Command-line interface

A command-line interface or command language interpreter (CLI), also known as command-line user interface, console user interface[1] and character user interface (CUI), is a means of interacting with a computer program where the user (or client) issues commands to the program in the form of successive lines of text (command lines). A program which handles the interface is called a command language interpreter or shell (computing).

The CLI was the primary means of interaction with most computer systems on computer terminals in the mid-1960s, and continued to be used throughout the 1970s and 1980s on OpenVMS, Unix systems and personal computer systems including MS-DOS, CP/M and Apple DOS. The interface is usually implemented with a command line shell, which is a program that accepts commands as text input and converts commands into appropriate operating system functions.

Today, many end users rarely, if ever, use command-line interfaces and instead rely upon graphical user interfaces and menu-driven interactions. However, many software developers, system administrators and advanced users still rely heavily on command-line interfaces to perform tasks more efficiently, configure their machine, or access programs and program features that are not available through a graphical interface.

Alternatives to the command line include, but are not limited to text user interface menus (see IBM AIX SMIT for example), keyboard shortcuts, and various other desktop metaphors centered on the pointer (usually controlled with a mouse). Examples of this include the Windows versions 1, 2, 3, 3.1, and 3.11 (an OS shell that runs in DOS), DosShell, and Mouse Systems PowerPanel.

Programs with command-line interfaces are generally easier to automate via scripting.

Command-line interfaces for software other than operating systems include a number of programming languages such as Tcl/Tk, PHP, and others, as well as utilities such as the compression utility WinZip, and some FTP and SSH/Telnet clients.

Linux command-line. Bash. GNOME Terminal. screenshot
Screenshot of a sample bash session in GNOME Terminal 3, Fedora 15
Windows PowerShell 1.0 PD
Screenshot of Windows PowerShell 1.0, running on Windows Vista

Comparison to graphical user interfaces

Apple Unix with Netscape
Screenshot of Apple Computer's CommandShell in A/UX 3.0.1

Compared with a graphical user interface, a command line requires fewer system resources to implement. Since options to commands are given in a few characters in each command line, an experienced user finds the options easier to access. Automation of repetitive tasks is simplified - most operating systems using a command line interface support some mechanism for storing frequently used sequences in a disk file, for re-use; 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 a "help" option provides a concise review of the options of a command. The command-line environment may not provide the 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 drop-down menus of a graphical user interface, without repeated reference to manuals.

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.

Examples of command-line interpreters include DEC's DIGITAL Command Language (DCL) in OpenVMS and RSX-11, the various Unix shells (sh, ksh, csh, tcsh, bash, etc.), CP/M's CCP, DOS's COMMAND.COM, as well as the OS/2 and the Windows CMD.EXE programs, the latter groups being based heavily on DEC's RSX-11 and RSTS CLIs. Under most operating systems, it is possible to replace the default shell program with alternatives; examples include 4DOS for DOS, 4OS2 for OS/2, and 4NT or Take Command for Windows.

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

Application command-line interfaces

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:

  1. Parameters: Most operating systems support a means to pass additional information to a program when it is launched. When a program is launched from an OS command line shell, additional text provided along with the program name is passed to the launched program.
  2. Interactive command line sessions: After launch, a program may provide an operator with an independent means to enter commands in the form of text.
  3. OS inter-process communication: Most operating systems support means of inter-process communication (for example; standard streams or named pipes). Command lines from client processes may be redirected to a CLI program by one of these methods.

Some applications support only a CLI, presenting a CLI prompt to the user and acting upon command lines as they are entered. 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 the CLI, whereas the MATLAB GUI exposes only a subset of features.

The early Sierra games, such as the first three King's Quest games (1984–1986), used commands from an internal command line to move the character around in the graphic window.


The command-line interface evolved from a form of dialog once conducted by humans over teleprinter (TTY) machines, in which human operators remotely exchanged information, usually one line of text at a time. Early computer systems often used teleprinter machines as the means of interaction with a human operator. The computer became one end of the human-to-human teleprinter model. So instead of a human communicating with another human over a teleprinter, a human communicated with a computer.

