Question

I need a help with regular expression as I do not have good knowledge in it.

I have regular expression as:

Regex myregex = new Regex("testValue=\"(.+?)\"");

What does (.+?) indicate?

The string it matches is "testValue=123e4567" and returns 123e4567 as output.

Now I need help in regular expression to match a string "<helpMe>123e4567</helpMe>" where I need 123e4567 as output. How do I write a regular expression for it?

Answer 1

This means:

(   Begin captured group
.   Match any character
+   One or more times
?   Non-greedy quantifier
)   End captured group

In the case of your regex, the non-greedy quantifier ? means that your captured group will begin after the first double-quote, and then end immediately before the very next double-quote it encounters. If it were greedy (without the ?), the group would extend to the very last double-quote it encounters on that line (i.e., “greedily” consuming as much of the line as possible).

For your “helpMe” example, you’d want this regex:

<helpMe>(.+?)</helpMe>

Given this string:

<div>Something<helpMe>ABCDE</helpMe></div>

You’d get this match:

ABCDE

The value of the non-greedy quantifier is evident in this variation:

Regex: <helpMe>(.+)</helpMe>
String: <div>Something<helpMe>ABCDE</helpMe><helpMe>FGHIJ</helpMe></div>

The greedy capture would look like this:

ABCDE</helpMe><helpMe>FGHIJ

There are some useful interactive tools to play with these variations:

• Regex Tester
• Regex Pal