04fa/notes/l4d.txt |url-status=live }}</ref>
<ref name="ibm">{{cite web |author-last=Jones |author-first=M. |title=Evolution of shells in Linux |website=developerWorks |publisher=[[Company:IBM|IBM]] |date=2011-12-06 |url=https://www.ibm.com/developerworks/library/l-linux-shells/ |access-date=2017-08-01 |archive-date=2017-07-08  |archive-url=https://web.archive.org/web/20170708215831/https://www.ibm.com/developerworks/library/l-linux-shells/ |url-status=live }}</ref>
<ref name="Bash">{{cite web |title=GNU BASH Reference |url=https://www.gnu.org/software/bash/manual/bashref.html#Shell-Commands |access-date=2015-12-20  |archive-date=2010-12-03  |archive-url=https://web.archive.org/web/20101203065719/https://www.gnu.org/software/bash/manual/bashref.html#Shell-Commands |url-status=live }}</ref>
<ref name="Microsoft_Windows">{{cite web |title=Microsoft Windows Command Shell Overview |url=https://technet.microsoft.com/en-us/library/bb490954.aspx |access-date=2015-07-12  |archive-date=2015-09-05  |archive-url=https://web.archive.org/web/20150905103923/https://technet.microsoft.com/en-us/library/bb490954.aspx |url-status=live }}</ref>
<ref name="Parker_2011">{{cite book |author-last=Parker |author-first=Steve |chapter=Chapter 11: Choosing and using shells |title=Shell Scripting: Expert Recipes for Linux, Bash and more |series=Programmer to programmer |location=Indianapolis, USA |publisher={{wipe|John Wiley & Sons}} |date=2011 |page=262 |isbn=978-111816632-1 |url=https://books.google.com/books?id=wWjqCF9HLfYC|quote=The shell has four different command prompts, called PS1, P52, P53, and PS4. PS stands for Prompt String.}}</ref>
<ref name="Acorn_1992">{{cite book |title=RISC OS 3 User Guide |publisher=Acorn Computers Limited |date=1992-03-01 |page=125 |url=http://www.4corn.co.uk/_archive/docs/RISC%20OS%203%20User%20Guide%20(3.0)-opt.pdf |access-date=2017-04-12  |archive-date=2017-01-09  |archive-url=https://web.archive.org/web/20170109183207/http://www.4corn.co.uk/_archive/docs/RISC%20OS%203%20User%20Guide%20(3.0)-opt.pdf |url-status=live }}</ref>
<ref name="OpenGroup_2008">{{cite web |title=The Open Group Base Specifications Issue 7, Chapter 12.1 Utility Argument Syntax |publisher=[[Company:The Open Group|The Open Group]] |date=2008 |url=http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap12.html |access-date=2013-04-07 |archive-date=2013-04-30  |archive-url=https://web.archive.org/web/20130430125310/http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap12.html |url-status=live }}{{man|7|man-pages|die.net}} (NB. Conventions for describing commands on Unix-like operating systems.)</ref>
<ref name="Microsoft_2005_Shell">{{cite web |title=Command shell overview |work=Windows Server 2003 Product Help |publisher=[[Company:Microsoft|Microsoft]] |date=2005-01-21 |url=https://technet.microsoft.com/en-us/library/cc737438.aspx |access-date=2013-04-07 |archive-date=2012-07-12  |archive-url=https://web.archive.org/web/20120712200546/http://technet.microsoft.com/en-us/library/cc737438.aspx |url-status=live }}</ref>
<ref name="Microsoft_2010_Syntax">{{cite web |title=Command-Line Syntax Key |work=Windows Server 2008 R2 TechNet Library |publisher=[[Company:Microsoft|Microsoft]] |date=2010-01-25 |url=https://technet.microsoft.com/en-us/library/cc771080.aspx |access-date=2013-04-07 |archive-date=2013-05-04  |archive-url=https://web.archive.org/web/20130504221131/http://technet.microsoft.com/en-us/library/cc771080.aspx |url-status=live }}</ref>
