command line interface
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A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive
command Command may refer to: Computing * Command (computing), a statement in a computer language * COMMAND.COM, the default operating system shell and command-line interpreter for DOS * Command key, a modifier key on Apple Macintosh computer keyboards * ...
s from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and providing information to them as to what actions they are to perform. In some cases the invocation is conditional based on conditions established by the user or previous executables. Such access was first provided by
computer terminal A computer terminal is an electronic or electromechanical hardware device that can be used for entering data into, and transcribing data from, a computer or a computing system. The teletype was an example of an early-day hard-copy terminal and ...
s starting in the mid-1960s. This provided an interactive environment not available with
punched cards A punched card (also punch card or punched-card) is a piece of stiff paper that holds digital data represented by the presence or absence of holes in predefined positions. Punched cards were once common in data processing applications or to di ...
or other input methods. Today, many users rely upon
graphical user interface The GUI ( "UI" by itself is still usually pronounced . or ), graphical user interface, is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicator such as primary notation, inst ...
s and menu-driven interactions. However, some programming and maintenance tasks may not have a graphical user interface and use a command line. Alternatives to the command-line interface include
text-based user interface In computing, text-based user interfaces (TUI) (alternately terminal user interfaces, to reflect a dependence upon the properties of computer terminals and not just text), is a retronym describing a type of user interface (UI) common as an ear ...
menus (for example,
IBM AIX SMIT The System Management Interface Tool (SMIT) is a menu-based management tool for the IBM AIX operating system. It allows a user to navigate a menu hierarchy of commands, rather than using the command line. See also * Object Data Manager * I ...
),
keyboard shortcut computing, a keyboard shortcut also known as hotkey is a series of one or several keys to quickly invoke a software program or perform a preprogrammed action. This action may be part of the standard functionality of the operating system or ...
s, and various
desktop metaphor In computing, the desktop metaphor is an interface metaphor which is a set of unifying concepts used by graphical user interfaces to help users interact more easily with the computer. The desktop metaphor treats the computer monitor as if it is ...
s centered on the pointer (usually controlled with a mouse). Examples of this include the Microsoft Windows,
DOS Shell DOS Shell is a file manager that debuted in MS-DOS and PC DOS version 4.0, released in June 1988. It was discontinued in MS-DOS version 6.22, but remained part of the Supplemental Disk. The Supplemental Disk could be ordered or could be do ...
, and Mouse Systems PowerPanel. Command-line interfaces are often implemented in terminal devices that are also capable of screen-oriented text-based user interfaces that use cursor addressing to place symbols on a display screen. Programs with command-line interfaces are generally easier to automate via scripting. Many software systems implement command-line interfaces for control and operation. This includes programming environments and utility programs.


Comparison to graphical user interfaces

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 A scripting language or script language is a programming language that is used to manipulate, customize, and automate the facilities of an existing system. Scripting languages are usually interpreted at runtime rather than compiled. A scripting ...
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
fonts In metal typesetting, a font is a particular size, weight and style of a typeface. Each font is a matched set of type, with a piece (a " sort") for each glyph. A typeface consists of a range of such fonts that shared an overall design. In mod ...
or extended 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
icons An icon () is a religious work of art, most commonly a painting, in the cultures of the Eastern Orthodox, Oriental Orthodox, and Catholic churches. They are not simply artworks; "an icon is a sacred image used in religious devotion". The most c ...
and
drop-down menu A drop-down list (abbreviated drop-down, or DDL; also known as a drop-down menu, drop menu, pull-down list, picklist) is a graphical control element, similar to a list box, that allows the user to choose one value from a list. When a drop-down ...
s of a graphical user interface, without reference to manuals.


Types


Operating system command-line interfaces

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
shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard o ...
. Examples of command-line interpreters include DEC's
DIGITAL Command Language DIGITAL Command Language (DCL) is the standard command language adopted by many of the operating systems created by Digital Equipment Corporation. DCL had its roots in IAS, TOPS-20, and RT-11 and was implemented as a standard across most of Digit ...
(DCL) in OpenVMS and
RSX-11 RSX-11 is a discontinued family of multi-user real-time operating systems for PDP-11 computers created by Digital Equipment Corporation. In widespread use through the late 1970s and early 1980s, RSX-11 was influential in the development of later ...
, the various
Unix shell A Unix shell is a command-line interpreter or shell that provides a command line user interface for Unix-like operating systems. The shell is both an interactive command language and a scripting language, and is used by the operating syste ...
s ( sh, ksh, csh,
tcsh tcsh ( “tee-see-shell”, “tee-shell”, or as “tee see ess aitch”, tcsh) is a Unix shell based on and backward compatible with the C shell (csh). Shell It is essentially the C shell with programmable command-line completion, command ...
,
zsh The Z shell (Zsh) is a Unix shell that can be used as an interactive login shell (computing), shell and as a command line interpreter, command interpreter for shell scripting. Zsh is an extended Bourne shell with many improvements, including som ...
,
Bash Bash or BASH may refer to: Arts and entertainment * ''Bash!'' (Rockapella album), 1992 * ''Bash!'' (Dave Bailey album), 1961 * '' Bash: Latter-Day Plays'', a dramatic triptych * ''BASH!'' (role-playing game), a 2005 superhero game * "Bash" ('' ...
, etc.), CP/M's CCP,
DOS DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems. DOS may also refer to: Computing * Data over signalling (DoS), multiplexing data onto a signalling channel * Denial-of-service attack (DoS), an attack on a communicat ...
'
COMMAND.COM COMMAND.COM is the default command-line interpreter for MS-DOS, Windows 95, Windows 98 and Windows Me. In the case of DOS, it is the default user interface as well. It has an additional role as the usual first program run after boot (init proc ...
, as well as the
OS/2 OS/2 (Operating System/2) is a series of computer operating systems, initially created by Microsoft and IBM under the leadership of IBM software designer Ed Iacobucci. As a result of a feud between the two companies over how to position OS/2 r ...
and the Windows
CMD.EXE Command Prompt, also known as cmd.exe or cmd, is the default command-line interpreter for the OS/2, eComStation, ArcaOS, Microsoft Windows (Windows NT family and Windows CE family), and ReactOS operating systems. On Windows CE .NET 4.2, Windo ...
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
4DOS 4DOS is a command-line interpreter by JP Software, designed to replace the default command interpreter COMMAND.COM in Microsoft DOS and Windows. It was written by Rex C. Conn and Tom Rawson and first released in 1989. Compared to the default, ...
for DOS,
4OS2 4OS2 is the OS/2 analogue of 4NT and 4DOS by JP Software, Inc. JP Software discontinued 4OS2, TCMDOS2 and TCMD16, making version 3.0, 2.0, 2.0 the final version of these. The code for 4OS2 has been released, and is maintained, first by Sci ...
for OS/2, and 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 File Explorer, previously known as Windows Explorer, is a file manager application that is included with releases of the Microsoft Windows operating system from Windows 95 onwards. It provides a graphical user interface for accessing the file ...
, 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

