Use String.Format to create regular expression

Question

Essentially I have a string for interpolation: Log_{0}.txt and the {0} is replaced with an integer during a different process. So the results could be something like Log_123.txt or Log_53623432.txt.

I'm trying to use string.Format() and replace {0} with a regular expression that checks for numbers. Eventually I want to be able to pull those numbers out as well.

I've tried a few different variations on something like this, but I haven't had any luck:

var stringFormat = new Regex(string.Format("Log_{0}.txt", @"^\d$"));

Also, here's the code that's checking the format:

        var fileNameFormat = new Regex(string.Format("Log_{0}.txt", @"^\d+$"));

        var existingFiles = Directory.GetFiles("c:\\projects\\something");

        foreach(var file in existingFiles)
        {
            var fileName = Path.GetFileName(file);
            if(fileNameFormat.Match(fileName).Success)
            {
                // do something here
            }              
        }

just-my-name · Accepted Answer · 2019-03-12 19:19:11Z

5

Problem is in your regex. ^ asserts start of the line and $ end of the line. Just replace it with @"\d+" and it should work.

Optionally you can use new Regex(string.Format("^Log_{0}.txt$", @"\d+")); to ensure that no files such as asdffff_Log_13255.txt.temp are matched.

edited Mar 12, 2019 at 19:19

answered Mar 12, 2019 at 19:14

just-my-name

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1 Comment

Dortimer Over a year ago

Worked like a charm. Thank you so much!

Rodrigo García · Accepted Answer · 2019-03-12 18:59:34Z

0

You forgot to put the plus + quantifier maybe?

+ Quantifier — Matches between one and unlimited times, as many times as possible, giving back as needed (greedy)

var stringFormat = new Regex(string.Format("Log_{0}.txt", @"^\d+$"));

answered Mar 12, 2019 at 18:59

Rodrigo García

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1 Comment

Dortimer Over a year ago

Haven't had any luck with that. I updated the question with the code I'm using to check against the regex. Maybe the issue is in there.

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