<ref name="Kerninghan_1984">{{cite book |author-first1=Brian W. |author-last1=Kernighan |author-first2=Rob |author-last2=Pike |author-link2=Rob Pike |title=The UNIX Programming Environment |location=Englewood Cliffs |publisher=Prentice-Hall |date=1984 |isbn=0-13-937699-2 |url=https://archive.org/details/unixprogramminge0000kern |url-access=registration}}</ref>
<ref name="Pouzin">{{cite web |author-last=Pouzin |author-first=Louis |title=The Origin of the Shell |work=Multicians.org |url=http://www.multicians.org/shell.html |access-date=2013-09-22 |archive-date=2017-12-21  |archive-url=https://web.archive.org/web/20171221142542/http://www.multicians.org/shell.html |url-status=live }}</ref>
<ref name="Betanews">{{cite web|title=Remembering Windows 95's launch 15 years later|date=24 August 2010|url=http://betanews.com/2010/08/24/remembering-windows-95-s-launch-15-years-later/|access-date=2015-02-18 |archive-date=2015-02-18 |archive-url=https://web.archive.org/web/20150218221032/http://betanews.com/2010/08/24/remembering-windows-95-s-launch-15-years-later/|url-status=live}}</ref>
<ref name="Microsoft_History">{{cite web |title=A history of Windows |website=windows.microsoft.com |url=http://windows.microsoft.com/en-US/windows/history#T1=era0 |archive-url=https://web.archive.org/web/20150301073112/http://windows.microsoft.com/en-US/windows/history |archive-date=2015-03-01}}</ref>
<ref name="Microsoft_POSIX">{{cite web |title=Windows POSIX shell compatibility |url=https://technet.microsoft.com/en-us/library/cc754351.aspx |access-date=2017-08-26  |archive-date=2017-07-03  |archive-url=https://web.archive.org/web/20170703090254/https://technet.microsoft.com/en-us/library/cc754351.aspx |url-status=live }}</ref>
<ref name="Android_mksh">{{cite web |title=master - platform/external/mksh - Git at Google |website=android.googlesource.com |url=https://android.googlesource.com/platform/external/mksh/+/master |access-date=2018-03-18 |archive-date=2016-01-21  |archive-url=https://web.archive.org/web/20160121112754/https://android.googlesource.com/platform/external/mksh/%2B/master |url-status=live }}</ref>
<ref name="Android_adb">{{cite web |title=Android adb shell - ash or ksh? |website=stackoverflow.com |url=https://stackoverflow.com/questions/11950131/android-adb-shell-ash-or-ksh |access-date=2018-03-14 |archive-date=2017-07-02  |archive-url=https://web.archive.org/web/20170702022904/https://stackoverflow.com/questions/11950131/android-adb-shell-ash-or-ksh |url-status=live }}</ref>
<ref name="Android_sh">{{cite web |title=Android sh source |website=[[GitHub]] |url=https://github.com/android/platform_system_core/tree/master/sh |url-status=dead |archive-url=https://archive.today/20121217165813/https://github.com/android/platform_system_core/tree/master/sh |archive-date=2012-12-17}}</ref>
<ref name="Android_Toolbox">{{cite web |title=Android toolbox source |website=[[GitHub]]|url=https://github.com/android/platform_system_core/tree/master/toolbox}}</ref>
<ref name="Cisco_IOS">{{cite web |title=Configuration Fundamentals Configuration Guide, Cisco IOS Release 15M&T |at=Using the Command-Line Interface |date=2013-10-30 |publisher=[[Company:Cisco|Cisco]] |url=http://www.cisco.com/c/en/us/td/docs/ios/12_2/configfun/configuration/guide/ffun_c/fcf001.html |quote=The Cisco IOS command-line interface (CLI) is the primary user interface… |access-date=2016-11-28  |archive-date=2016-11-18  |archive-url=https://web.archive.org/web/20161118234827/http://www.cisco.com/c/en/us/td/docs/ios/12_2/configfun/configuration/guide/ffun_c/fcf001.html |url-status=live }}</ref>
<ref name="Juniper">{{cite web |title=Command-Line Interface Overview |website=www.juniper.net |url=http://www.juniper.net/techpubs/software/junos/junos55/swconfig55-getting-started/html/cli-overview-getting-started.html |access-date=2018-03-14 |archive-date=2003-09-08  |archive-url=https://web.archive.org/web/20030908113531/http://www.juniper.net/techpubs/software/junos/junos55/swconfig55-getting-started/html/cli-overview-getting-started.html |url-status=live }}</ref>
