Regex from VB to C# (LIKE to Regex)

Question

So, VB6/VB.NET has a Like keyword, which is kind of like a Regex.

I know what this is doing but I am not an expert in Regex and was hoping someone could kindly help (AND I want to use Regex and not string specific stuff like IndexOf/get the last char):

VB code:

If (someDataStr Like "[*]??????????????8") Then
 ...
end if

So I am focusing on this:

"[*]??????????????8"

what would this be in terms of a Regex expression?

Well, if you know what this is doing, then why don't you tell us? :) — Martin Ender
– Martin Ender, Commented Oct 30, 2012 at 15:17
So, that matches a literal *, any 14 arbitrary characters, and a literal 8? That's what I got from here — Damien_The_Unbeliever
– Damien_The_Unbeliever, Commented Oct 30, 2012 at 15:19

Martin Ender · Accepted Answer · 2012-10-30 15:30:05Z

9

Based on Damien_The_Unbeliever's link, I assume that your pattern matches a literal *, 14 arbitrary characters and then a literal 8.

Then this would be your regex:

@"^\*.{14}8$"

Note that . will not generally match line breaks. If you need it to, then set the SingleLline option.

Match match = Regex.Match(input, @"^\*.{14}8$", RegexOptions.Singleline)

if (match.Success)
{
    // string has valid format
}

edited Oct 30, 2012 at 15:30

answered Oct 30, 2012 at 15:24

Martin Ender

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2 Comments

Ahmed ilyas Over a year ago

Thank you. answer accepted. that seems to do the trick! Now what if lets say we did not care about the character length but wanted to see if the string ends in "8", but using Regex?

Martin Ender Over a year ago

If it still has to start with * use ^\*.*8$. If you just want to check whether the string ends with 8 use 8$. As opposed to LIKE regexes do not have to match the full string. We added that requirement explicitly by using string-start and -end anchors ^ and $, respectively.

Zarepheth · Accepted Answer · 2016-04-21 19:09:57Z

Building on Martin Büttner's answer, this is what I did to convert the VB Like operator into a C# Regex. As the Like operator in Visual Studio 2013 supports some additional Regular Expression like features, there is a bit of extra work to convert the pattern.

// escape RegEx special characters
var pattern = Regex.Escape(likePattern);
// convert negative character lists into RegEx negative character classes
pattern = Regex.Replace(pattern, @"\\\[!(?<c>[^\]]*)\\\]", @"[^${c}]", RegexOptions.Compiled | RegexOptions.Singleline | RegexOptions.ExplicitCapture);
// convert positive character lists into RegEx positive character classes
pattern = Regex.Replace(pattern, @"\\\[(?<c>[^\]]*)\\\]", @"[${c}]", RegexOptions.Compiled | RegexOptions.Singleline | RegexOptions.ExplicitCapture);
// convert asterisks into RegEx pattern for zero or more characters
pattern = Regex.Replace(pattern, @"(?<!\[[^\]]*)\\*(?![^\]*\])", @".*", RegexOptions.Compiled | RegexOptions.Singleline | RegexOptions.ExplicitCapture);
// convert question marks into RegEx pattern for any single character
pattern = Regex.Replace(pattern, @"(?<!\[[^\]]*)\\?(?![^\]*\])", @".", RegexOptions.Compiled | RegexOptions.Singleline | RegexOptions.ExplicitCapture);
// convert hash/number sign into RegEx pattern for any single digit (0 - 9)
pattern = Regex.Replace(pattern, @"(?<!\[[^\]]*)#(?![^\]*\])", @"[0-9]", RegexOptions.Compiled | RegexOptions.Singleline | RegexOptions.ExplicitCapture);
// make pattern match whole string with RegEx start and end of string anchors
pattern = @"^" + pattern + @"$";

// perform "like" comparison
return Regex.IsMatch(input, pattern, RegexOptions.IgnoreCase | RegexOptions.Singleline);

Warning: This code is has not been tested!

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