Regex to identify valid filepath and filename is too slow

Question

I have a C# application that needs to recognize whether a given string is a valid Windows file path that ends in a file name with extension. Currently I have:

public static bool IsValidWindowsFilePathWithFileName(string filepath)
{
    string scriptFilePathPattern = @"^[A-Za-z]:(\\\w+(\s*\w+)*)*(\\\w+(\s*\w+)*\.[a-zA-Z]\w*)$";
    return Regex.IsMatch(filepath, scriptFilePathPattern);
}

This normally works fine. However, if I put in something that ends with a long string, such as

"C:\Windows\System32\ThisIsALongBadFileName"

it takes several minutes to process. Is there a better way to do this?

What's wrong with one of the solutions in https://stackoverflow.com/q/62771/62576 Also, WIndows filenames are not required to end with an extension. — Ken White, Jul 10 '18 at 22:28
Provide examples of what is valid, and what would be invalid. Saying a path is wrong...doesn't provide enough information. — ΩmegaMan, Jul 10 '18 at 22:31
Please stop trying to validate filenames with strings or regular expressions. [That doesn't work](https://stackoverflow.com/questions/1976007). The only way to validate a filename is to try to create it and see if it throws an exception at runtime. — Dour High Arch, Jul 10 '18 at 22:35
I'm not using File.Exists because the computer that the path is stored on may not be the same computer where the path is used. — William, Jul 11 '18 at 12:34

ΩmegaMan · Answer 1 · 2018-07-10T23:24:40.417

1

Where possible remove * (zero or more) and replace with + 1 or more. Every * used, adds to the backtracking of the parser. If you know there is not zero condition, don't put it in...use the +.

edited Jul 10 '18 at 23:24

answered Jul 10 '18 at 22:28

ΩmegaMan

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score 1 · Answer 2 · answered Jul 11 '18 at 13:24

1

I decided to simply accept that any file path which doesn't end in a slash is valid, rather than trying to police legitimate filenames.

answered Jul 11 '18 at 13:24

William

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Regex to identify valid filepath and filename is too slow

2 Answers2