Path (computing)

A path (or filepath, file path, pathname, or similar) is a string that uniquely identifies an item in a hierarchical file system. Generally, a path is composed of directory names, special format specifiers, and optionally a filename, all separated by delimiters. This delimiter can vary by operating system, but popular, modern systems use the slash /, backslash \, or colon :.

The case-sensitivity of individual path components will vary based on operating system, or based on options specified at the time of a file system's creation or first use. In practice, this means that for a case-sensitive system, path components named component1 and Component1 can coexist at the same level in the hierarchy, whereas for a case-insensitive file system, they cannot (an error will occur). macOS and Windows' native file systems are case-insensitive by default, whereas typical Linux file systems are case-sensitive.

A path can be either relative or absolute. A relative path is a path in relation to another, most often the working directory. An absolute path indicates a location regardless of the current directory; that is, it specifies all path components starting from the file system's root, and does not depend on context like a relative path does.

Paths are also essential for locating hierarchically-organized network resources, as seen in URLs and UNC paths.

History

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

Around 1970, Unix introduced the slash / as its directory separator.

Originally, MS-DOS did not support directories. When adding the feature, using the Unix standard of a slash was not a good option since many existing commands used a slash as the switch prefix (i.e., dir /w). In contrast, Unix uses the dash - as the switch prefix. The backslash \ was ultimately chosen instead for its similarity to the slash and not conflicting with existing commands. This convention continued into Windows. However, some areas of Windows do accept or understand Unix-style slashes also, such as PowerShell.

Summary of systems

The following table describes the syntax of paths in notable operating systems:Template:Table alignment

In programming languages

Most programming languages use the path representation of the underlying system, but some may also be system-independent.

For instance, this C code is system-dependent and may fail on opposing systems:

uxFile = fopen("project/readme.txt", "r") // Fails on Windows
winFile = fopen("C:\\Program Files\\bin\\config.bat", "r") // Fails on Unix

• In Java, the Template:Var field stores the system-dependent separator. Some functions preclude the need for the separator entirely.

import java.io.File;
import java.nio.file.Path;
import java.nio.file.Paths;
// ...
File file = new File("path" + File.separator + "file.txt");
Path path = Paths.get("path", "file.txt");

• In Python, the pathlib module offers system-independent path operations.

from pathlib import Path

with (Path("path") / "to" / "file.txt").open() as open_file:
    ...

In Unix

Most Unix-like systems use a similar syntax. POSIX allows treating a path beginning with two slashes in an implementation-defined manner, though in other cases systems must treat consecutive slashes as one.

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'), like smb://hostname/directorypath/resource.

In macOS

When macOS was being developed, it inherited some pathname choices from Classic Mac OS and the Unix-like NeXTSTEP. The classic Mac OS uses a : while Unix and Unix-like systems use a / as the path delimiter. As a solution, to preserve compatibility for software and familiarity for users, and to allow disk file systems to be used both by the classic Mac OS and macOS, some portions of macOS convert between colons and slashes in pathnames; for example, the HFS+ file system, from the classic Mac OS, converts colons in file names to slashes and, when reading a directory, converts slashes in filenames to colons, as and the Carbon toolkit converts colons in pathnames to slashes and slashes in path names to colons, and converts them back when providing filenames and pathnames to the caller.

In DOS and Windows

File:Dir command in Windows Command Prompt.png

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

DOS and Windows have no single root directory; a root exists for each storage drive, indicated with a drive letter or through UNC.

Directory and file name comparisons are case-insensitive: "test.TXT" would match "Test.txt".

Windows understands the following kinds of paths:

• Local paths, such as C:\File.
• Universal naming convention (UNC).
• DOS device paths, such as \\?\C:\File or \\.\UNC\Server\Volume\File. The first, \\?\ skips path normalization. The second, \\.\ uses the raw device namespace.

In the Windows API, file I/O functions automatically convert / into \ (except when using the \\?\ prefix). Unless the \\?\ prefix is used, paths are limited to the length defined by Template:Var. This variable defaulted to 260 characters until Windows 10, when it could be expanded to 32,767.

PowerShell allows slash-interoperability for backwards-compatibility:

PS C:\>Get-Content -Path "C:/path/to/file.txt"

Here is some text within a file

Yen/won character error

Japanese and Korean versions of Windows often displayed the '¥' character or the '₩' character instead of the directory separator. This is because while in ANSI codepages, the character at 0x5C was the backslash, and in Japanese and Korean codepages, 0x5C was the yen and won signs, respectively. Therefore, when the character for a backslash was used, other glyphs appeared.

Universal Naming Convention

The Microsoft Universal Naming Convention (UNC, uniform naming convention, or network path), is 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:

Some Windows interfaces allow or require UNC syntax for WebDAV share access, rather than a URL. The UNC syntax is extended with optional components to denote use of SSL and TCP/IP port number. Thus, the WebDAV URL of https://hostname:443/SharedFolder/Resource becomes \\hostname@SSL@443\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 during creation of the share.

Since UNCs start with two backslashes, and the backslash is also used for escape sequences and in regular expressions, cases of leaning toothpick syndrome may arise. 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, such as @"\\\\" in C#, r'\\\\' in Python, or qr{\\\\} in Perl.

See also

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