<ref name="Google">{{cite web |title=Google strange goodness |url=http://www.knaster.com/2004/04/google_strange_.html |access-date=2014-02-27  |archive-date=2014-03-04  |archive-url=https://web.archive.org/web/20140304185253/http://www.knaster.com/2004/04/google_strange_.html |url-status=live }}</ref>
<ref name="4DOS_8.00_HELP">{{cite book |title=4DOS 8.00 online help |title-link=4DOS 8.00 |author-first1=Hardin |author-last1=Brothers |author-first2=Tom |author-last2=Rawson |author-first3=Rex C. |author-last3=Conn |author-link3=Rex C. Conn |author-first4=Matthias R. |author-last4=Paul |author-first5=Charles E. |author-last5=Dye |author-first6=Luchezar I. |author-last6=Georgiev |date=2002-02-27}}</ref>
<ref name="Caldera_1998_DELTREE101">{{cite book |title=DELTREE.BAT R1.01 Extended file and directory delete |author-first=Matthias R. |author-last=Paul |publisher=Caldera, Inc. |date=1998-01-09 |url=http://www.lookas.net/ftp/incoming/darbui/Justas/DRDOS/DELTREE.BAT |access-date=2019-04-08 |url-status=dead |archive-url=https://web.archive.org/web/20190408145354/http://www.lookas.net/ftp/incoming/darbui/Justas/DRDOS/DELTREE.BAT |archive-date=2019-04-08}}</ref>
<ref name="Caldera_1998_NEW703">{{cite book |title=DR-DOS 7.03 WHATSNEW.TXT&nbsp;— Changes from DR-DOS 7.02 to DR-DOS 7.03 |publisher=Caldera, Inc. |date=1998-12-24 |url=http://www.lookas.net/ftp/incoming/darbui/Justas/DRDOS/WHATSNEW.TXT |access-date=2019-04-08 |url-status=dead |archive-url=https://web.archive.org/web/20190408142232/http://www.lookas.net/ftp/incoming/darbui/Justas/DRDOS/WHATSNEW.TXT |archive-date=2019-04-08}}</ref>
<ref name="Paul_2006_FreeKEYB">{{cite book |title=FreeKEYB - Advanced international DOS keyboard and console driver |edition=v7 preliminary |author-first1=Matthias R. |author-last1=Paul |author-first2=Axel C. |author-last2=Frinke |type=User Manual |date=2006-01-16}}</ref>
<ref name="Paul_1997_DRDOSTIP">{{cite web |title=DRDOSTIP.TXT – Tips und Tricks für DR DOS 3.41 - 5.0 |work=MPDOSTIP |author-first=Matthias R. |author-last=Paul |date=1997-05-24 |orig-year=1991 |edition=47 |language=de |url=http://www.antonis.de/dos/dos-tuts/mpdostip/html/drdostip.htm |access-date=2016-11-07 |url-status=live |archive-url=https://web.archive.org/web/20161107125452/http://www.antonis.de/dos/dos-tuts/mpdostip/html/drdostip.htm |archive-date=2016-11-07}}</ref>
<ref name="Paul_2002_DEBUG">{{cite newsgroup |title=SID86 |author-first=Matthias R. |author-last=Paul |date=2002-01-09 |newsgroup=comp.os.cpm |url=https://groups.google.com/d/msg/comp.os.cpm/KG4R7ZNvHK8/U5LAkmjcxYgJ |access-date=2018-04-08 |quote=[…] Since the DR-DOS 7.03 DEBUG is still based on the old SID86.EXE, I suggest to run DEBUG 1.51 and enter the extended help system with ?? from the debug prompt. This will give you eight screens full of syntax and feature help. Some of these features were also supported by older issues. […]}}</ref>
<ref name="Paul_1997_NWDOSTIP">{{cite web |title=NWDOS-TIPs – Tips & Tricks rund um Novell DOS 7, mit Blick auf undokumentierte Details, Bugs und Workarounds |work=MPDOSTIP |author-first=Matthias R. |author-last=Paul |date=1997-07-30 |edition=3 |version=Release 157 |language=de |url=http://www.antonis.de/dos/dos-tuts/mpdostip/html/nwdostip.htm |access-date=2014-09-06 |url-status=live |archive-url=https://web.archive.org/web/20170910194752/http://www.antonis.de/dos/dos-tuts/mpdostip/html/nwdostip.htm |archive-date=2017-09-10}} (NB. NWDOSTIP.TXT is a comprehensive work on Novell DOS 7 and OpenDOS 7.01, including the description of many undocumented features and internals. It is part of the author's yet larger MPDOSTIP.ZIP collection maintained up to 2001 and distributed on many sites at the time. The provided link points to a HTML-converted older version of the NWDOSTIP.TXT file.)</ref>