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 (for example,
standard streams In computer programming, standard streams are interconnected input and output communication channels between a computer program and its environment when it begins execution. The three input/output (I/O) connections are called standard input (stdin ...
or
named pipe In computing, a named pipe (also known as a FIFO for its behavior) is an extension to the traditional pipe concept on Unix and Unix-like systems, and is one of the methods of inter-process communication (IPC). The concept is also found in OS/2 and ...
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 around a separate CLI
executable file In computing, executable code, an executable file, or an executable program, sometimes simply referred to as an executable or binary, causes a computer "to perform indicated tasks according to encoded instructions", as opposed to a data fil ...
. 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
MATLAB MATLAB (an abbreviation of "MATrix LABoratory") is a proprietary multi-paradigm programming language and numeric computing environment developed by MathWorks. MATLAB allows matrix manipulations, plotting of functions and data, implementa ...
, a
numerical analysis Numerical analysis is the study of algorithms that use numerical approximation (as opposed to symbolic manipulations) for the problems of mathematical analysis (as distinguished from discrete mathematics). It is the study of numerical methods ...
computer program, are available via the CLI, whereas the MATLAB GUI exposes only a subset of features. In
Colossal Cave Adventure ''Colossal Cave Adventure'' (also known as ''Adventure'' or ''ADVENT'') is a text-based adventure game, released in 1976 by developer Will Crowther for the PDP-10 mainframe computer. It was expanded upon in 1977 by Don Woods. In the game, the ...
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
teleprinter A teleprinter (teletypewriter, teletype or TTY) is an electromechanical device that can be used to send and receive typed messages through various communications channels, in both point-to-point and point-to-multipoint configurations. Init ...
(TTY) machines. Sometimes these involved sending an order or a confirmation using
telex The telex network is a station-to-station switched network of teleprinters similar to a telephone network, using telegraph-grade connecting circuits for two-way text-based messages. Telex was a major method of sending written messages electroni ...
. 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. "Smart" terminals 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
microcomputer revolution The history of the personal computer as a mass-market consumer electronic device began with the microcomputer revolution of the 1970s. A personal computer is one intended for interactive individual use, as opposed to a mainframe computer where ...
replaced the traditionalminicomputer + terminals
time sharing In computing, time-sharing is the sharing of a computing resource among many users at the same time by means of multiprogramming and multi-tasking.DEC Timesharing (1965), by Peter Clark, The DEC Professional, Volume 1, Number 1 Its emergence ...
architecture, hardware terminals were replaced by
terminal emulator A terminal emulator, or terminal application, is a computer program that emulates a video terminal within some other display architecture. Though typically synonymous with a shell or text terminal, the term ''terminal'' covers all remote term ...
s — PC software that interpreted terminal signals sent through the PC's
serial port In computing, a serial port is a serial communication interface through which information transfers in or out sequentially one bit at a time. This is in contrast to a parallel port, which communicates multiple bits simultaneously in parallel. ...
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
resident monitor In computing, a resident monitor is a type of system software program that was used in many early computers from the 1950s to 1970s. It can be considered a precursor to the operating system. The name is derived from a program which is always pre ...
programs, and could not easily be replaced. The first implementation of the shell as a replaceable component was part of the
Multics Multics ("Multiplexed Information and Computing Service") is an influential early time-sharing operating system based on the concept of a single-level memory.Dennis M. Ritchie, "The Evolution of the Unix Time-sharing System", Communications of ...
time-sharing In computing, time-sharing is the sharing of a computing resource among many users at the same time by means of multiprogramming and multi-tasking.DEC Timesharing (1965), by Peter Clark, The DEC Professional, Volume 1, Number 1 Its emergence ...
operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also i ...
. In 1964, MIT Computation Center staff member
Louis Pouzin Louis Pouzin (April 20, 1931 in Chantenay-Saint-Imbert, Nièvre, France) is a French computer scientist. He designed an early packet communications network, CYCLADES. This network was the first actual implementation of the pure datagram model, ...
developed the
RUNCOM RUNCOM is a CTSS macro command (script) processor. History Louis Pouzin created RUNCOM for CTSS circa 1963. He wrote a paper in 1965 describing a design for the Multics shell which includes a brief description of RUNCOM followed by a second p ...
tool for executing command scripts while allowing argument substitution. Pouzin coined the term "
shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard o ...
" to describe the technique of using commands like a programming language, and wrote a paper about how to implement the idea in the
Multics Multics ("Multiplexed Information and Computing Service") is an influential early time-sharing operating system based on the concept of a single-level memory.Dennis M. Ritchie, "The Evolution of the Unix Time-sharing System", Communications of ...
operating system. Pouzin returned to his native France in 1965, and the first Multics shell was developed by
Glenda Schroeder Glenda Schroeder is an American software engineer noted for implementing the first command-line user interface shell and publishing one of the earliest research papers describing electronic mail systems while working as a member of the staff at th ...
. The first
Unix shell A Unix shell is a command-line interpreter or shell that provides a command line user interface for Unix-like operating systems. The shell is both an interactive command language and a scripting language, and is used by the operating syste ...
, the V6 shell, was developed by
Ken Thompson Kenneth Lane Thompson (born February 4, 1943) is an American pioneer of computer science. Thompson worked at Bell Labs for most of his career where he designed and implemented the original Unix operating system. He also invented the B programmi ...
in 1971 at
Bell Labs Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial Research and development, research and scientific developm ...
and was modeled after Schroeder's Multics shell. The 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 KornShell (ksh), Almquist shell (ash), and the popular
