PATH is an

environment variable An environment variable is a dynamic-named value that can affect the way running processes will behave on a computer. They are part of the environment in which a process runs. For example, a running process can query the value of the TEMP envi ...

Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...

DOS DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems. DOS may also refer to: Computing * Data over signalling (DoS), multiplexing data onto a signalling channel * Denial-of-service attack (DoS), an attack on a communicat ...

OS/2 OS/2 (Operating System/2) is a series of computer operating systems, initially created by Microsoft and IBM under the leadership of IBM software designer Ed Iacobucci. As a result of a feud between the two companies over how to position OS/2 ...

, and

Microsoft Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for serv ...

, specifying a set of

directories Directory may refer to: * Directory (computing), or folder, a file system structure in which to store computer files * Directory (OpenVMS command) * Directory service, a software application for organizing information about a computer network's u ...

where executable programs are located. In general, each executing

process A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management *Business process, activities that produce a specific se ...

or user session has its own PATH setting.

History

Multics Multics ("Multiplexed Information and Computing Service") is an influential early time-sharing operating system based on the concept of a single-level memory.Dennis M. Ritchie, "The Evolution of the Unix Time-sharing System", Communications of t ...

originated the idea of a search path. The early

Unix shell A Unix shell is a command-line Interpreter (computing), interpreter or shell (computing), shell that provides a command line user interface for Unix-like operating systems. The shell is both an interactive command language and a scripting langua ...

only looked for program names in /bin, but by

Version 3 Unix The term "Research Unix" refers to early versions of the Unix operating system for DEC PDP-7, PDP-11, VAX and Interdata 7/32 and 8/32 computers, developed in the Bell Labs Computing Sciences Research Center (CSRC). History The term ''Resear ...

the directory was too large and /usr/bin, and a search path, became part of the operating system.

Unix and Unix-like

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 interf ...

and Unix-like operating systems, the $PATH variable is specified as a list of one or more directory names separated by colon (:) characters. Directories in the PATH-string are not meant to be escaped, making it impossible to have directories with : in their name. The /bin, /usr/bin, and /usr/local/bin directories are typically included in most users' $PATH setting (although this varies from implementation to implementation). The

superuser In computing, the superuser is a special user account used for system administration. Depending on the operating system (OS), the actual name of this account might be root, administrator, admin or supervisor. In some cases, the actual name of t ...

also typically has /sbin and /usr/sbin entries for easily executing

system administration A system administrator, or sysadmin, or admin is a person who is responsible for the upkeep, configuration, and reliable operation of computer systems, especially multi-user computers, such as servers. The system administrator seeks to ensu ...

commands. The current directory (.) is sometimes included by users as well, allowing programs residing in the

current working directory In computing, the working directory of a process is a directory of a hierarchical file system, if any, dynamically associated with each process. It is sometimes called the current working directory (CWD), e.g. the BSD getcwd function, or just ...

to be executed directly. System administrators as a rule do ''not'' include it in $PATH in order to prevent the accidental execution of scripts residing in the current directory, such as may be placed there by a malicious

tarbomb In computing, tar is a computer software utility for collecting many files into one archive file, often referred to as a tarball, for distribution or backup purposes. The name is derived from "tape archive", as it was originally developed to ...

. In that case, executing such a program requires specifying an absolute (/home/userjoe/bin/script.sh) or relative path (./script.sh) on the command line. When a command name is specified by the user or an

exec Exec or EXEC may refer to: * Executive officer, a person responsible for running an organization * Executive producer, provides finance and guidance for the making of a commercial entertainment product * A family of kit helicopters produced by Rot ...

call is made from a program, the system searches through $PATH, examining each directory from left to right in the list, looking for a

filename A filename or file name is a name used to uniquely identify a computer file in a directory structure. Different file systems impose different restrictions on filename lengths. A filename may (depending on the file system) include: * name &ndas ...

that matches the command name. Once found, the program is executed as a

child process A child process in computing is a process created by another process (the parent process). This technique pertains to multitasking operating systems, and is sometimes called a subprocess or traditionally a subtask. There are two major procedures ...

of the command shell or program that issued the command.

DOS, OS/2, and Windows

On DOS, OS/2, and Windows operating systems, the %PATH% variable is specified as a list of one or more directory names separated by semicolon (;) characters.Microsoft.com, PATH command
/ref> The Windows system directory (typically C:\WINDOWS\system32) is typically the first directory in the path, followed by many (but not all) of the directories for installed software packages. Many programs do not appear in the path as they are not designed to be executed from a command window, but rather from a

Graphical User Interface The GUI ( "UI" by itself is still usually pronounced . or ), graphical user interface, is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicator such as primary notation, inste ...

. Some programs may add their directory to the front of the PATH variable's content during installation, to speed up the search process and/or override OS commands. In the DOS era, it was customary to add a PATH ;%PATH% or SET PATH=;%PATH% line to

AUTOEXEC.BAT AUTOEXEC.BAT is a system file that was originally on DOS-type operating systems. It is a plain-text batch file in the root directory of the boot device. The name of the file is an abbreviation of "automatic execution", which describes its funct ...

. When a command is entered in a command shell or a system call is made by a program to execute a program, the system first searches the

and then searches the path, examining each directory from left to right, looking for an

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 instruction (computer science), instructi ...

filename that matches the command name given. Executable programs have

filename extension A filename extension, file name extension or file extension is a suffix to the name of a computer file (e.g., .txt, .docx, .md). The extension indicates a characteristic of the file contents or its intended use. A filename extension is typically d ...

s of

EXE 
Exe or EXE may refer to:


* .exe, a file extension
* exe., abbreviation for executive
 Places
* River Exe, in England
* Exe Estuary, in England
* Exe Island, in Exeter, England
 Transportation and vehicles
* Exe (locomotive), a British locomotive
 ...

COM 
Com or COM may refer to:

 Computing
* COM (hardware interface), a serial port interface on IBM PC-compatible computers
* COM file, or .com file, short for "command", a file extension for an executable file in MS-DOS
* .com, an Internet top-level d ...

, and batch scripts have extensions of

BAT 







Bats are  mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as  wings, they are the only mammals capable of true and sustained  flight. Bats are more agile in flight than most  ...

or CMD. Other executable filename extensions can be registered with the system as well. Once a matching executable file is found, the system

spawns Spawn is the eggs and sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of releasing the eggs and sperm, and the act of both sexes is called spawning. Most aquatic animals, except for aquat ...

a new process which runs it. The PATH variable makes it easy to run commonly used programs located in their own folders. If used unwisely, however, the value of the PATH variable can slow down the operating system by searching too many locations, or invalid locations. Invalid locations can also ''stop'' services from running altogether, especially the 'Server' service which is usually a dependency for other services within a Windows Server environment.

References

{{DEFAULTSORT:Path (Variable) Computer file systems Environment variables