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 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 was part of the Multics time-sharing operating system.[2] In 1964, MIT Computation Center staff member Louis Pouzin developed the RUNCOM tool for executing command scripts while allowing argument substitution.[3] 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.[4] Pouzin returned to his native France in 1965, and the first Multics shell was developed by Glenda Schroeder.[3]

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.[5][6] 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 Korn shell (ksh), Almquist shell (ash), and the popular Bourne-again shell (or Bash).[6]

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 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 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 is found in the Utilities sub-folder of the Applications folder, or by remotely logging into the machine using ssh. bash is the default shell for macOS; tcsh, the Korn shell, and the Z shell are also provided.

Screenshot of the MATLAB 7.4 command-line interface and GUI


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, Forth, LISP, Rexx, and many dialects of BASIC) provide an interactive command-line mode to allow for rapid evaluation of code.

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

Anatomy of a shell CLI

The general pattern of an OS command line interface[7][8] is:

Prompt command param1 param2 param3 ... paramN

  • Prompt - generated by the program to provide context for the client.
  • Command — provided by the client. Commands are usually one of three classes:
    1. Internal — recognized and processed by the command line interpreter itself and not dependent upon any external executable file.
    2. Included — A separate executable file generally considered part of the operating environment and always included with the OS.
    3. External — External executable files not part of the basic OS, but added by other parties for specific purposes and applications.
  • param1 ...paramN — Optional parameters provided by the client. The format and meaning of the parameters depends upon the command issued. In the case of Included or External commands, the values of the parameters are delivered to the program (specified by the Command) as it is launched by the OS. Parameters may be either Arguments or Options.

In this example, 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 for command-line interfaces.

A CLI can generally be considered as consisting of syntax and semantics. The syntax 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 that all commands within their CLI conform to. These rules also dictate how a user navigates through the system of commands. The semantics define what sort of operations are possible, on what sort of data these operations can be performed, and how the grammar represents these operations and data—the symbolic meaning in the syntax.

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

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

Unlike a button or menu item in a GUI, a command line is typically self-documenting, stating exactly what the user wants done. In addition, command lines usually include many 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 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:

  • doSomething how toFiles
  • doSomething how sourceFile destinationFile
  • doSomething how < inputFile > outputFile
  • doSomething how | doSomething how | doSomething how > outputFile

where doSomething is, in effect, a verb, how an adverb (for example, should the command be executed "verbosely" or "quietly") and toFiles an object or objects (typically one or more files) on which the command should act. The > 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 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 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 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 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 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

Hard reset BBC Micro 32K Acorn DFS
Prompt of a BBC Micro after switch-on or hard reset.

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 $, %, #, :, > and often includes other information, such as 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 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's 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 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),[9] although other variables also may affect the prompt (depending on the shell used). In the bash shell, a prompt of the form:

[time] user@host: work_dir $

could be set by issuing the command

export PS1='[\t] \u@\H: \W $'

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".[10] One can also access the same commands from other command lines (such as the BBC BASIC command line), by preceding the command with a *.


An MS DOS command line, illustrating parsing into command and arguments

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 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:

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++ and Java, allow a program to interpret the command-line arguments by handling them as string parameters in the main function. Other languages, such as Python, expose these arguments as global variables.

In Unix-like operating systems, a single hyphen-minus by itself is usually a special value specifying that a program should handle data coming from the standard input or send data to the standard output.

Command-line option

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, for example Dir/? and DIR /? have the same effect in DOS (list the DIR command's 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:

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

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

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

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.
  • 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, OS/2 and Windows, 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, Embedded DOS, FreeDOS and RxDOS) the switch character (sometimes abbreviated switchar or switchchar) to be used is defined by a value returned from a system call (INT 21h/AH=37h). 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 directive in CONFIG.SYS. General Software's Embedded DOS provides a SWITCH command for the same purpose, whereas 4DOS allows the setting to be changed via SETDOS /W:n.[11] Under DR-DOS, if the setting has been changed from /, the first directory separator \ in the display of the PROMPT 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. Some versions of DR-DOS COMMAND.COM also support a PROMPT token $/ to display the current setting. COMMAND.COM since DR-DOS 7.02 also provides a pseudo-environment variable named %/% to allow portable batchjobs to be written.[12][13] Several external DR-DOS commands additionally support an environment variable %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 and ping, supplied with Windows, will accept the /? option to list available options, and yet the list will specify the "-" convention).

