computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, ...

, which is a

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 ...

for various

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...

s used to identify the location of

executable 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 ...

s. The command is available 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, a ...

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 ...

systems, the

AROS Aros may refer to: * Aros (Middle-earth), a river in J. R. R. Tolkien's Middle-earth legendarium * Aros, Mull, the location of Aros Castle, a ruined 13th-century castle on the Isle of Mull, Scotland *AROS Research Operating System, a free software ...

shell, for

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 ca ...

and for Microsoft Windows. The functionality of the ''which'' command is similar to some implementations of the

type Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * Ty ...

command.

POSIX The Portable Operating System Interface (POSIX) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines both the system- and user-level application programming inte ...

specifies a command named

that also covers this functionality.

Implementations

Unix, Unix-like

The command takes one or more arguments; for each of these arguments, it prints the full path of the executable to

stdout 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 ...

that would have been executed if this argument had been entered into 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 ...

. It does this by searching for an executable or script in the directories listed in the environment variable

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 ...

. The ''which'' command is part of most

computers. It is also part of the

C Shell The C shell (csh or the improved version, tcsh) is a Unix shell created by Bill Joy while he was a graduate student at University of California, Berkeley in the late 1970s. It has been widely distributed, beginning with the 2BSD release of the B ...

. A which command first appeared in

3BSD The History of the Berkeley Software Distribution begins in the 1970s. 1BSD (PDP-11) The earliest distributions of Unix from Bell Labs in the 1970s included the source code to the operating system, allowing researchers at universities to modify an ...

. Carlo Wood developed the

GNU GNU () is an extensive collection of free software Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any ...

implementation used in most

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which i ...

-based operating systems. On FreeBSD, the which utility was originally written in

Perl Perl is a family of two High-level programming language, high-level, General-purpose programming language, general-purpose, Interpreter (computing), interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it ...

by Wolfram Schneider. The current version of which was rewritten by Daniel Papasian using the C

programming language A programming language is a system of notation for writing computer programs. Most programming languages are text-based formal languages, but they may also be graphical. They are a kind of computer language. The description of a programming l ...

Microsoft Windows, MS-DOS, FreeDOS

The command is available as a separate package for Microsoft Windows as part of the

GnuWin32 The G''nu''W''in''32 project provides native ports in the form of executable computer programs, patches, and source code for various GNU and open source tools and software, much of it modified to run on the 32-bit Windows platform. The ports in ...

project and the

UnxUtils UnxUtils is a collection of ports of common GNU Unix-like utilities to native Win32, with executables only depending on the Microsoft C- runtime msvcrt.dll. The collection was last updated externally on April 15, 2003, by Karl M. Syring. ...

collection of

native Native may refer to: People * Jus soli, citizenship by right of birth * Indigenous peoples, peoples with a set of specific rights based on their historical ties to a particular territory ** Native Americans (disambiguation) In arts and enterta ...

Win32 The Windows API, informally WinAPI, is Microsoft's core set of application programming interfaces (APIs) available in the Microsoft Windows operating systems. The name Windows API collectively refers to several different platform implementations ...

ports A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as Ha ...

of common

utilities A public utility company (usually just utility) is an organization that maintains the infrastructure for a public service (often also providing a service using that infrastructure). Public utilities are subject to forms of public control and ...

. Windows also includes the similar where.exe command. The same functionality is available in

MS-DOS MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few oper ...

, but not Windows, as the built-in TRUENAME command. In

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-sou ...

, the functionality is provided by the Get-Command Cmdlet. The

version was developed by Trane Francks.

AmigaOS compatible

The command is used to find and print the location of a specific program. Inputs: * FILE – Specifies the command to search for * NORES – Resident programs are not included in the search * RES – Only resident programs are considered * ALL – Will find all locations of the FILE, which may cause the printing of the same location several times

References

External links

* * * * {{Unix commands Unix user management and support-related utilities