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52-454: Under command-line based operating systems such as MS-DOS , this key causes the contents of the current text mode screen memory buffer to be copied to the standard printer port , usually LPT1. In essence, whatever is currently on the screen when the key is pressed will be printed. Pressing the Ctrl key in combination with Prt Sc turns on and off the "printer echo" feature. When echo

104-409: A command is a directive to a computer program to perform a specific task. It may be issued via a command-line interface or as input to a network service as part of a network protocol , or as an event triggered in a graphical user interface . Specifically, the term command is used in imperative programming languages. The name arises because statements in these languages are usually written in

156-411: A command-line interpreter ( Unix shell ). The following command changes the user's working position in the directory tree to the directory /home/pete . The utility program is cd and the argument is /home/pete : The following command prints the text Hello World on the standard output stream, which, in this case, just prints the text on the screen. The program name is echo and the argument

208-519: 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

260-507: 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 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 and drop-down menus of a graphical user interface, without reference to manuals. Operating system (OS) command-line interfaces are usually distinct programs supplied with

312-478: A pipeline where the output of one command becomes the input to the next command. One can modify the set of available commands by modifying which paths appear in the PATH 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

364-438: 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 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 , a numerical analysis computer program, are available via

416-458: A Unix-like CLI. Microsoft provides MKS Inc. 's ksh implementation MKS Korn shell for Windows through their Services for UNIX add-on. Since 2001, the Macintosh operating system macOS has been based on a Unix-like operating system called Darwin . On these computers, users can access a Unix-like command-line interface by running the terminal emulator program called Terminal , which

468-504: 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 , 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

520-439: A manner similar to the imperative mood used in many natural languages . A statement in an imperative programming language would then be a sentence in a natural language, and the command would be the predicate . Many programs allow specifically formatted arguments , known as flags or options, which modify the default behaviour of the program, while further arguments may provide objects, such as files, to act on. As an analogy to

572-628: A natural language, the flags are adverbs, while the other arguments are objects . The meaning of command is highly dependent on context. For example, some authors refer to conditionals as commands while they are called expressions in Python or Bash and statements in JAVA. Similarly, writing to stdout is done in Bash with the builtin command printf , while it is done with the built-in function print() in Python. Here are some commands given to

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624-588: 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 , 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

676-490: A screenshot tool (Spectacle or GNOME Screenshot respectively), giving options to save the screenshot, plus more options like manually picking a specific window, screen area, using a timeout, etc. Sending the image to many services (KDE), or even screen recording (GNOME), is built-in too. Macintosh does not use a print screen key; instead, key combinations are used that start with ⌘ Cmd + ⇧ Shift . These key combinations are used to provide more functionality including

728-461: Is "Hello World". The quotes are used to prevent Hello and World being treated as separate tokens: The following commands are equivalent. They list files in the directory /bin . The program is ls , having three flags ( l , t , r ), and the argument is the directory /bin : The following command displays the contents of the files ch1.txt and ch2.txt . The program name is cat , having two file name arguments: Here are some commands for

780-513: Is active a program is typically invoked by typing its name followed by command-line arguments (if any). For example, in Unix and Unix-like environments, an example of a command-line argument is: file.s is a command-line argument which tells the program rm to remove the file named file.s . Some programming languages, such as C , C++ and Java , allow a program to interpret the command-line arguments by handling them as string parameters in

832-600: Is found in the Utilities sub-folder of the Applications folder, or by remotely logging into the machine using ssh . Z shell is the default shell for macOS; Bash, tcsh , and the KornShell are also provided. Before macOS Catalina , Bash was the default. 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

884-421: Is in effect, any conventional text output to the screen will be copied ("echoed") to the printer. There is also a Unicode character for print screen, U+2399 ⎙ PRINT SCREEN SYMBOL . Newer-generation operating systems using a graphical interface tend to save a bitmap image of the current screen, or screenshot , to their clipboard or comparable storage area. Some shells allow modification of

936-516: Is the grammar that all commands must follow. In the case of operating systems , DOS and Unix each define their own set of rules that all commands must follow. In the case of embedded systems , each vendor, such as Nortel , Juniper Networks or 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

988-594: The Prt Sc key can be configured to open the 'New' function of the Snip & Sketch tool. This allows the user to take a full screen, specific window, or defined area screenshot and copy it to clipboard. This behaviour can be enabled by going to Snip & Sketch, accessing Settings via the menu and enabling the 'Use the PrtScn button to open screen snipping'. In KDE and GNOME , very similar shortcuts are available, which open

1040-476: The main function . Other languages, such as Python , expose operating system specific API (functionality) through sys module , and in particular sys.argv 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 . A command-line option or simply option (also known as

1092-533: The CLI, whereas the MATLAB GUI exposes only a subset of features. In Colossal Cave Adventure from 1975, the user uses a CLI to enter one or two words to explore a cave system. The command-line interface evolved from a form of communication conducted by people over teleprinter (TTY) machines. Sometimes these involved sending an order or a confirmation using telex . Early computer systems often used teleprinter as

