Question

I need a regex for finding a substring like

from xyzTableName     with   (  index =...  

and

from xyzTableName     (  index =...

If with keyword is not there then it should return a match and if with exists after FROM keyword and before ( then there should be no match. All the other words between from and ( must be ignored.

I have tried with below expression :

    @"\bfrom.*[\s\t\n]+(?<!with)[\s\t\n]([\s\t\n]+index"

And some variants of same. I was able to work it out when there are only normal/single whitespaces. But when I tried with multiple white-spaces and line-breaks, It failed.

Answer 1

Try this pattern: \bfrom\b(?!.+\bwith\b)[^(]+\(\s*index

string input = @"from xyzTableName     
with   (  index =...";
string pattern = @"\bfrom\b(?!.+\bwith\b)[^(]+\(\s*index";
bool result = Regex.IsMatch(input, pattern,
                RegexOptions.Singleline | RegexOptions.IgnoreCase);

The above returns false. Change the input to remove the word “with” and it will return true. By using RegexOptions.Singleline the . metacharacter will match all characters, including newlines (\n).

Pattern breakdown:

• \bfrom\b: exactly matches the word “from” and uses word-boundary metacharacters
• (?!.+\bwith\b): negative look-ahead to check for “with” and the match will fail if it does
• [^(]+: negative character class to match any character that is not an opening parenthesis, at least once.
• \(\s*index: match an opening parenthesis (note that it has to be escaped), any whitespace, then the word “index”