In Unix-like 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).

FlexOS, 4680 OS and 4690 OS use -.

CP/M typically used [.

Conversational Monitor System (CMS) uses a single 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 RDOS, 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 brief summary of its valid parameters, typically when invoked with no arguments or one of ?, -?, -h, -H, /?, /h, /H, -help, or --help.

However, entering a program name without parameters in the hope that it will display usage help can be hazardous, as some programs and scripts execute without further notice.

Although desirable at least for the help parameter, programs may not support all option lead-in characters exemplified above. Under DOS, where the default command-line option character can be changed from / to -, programs may query the SwitChar API in order to determine the current setting. So, if a program is not hard-wired 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.[11]

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.[14]

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)).[15][16][17][18][14][nb 1]

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.[18]

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.

RT-11 help
The end of the HELP command output from RT-11SJ displayed on a VT100.

If more detailed help is necessary than provided by a program's built-in internal help, many systems support a dedicated external "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 prompt instead of a command itself will display a dynamically generated list of available internal commands;[19] 4DOS and NDOS support the same feature by typing ? at the prompt[11] (which is also accepted by newer versions of DR-DOS COMMAND.COM); internal commands can be individually disabled or reenabled via SETDOS /I.[11] In addition to this, some newer versions of DR-DOS COMMAND.COM also accept a ?% command to display a list of available built-in pseudo-environment variables. Besides their purpose as quick help reference this can be used in batchjobs to query the facilities of the underlying command-line processor.[19]

Command description syntax

Built-in usage help and man pages commonly employ a small syntax to describe the valid command form:[20][nb 2]

  • angle brackets for required parameters: ping <hostname>
  • square brackets for optional parameters: mkdir [-p] <dirname>
  • ellipses for repeated items: cp <source1> [source2...] <dest>
  • vertical bars for choice of items: netstat {-t|-u}

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 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" ...


Long\ path/Long\ program\ name Parameter\ one Parameter\ two ...

are not ambiguous. Unix-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

Although most users think of the shell as an interactive command interpreter, it is really a programming language in which each statement runs a command. Because it must satisfy both the interactive and programming aspects of command execution, it is a strange language, shaped as much by history as by design.

The terms command-line interpreter (abbreviated CLI), command-line shell, or command language interpreter (also abbreviated CLI) are applied to computer programs designed to interpret a sequence of lines of text which may be entered by a user, read from a file or another kind of data stream. The context of interpretation is usually one of a given operating system 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 language that is interpreted.

The 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 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 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 CRT-based computer terminals such as the VT52.

All of these devices were purely text based, with no ability to display graphic or pictures.[nb 3] For business application programs, text-based menus were used, but for more general interaction the command line was the interface.

Around 1964 Louis Pouzin introduced the concept and the name shell in Multics, building on earlier, simpler facilities in the Compatible Time-Sharing System (CTSS).[22]

From the early 1970s the Unix operating system adapted the concept of a powerful command-line environment, and introduced the ability to 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 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 piping of output.

The command-line was first seriously challenged by the PARC GUI approach used in the 1983 Apple Lisa and the 1984 Apple Macintosh. A few computer users used GUIs such as GEOS and Windows 3.1 but the majority of IBM PC users did not replace their COMMAND.COM shell with a GUI until Windows 95 was released in 1995.[23][24]

