跳过比赛集合正则表达式中单词的最后一个字符

Question

I am matching few words strings with below expression.

    string pattern = "(?=.*\bgoods\b|\bitems\b|\bthings\b).*$;

    string matchWord1 = goods;
    string matchWord2 = items;
    string matchWord3 = things;

Could you also please guide if below expression can be amended to skip last character at the end of every word in boundary? .ie

Desire matchWords with the same string pattern:

    string matchWord1 = good;
    string matchWord2 = item;
    string matchWord3 = thing;

So that Regex ignore the plural s at the end and still match above plural words.

I have tried using ? with the following but its not working.

    string pattern = "^(?=.*\bgoods?\b|\bitems?\b|\bthings?\b).*$;

or

    string pattern = "^(?=.*\b(?:good|item|thing)s?\b).*$";



    string input = @"\b(?:I|would|like|to|see|id|of|bought|things|items)\b";

    MatchCollection mat = Regex.Matches(pattern, input, RegexOptions.IgnoreCase);
    foreach (var item in mat)
    {
      Console.WriteLine(item.ToString());
    }

Thanks in advance.

Answer 1

If you want to validate with a regular expression match if the entire string is either good or item or thing in singular or plural with getting returned the singular word only on match, use

string pattern = "^(good|item|thing)s?$";

But if the matching word should be returned in singular or plural as found, use

string pattern = "^((?:good|item|thing)s?)$";

In case of wanting to find anywhere within a string at least one of the 3 words in singular or plural with getting returned the singular word only on match, use

string pattern = "\\b(good|item|thing)s?\\b";

And again if the found word should be returned in singular or plural as found, use

string pattern = "\\b((?:good|item|thing)s?)\\b";

---

The main mistake you have made resulting in not working regular expressions is that \\b in a Perl regular expression means word boundary .

But the escape character in C# regular-string-literals is the backslash character and therefore the compiler stores in the EXE for \\b in source code just character b . Now it is clear why non of your regular expression matched something.

By escaping the backslash for the regular expression with another backslash and therefore use in source code \\\\b , the compiler really writes into EXE the string \\b and regular expression works.

Keep that in mind for the future: each backslash in a regular expression string in C# source code must be escaped with an additional backslash, except you use a verbatim-string-literal definition which is better for regular expressions.

Example for a verbatim-string-literal definition of last regular expression string from above:

string pattern = @"\b((?:good|item|thing)s?)\b";