Bourne-again shell Bash is a Unix shell and command language written by Brian Fox (computer programmer), Brian Fox for the GNU Project as a free software replacement for the Bourne shell. First released in 1989, it has been used as the default login shell for most ...
(or Bash). Early microcomputers themselves were based on a command-line interface such as CP/M,
DOS DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems. DOS may also refer to: Computing * Data over signalling (DoS), multiplexing data onto a signalling channel * Denial-of-service attack (DoS), an attack on a communicat ...
or
AppleSoft BASIC Applesoft BASIC is a dialect of Microsoft BASIC, developed by Marc McDonald and Ric Weiland, supplied with the Apple II series of computers. It supersedes Integer BASIC and is the BASIC in ROM in all Apple II series computers after the origina ...
. During the 1980s and 1990s, the introduction of the
Apple Macintosh The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc., Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and ...
and of Microsoft Windows on PCs saw the command line interface as the primary user interface replaced by the
Graphical User Interface The GUI ( "UI" by itself is still usually pronounced . or ), graphical user interface, is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicator such as primary notation, inst ...
. The command line remained available as an alternative user interface, often used by
system administrators A system administrator, or sysadmin, or admin is a person who is responsible for the upkeep, configuration, and reliable operation of computer systems, especially multi-user computers, such as servers. The system administrator seeks to en ...
and other advanced users for system administration,
computer programming Computer programming is the process of performing a particular computation (or more generally, accomplishing a specific computing result), usually by designing and building an executable computer program. Programming involves tasks such as anal ...
and
batch processing Computerized batch processing is a method of running software programs called jobs in batches automatically. While users are required to submit the jobs, no other interaction by the user is required to process the batch. Batches may automatically ...
. In November 2006,
Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washin ...
released version 1.0 of
Windows PowerShell PowerShell is a task automation and configuration management program from Microsoft, consisting of a command-line shell and the associated scripting language. Initially a Windows component only, known as Windows PowerShell, it was made open-so ...
(formerly codenamed ''Monad''), which combined features of traditional Unix shells with their proprietary object-oriented
.NET Framework The .NET Framework (pronounced as "''dot net"'') is a proprietary software framework developed by Microsoft that runs primarily on Microsoft Windows. It was the predominant implementation of the Common Language Infrastructure (CLI) until bein ...
.
MinGW MinGW ("Minimalist GNU for Windows"), formerly mingw32, is a free and open source software development environment to create Microsoft Windows applications. MinGW includes a port of the GNU Compiler Collection (GCC), GNU Binutils for Windows ...
and Cygwin are open-source packages for Windows that offer a Unix-like CLI. Microsoft provides
MKS Inc. MKS, Inc (formerly called Mortice Kern Systems) is a subsidiary of PTC, Inc. It was previously a multinational independent software vendor that was acquired by Parametric Technology Corporation (now PTC) on May 31, 2011. MKS operated in the A ...
's ksh implementation ''MKS Korn shell'' for Windows through their
Services for UNIX Windows Services for UNIX (SFU) is a discontinued software package produced by Microsoft which provided a Unix environment on Windows NT and some of its immediate successor operating-systems. SFU 1.0 and 2.0 used the MKS Toolkit; starting with ...
add-on. Since 2001, the
Macintosh The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and software en ...
operating system
macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...
has been based on a
Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...
operating system called Darwin. On these computers, users can access a Unix-like command-line interface by running the
terminal emulator A terminal emulator, or terminal application, is a computer program that emulates a video terminal within some other display architecture. Though typically synonymous with a shell or text terminal, the term ''terminal'' covers all remote term ...
program called
Terminal Terminal may refer to: Computing Hardware * Terminal (electronics), a device for joining electrical circuits together * Terminal (telecommunication), a device communicating over a line * Computer terminal, a set of primary input and output dev ...
, which is found in the Utilities sub-folder of the Applications folder, or by remotely logging into the machine using
ssh The Secure Shell Protocol (SSH) is a cryptographic network protocol for operating network services securely over an unsecured network. Its most notable applications are remote login and command-line execution. SSH applications are based on ...
.
Z shell The Z shell (Zsh) is a Unix shell that can be used as an interactive login shell and as a command interpreter for shell scripting. Zsh is an extended Bourne shell with many improvements, including some features of Bash, ksh, and tcsh. History ...
is the default shell for macOS; Bash,
tcsh tcsh ( “tee-see-shell”, “tee-shell”, or as “tee see ess aitch”, tcsh) is a Unix shell based on and backward compatible with the C shell (csh). Shell It is essentially the C shell with programmable command-line completion, command ...
, and the KornShell are also provided. Before
macOS Catalina macOS Catalina (version 10.15) is the sixteenth major release of macOS, Apple Inc.'s desktop operating system for Macintosh computers. It is the successor to macOS Mojave and was announced at WWDC 2019 on June 3, 2019 and released to the publ ...
, 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 command shells. CLIs are also used by systems with insufficient resources to support a graphical user interface. Some computer language systems (such as
Python Python may refer to: Snakes * Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia ** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia * Python (mythology), a mythical serpent Computing * Python (pro ...
,
Forth Forth or FORTH may refer to: Arts and entertainment * ''forth'' magazine, an Internet magazine * ''Forth'' (album), by The Verve, 2008 * ''Forth'', a 2011 album by Proto-Kaw * Radio Forth, a group of independent local radio stations in Scotla ...
, 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 display A refreshable braille display or braille terminal is an electro-mechanical device for displaying braille characters, usually by means of round-tipped pins raised through holes in a flat surface. Visually impaired computer users who cannot use a s ...
s.


