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Path (computing)

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For the environment variable, see PATH (variable).

A path (or filepath, file path, pathname, or similar) is text that uniquely specifies an item in a hierarchical file system. Generally, a path is composed of directory names, special directory specifiers and optionally a filename, separated by delimiting text. The delimiter varies by file system and in theory can be anything, but popular, modern systems use slash /, backslash \, or colon :.

A path can be either relative or absolute. A relative path includes information that is relative to a particular directory whereas an absolute path indicates a location relative to the file system root directory, and therefore, does not depends on context like a relative path does. Often, a relative path is relative to the working directory. For example, in command ls f, f is a relative path to the file with that name in the working directory.

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).

History

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Multics first introduced a hierarchical file system with directories (separated by ">") in the mid-1960s.[1]

Around 1970, Unix introduced the slash character ("/") as its directory separator.

Originally, MS-DOS did not support directories, but when adding the feature, using the Unix standard of slash was not a good option since many existing commands used slash as the switch prefix. For example, dir /w. In contrast, Unix uses dash - as the switch prefix. In this context, MS-DOS version 2.0 used backslash \ for the path delimiter since it is similar to slash but did not conflict with existing commands. This convention continued into Windows in its shell Command Prompt. Eventually, PowerShell, was introduced to Windows that is slash-agnostic, allowing the use of either slash in a path.[2][3]

Path syntax

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The following table describes the syntax of paths in notable file systems (identified by operating system in some cases) and with notable aspects by shell.

Context Root
dir 		Path
delim 		Working
dir 		Parent
dir 		Home
dir 		Examples
Unix / / . .. ~ /home/user/docs/Letter.txt
./inthisdir
../../greatgrandparent
~/.rcinfo
DOS COMMAND.COM [drive letter:]\
or \\[server name]\[volume]\ 		\ . .. C:\USER\DOCS\LETTER.TXT
A:PICTURE.JPG
\\SERVER01\USER\DOCS\LETTER.TXT
OS/2 cmd.exe [drive letter:]\
or \\[server name]\[volume]\ 		/
or
\ 		. .. C:\user\docs\Letter.txt
A:Picture.jpg
\\SERVER01\USER\docs\Letter.txt
Windows Command Prompt \ (relative to current working directory root)
or [drive_letter]:\
or \\[server]\[sharename]\
or \\?\[drive_spec]:\
or \\?\UNC\[server]\[sharename]\
or \\.\[physical_device]\[4] 		/
or
\ 		. ..[5] C:\user\docs\Letter.txt
/user/docs/Letter.txt
C:\Letter.txt
\\Server01\user\docs\Letter.txt
\\?\UNC\Server01\user\docs\Letter.txt
\\?\C:\user\docs\Letter.txt
C:\user\docs\somefile.ext:alternate stream name
./inthisdir
../../greatgrandparent
Windows PowerShell [drive letter:]/
or [drive name:]\
or \\[server name]\
or [PSSnapIn name]\[PSProvider name:][:PSDrive root] 		/
or
\ 		. .. ~ C:\user\docs\Letter.txt
C:\user/docs\Letter.txt
\\Server01\user\docs\Letter.txt
cd ~\Desktop

UserDocs:/Letter.txt
Variable:PSVersionTable
Registry::HKEY_LOCAL_MACHINE\SOFTWARE\
Microsoft.PowerShell.Security\Certificate::CurrentUser\

TOPS-20 DCL [device name:] . PS:<USER.DOCS>LETTER.TXT,4
RSX-11 MCR [device name:] DR0:[30,12]LETTER.TXT;4
OpenVMS DCL [device name:][000000]
or [NODE["accountname password"]]::[device name][000000]: 		. [] [-] SYS$LOGIN: SYS$SYSDEVICE:[USER.DOCS]PHOTO.JPG

[]IN_THIS_DIR.COM;
[-.-]GreatGrandParent.TXT
SYS$SYSDEVICE:[.DRAFTS]LETTER.TXT;4
GEIN::[000000]LETTER.TXT;4
SYS$LOGIN:LOGIN.COM

Classic
Mac OS 		[volume or drive name]: : : :: Macintosh HD:Documents:Letter
:fileincurrentdir
::fileinparent
:::fileingrandparent
ProDOS AppleSoft BASIC /[volume or drive name]/ / /SCHOOL.DISK/APPLEWORKS/MY.REPORT

FLIGHT.SIMULATOR,D2

AmigaOS Amiga CLI /
AmigaShell 		[drive, volume, device, or assign name]: / empty
string 		/ Workbench:Utilities/MultiView
DF0:S/Startup-Sequence
S:Startup-Sequence
TCP:en.wikipedia.com/80
RISC OS ShellCLI [fs type[#option]:][:drive number or disc name.]$

note: &, %, and @ can also be used to reference the root
of the current user, the library and the current (working) directory respectively.