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1144-524: The PC's serial ports . 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 programs, and could not easily be replaced. The first implementation of the shell as a replaceable component

1196-498: 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 4DOS for DOS, 4OS2 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

1248-451: The ability to select screen objects. ⌘ Cmd + ⇧ Shift + 3 captures the whole screen, while ⌘ Cmd + ⇧ Shift + 4 allows for part of the screen to be selected. The standard print screen functions described above save the image to the desktop . However, using any of the key sequences described above, but additionally pressing the Ctrl will modify the behavior to copy the image to

1300-423: The command In zsh 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 the command prompt is a * symbol, and thus (OS) CLI commands are often referred to as star commands . One can also access

1352-670: 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 administrators and other advanced users for system administration, computer programming and batch processing . In November 2006, 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 . MinGW and Cygwin are open-source packages for Windows that offer

1404-399: 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

1456-431: The commands and responses can be displayed using refreshable Braille displays . The general pattern of a command line interface is: In this format, the delimiters between command-line elements are whitespace characters 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 . The syntax

1508-466: The commands. Alternatives to CLIs include GUIs (most notably desktop metaphors with a mouse pointer , such as Microsoft Windows ), text-based user interface menus (such as DOS Shell and IBM AIX SMIT ), and keyboard shortcuts . 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

1560-407: 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

1612-422: 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

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1664-451: The exact behavior using modifier keys such as the control key . In Microsoft Windows , pressing Prt Sc will capture the entire screen, while pressing the Alt key in combination with Prt Sc will capture the currently selected window. The captured image can then be pasted into an editing program such as a graphics program or even a word processor . Pressing Prt Sc with both

1716-501: 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 (or Bash). Early microcomputers themselves were based on a command-line interface such as CP/M , DOS or AppleSoft BASIC . During the 1980s and 1990s, the introduction of the Apple Macintosh and of Microsoft Windows on PCs saw

1768-506: The first Multics shell was developed by Glenda Schroeder . The first Unix shell , the V6 shell , was developed by Ken Thompson in 1971 at Bell Labs 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

1820-412: 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

1872-501: 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. 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 $ , % , # , : , > or - and often includes other information, such as

1924-538: The left Alt key and left ⇧ Shift pressed turns on a high contrast mode (this keyboard shortcut can be turned off by the user). Since Windows 8, pressing the ⊞ Win key in combination with Prt Sc (and optionally in addition to the Alt key) will save the captured image to disk (the default pictures location). This behavior is therefore backward compatible with users who learned Print Screen actions under operating systems such as MS-DOS . In Windows 10,

1976-598: 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 replaced the traditional – minicomputer + terminals – time sharing architecture, hardware terminals were replaced by terminal emulators  — PC software that interpreted terminal signals sent through

2028-706: The mid-1960s, on computer terminals , as an interactive and more user-friendly alternative to the non-interactive interface available with punched cards . Today, most computer users rely on graphical user interfaces ("GUIs") instead of CLIs. However, many programs and 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

2080-410: 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 used). In the Bash shell, a prompt of the form: could be set by issuing

2132-515: The operating system. A program that implements such a text interface is often called a command-line interpreter, command processor or shell . Examples of command-line interpreters include Nushell , DEC's DIGITAL Command Language (DCL) in OpenVMS and RSX-11 , the various Unix shells ( sh , ksh , csh , tcsh , zsh , Bash , etc.), CP/M 's CCP , DOS ' COMMAND.COM , as well as the OS/2 and

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2184-490: 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. Command (computing) In computing ,

2236-422: 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 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

2288-468: The path of the current working directory and the hostname . On many Unix 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

2340-428: The prompt. Some CLIs, such as those in network routers , have a hierarchy of modes , 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

2392-548: The prompt. In DOS' COMMAND.COM and in Windows NT's cmd.exe users can modify the prompt by issuing a PROMPT command or by directly changing the value of the corresponding %PROMPT% environment variable . 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

2444-463: The same commands from other command lines (such as the BBC BASIC command line), by preceding the command with a * . A command-line argument or 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

2496-477: The system clipboard instead. On the IBM Model F keyboard, the key is labeled PrtSc and is located under ↵ Enter . On the IBM Model M , it is located next to F12 and is labeled Print Screen. Command line interface A command-line interface ( CLI ) is a means of interacting with a computer program by inputting lines of text called command-lines . Command-line interfaces emerged in

2548-455: 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

2600-410: 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 or alias 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

2652-615: 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 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: Some applications support

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2704-568: Was part of the Multics time-sharing operating system . In 1964, MIT Computation Center staff member Louis Pouzin developed the RUNCOM tool for executing command scripts while allowing argument substitution. Pouzin coined the term shell to describe the technique of using commands like a programming language, and wrote a paper about how to implement the idea in the Multics operating system. Pouzin returned to his native France in 1965, and

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