Anatomy of a shell CLI

The general pattern of a command line interface is:
Prompt Prompt may refer to: Computing * Command prompt, characters indicating the computer is ready to accept input * Command Prompt, also known as cmd.exe or cmd, the command-line interpreter in some operating systems * Prompt (natural language), instr ...
command param1 param2 param3 … paramN *
Prompt Prompt may refer to: Computing * Command prompt, characters indicating the computer is ready to accept input * Command Prompt, also known as cmd.exe or cmd, the command-line interpreter in some operating systems * Prompt (natural language), instr ...
— generated by the program to provide context for the user. * Command — 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. * param1 …paramN — 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 An argument is a statement or group of statements called premises intended to determine the degree of truth or acceptability of another statement called conclusion. Arguments can be studied from three main perspectives: the logical, the dialectic ...
or Options. In this format, the delimiters between command-line elements are
whitespace character In computer programming, whitespace is any character or series of characters that represent horizontal or vertical space in typography. When rendered, a whitespace character does not correspond to a visible mark, but typically does occupy an area ...
s and the end-of-line delimiter is the newline delimiter. This is a widely used (but not universal) convention. A CLI can generally be considered as consisting of syntax and
semantics Semantics (from grc, σημαντικός ''sēmantikós'', "significant") is the study of reference, meaning, or truth. The term can be used to refer to subfields of several distinct disciplines, including philosophy, linguistics and comp ...
. The ''syntax'' is the grammar that all commands must follow. In the case of
operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also i ...
s,
DOS DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems. DOS may also refer to: Computing * Data over signalling (DoS), multiplexing data onto a signalling channel * Denial-of-service attack (DoS), an attack on a communicat ...
and
Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, an ...
each define their own set of rules that all commands must follow. In the case of
embedded systems An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is ''embedded'' ...
, each vendor, such as
Nortel Nortel Networks Corporation (Nortel), formerly Northern Telecom Limited, was a Canadian multinational telecommunications and data networking equipment manufacturer headquartered in Ottawa, Ontario, Canada. It was founded in Montreal, Quebec, ...
,
Juniper Networks Juniper Networks, Inc. is an American multinational corporation headquartered in Sunnyvale, California. The company develops and markets networking products, including routers, switches, network management software, network security product ...
or
Cisco Systems Cisco Systems, Inc., commonly known as Cisco, is an American-based multinational digital communications technology conglomerate corporation headquartered in San Jose, California. Cisco develops, manufactures, and sells networking hardware, ...
, 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 On computer keyboards, the enter key and return key are two closely related keys with overlapping and distinct functions dependent on operating system and application. Functions The return key has its origins in two typewriter functions: ca ...
, 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 defaults that can be changed to customize the results. Useful command lines can be saved by assigning a
character string In computer programming, a string is traditionally a sequence of characters, either as a literal constant or as some kind of variable. The latter may allow its elements to be mutated and the length changed, or it may be fixed (after creation). ...
or
alias Alias may refer to: * Pseudonym * Pen name * Nickname Arts and entertainment Film and television * ''Alias'' (2013 film), a 2013 Canadian documentary film * ''Alias'' (TV series), an American action thriller series 2001–2006 * ''Alias the ...
to represent the full command, or several commands can be grouped to perform a more complex sequence – for instance, compile the program, install it, and run it — 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: * * * * where ''doSomething'' is, in effect, a
verb A verb () is a word ( part of speech) that in syntax generally conveys an action (''bring'', ''read'', ''walk'', ''run'', ''learn''), an occurrence (''happen'', ''become''), or a state of being (''be'', ''exist'', ''stand''). In the usual descr ...
, ''how'' an
adverb An adverb is a word or an expression that generally modifies a verb, adjective, another adverb, determiner, clause, preposition, or sentence. Adverbs typically express manner, place, time, frequency, degree, level of certainty, etc., answering ...
(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 > 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 >> will redirect the output and append it to the file. Another redirection operator is the vertical bar (, ), which creates a
pipeline Pipeline may refer to: Electronics, computers and computing * Pipeline (computing), a chain of data-processing stages or a CPU optimization found on ** Instruction pipelining, a technique for implementing instruction-level parallelism within a s ...
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 A path is a route for physical travel – see Trail. Path or PATH may also refer to: Physical paths of different types * Bicycle path * Bridle path, used by people on horseback * Course (navigation), the intended path of a vehicle * Desire p ...
environment variable. Under Unix, commands also need be marked as 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 Command Prompt, also known as cmd.exe or cmd, is the default command-line interpreter for the OS/2, eComStation, ArcaOS, Microsoft Windows (Windows NT family and Windows CE family), and ReactOS operating systems. On Windows CE .NET 4.2, Windo ...
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. Some CLIs, such as those in
network router A router is a networking device that forwards data packets between computer networks. Routers perform the traffic directing functions between networks and on the global Internet. Data sent through a network, such as a web page or email, is i ...
s, have a hierarchy of
mode Mode ( la, modus meaning "manner, tune, measure, due measure, rhythm, melody") may refer to: Arts and entertainment * '' MO''D''E (magazine)'', a defunct U.S. women's fashion magazine * ''Mode'' magazine, a fictional fashion magazine which is ...
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

