Pathrelativize

Pathrelativize is a computational operation used in file systems and programming languages to derive a path that, when resolved against a base path, yields a target path. It produces a relative path string that encodes how to navigate from the base to the target. If the target is the same as the base, the result is typically ".". When the two paths reside on different roots (for example, separate drives on Windows), most implementations cannot produce a meaningful relative path and may return the absolute target path or signal an error.

The standard algorithm for pathrelativize involves normalization and segment comparison. First, both paths are normalized by removing redundant separators and resolving "." and ".." where possible. If the roots differ, the target is returned as is. Otherwise, the paths are split into segments, and the longest common prefix of segments is found. The number of remaining segments in the base determines how many ".." steps are needed to ascend to the common ancestor, and the remaining segments from the target after the common prefix are appended. The resulting sequence forms the relative path.

Examples illustrate common cases. From /a/b/c to /a/d/e, the relative path is ../../d/e. From /a/b/c to /a/b/c/d.txt, it is d.txt. On Windows, from C:\foo\bar to C:\foo\baz\qux.txt, the result is ..\baz\qux.txt. Identified edge cases include identical paths, subpath relationships, and cross-root scenarios, which may yield "." or the absolute target depending on the implementation.

Limitations and considerations include sensitivity to path normalization rules, case handling on various file systems, and the potential impact of symbolic links. Different environments may diverge in behavior when roots differ or when trailing separators are involved. See also: relativize, path normalization, path join.