. @ ^ & ADFS::MyDrive.$.Documents.Letter
Net#MainServer::DataDrive.$.Main.sy10823
LanMan::WindowsC.$.Pictures.Japan/gif
NFS:&.!Choices
ADFS:%.IfThere
@.inthisdir
^.^.greatgrandparent

When filesystems with filename extensions are mounted,
'.' characters are changed to '/', as in the Japan/gif example above.

Symbian OS File manager \ \ \user\docs\Letter.txt
Domain/OS Shell

// (root of domain)
/ (root of current node)

 / . \ ~ //node/home/user/docs/Letter.txt
./inthisdir
\\greatgrandparent
~rcinfo
MenuetOS CMD / /
Stratus VOS VOS command-line
interpreter 		%[system_name]#[module_name]> > < %sysname#module1>SubDir>AnotherDir
NonStop
Kernel TACL
Tandem Advanced
Command Language 		No root . none \NODE.$DISK.SUBVOL.FILE
\NODE.$DEVICE
\NODE.$DEVICE.#SUBDEV.QUALIFIER
CP/M CCP [drive letter:] no directory support, just user areas 0–F A:LETTER.TXT
GS/OS :[volume name]: or .[device name]: or [prefix]:

note: prefix may be a number (0–31), * (boot volume) or @ (AppleShare home directory)

:
or
/ 		@ :Apps:Platinum.Paint:Platinum.Paint
*:System:Finder
.APPLEDISK3.5B/file
OpenHarmony (incl. HarmonyOS) exec[6][7] hb set -root [ROOT_PATH]

hb set -p --product [PRODUCT_NAME]

> ./ ../ LOCAL>MEDIA_TYPE_>Download>Letter.txt

Japanese and Korean versions of Windows often display the '¥' character or the '₩' character instead of the directory separator. In such cases the code for a 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)). 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 backward compatibility.[8]

Mac OS X, as a derivative of UNIX, 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).

Paths in programming languages

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Programming languages also use paths. E.g.: When a file is opened. Most programming languages use the path representation of the underlying operating system: 

 uxFile = fopen("project/readme.txt", "r")

 winFile = fopen("C:\\Program Files\\bin\\config.bat", "r")

This direct access to the operating system paths can hinder the portability of programs. To support portable programs Java uses File.separator to distinguish between / and \ separated paths. Seed7 has a different approach for the path representation. In Seed7 all paths use the Unix path convention, independent of the operating system. Under windows a mapping takes place (e.g.: The path /c/users is mapped to c:\users).

Universal Naming Convention

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The Microsoft universal naming convention (UNC), a.k.a. uniform naming convention, a.k.a. network path, specifies a syntax to describe the location of a network resource, such as a shared file, directory, or printer. A UNC path has the general form: 

\\ComputerName\SharedFolder\Resource

Some Windows interfaces allow or require UNC syntax for WebDAV share access, rather than a URL. The UNC syntax is extended[9] with optional components to denote use of SSL and TCP/IP port number, a WebDAV URL of http[s]://HostName[:Port]/SharedFolder/Resource becomes 

\\HostName[@SSL][@Port]\SharedFolder\Resource

When viewed remotely, the "SharedFolder" may have a name different from what a program on the server sees when opening "\SharedFolder". Instead, the SharedFolder name consists of an arbitrary name assigned to the folder when defining its "sharing".

Some Windows interfaces also accept the "Long UNC": 

\\?\UNC\ComputerName\SharedFolder\Resource

Windows uses the following types of paths:

  • local file system (LFS), such as C:\File
  • universal naming convention (UNC), such as \\Server\Volume\File or /<internet resource name>[\Directory name] (at least in Windows 7 and later)
  • "long" device path such as \\?\C:\File or \\?\UNC\Server\Volume\File.[10] This path points to the local file namespace and \\.\ is a similar one that points to the local DOS device namespace. This format is also the "raw" or "uninterpreted" path, since it sends paths straight to the file system without converting / to \ and interpreting names like ...[4]
  • Windows NT object manager \\??\-prefixed paths (global DOS namespace).[11][12]

In versions of Windows prior to Windows XP, only the APIs that accept "long" device paths could accept more than 260 characters.

The shell in Windows XP and Windows Vista, explorer.exe, allows path names up to 248 characters long.[citation needed]

Since UNCs start with two backslashes, and the backslash is also used for string escaping and in regular expressions, this can result in extreme cases of leaning toothpick syndrome: an escaped string for a regular expression matching a UNC begins with 8 backslashes – \\\\\\\\ – because the string and regular expression both require escaping. This can be simplified by using raw strings, as in C#'s @"\\\\" or Python's r'\\\\', or regular expression literals, as in Perl's qr{\\\\}.