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
prompt Prompt may refer to: Computing * Command prompt, characters indicating the computer is ready to accept input * Command Prompt, also known as cmd.exe or cmd, the command-line interpreter in some operating systems * Prompt (natural language), instr ...
s the user to take action. A prompt usually ends with one of the characters $, %, #, :, > or - and often includes other information, such as the path of the current
working directory In computing, the working directory of a process is a directory of a hierarchical file system, if any, dynamically associated with each process. It is sometimes called the current working directory (CWD), e.g. the BSD getcwd function, or just c ...
and the
hostname In computer networking, a hostname (archaically nodename) is a label that is assigned to a device connected to a computer network and that is used to identify the device in various forms of electronic communication, such as the World Wide Web. Hos ...
. On many
Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, an ...
and derivative systems, the prompt commonly ends in $ or % if the user is a normal user, but in # if the user is a 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
cmd.exe Command Prompt, also known as cmd.exe or cmd, is the default command-line interpreter for the OS/2, eComStation, ArcaOS, Microsoft Windows (Windows NT family and Windows CE family), and ReactOS operating systems. On Windows CE .NET 4.2, Windo ...
users can modify the prompt by issuing a PROMPT command or by directly changing the value of the corresponding %PROMPT%
environment variable An environment variable is a dynamic-named value that can affect the way running processes will behave on a computer. They are part of the environment in which a process runs. For example, a running process can query the value of the TEMP envi ...
. The default of most modern systems, the C:\> style is obtained, for instance, with PROMPT $P$G. The default of older DOS systems, C> is obtained by just PROMPT, although on some systems this produces the newer C:\> style, unless used on floppy drives A: or B:; on those systems PROMPT $N$G can be used to override the automatic default and explicitly switch to the older style. Many Unix systems feature the $PS1 variable (Prompt String 1), although other variables also may affect the prompt (depending on the
shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard o ...
used). In the Bash shell, a prompt of the form: imeuser@host: work_dir $ could be set by issuing the command export PS1=' t\u@\H: \W $' In
zsh The Z shell (Zsh) is a Unix shell that can be used as an interactive login shell (computing), shell and as a command line interpreter, command interpreter for shell scripting. Zsh is an extended Bourne shell with many improvements, including som ...
the $RPROMPT 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
RISC OS RISC OS is a computer operating system originally designed by Acorn Computers Ltd in Cambridge, England. First released in 1987, it was designed to run on the ARM chipset, which Acorn had designed concurrently for use in its new line of Archi ...
the command prompt is a * symbol, and thus (OS) CLI commands are often referred to as "star commands". One can also access the same commands from other command lines (such as the
BBC BASIC BBC BASIC is a version of the BASIC programming language released in 1981 as the native programming language for the BBC Micro home/personal computer, providing a standardized language for a UK computer literacy project of the BBC. It was wr ...
command line), by preceding the command with a *.


Arguments

A command-line argument or
parameter A parameter (), generally, is any characteristic that can help in defining or classifying a particular system (meaning an event, project, object, situation, etc.). That is, a parameter is an element of a system that is useful, or critical, when ...
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
Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, an ...
and
Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...
environments, an example of a command-line argument is: rm file.s "file.s" is a command-line argument which tells the program rm to remove the file "file.s". Some programming languages, such as C,
C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...
and
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mos ...
, allow a program to interpret the command-line arguments by handling them as string parameters in the
main function In computer programming, an entry point is the place in a program where the execution of a program begins, and where the program has access to command line arguments. To start a program's execution, the loader or operating system passes contr ...
. Other languages, such as
Python Python may refer to: Snakes * Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia ** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia * Python (mythology), a mythical serpent Computing * Python (pro ...
, expose operating system specific
API An application programming interface (API) is a way for two or more computer programs to communicate with each other. It is a type of software interface, offering a service to other pieces of software. A document or standard that describes how ...
(functionality) through sys
module Module, modular and modularity may refer to the concept of modularity. They may also refer to: Computing and engineering * Modular design, the engineering discipline of designing complex devices using separately designed sub-components * Mo ...
, and in particular sys.argv for "command-line arguments". In
Unix-like operating system A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...
s, 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 In computer programming, standard streams are interconnected input and output communication channels between a computer program and its environment when it begins execution. The three input/output (I/O) connections are called standard input (stdin ...
or send data to the
standard output In computer programming, standard streams are interconnected input and output communication channels between a computer program and its environment when it begins execution. The three input/output (I/O) connections are called standard input (stdin ...
.


Command-line option

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 Dir/? and DIR /? in DOS, which have the same effect of listing the DIR command's available options, whereas dir --help (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:


=Abbreviating commands

= In
Multics Multics ("Multiplexed Information and Computing Service") is an influential early time-sharing operating system based on the concept of a single-level memory.Dennis M. Ritchie, "The Evolution of the Unix Time-sharing System", Communications of ...
, 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 SU as an abbreviation for SUPERUSER) while others may have some specific abbreviations pre-programmed (e.g. MD for
MKDIR The mkdir (make directory) command in the Unix, DOS, DR FlexOS, IBM OS/2, Microsoft Windows, and ReactOS operating systems is used to make a new directory. It is also available in the EFI shell and in the PHP scripting language. In DOS, OS/2, ...
in COMMAND.COM) or user-defined via batch scripts and aliases (e.g. alias md mkdir in
tcsh tcsh ( “tee-see-shell”, “tee-shell”, or as “tee see ess aitch”, tcsh) is a Unix shell based on and backward compatible with the C shell (csh). Shell It is essentially the C shell with programmable command-line completion, command ...
).


