File System - Path


URI - Path in a file system.

A file is identified by its path through the file system.


A file path is a hierarchical URI



Operating System

Os Root Node Directory Delimiter
in the
Path Delimiter
in the
Environment Variable
Windows Path maps to a volume, such as C:\ or D:\ back slashes semicolon (;)
Unix/Linux A single root node is supported, which is denoted by the slash character, /. forward slashes colon


  • Unix
  • Windows

Relative file paths are much more portable.


  • DOS descended file systems are case insensitive
  • Windows pretends that all file extensions with four or more letters are also three letter extensions (try DELETE *.jav in your java directories to see a disastrous example of this).


The character used to separate the directory names (also called the delimiter) is specific to the file system.

Unix paths use forward slashes between directories.


Relative or Absolute

A path is either relative or absolute.


An absolute path always contains the root element and the complete directory list required to locate the file.

Example of an absolute path


All of the information needed to locate the file is contained in the path string.


A relative path needs to be combined with another path (very often with the current path) in order to access a file. Relative file paths are much more portable.

Example of a relative path.



An abstract pathname has two components:

  • An optional system-dependent prefix string
  • A sequence of zero or more string names.

The first name in an abstract pathname may be:

  • a directory name
  • or a hostname (in the case of Microsoft Windows UNC pathnames),

Each subsequent name in an abstract pathname denotes a directory; the last name may denote either a directory or a file.

A pathname, whether abstract or in string form, may be either absolute or relative.


The canonical path is both an absolute and unique representation of a file in a file system.

The precise definition of canonical form is system-dependent.

A canonical method first converts the pathname to absolute form if necessary and then maps it to its unique form in a system-dependent way. This typically involves:

  • removing redundant names such as “.” and “..” from the pathname,
  • resolving symbolic links (on UNIX platforms),
  • and converting drive letters to a standard case (on Microsoft Windows platforms).


The prefix concept is used to handle:

  • root directories on UNIX platforms,

For UNIX platforms, the prefix of an absolute pathname is always “/”. Relative pathnames have no prefix. The abstract pathname denoting the root directory has the prefix “/” and an empty name sequence.

  • and drive specifiers, root directories and UNC pathnames on Microsoft Windows platforms

For Microsoft Windows platforms, the prefix of a pathname that contains a drive specifier consists of the drive letter followed by “:” and possibly followed by “\\” if the pathname is absolute. The prefix of a UNC pathname is “\\\\”; the hostname and the share name are the first two names in the name sequence. A relative pathname that does not specify a drive has no prefix.

Prefix can then be:

  • a disk-drive specifier (C:\),
  • “/” for a UNIX root directory,
  • or “\\\\” for a Microsoft Windows UNC pathname




resolve is an operation that will execute (in a change directory way) all its argument in a serial way to create a path


join('/b','/c') = '/c'

More File System - Resolve (Path Resolving)


join is an operation that will join all its argument to create a path


join('/b','/c') = '/b/c'


oracle: The second element of a path. See Oracle Database - SQL - Regular expression

REGEXP_REPLACE(path, '(/[^/]+)/([^/]+)(.*)','\2') 

Documentation / Reference

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