POSIX pathname definition

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Most Unix-like systems use a similar syntax.[13] POSIX allows treating a path beginning with two slashes in an implementation-defined manner,[14] though in other cases systems must treat multiple slashes as single slashes.[15] Many applications on Unix-like systems (for example, scp, rcp, and rsync) use resource definitions such as: 

hostname:/directorypath/resource

or URI schemes with the service name (here 'smb'): 

smb://hostname/directorypath/resource

Examples

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Unix

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The following examples are for typical, Unix-based file systems:

Given the working directory is /home/mark/ and it contains subdirectory bobapples, relative paths to the subdirectory include ./bobapples and bobapples, and the absolute path is /home/mark/bobapples. A command to change the working directory to the subdirectory: 

$ cd bobapples

If the working directory was /home/jo, then the relative path ../mark/bobapples specifies the subdirectory. The double dots .. indicates a move up the directory hierarchy one level to /home, the rest indicates moving down to mark and then boapples.

Microsoft shells

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Screenshot of a Windows Command Prompt shell showing filenames in a directory

The Windows API accepts slash for path delimiter, and thus Unix-like syntax should work. But Windows applications interpret a slash for other purposes or treat it as invalid, and require backslash. In particular, the legacy shell, Command Prompt, does not handle slash, but other shells available for Windows, such as tcsh and PowerShell, support slash.

Unlike Unix that always has a single root directory, a Windows file system has a root for each storage drive. An absolute path includes a drive letter or uses the UNC format.

A UNC path (starting with \\?\) does not support slashes.[4]

A:\Temp\File.txt is an absolute path that specifies a file named File.txt in the directory Temp which is in the root of drive A::

C:..\File.txt is a relative path that specifies file File.txt located in the parent of the working directory on drive C::

Folder\SubFolder\File.txt is a relative path that specifies file File.txt in directory SubFolder which is in directory Folder which is in the working directory of the current drive:

File.txt is a relative path that specifies File.txt in the working directory:

\\.\COM1 specifies the first serial port, COM1:

The following uses a path with slashes for directory delimiter: 

C:\>more < C:/Windows/system.ini
; for 16-bit app support
[386Enh]
woafont=dosapp.fon
EGA80WOA.FON=EGA80WOA.FON
EGA40WOA.FON=EGA40WOA.FON
CGA80WOA.FON=CGA80WOA.FON
CGA40WOA.FON=CGA40WOA.FON
...

A path with forward slashes may need to be surrounded by double quotes to disambiguate from command-line switches. For example, dir /windows is invalid, but dir "/window" is valid. And cd is more lenient by allowing cd /windows.

See also

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  • basename – Unix string manipulation utility
  • Device file – Interface to a device driver that appears in a file system as if it were an ordinary file
  • dirname – Program on Unix & Unix operating systems
  • Distributed file system – Type of decentralized filesystem
  • Filename – Text string used to uniquely identify a computer file
  • Filesystem Hierarchy Standard – Linux standard for directory structure
  • Fully qualified file name – unambiguous name for an entity in a computing language containing an identifier and all enclosing namespaces
  • PATH (variable) – Computer environment variable
  • URL – Web address to a particular file or page

References

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  1. ^ Daley, R.C.; Neumann, P.G. (1965). "A general-purpose file system for secondary storage". Proceedings of the November 30--December 1, 1965, fall joint computer conference, Part I on XX - AFIPS '65 (Fall, part I). Vol. Part I. pp. 213–229. doi:10.1145/1463891.1463915. S2CID 16236414.
  2. ^ "Why Windows Uses Backslashes and Everything else Uses Forward Slashes". 10 February 2014.
  3. ^ "Why is the DOS path character ""?". 24 June 2005.
  4. ^ a b c "Naming Files, Paths, and Namespaces". Microsoft Docs. 15 December 2022.
  5. ^ "cd". Windows Commands: Windows Server. Microsoft Docs. 3 February 2023. Retrieved 4 October 2023.
  6. ^ "Introduction to the Shell". GitHub. OpenAtom OpenHarmony. Retrieved 13 March 2024.
  7. ^ "exec". GitHub. OpenAtom OpenHarmony. Retrieved 14 March 2024.
  8. ^ "When is a backslash not a backslash?". Sorting it all Out.
  9. ^ "DavGetHTTPFromUNCPath function". WebDAV: Windows. Microsoft Docs. series. 13 October 2021. Retrieved 4 October 2023.
  10. ^ "File path formats on Windows systems". File and Stream I/O: .NET. Microsoft Docs. Retrieved 14 July 2019.
  11. ^ "winapi - Is there a difference between \??\ and \\?\ paths?". Stack Overflow.
  12. ^ "Path prefixes \??\ and \\?\". Stack Overflow.
  13. ^ "UNC Definition". ComputerLanguage.com.
  14. ^ "POSIX pathname resolution specification".
  15. ^ "POSIX pathname definition".
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