=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": /, -, or either may be allowed. See below. * They may or may not be
case-sensitive In computers, case sensitivity defines whether uppercase and lowercase letters are treated as distinct (case-sensitive) or equivalent (case-insensitive). For instance, when users interested in learning about dogs search an e-book, "dog" and "Dog" a ...
. * Sometimes options and their arguments are run together, sometimes separated by whitespace, and sometimes by a character, typically : or =; thus Prog -fFilename, Prog -f Filename, Prog -f:Filename, Prog -f=Filename. * Some programs allow single-character options to be combined; others do not. The switch -fA may mean the same as -f -A, or it may be incorrect, or it may even be a valid but different parameter. In
DOS DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems. DOS may also refer to: Computing * Data over signalling (DoS), multiplexing data onto a signalling channel * Denial-of-service attack (DoS), an attack on a communicat ...
,
OS/2 OS/2 (Operating System/2) is a series of computer operating systems, initially created by Microsoft and IBM under the leadership of IBM software designer Ed Iacobucci. As a result of a feud between the two companies over how to position OS/2 r ...
and
Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for ser ...
, the forward slash (/) is most prevalent, although the hyphen-minus is also sometimes used. In many versions of DOS (MS-DOS/PC DOS 2.xx and higher, all versions of DR-DOS since 5.0, as well as
PTS-DOS PTS-DOS (aka PTS/DOS) is a disk operating system, a DOS clone, developed in Russia by PhysTechSoft and Paragon Technology Systems. History and versions PhysTechSoft was formed in 1991 in Moscow, Russia by graduates and members of MIPT, inf ...
, Embedded DOS,
FreeDOS FreeDOS (formerly Free-DOS and PD-DOS) is a free software operating system for IBM PC compatible computers. It intends to provide a complete MS-DOS-compatible environment for running legacy software and supporting embedded systems. FreeDOS can ...
and
RxDOS DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems. DOS may also refer to: Computing * Data over signalling (DoS), multiplexing data onto a signalling channel * Denial-of-service attack (DoS), an attack on a communicati ...
) the switch character (sometimes abbreviated switchar or switchchar) to be used is defined by a value returned from a
system call In computing, a system call (commonly abbreviated to syscall) is the programmatic way in which a computer program requests a service from the operating system on which it is executed. This may include hardware-related services (for example, acc ...
( INT 21h/AX=3700h). The default character returned by this API is /, but can be changed to a hyphen-minus on the above-mentioned systems, except for under Datalight ROM-DOS and MS-DOS/PC DOS 5.0 and higher, which always return / from this call (unless one of many available TSRs to reenable the SwitChar feature is loaded). In some of these systems (MS-DOS/PC 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 A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...
directive in CONFIG.SYS. General Software's Embedded DOS provides a SWITCH command for the same purpose, whereas
4DOS 4DOS is a command-line interpreter by JP Software, designed to replace the default command interpreter COMMAND.COM in Microsoft DOS and Windows. It was written by Rex C. Conn and Tom Rawson and first released in 1989. Compared to the default, ...
allows the setting to be changed via SETDOS /W:n. Under DR-DOS, if the setting has been changed from /, the first directory separator \ in the display of the
PROMPT Prompt may refer to: Computing * Command prompt, characters indicating the computer is ready to accept input * Command Prompt, also known as cmd.exe or cmd, the command-line interpreter in some operating systems * Prompt (natural language), instr ...
parameter $G will change to a forward slash / (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. Also, the current setting is reflected also in the built-in help screens. Some versions of DR-DOS
COMMAND.COM COMMAND.COM is the default command-line interpreter for MS-DOS, Windows 95, Windows 98 and Windows Me. In the case of DOS, it is the default user interface as well. It has an additional role as the usual first program run after boot (init proc ...
also support a PROMPT token $/ to display the current setting. COMMAND.COM since DR-DOS 7.02 also provides a
pseudo-environment variable An environment variable is a dynamic-named value that can affect the way running processes will behave on a computer. They are part of the environment in which a process runs. For example, a running process can query the value of the TEMP env ...
named %/% to allow portable batchjobs to be written. Several external DR-DOS commands additionally support an
environment variable An environment variable is a dynamic-named value that can affect the way running processes will behave on a computer. They are part of the environment in which a process runs. For example, a running process can query the value of the TEMP envi ...
%SWITCHAR% to override the system setting. However, many programs are hardwired to use / 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
netstat In computing, netstat (''network statistics'') is a command-line network utility that displays network connections for Transmission Control Protocol (both incoming and outgoing), routing tables, and a number of network interface (network interf ...
and ping (networking utility), ping, supplied with 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 A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...
systems, the ASCII hyphen-minus begins options; the new (and GNU) convention is to use ''two'' hyphens then a word (e.g. --create) 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., -c); 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. Two hyphen-minus characters without following letters (--) 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., 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 GNU software. The ''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

