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.^[1][2][3]

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.^[4]

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.^[5][6]

Summary of systems

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

In programming languages

Most programming languages use the path representation of the underlying system, but some may also be system-independent.^[2]

For instance, this C code is system-dependent and may fail on opposing systems:^[1]

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

• In Java, the File.separator field stores the system-dependent separator.^[20] 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.^[21]

from pathlib import Path

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

In Unix

Most Unix-like systems use a similar syntax.^[22] POSIX allows treating a path beginning with two slashes in an implementation-defined manner,^[23] though in other cases systems must treat consecutive slashes as one.^[24]

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.^[3]

In DOS and Windows

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".^[27]

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.^[27][28]

In the Windows API, file I/O functions automatically convert / into \ (except when using the \\?\ prefix). Paths using standard Windows APIs (dating back to DOS and Win9x), were limited to 260 characters, or less, as defined by the environment variable MAX_PATH. For backwards compatibility with legacy applications this limitation was not removed until Windows 10, build 1607, when it could be expanded to 32,767. Windows NT always supported the 32,767 path length internally but only if using Unicode APIs or forcing UNC paths by the \\?\ prefix.^[29]

PowerShell allows slash-interoperability for backwards-compatibility:^[30]

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

Here is some text within a file

See also

• basename – Shell command for extracting the last name from a path
• Device file – Interface to device driver that appears in filesystem
• dirname – Shell command for extracting the directory path portion from a path
• Distributed file system – Type of decentralized filesystemPages displaying short descriptions of redirect targets
• Filename – Text string used to uniquely identify a computer file
• Filesystem Hierarchy Standard – Linux standard for directory structure
• Fully qualified file name – Unambiguous name in computer codePages displaying short descriptions of redirect targets
• PATH (variable) – Computer environment variable
• URL – Address on the World Wide Web

Notes

References