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 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 and Windows NT cmd.exe have been ported to Windows CE and presumably works on Microsoft Windows NT Embedded 4.0
  • Windows Resource Kit and Windows Services for Unix include Korn and the Bourne shells along with a Perl interpreter (Services of Unix contains Active State ActivePerl in later versions and Interix for versions 1 and 2 and a shell compiled by Microsoft)
  • IBM OS/2 has the cmd.exe processor. This copies the COMMAND.COM commands, with extensions to REXX.
  • cmd.exe and COMMAND.COM are 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
  • PocketConsole is a Windows NT 4.0 shell for Windows CE that is much like 4NT.
  • Windows users have a CLI environment named Windows Command Prompt, which might use the CScript interface to alternate programs. PowerShell provides a command-line interface, but its applets are not written in Shell script. Implementations of the Unix shell are also available as part of the POSIX sub-system,[25] Cygwin, MKS Toolkit, UWIN, Hamilton C shell and other software packages. Available shells for these interoperability tools include csh, ksh, sh, bash, rsh, tclsh and less commonly zsh, psh
  • COMMAND.COM (4DOS), Windows NT cmd.exe (4NT, TCC), and OS/2 cmd.exe (4OS2) and others based on them are enhanced shells which can be a replacement for the native shell or a means of enhancement of the default shell
  • 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, Ruby, Lua, XLNT, and other interpreters also have command shells for interactive use.
  • FreeBSD uses tcsh as its default interactive shell for the superuser.
  • Apple macOS[nb 4] and many Linux distributions have the Bash implementation of the Unix shell. Early versions of macOS used tcsh as the default shell.
  • Embedded Linux (and other embedded Unix-like) devices often use the Ash implementation of the Unix shell, as part of Busybox.
  • Android uses the mksh shell,[26][27] which replaces a shell derived from ash[28] that was used in older Android versions, supplemented with commands from the separate toolbox[29] binary.
  • Routers with Cisco IOS,[30] Junos[31] and many others are commonly configured from the command line.


Most command-line interpreters support scripting, to various extents. (They are, after all, interpreters of an interpreted programming language, albeit in many cases the language is unique to the particular command-line interpreter.) They will interpret scripts (variously termed shell scripts or batch files) written in the 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 (such as REXX, Perl, Python, Ruby or Jython), can be used to implement command-line interpreters and filters. For a few operating systems, most notably DOS, such a command interpreter provides a more flexible command-line interface than the one supplied. In other cases, such a command interpreter can present a highly customised user interface employing the user interface and input/output facilities of the language.

Other command-line interfaces

The command line provides an interface between programs as well as the user. In this sense, a command line is an alternative to a dialog box. 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 Adventure or King's Quest 1-3, which relied on the user typing commands at the bottom of the screen. One controls the character by typing commands like 'get ring' or 'look'. The program returns a text which describes how the character sees it, or makes the action happen. The text adventure The Hitchhiker's Guide to the Galaxy, a piece of interactive fiction based on 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 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, devices are files too, so the normal type of file for the shell used for stdin,stdout and stderr is a 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 editor and some other IBM editors, can process command-lines normally meant for the shell, the output being placed directly in the document window.

A web browser's URL input field can be used as a command line. It can be used to "launch" web apps, access browser configuration, as well as perform a search. 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.[32] This functionality is present whether the search is triggered from a browser field or on Google's website.

See also


  1. ^ An example is the comprehensive internal help system of the DR-DOS 7.03 DEBUG command, which can be invoked via ?? at the debug prompt (rather than only the default ? overview). Specific help pages can be selected via ?n (where n is the number of the page). Additionally, help for specific commands can be displayed by specifying the command name after ?, f.e. ?D will invoke help for the various dump commands (like D etc.). Some of these features were already supported by the DR DOS 3.41 SID86 and GEMSID.
  2. ^ Conventions for describing commands on DOS-like operating systems. Notable difference: The Windows Server 2003 R2 documentation uses italic letters for "Information that the user must supply", while the Server 2008 documentation uses angle brackets. Italics can not be displayed by the internal "help" command while there is no problem with angle brackets."Command shell overview". Windows Server 2003 Product Help. Microsoft. 2005-01-21. Retrieved 2013-04-07."Command-Line Syntax Key". Windows Server 2008 R2 TechNet Library. Microsoft. 2010-01-25. Retrieved 2013-04-07.
  3. ^ With the exception of ASCII art
  4. ^ via Finder, Applications, Utilities, Terminal


