Regex replace only matched strings - C#

Question

I'm trying to work out how to use the Regex.Replace method for my needs, basically I need to find a particular word which doesn't have any "a-z" letters either side of it and replace only the matches with another word.

In the example below I search for all "man" occurrences and replace with "coach". I use this regex pattern "[^a-z](man)[^a-z]" which does capture what I want.

//String to search
"The man managed the football team"

//After using Regex.Replace I expect to see
"The coach managed the football team"

//But what I actually get is
"The coach coachaged the football team"

What about testing if it has a space in front or after \sman\s ? — Mivaweb
– Mivaweb, Commented Jun 26, 2015 at 12:13
Can you please produce a MVCE since using the regex you've provided will not replace managed for me. — Lasse V. Karlsen
– Lasse V. Karlsen, Commented Jun 26, 2015 at 12:13
Regex.Replace("The man managed the football team", "[^a-z](man)[^a-z]", "coach") => Thecoachmanaged the football team, because you also replace the spaces around man. — Patrik
– Patrik, Commented Jun 26, 2015 at 12:15

vks · Accepted Answer · 2015-06-26 12:28:53Z

4

You need \b aka word boundary.

\b assert position at a word boundary (^\w|\w$|\W\w|\w\W)

Use \bman\b

See demo.

https://regex101.com/r/yG7zB9/31

Your regex will replace 5 characters always.\b is a 0 width assertion so it doesnt consume a character.

string strRegex = @"\bman\b";
Regex myRegex = new Regex(strRegex, RegexOptions.Multiline);
string strTargetString = @"The man managed the football team";
string strReplace = @"coach";

return myRegex.Replace(strTargetString, strReplace);

edited Jun 26, 2015 at 12:28

answered Jun 26, 2015 at 12:13

vks

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6 Comments

Lasse V. Karlsen Over a year ago

Considering his original regular expression does indeed do what he wants (though yours is obviously better), I'm not entirely sure we've seen the entire question yet.

vks Over a year ago

@LasseV.Karlsen OP's regex replaces <1 character>man<` character> so in effect it will never replace man but 5 characters which has man in between

Lasse V. Karlsen Over a year ago

Yes, you're right. Let me rephrase, it will not touch managed.

chillydk147 Over a year ago

Hi, I have tried var res = Regex.Replace(str, "\bman\b", "coach");

chillydk147 Over a year ago

Perfect thank you "var res = Regex.Replace(str, @"\bman\b", "coach");" worked

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