正则表达式匹配内部字符串的开始

Question

I am trying to match just the word Hello on the first and third lines:

     Hello should be matched
I do not want this Hello to be matched
Hello should be matched

When I use ^\\s*Hello , things almost work but I do not want the spaces to actually be included in the result.

(?=\\s*)Hello is closer but matches all 3 Hellos.

I would expected either ^(?=\\s*)Hello or (?=^\\s*)Hello to work, and am confused as to why they don't. Why don't these work and how can I create a regex that matches only the "Hello" after some whitespace?

Answer 1

There is no way to specify where the match came from (first line, third line, etc.). The only way to do this properly is to input the sentences, line by line, and programatically keep track of which line the match came from.

This regex will match what you are looking for

\b([H|h]ello)\b

What you need to do is wrap what you are looking for in ( ) which act as the capture goup

Edited -

^\s*(Hello)

Answer 2

Create a capture group:

 str1 = ' Hello should be matched'; str2 = 'I do not want this Hello to be matched'; str3 = 'Hello should be matched'; str1 = str1.match(/^\\s*(Hello)/); if (str1) { str1 = str1[1]; } else { str1 = ''; } str2 = str2.match(/^\\s*(Hello)/); if (str2) { str2 = str2[1]; } else { str2 = ''; } str3 = str3.match(/^\\s*(Hello)/); if (str3) { str3 = str3[1]; } else { str3 = ''; } $('#output').append('str1: ' + str1 + '<br>str2: ' + str2 + '<br>str3: ' + str3 + ''); 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script> <div id="output"></div> 

Answer 3

Here's the solution for you:

^\b(Hello)\b.*\n.*\n\b(Hello)\b.*$

https://regex101.com/r/vZ9pF8/1