  1. ^ "Text mode programs (CUI: Console User Interface)". Wine User Guide. Retrieved 2013-09-22.
  2. ^ "Unix Shells". the notion of having a replaceable "command shell" rather than a "monitor" tightly integrated with the OS kernel tends to be attributed to Multics.
  3. ^ a b "The Origin of the Shell". Retrieved 2017-04-12.
  4. ^ Metz, Cade (2013-01-03). "Say Bonjour to the Internet's Long-Lost French Uncle". WIRED. Retrieved 2017-07-31.
  5. ^ Mazières, David (Fall 2004). "MULTICS - The First Seven Years". Advanced Operating Systems. Stanford Computer Science Department. Retrieved 2017-08-01.
  6. ^ a b Jones, M. (2011-12-06). "Evolution of shells in Linux". developerWorks. IBM. Retrieved 2017-08-01.
  7. ^ "GNU BASH Reference".
  8. ^ "Microsoft Windows Command Shell Overview".
  9. ^ Parker, Steve (2011). "Chapter 11: Choosing and using shells". Shell Scripting: Expert Recipes for Linux, Bash and more. Programmer to programmer. Indianapolis, USA: John Wiley & Sons. p. 262. ISBN 978-111816632-1. Retrieved 2017-03-23. The shell has four different command prompts, called PS1, P52, P53, and PS4. PS stands for Prompt String.
  10. ^ RISC OS 3 User Guide (PDF). Acorn Computers Limited. 1992-03-01. p. 125.
  11. ^ a b c d Brothers, Hardin; Rawson, Tom; Conn, Rex C.; Paul, Matthias; Dye, Charles E.; Georgiev, Luchezar I. (2002-02-27). 4DOS 8.00 online help.
  12. ^ Paul, Matthias (1998-01-09). DELTREE.BAT R1.01 Extended file and directory delete. Caldera, Inc. Archived from the original on 2019-04-08. Retrieved 2019-04-08.
  13. ^ DR-DOS 7.03 WHATSNEW.TXT — Changes from DR-DOS 7.02 to DR-DOS 7.03. Caldera, Inc. 1998-12-24. Archived from the original on 2019-04-08. Retrieved 2019-04-08.
  14. ^ a b Paul, Matthias; Frinke, Axel C. (2006-01-16), FreeKEYB - Advanced international DOS keyboard and console driver (User Manual) (v7 preliminary ed.)
  15. ^ CCI Multiuser DOS 7.22 GOLD Online Documentation. Concurrent Controls, Inc. (CCI). 1997-02-10. HELP.HLP. (NB. The symbolic instruction debugger SID86 provides a short help screen on ? and comprehensive help on ??.)
  16. ^ Paul, Matthias (1997-05-24) [1991]. DRDOSTIP.TXT — Tips und Tricks für DR DOS 3.41 - 5.0. MPDOSTIP (in German) (47 ed.). Archived from the original on 2016-11-07. Retrieved 2016-11-07.
  17. ^ Paul, Matthias (2002-01-09). "SID86". comp.os.cpm. Retrieved 2018-04-08. […] Since the DR-DOS 7.03 DEBUG is still based on the old SID86.EXE, I suggest to run DEBUG 1.51 and enter the extended help system with ?? from the debug prompt. This will give you eight screens full of syntax and feature help. Some of these features were also supported by older issues. […]
  18. ^ a b Paul, Matthias (2002-05-13). "[fd-dev] mkeyb". freedos-dev. Archived from the original on 2018-09-10. Retrieved 2018-09-10. […] CPI /H […] CPI [@] [@] [/?|/Help[:topic]] [/!|/About] […] [?|&] […] /?, /Help Display this help screen or specific help for a topic (+) […] /!, /About Display the 'About' info screen […] /Cpifile (+) .CPI/.CP file name <EGA.CPI>; extension: <.CPI>; CPI.EXE=StdIn […] /Report Report file name <''=StdOut>; extension: <.RPT> […] /Style (+) Export <0>-6=BIN-raw/ROM/RAM/PSF0/1/SH/CHED; 7-12/13-18/19-24=ASM-hex/dec/bin/ip/il/p/l/mp/ml […] CPI /H:C […] Overview on codepage file parameter usage: […] CPI /H:S […] Overview on /Style parameters: […] ?, & Online edit mode (prompts for additional parameter input) […]
  19. ^ a b Paul, Matthias (1997-07-30). NWDOS-TIPs — Tips & Tricks rund um Novell DOS 7, mit Blick auf undokumentierte Details, Bugs und Workarounds. MPDOSTIP (e-book) (in German) (edition 3, release 157 ed.). Archived from the original on 2017-09-10. Retrieved 2014-09-06. NWDOSTIP.TXT is a comprehensive work on Novell DOS 7 and OpenDOS 7.01, including the description of many undocumented features and internals. It is part of the author's yet larger MPDOSTIP.ZIP collection maintained up to 2001 and distributed on many sites at the time. The provided link points to a HTML-converted older version of the NWDOSTIP.TXT file.
  20. ^ Conventions for describing commands on Unix-like operating systems:"The Open Group Base Specifications Issue 7, Chapter 12.1 Utility Argument Syntax". The Open Group. 2008. Retrieved – Linux Conventions and Miscellany Manual
  21. ^ Kernighan, Brian Wilson; Pike, Robert C. (1984). The UNIX Programming Environment. Englewood Cliffs: Prentice-Hall. ISBN 0-13-937699-2.
  22. ^ Pouzin, Louis. "The Origin of the Shell". Retrieved 2013-09-22.
  23. ^ "Remembering Windows 95's launch 15 years later".
  24. ^ "A history of Windows". Archived from the original on 2015-03-01.
  25. ^ "Windows POSIX shell compatibility".
  26. ^ "master - platform/external/mksh - Git at Google". Retrieved 2018-03-18.
  27. ^ "Android adb shell - ash or ksh?". Retrieved 2018-03-14.
  28. ^ "Android sh source".
  29. ^ "Android toolbox source".
  30. ^ "Cisco IOS Configuration Fundamentals Configuration Guide, Release 12.2". Cisco. 2013-10-30. Using the Command-Line Interface. The Cisco IOS command-line interface (CLI) is the primary user interface...
  31. ^ "Command-Line Interface Overview". Retrieved 2018-03-14.
  32. ^ "Google strange goodness".

