C# - Regex for file paths e.g. C:\test\test.exe

Question

I am currently looking for a regex that can help validate a file path e.g.:

C:\test\test2\test.exe

Solution 1

I decided to post this answer which does use a regular expression.

^(?:[a-zA-Z]\:|\\\\[\w\.]+\\[\w.$]+)\\(?:[\w]+\\)*\w([\w.])+$

Works for these:

\\test\test$\TEST.xls
\\server\share\folder\myfile.txt
\\server\share\myfile.txt
\\123.123.123.123\share\folder\myfile.txt
c:\folder\myfile.txt
c:\folder\myfileWithoutExtension

Edit: Added example usage:

if (Regex.IsMatch (text, @"^(?:[a-zA-Z]\:|\\\\[\w\.]+\\[\w.$]+)\\(?:[\w]+\\)*\w([\w.])+$"))
{
  // Valid
}

*Edit: * This is an approximation of the paths you could see. If possible, it is probably better to use the Path class or FileInfo class to see if a file or folder exists.

Solution 2

I would recommend using the Path class instead of a Regex if your goal is to work with filenames.

For example, you can call Path.GetFullPath to "verify" a path, as it will raise an ArgumentException if the path contains invalid characters, as well as other exceptiosn if the path is too long, etc. This will handle all of the rules, which will be difficult to get correct with a Regex.

Solution 3

This is regular expression for Windows paths:

(^([a-z]|[A-Z]):(?=\\(?![\0-\37<>:"/\\|?*])|\/(?![\0-\37<>:"/\\|?*])|$)|^\\(?=[\\\/][^\0-\37<>:"/\\|?*]+)|^(?=(\\|\/)$)|^\.(?=(\\|\/)$)|^\.\.(?=(\\|\/)$)|^(?=(\\|\/)[^\0-\37<>:"/\\|?*]+)|^\.(?=(\\|\/)[^\0-\37<>:"/\\|?*]+)|^\.\.(?=(\\|\/)[^\0-\37<>:"/\\|?*]+))((\\|\/)[^\0-\37<>:"/\\|?*]+|(\\|\/)$)*()$

And this is for UNIX/Linux paths

^\/$|(^(?=\/)|^\.|^\.\.)(\/(?=[^/\0])[^/\0]+)*\/?$

Here are my tests:

Win Regex

Unix Regex

These works with Javascript

EDIT I've added relative paths, (../, ./, ../something)

EDIT 2 I've added paths starting with tilde for unix, (~/, ~, ~/something)

Solution 4

The proposed one is not really good, this one I build for XSD, it's Windows specific:

^(?:[a-zA-Z]\:(\\|\/)|file\:\/\/|\\\\|\.(\/|\\))([^\\\/\:\*\?\<\>\"\|]+(\\|\/){0,1})+$

Solution 5

Try this one for Windows and Linux support: ((?:[a-zA-Z]\:){0,1}(?:[\\/][\w.]+){1,})

View more solutions

Comments

[cordsen]

Can you post what you have tried so far and some samples of input and expected output?

[agent-j]

Do you need to support UNC paths like \\server\share\file.txt?

[ulrichb]

the regex C:\\test\\test2\\test\.exe validates your path.

[Random Developer]

59 seconds before my answer of the same thing, Bump for speed!

[Dan]

Could you provide a validation example please?

[Dan]

Thanks, remember to souce where you get stuff from ;)

[agent-j]

@Dan. Wrote it for my own edification. Fun!

[Random Developer]

@Dan here is an example, note that the path can be UNC or local: if(Directory.Exists(Path.GetDirectoryName(@"C:\Windows\win.i‌​ni"))) { /*Directory exists and valid*/ }

[Jānis Gruzis]

Does not work for \\test\test$\TEST.xls - problem with $ character probably there are other bad cases.

[agent-j]

@janisCruzis, thanks for pointing out that case. I have improved my answer, though you are probably right about other edge cases.

[Junior Mayhé]

Your regular expression will NOT work if your path / filename contains blank spaces: Regex.IsMatch(@"c:\your folder\sub folder\your file.txt", @"^(?:[a-zA-Z]\:|\\\\[\w\.]+\\[\w.$]+)\\(?:[\w]+\\)*\w([\w.]‌​)+$")

[Umesh]

correction - have to remove " otherwise throws error while using

[Eirik H]

This one worked better for me (detected all UNC paths I sent to it), but I'm not familiar enough with regex to know if the " should be removed or escaped (e.g. changed to "" for vb.net). I didn't actually see a difference in testing, the regex worked both ways.

[Good Night Nerd Pride]

This fails for C:/ (also with back slash). Fixed version: ^(?:[A-Z]\:|\.|(?:file\:\/\/|\\\\)[^\\\/\:\*\?\<\>\"\|]+)(?:‌​(?:\\|\/)[^\\\/\:\*\‌​?\<\>\"\|]+)*(?:\\|\‌​/)?$. This one works under the assumption that in the cases \\name, C:\name, and file://name for all occurences of name the same rules apply (i.e. name cannot contain any of the characters in \/:*?<>"|.

[maddisoj]

To be pedantic: characters 0 through to 32 are also not allowed.

[raythurnevoid]

This would validate unvalid file paths as: \\, \\\, C:\a\\ and it doesn't validate these: C:, C:\folder.something, C:\.folder: regex101.com/r/7UgtQA/2/tests

[John Demetriou]

what about relatives paths?

[John Demetriou]

what if it is a relative path? e.g. starts with ..? btw I tried it and it only matches part of the path

[Gabriel Marius Popescu]

The pattern above lacks a '\' next too the '/' in order to be recognized as regex pattern. The pattern should look like: ((?:[a-zA-Z]\:){0,1}(?:[\\\/][\w.]+){1,})

[Herb]

@JohnDemetriou, a valid point. The "A:-Z:|\\ServerName" prefix would be needed to be made optional.

[Renan Degrandi]

Your expression will not work if your path has ".", example: "C:\folder.folder\folder.txt"

[Bogdan Popa]

could you please also make an edit for paths like ~/ ?

[raythurnevoid]

@BogdanPopa Done! :)

[Dai]

The problem is that in some situations (esp. high-performance code) you really don't want to have to catch exceptions to validate user-input. It's disappointing that .NET doesn't have a Path.TryParse or FileInfo.TryParse method which avoids exceptions entirely. Another reason is if you're using a debugger then every time Path's constructor throws an ArgumentException the debugger will break - and while you can opt to not break on ArgumentException it doesn't let you ignore only ArgumentException thrown from Path - so if you're SOL if you need to break elsewhere.

[Jay]

Pasting this into Regex101 throws un-escaped delimiter errors.

[Jay]

This expression incorrectly validates `\\192.168.0.1\INVALID SHARE` The share name cannot include spaces in UNC paths.