Path (computing)

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For other meanings for this term, see Path.

A path is the general form of a file or directory name, giving a file's name and its unique location in a file system. Paths point to their location using a string of characters signifying directories, separated by a delimiting character, most commonly the slash "/" or backslash character "\", or colon ":" though some operating systems may use a different delimiter. Paths are used extensively in computer science to represent the directory/file relationships common in modern operating systems, and are essential in the construction of Uniform Resource Locators (URLs).

A path can be either absolute or relative. A full path or absolute path is a path that points to the same location on one file system regardless of the working directory or combined paths. It is usually written in reference to a root directory.

A relative path is a path relative to the current working directory, so the full absolute path may not need to be given.

Contents

[edit] Representations of paths by operating system and shell

Operating System Shell Parent-Child Direction Root Directory Directory Separator
Unix-like OS Unix shell Left-Right / /
DOS COMMAND.COM Left-Right [drive letter]:\ / or \
OS/2 cmd.exe Left-Right [drive letter]:\ / or \
Microsoft Windows cmd.exe Left-Right [drive letter]:/ or [drive letter]:\ / or \
Microsoft Windows Windows PowerShell Left-Right [drive name]:/ or [drive name]:\ or

[PSSnapIn name]\[PSProvider name]::[PSDrive root]

 / or \
Classic Mac OS Left-Right [drive name]: :
AmigaOS Amiga CLI / AmigaShell Left-Right [drive, volume or assign name]: /
RISC OS Task window Left-Right [fs type]::[drive number or disc name].$ .

On Japanese and Korean versions of Windows it may often look like the '¥' character or the '₩' character is the path separator. This is not true however, instead the code for backslash is being drawn as these characters. Very early versions of MS-DOS replaced the backslash with these glyphs on the display to make it possible to display them by programs that only understood 7-bit ASCII (other characters such as the square brackets were replaced as well, see ISO 646, Windows Codepage 932 (Japanese Shift JIS), and Codepage 949 (Korean)). This predates the addition of paths in MS-DOS 2 and is a good indication that Microsoft never intended backslash to be the path separator, as a normal slash would display correctly. Although even the first version of Windows supported the 8-bit ISO-8859-1 character set which has the Yen sign at U+00A5, and modern versions of Windows supports Unicode which has the Won sign at U+20A9, much software will continue to display backslashes found in ASCII files this way to preserve backwards compatibility.

Mac OS X is UNIX-based and thus uses UNIX paths internally. However, to preserve compatibility for software and familiarity for users, many portions of the GUI switch "/" typed by the user to ":" internally, and switch them back when displaying filenames (a ":" entered by the user is also changed into "-" but the inverse translation does not happen).

[edit] PATH variable

On Unix-like operating systems, DOS, OS/2 and Microsoft Windows, PATH is an environment variable listing a set of paths to directories where executables may be found.

[edit] Uniform Naming Convention

The UNC, short for Universal Naming Convention or Uniform Naming Convention, specifies a common syntax to describe the location of a network resource, such as a shared file, directory, or printer. The UNC syntax for Windows systems is as follows:

\\ComputerName\SharedFolder\Resource

Note: The UNC syntax is sometimes written with forward slashes. In Windows the forward slashes and back slashes are equivalent, but many programs will accept only backward slashes, and some that will only accept *double* backslashes (ie \\\\ComputerName\\SharedFolder)), especially in quoted string constants, due to the standard use of backslash as a Escape character.

The "SharedFolder" is not necessarily the same as what a program on the server would see if it tries to open "\SharedFolder". Instead it is a name assigned to an arbitrary folder by the server when it made it "shared".

Unix-like systems occasionally use a similar syntax, but a POSIX requirement that double slashes must be treated as single slashes breaks this.[citation needed] More often this syntax is used:

ComputerName:/SharedFolder/Resource [1]

or, like URLs with the service name:

smb://ComputerName/SharedFolder/Resource

Some Windows APIs also accepts the "Long UNC":

\\?\UNC\ComputerName\SharedFolder\Resource

The different types of paths in Windows are local file system (LFS), such as C:\File, uniform naming convention (UNC), such as \\Server\Volume\File, and Long UNC or UNCW, such as \\?\C:\File or \\?\UNC\Server\Volume\File. In earlier versions of Windows only the API's that accept "Long UNC" would accept more than 260 characters. This has been fixed in recent versions.

[edit] Example

[edit] Unix style

Here is an example with a Unix style file system as it would appear from a terminal or terminal application (command-line window):

Your current working directory (cwd) is:

/users/mark/

You want to change your current working directory to:

/users/mark/bobapples

At that moment, the relative path for the directory you want is:

./bobapples

and the absolute path for the directory you want is

/users/mark/bobapples

Because bobapples is the relative path for the directory you want, you may type the following at the command prompt to change your current working directory to bobapples:

cd bobapples

Two dots ("..") are used for moving up in the hierarchy, to indicate the parent directory; one dot (".") represents the directory itself. Both can be components of a complex relative path (e.g., "../mark/./bobapples"), where "." alone or as the first component of such a relative path represents the working directory. (Using "./foo" to refer to a file "foo" in the current working directory can sometimes be useful to distinguish it from a resource "foo" to be found in a default directory or by other means; for example, to view a specific version of a man page instead of the one installed in the system.)

[edit] MS-DOS/Microsoft Windows style

Contrary to popular belief, the Windows system API accepts slash, and thus all the above Unix examples should work. But many applications on Windows interpret a slash for other purposes or think it is an invalid character, and thus require you to enter backslash. One of the prime examples is the cmd.exe shell (often called the "terminal" as it is typically run in a terminal window). Note that many other shells available for Windows, such as tcsh and Windows PowerShell, allow the forward slash.

In addition "\" does not indicate a single root, but instead the root of the "current disk". Indicating a file on a disk other than the current one requires prefixing a drive letter and colon. This is not ambiguous because colon is not a valid character in an MS-DOS filename, and thus you cannot have a file called "A:" in your current directory.

Here are some examples of MS-DOS/Windows style paths, with backslashes used to match the most common syntax:

A:\Temp\File

This path points to a file whose name is File, which is located in the directory Temp, which in turn is located in the root directory of the drive A:.

C:..\File

This path refers to a file called File located in the parent directory of the current directory on drive C:.

Folder\SubFolder\File

This path denotes a file called File located in SubFolder directory which in turn is located in Folder directory which is located in the current directory of the current drive (since no drive specification is present in this example).

File

This rather simple path points to a file named File located in the current directory (since no directory specification is present) on the current drive (since no drive specification is present).

\\.\COM1

This path refers to the first serial port (COM1).

[edit] See also

[edit] References

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.

[edit] External links