External links


AWStats is an open source Web analytics reporting tool, suitable for analyzing data from Internet services such as web, streaming media, mail, and FTP servers. AWStats parses and analyzes server log files, producing HTML reports. Data is visually presented within reports by tables and bar graphs. Static reports can be created through a command line interface, and on-demand reporting is supported through a Web browser CGI program.AWStats supports most major web server log file formats including Apache (NCSA combined/XLF/ELF log format or Common Log Format (CLF)), WebStar, IIS (W3C log format), and many other common web server log formats.

Development was moved from SourceForge to GitHub in 2014.

Columbia MM

Columbia MM (Mail Manager) is a computer program for reading email using a command-line interface. It was developed at Columbia University between 1984 and 1990, and is a Unix reimplementation of a 1978 TOPS-20 email program, also known as MM, which in turn was an update of an earlier program by Michael McMahon of SRI International. Columbia MM has also been built on other platforms, including DOS and VMS.

MM was unusual for its time in its support of "message sequences," which allowed the user to select a subset of messages in a mailbox for batch operations. The message sequence feature proved so popular with MM users that TOPS-20 MM author Mark Crispin went on to implement similar filtering capabilities in Pine. Columbia MM also offered context-sensitive help, command completion, and command history, carried over from the TOPS-20 version, before such features were commonplace in Unix software.

After a lull in development in 1990, MM development picked up again in 2002 with an interim release, including changes for Linux portability and POP support.

Command (computing)

In computing, a command is a directive to a computer program acting as an interpreter of some kind to perform a specific task. Most commonly a command is either a directive to some kind of command-line interface, such as a shell, or an event in a graphical user interface triggered by the user selecting an option in a menu.

Specifically, the term command is used in imperative computer languages. These languages are called this, because statements in these languages are usually written in a manner similar to the imperative mood used in many natural languages. If one views a statement in an imperative language as being like a sentence in a natural language, then a command is generally like a verb in such a language.

