A general regex to extract file paths (not urls)

Question

I am trying to parse urls and filepaths from files using Python. I already have a url regex.

Issue

I want a regex pattern that extracts file paths from a string. Requirements:

exclusive (does not include urls)
OS-independent, i.e. Windows and UNIX style paths e.g. (C:\, \\, /)
all path types, i.e. absolute & relative paths e.g. (/, ../)

Please assist by modifying my attempt below or suggesting an improved pattern.

Attempt

Here is the regex I have so far:

(?:[A-Z]:|\\|(?:\.{1,2}[\/\\])+)[\w+\\\s_\(\)\/]+(?:\.\w+)*

Description

(?:[A-Z]:|\\|(?:\.{1,2}[\/\\])+): any preceding drive letter, backslash or dotted path
[\w+\\\s_\(\)\/]+: any path-like characters - alphanumerics, slashes, parens, underscores, ...
(?:\.\w+)*: optional extension

Result

Note: I have confirmed these results in Python using an input list of strings and the re module.

Expected

This regex satisfies most of my requirements - namely excluding urls while extracting most file paths. However, I would like to match all paths (including UNIX-style paths that begin with a single slash, e.g. /foo/bar.txt) without matching urls.

Research

I have not found a general solution. Most work tends to satisfy specific cases.

SO Posts

External sites

You could match the preceding character if it is going to be portable. You shouldn't use non-capturing groups either. Try this regex101.com/r/IsmBeL/8 — revo
Or perhaps add another alternation with a negative lookbehind to match the first 2 paths regex101.com/r/5Dyith/1 — The fourth bird
Well, this is going to be fun. command.com is literally a filename and an internet host. — melpomene
To match that a file name is valid in UNIX you do this: '\0' not in filename and filename[-1] != '/'. The only limitation is that the filename cannot include \0 and a file cannot contain / in its name (obviously its absolute path will contain /s). (I might add that using normal APIs you really cannot include / in the name part of the filename except as placing it at the end of the name... in other positions it will be interpreted as separator in the path). — Bakuriu

Alain T. Alain T. · Accepted Answer · 2019-03-05T03:15:31

You could split the problem in 3 alternative patterns: (note that I didn't implement all character exclusions for path/file names)

Non-quoted Windows paths
quoted Windows paths
unix paths

This would give something like this:

((((?<!\w)[A-Z,a-z]:)|(\.{1,2}\\))([^\b%\/\|:\n\"]*))|("\2([^%\/\|:\n\"]*)")|((?<!\w)(\.{1,2})?(?<!\/)(\/((\\\b)|[^ \b%\|:\n\"\\\/])+)+\/?)

Broken down:

Wind-Non-Quoted: ((((?<!\w)[A-Z,a-z]:)|(\.{1,2}\\))([^\b%\/\|:\n\"]*))
Wind-Quoted:     ("\2([^%\/\|:\n\"]*)")
Unix:            ((?<!\w)(\.{1,2})?(?<!\/)(\/((\\\b)|[^ \b%\|:\n\"\\\/])+)+\/?)


Wind-Non-Quoted:
    prefix: (((?<!\w)[A-Z,a-z]:)|(\.{1,2}\\))
         drive: ((?<!\w)[A-Z,a-z]:) *Lookback to ensure single letter*
      relative: (\.{1,2}\\))
      path: ([^\b%\/\|:\n\"]*))     *Excluding invalid name characters (The list is not complete)*

Wind-Quoted:
    prefix: \2                *Reuses the one from non-Quoted*
      path: ([^%\/\|:\n\"]*)  *Save as above but does not exclude spaces*

Unix:
    prefix: (?<!\w)(\.{1,2})?                . or .. not preceded by letters
      path: (?<!\/)                          repeated /name (exclusions as above)
            (\/((\\\b)|[^ \b%\|:\n\"\\\/])+) not preceded by /
            \/?                              optionally ending with /

            *(excluding the double slashes is intended to prevent matching urls)*

A general regex to extract file paths (not urls)

1 Answers