检查正则表达式是在字符串的开头还是在特定字符之后开始

Question

I have a regex pattern. I want to check if it matches at the beginning of the string or after a new line or after a white space.

I also would like to make sure it matches the end of the string, after a new line or a white space.

How do I make this condition "beginning or white space" ? Do I have to repeat myself

Example:

"Crazy Fredrick bought many very exquisite opal jewels"

The search for s should only match the last character "s" in "jewels". The "s" in "exquisite" should not match.

Answer 1

This code is a regular expression starting with T and ending with s.Now if you want to check for each word in sentence split it by space and then use regular expression as per your requirement.

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegularExpression {
   public static void main(String[] args) {
   Pattern p = Pattern.compile("^(T).*[s]$");
   Matcher m = p.matcher("This is testingsd");
   System.out.println(m.matches());
   }
}

Answer 2

In JavaScript, you can use the character \\b , which according to MDN's RegExp page

Matches a zero-width word boundary, such as between a letter and a space.

So to match the s in the word "jewels" in your example, I would use the regex:

var regex = /s\b/g;

To match every word that ends with "y", I can use

var regex = /\w*y\b/gi;

and it would produce the result "Crazy, very, many".