Many programs allow specially formatted arguments, known as flags or options, which modify the default behaviour of the command, while further arguments describe what the command acts on. Comparing to a natural language: the flags are adverbs, whilst the other arguments are objects.

Comparison of file archivers

The following tables compare general and technical information for a number of file archivers. Please see the individual products' articles for further information. They are neither all-inclusive nor are some entries necessarily up to date. Unless otherwise specified in the footnotes section, comparisons are based on the stable versions—without add-ons, extensions or external programs.

Console (video game CLI)

A console is a command line interface where the personal computer game's settings and variables can be edited while the game is running. Consoles also usually display a log of warnings, errors, and other messages produced during the program's execution. Typically it can be toggled on or off and appears over the normal game view.

The console is normally accessed by pressing the backtick key ` (frequently also called the ~ key; normally located below the ESC key) on QWERTY keyboards or the ² on AZERTY keyboards, and is usually hidden by default. In most cases it cannot be accessed unless enabled by either specifying a command line argument when launching the game or by changing one of the game's configuration files.

Event Viewer

Event Viewer is a component of Microsoft's Windows NT line of operating systems that lets administrators and users view the event logs on a local or remote machine. In Windows Vista, Microsoft overhauled the event system.Due to the Event Viewer's routine reporting of minor start-up and processing errors (which do not in fact harm or damage the computer), the software is frequently used by technical support scammers to convince users unfamiliar with Event Viewer that their computer contains critical errors requiring immediate technical support. An example is the "Administrative Events" field under "Custom Views" which can have over a thousand errors or warnings logged over a month's time.

File Manager (Windows)

File Manager is a file manager program bundled with releases of Microsoft Windows between 1990 and 1999 and available from 6 April 2018 as an optional download for all modern releases of Windows, including Windows 10.It is a single-instance graphical interface, replacing the command-line interface of MS-DOS, to manage files (copy, move, open, delete, search, etc.) and MS-DOS Executive file manager from previous Windows versions. Although File Manager was included in Windows 95 and Windows NT 4.0 and some later versions, Windows Explorer was introduced and used as the primary file manager, with file management via a two-pane view different from that of File Manager, and a single-pane view obtained by clicking a "My Computer" icon.


Kompare (formerly "Kdiff") is a graphical diff and merge tool targeting developers. It allows users to compare two different text files or two directories. It is part of KDE Applications (and formerly part of KDE Software Compilation) and therefore primarily used on Linux and other Unix-like operating systems, as well as Windows. Kompare does not actually compute the differences between the compared files itself, but is merely a graphical front end to the command line interface diff utility.

It is a standard KDE SC tool, it comes packaged with the kdesdk module.


OSv (stylized OSv) is a cloud computing focused computer operating system released on September 16, 2013. It is a special-purpose operating system built to run as a guest on top of a virtual machine, thus it does not include drivers for bare-metal hardware. It is a unikernel, designed to run a single Linux executable or an application written in one of the supported runtime environments (such as Java). For this reason, it does not support a notion of users (it's not a multiuser system) or processes - everything runs in the kernel address space. Using a single address space removes some of the time-consuming operations associated with context switching. It uses large amounts of code from the FreeBSD operating system, in particular the network stack and the ZFS file system. OSv can be managed using a REST Management API and an optional command line interface written in Lua.


PSPP is a free software application for analysis of sampled data, intended as a free alternative for IBM SPSS Statistics. It has a graphical user interface and conventional command-line interface. It is written in C and uses GNU Scientific Library for its mathematical routines. The name has "no official acronymic expansion".

Pip (package manager)

pip is a package-management system used to install and manage software packages written in Python. Many packages can be found in the default source for packages and their dependencies — Python Package Index (PyPI).Python 2.7.9 and later (on the python2 series), and Python 3.4 and later include pip (pip3 for Python 3) by default.pip is a recursive acronym for "Pip Installs Packages".