= FlexOS, IBM 4680 OS, 4680 OS and IBM 4690 OS, 4690 OS use -. CP/M typically used [. Conversational Monitor System (CMS) uses a single Bracket#Parentheses .28 .29, 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: COPY source file a target file b (REPLACE OLDDATE Data General's CLI under their Data General RDOS, RDOS, Data General AOS, AOS, etc. operating systems, as well as the version of CLI that came with their Business Basic, uses only / as the switch character, is case-insensitive, and allows "local switches" on some arguments to control the way they are interpreted, such as MAC/U LIB/S A B C $LPT/L 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. In contrast, GUIs usually inform the user of available actions with menus, icons, or other visual cues. To overcome this limitation, many CLI programs display a usage message, typically when invoked with no arguments or one of ?, -?, -h, -H, /?, /h, /H, /Help, -help, or --help. 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 interface#Option conventions in DOS.2C Windows.2C OS.2F2, command-line option character can be changed from / to -, 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 - and therefore the / character is accepted as alternative path delimiter also at the DOS command line, programs may misinterpret options like /h or /H as paths rather than help parameters. However, if given as first or only parameter, most DOS programs will, by convention, accept it as request for help regardless of the current SwitChar setting. 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 /H:1, /H:2, etc.) or they give just a short help on help parameters with question mark and a longer help screen for the other help options. 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 /H:W or in /W:? (assuming /W would be another parameter supported by the program)). 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 -!, /!, -about, or --about. Since the ? and ! 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. If more detailed help is necessary than provided by a program's built-in internal help, many systems support a dedicated external "help (command), help ''command''" command (or similar), which accepts a command name as calling parameter and will invoke an external help system. In the DR-DOS family, typing /? or /H at the
COMMAND.COM COMMAND.COM is the default command-line interpreter for MS-DOS, Windows 95, Windows 98 and Windows Me. In the case of DOS, it is the default user interface as well. It has an additional role as the usual first program run after boot (init proc ...
prompt instead of a command itself will display a dynamically generated list of available internal commands;
4DOS 4DOS is a command-line interpreter by JP Software, designed to replace the default command interpreter COMMAND.COM in Microsoft DOS and Windows. It was written by Rex C. Conn and Tom Rawson and first released in 1989. Compared to the default, ...
and NDOS support the same feature by typing ? at the prompt (which is also accepted by newer versions of DR-DOS COMMAND.COM); internal commands can be individually disabled or reenabled via SETDOS /I. In addition to this, some newer versions of DR-DOS COMMAND.COM also accept a ?% command to display a list of available built-in DR-DOS system information variable, 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.


Command description syntax

Built-in usage help and man pages commonly employ a small syntax to describe the valid command form: * angle brackets for ''required'' parameters: ping * square brackets for ''optional'' parameters: mkdir [-p] * ellipses for ''repeated'' items: cp [source2…] * vertical bars for ''choice'' of items: netstat 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

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 _), or by enclosing a name with embedded spaces between quote characters or using an escape character before the space, usually a backslash (\). For example :Long path/Long program name Parameter one Parameter two … is ambiguous (is "program name" part of the program name, or two parameters?); however :Long_path/Long_program_name Parameter_one Parameter_two …, :LongPath/LongProgramName ParameterOne ParameterTwo …, :"Long path/Long program name" "Parameter one" "Parameter two" … and :Long\ path/Long\ program\ name Parameter\ one Parameter\ two … are not ambiguous.
Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, an ...
-based operating systems minimize the use of embedded spaces to minimize the need for quotes. In Microsoft Windows, one often has to use quotes because embedded spaces (such as in directory names) are common.


Command-line interpreter

The term command-line interpreter (CLI) is applied to computer programs 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. The context of interpretation is usually one of a given
operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also i ...
or 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), #! 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 or in files like the registry or the
OS/2 OS/2 (Operating System/2) is a series of computer operating systems, initially created by Microsoft and IBM under the leadership of IBM software designer Ed Iacobucci. As a result of a feud between the two companies over how to position OS/2 r ...
OS2USER.INI file.


Early history

The earliest computers did not support interactive input/output devices, often relying on sense switches and lights to communicate with the computer operator. This was adequate for 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 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 Teletype Model 33 ASR, but then on early Cathode ray tube, CRT-based computer terminals such as the VT52. All of these devices were purely text based, with no ability to display graphic or pictures. For business Application software, application programs, text-based menus were used, but for more general interaction the command line was the interface. Around 1964
Louis Pouzin Louis Pouzin (April 20, 1931 in Chantenay-Saint-Imbert, Nièvre, France) is a French computer scientist. He designed an early packet communications network, CYCLADES. This network was the first actual implementation of the pure datagram model, ...
introduced the concept and the name ''shell'' in
Multics Multics ("Multiplexed Information and Computing Service") is an influential early time-sharing operating system based on the concept of a single-level memory.Dennis M. Ritchie, "The Evolution of the Unix Time-sharing System", Communications of ...
, building on earlier, simpler facilities in the Compatible Time-Sharing System (CTSS). From the early 1970s the
Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, an ...
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 BBC Micro – almost always in the form of a BASIC interpreter. When more powerful business oriented microcomputers arrived with CP/M and later
DOS DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems. DOS may also refer to: Computing * Data over signalling (DoS), multiplexing data onto a signalling channel * Denial-of-service attack (DoS), an attack on a communicat ...
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 PARC (company), PARC GUI approach used in the 1983 Apple Lisa and the 1984
Apple Macintosh The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc., Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and ...
. A few computer users used GUIs such as GEOS (16-bit operating system), GEOS and Windows 3.1 but the majority of IBM PC users did not replace their
COMMAND.COM COMMAND.COM is the default command-line interpreter for MS-DOS, Windows 95, Windows 98 and Windows Me. In the case of DOS, it is the default user interface as well. It has an additional role as the usual first program run after boot (init proc ...
shell with a GUI until Windows 95 was released in 1995.