<ref name="CCI_1997_HELP">{{cite book |title=CCI Multiuser DOS 7.22 GOLD Online Documentation |id=HELP.HLP |date=1997-02-10 |publisher=Concurrent Controls, Inc. (CCI)}} (NB. The symbolic instruction debugger SID86 provides a short help screen on <code>?</code> and comprehensive help on <code>??</code>.)</ref>
<ref name="Paul_2002_CPI">{{cite web |title=[fd-dev] mkeyb |author-first=Matthias R. |author-last=Paul |date=2002-05-13 |work=freedos-dev |url=https://marc.info/?l=freedos-dev&m=102133580113139&w=2 |access-date=2018-09-10 |url-status=live |archive-url=https://archive.today/20180910213410/https://marc.info/?l=freedos-dev&m=102133580113139&w=2 |archive-date=2018-09-10 |quote=[…] CPI /H […] CPI [@] [@] [/?{{!}}/Help[:topic]] [/!{{!}}/About] […] [?{{!}}&] […] /?, /Help Display this help screen or specific help for a topic (+) […] /!, /About Display the 'About' info screen […] /Cpifile (+) .CPI/.CP file name <EGA.CPI>; extension: <.CPI>; CPI.EXE=StdIn […] /Report Report file name <'<s></s>'=StdOut>; extension: <.RPT> […] /Style (+) Export <0>-6=BIN-raw/ROM/RAM/PSF0/1/SH/CHED; 7-12/13-18/19-24=ASM-hex/dec/bin/ip/il/p/l/mp/ml […] CPI /H:C […] Overview on codepage file parameter usage: […] CPI /H:S […] Overview on /Style parameters: […] ?, & Online edit mode (prompts for additional parameter input) […]}}</ref>
<ref name="DR_1978_SID">{{cite book |title=SID Users Guide |date=1978 |publisher=[[Company:Digital Research|Digital Research]] |id=595-2549 |url=http://www.cpm.z80.de/randyfiles/DRI/SID_ZSID.pdf |access-date=2020-02-06 |url-status=live |archive-url=https://web.archive.org/web/20191020124044/http://www.cpm.z80.de/randyfiles/DRI/SID_ZSID.pdf |archive-date=2019-10-20}} (4+69 pages)</ref>
<ref name="DR_1982_SID86">{{cite book |title=SID-86 User's Guide for CP/M-86 |date=August 1982 |orig-year=March 1982 |edition=2 |publisher=[[Company:Digital Research|Digital Research]] |id=SID86UG.WS4 |url=http://www.cpm.z80.de/manuals/SID86_User_Guide.txt |access-date=2020-02-06 |url-status=live |archive-url=https://web.archive.org/web/20191020123025/http://www.cpm.z80.de/manuals/SID86_User_Guide.txt |archive-date=2019-10-20}} [https://web.archive.org/web/20200208055456/https://archive.computerhistory.org/resources/access/text/2016/12/102762507-05-01-acc.pdf<!-- https://archive.computerhistory.org/resources/access/text/2016/12/102762507-05-01-acc.pdf -->] (NB. A retyped version of the manual by Emmanuel Roche with Q, SR, and Z commands added.)</ref>
}}

==External links==
* [http://www.patersontech.com/Dos/Softalk/Softalk.html The Roots of DOS] David Hunter, ''Softalk for the IBM Personal Computer'' March 1983. Archived at Patersontech.com since [https://web.archive.org/web/20001003150623/http://www.patersontech.com/Dos/Softalk/Softalk.html 2000].
* [https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/windows-commands Command-Line Reference]: Microsoft TechNet Database "Command-Line Reference"

{{Operating system|state=collapsed}}
{{Unix commands|state=collapsed}}
{{Windows commands|state=collapsed}}

{{DEFAULTSORT:Command-Line Interface}}
[[Category:Computing commands| ]]
[[Category:History of human–computer interaction]]
[[Category:Software architecture]]
[[Category:User interface techniques]]
[[Category:User interfaces]]

{{Sourceattribution|Command-line interface}}