Progress indicator

A progress indicator is an element of a command-line interface, a textual user interface, or a graphical user interface that is intended to inform the user that an operation is in progress, to reassure that the system is not hung or waiting for user input,

and often to provide the user with an estimate of how far through a task the system has progressed.

Recovery Console

The Recovery Console is a feature of the Windows 2000, Windows XP and Windows Server 2003 operating systems. It provides the means for administrators to perform a limited range of tasks using a command line interface. Its primary function is to enable administrators to recover from situations where Windows does not boot as far as presenting its graphical user interface. The recovery console is used to provide a way to access the hard drive in an emergency through the command prompt. As such, the Recovery Console can be accessed either through the original installation media used to install Windows, or it can also be installed to the hard drive and added to the NTLDR menu, however, relying on the latter is more risky because it requires that the computer can boot to the point that NTLDR loads.


SharpOS is a computer operating system based on the .NET Framework and related programming language C#. It was developed by a group of volunteers and presided over by a team of six project administrators: Mircea-Cristian Racasan, Bruce Markham, Johann MacDonagh, Sander van Rossen, Jae Hyun, and William Lahti. It is no longer in active development, and resources have been moved to the MOSA project. As of 2017, SharpOS is one of three C#-based operating systems released under a free and open-source software license. SharpOS has only one public version available and a basic command line interface.

Shell (computing)

In computing, a shell is a user interface for access to an operating system's services. In general, operating system shells use either a command-line interface (CLI) or graphical user interface (GUI), depending on a computer's role and particular operation. It is named a shell because it is the outermost layer around the operating system kernel.CLI shells require the user to be familiar with commands and their calling syntax, and to understand concepts about the shell-specific scripting language (for example bash script). They are also more easily operated via refreshable braille display, and provide certain advantages to screen readers.

Graphical shells place a low burden on beginning computer users, and are characterized as being easy to use. Since they also come with certain disadvantages, most GUI-enabled operating systems also provide CLI shells.


Sqoop is a command-line interface application for transferring data between relational databases and Hadoop.


In computing, WBAdmin is a command-line utility built into Windows Vista, Windows Server 2008, Windows 7, Windows Server 2008 R2, Windows 8, Windows Server 2012, and Windows 10 operating systems. The command is used to perform backups and restores of operating systems, drive volumes, computer files, folders, and applications from a command-line interface.


WinAce was an archiving program for Windows with its own "ACE" compressed archive format and built-in support for other common archive formats types such as ZIP, RAR and CAB. They also offer a freeware (but not free software) command-line interface decompression (including listing and testing) program called Unace for macOS and Linux.

Beginning with version 2.65, WinAce was bundled with the WhenU SaveNow adware program. This bundle has been removed from the current version (2.69) and has been replaced with an opt-in sponsorship deal via TrialPay.

The application seems to be discontinued since it hasn't seen any updates since 2007 and as of August 2017 also their official Website went offline ( snapshots from July 2017 are the last ones which do not show a "Domain parked" message).

Yum (software)

The Yellowdog Updater, Modified (YUM) is a free and open-source command-line package-management utility for computers running the Linux operating system using the RPM Package Manager. Though YUM has a command-line interface, several other tools provide graphical user interfaces to YUM functionality.

YUM allows for automatic updates and package and dependency management on RPM-based distributions. Like the Advanced Package Tool (APT) from Debian, YUM works with software repositories (collections of packages), which can be accessed locally or over a network connection.

Under the hood, YUM depends on RPM, which is a packaging standard for digital distribution of software, which automatically uses hashes and digisigs to verify the authorship and integrity of said software; unlike some app stores, which serve a similar function, neither YUM nor RPM provide built-in support for proprietary restrictions on copying of packages by end-users. YUM is implemented as libraries in the Python programming language, with a small set of programs that provide a command-line interface. GUI-based wrappers such as YUM Extender (yumex) also exist.A rewrite of YUM named DNF replaced YUM as the default package manager in Fedora 22. DNF was created to improve on YUM in several ways - improved performance, better resolution of dependency conflicts, and easier integration with other software applications.

Process management
Memory management and
resource protection
Storage access and
file systems
Miscellaneous concepts

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