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. *
COMMAND.COM COMMAND.COM is the default command-line interpreter for MS-DOS, Windows 95, Windows 98 and Windows Me. In the case of DOS, it is the default user interface as well. It has an additional role as the usual first program run after boot (init proc ...
is the command-line interpreter of MS-DOS, IBM PC DOS, and clones such as DR-DOS, SISNE plus,
PTS-DOS PTS-DOS (aka PTS/DOS) is a disk operating system, a DOS clone, developed in Russia by PhysTechSoft and Paragon Technology Systems. History and versions PhysTechSoft was formed in 1991 in Moscow, Russia by graduates and members of MIPT, inf ...
, ROM-DOS, and
FreeDOS FreeDOS (formerly Free-DOS and PD-DOS) is a free software operating system for IBM PC compatible computers. It intends to provide a complete MS-DOS-compatible environment for running legacy software and supporting embedded systems. FreeDOS can ...
. * Windows Resource Kit and Windows Services for UNIX include Korn and the Bourne shells along with a Perl interpreter (Services for UNIX contains ActiveState ActivePerl in later versions and Interix for versions 1 and 2 and a shell compiled by Microsoft) * IBM OS/2 (and derivatives such as eComStation and ArcaOS) has the
cmd.exe Command Prompt, also known as cmd.exe or cmd, is the default command-line interpreter for the OS/2, eComStation, ArcaOS, Microsoft Windows (Windows NT family and Windows CE family), and ReactOS operating systems. On Windows CE .NET 4.2, Windo ...
processor. This copies the
COMMAND.COM COMMAND.COM is the default command-line interpreter for MS-DOS, Windows 95, Windows 98 and Windows Me. In the case of DOS, it is the default user interface as well. It has an additional role as the usual first program run after boot (init proc ...
commands, with extensions to REXX. * cmd.exe is part of the Windows NT stream of operating systems. * Yet another cmd.exe is a stripped-down shell for 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 DOS 7, DR DOS 3.xx, and others. * Windows users might use the 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 A Unix shell is a command-line interpreter or shell that provides a command line user interface for Unix-like operating systems. The shell is both an interactive command language and a scripting language, and is used by the operating syste ...
are also available as part of the Microsoft POSIX subsystem, POSIX sub-system, Cygwin, MKS Toolkit, UWIN, Hamilton C shell and other software packages. Available shells for these interoperability tools include csh, ksh, sh, Bash, Restricted shell, rsh, tclsh and less commonly
zsh The Z shell (Zsh) is a Unix shell that can be used as an interactive login shell (computing), shell and as a command line interpreter, command interpreter for shell scripting. Zsh is an extended Bourne shell with many improvements, including som ...
, psh * Implementations of 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 Python may refer to: Snakes * Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia ** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia * Python (mythology), a mythical serpent Computing * Python (pro ...
, Ruby (programming language), Ruby, Lua (programming language), Lua, XLNT, and other interpreters also have command shells for interactive use. * FreeBSD uses
tcsh tcsh ( “tee-see-shell”, “tee-shell”, or as “tee see ess aitch”, tcsh) is a Unix shell based on and backward compatible with the C shell (csh). Shell It is essentially the C shell with programmable command-line completion, command ...
as its default interactive shell for the superuser, and Almquist shell, ash as default scripting shell. * Many Linux distributions have the Bash implementation of the
Unix shell A Unix shell is a command-line interpreter or shell that provides a command line user interface for Unix-like operating systems. The shell is both an interactive command language and a scripting language, and is used by the operating syste ...
. *Apple
macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...
and some Linux distributions use
zsh The Z shell (Zsh) is a Unix shell that can be used as an interactive login shell (computing), shell and as a command line interpreter, command interpreter for shell scripting. Zsh is an extended Bourne shell with many improvements, including som ...
. Previously, macOS used
tcsh tcsh ( “tee-see-shell”, “tee-shell”, or as “tee see ess aitch”, tcsh) is a Unix shell based on and backward compatible with the C shell (csh). Shell It is essentially the C shell with programmable command-line completion, command ...
and Bash. * Embedded Linux (and other embedded
Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...
) devices often use the Almquist shell, Ash implementation of the Unix shell, as part of Busybox. * Android (operating system), Android uses the KornShell, mksh shell, which replaces a shell derived from Almquist shell, ash that was used in older Android versions, supplemented with commands from the separate ''toolbox'' binary. * Routers with Cisco IOS, Junos and many others are commonly configured from the command line. * The 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 script (computer programming), 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 scripts or batch files) 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 function (programming), function (such as REXX, Perl,
Python Python may refer to: Snakes * Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia ** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia * Python (mythology), a mythical serpent Computing * Python (pro ...
, Ruby (programming language), Ruby or Jython), can be used to implement command-line interpreters and filters. For a few
operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also i ...
s, most notably
DOS DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems. DOS may also refer to: Computing * Data over signalling (DoS), multiplexing data onto a signalling channel * Denial-of-service attack (DoS), an attack on a communicat ...
, 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. 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, diskpart, 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. 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 ''Colossal Cave Adventure, Adventure'' or ''King's Quest#Series, 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 (video game), The Hitchhiker's Guide to the Galaxy'', a piece of interactive fiction based on 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 In computer programming, standard streams are interconnected input and output communication channels between a computer program and its environment when it begins execution. The three input/output (I/O) connections are called standard input (stdin ...
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 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 – console or graphical, which then usually process the command line without presenting a user-console. Programs like the OS/2 E (PC DOS), E editor and some other IBM 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, about:config, access browser configuration, as well as perform a search. 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. 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. An example of such a website is the CLI interface to DuckDuckGo.DuckDuckGo TTY
/ref> There are also Web-based SSH applications, that allow to give access to server command line interface from a browser. Many video games on the PC 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

* Comparison of command shells * List of command-line interpreters * Console application * Interpreter directive * Read-eval-print loop * Shell script * Run command * * ''In the Beginning... Was the Command Line''


Notes


References


External links


The Roots of DOS
David Hunter, ''Softalk for the IBM Personal Computer'' March 1983. Archived at Patersontech.com sinc


Command-Line Reference
Microsoft TechNet Database "Command-Line Reference" {{DEFAULTSORT:Command-Line Interface Computing commands, History of human–computer interaction Software architecture User interface techniques User interfaces