C# string replace if exact match is found

Question

I need to replace only if the string has an exact match. How can I do this ?

At the moment it replaces the string expression if it matches any part of the string.

string strExpression  = "hey! Hello World. SpecialDayForMe";

strExpression = strExpression .Replace("SpecialDay", "ABC") ;

The result of the strExpression is "hey! Hello World. ABCForMe".

What I want it to ONLY match if there's a match of SpecialDay in the string and not for a partial match. How can I do this ?

Note: Would be great if I can do this without using REGEX.

What is an exact match? Is `Specialday;forMe` exact or `special-day.ForMe`? — Tim Schmelter, Dec 17 '18 at 08:59
Please clarify your question significantly - talk about an "exact match" sounds like you're distinguishing between matches that vary in case, etc. "hey! Hello World. SpecialDayForMe" does contain *exactly* "SpecialDay". I believe you're really interested in whether it's a match for a complete word. For that, you'll need to come up with detailed requirements. How do you want hyphens and other punctuation to behave? Do you have a precise list of characters that are allowed before/after the token you're trying to match? — Jon Skeet, Dec 17 '18 at 09:03
Possible duplicate of [Way to have String.Replace only hit "whole words"](https://stackoverflow.com/questions/6143642/way-to-have-string-replace-only-hit-whole-words) — marsze, Dec 17 '18 at 09:04
This might help https://www.codeproject.com/Questions/644729/Find-Replace-exact-Words-in-Csharp — Vishwa Ratna, Dec 17 '18 at 09:04
Is there any particular reason you want to do this without regex? I don't think there's another way which wouldn't involve doing some parsing on your own, basically building your own little regex engine for this purpose. — marsze, Dec 17 '18 at 09:09

score 5 · Accepted Answer · edited Dec 17 '18 at 09:08

5

When replacing whole words, try using regular expressions (\b to mark word's border):

 using System.Text.RegularExpressions;

 ...

 string strExpression  = "hey! Hello World. SpecialDayForMe";
 string toFind = "SpecialDay";

 strExpression = Regex.Replace(
   strExpression, 
  @"\b" + Regex.Escape(toFind) + @"\b", // Regex.Escape to be on the safe side
   "ABC");

It matches "Hello world. SpecialDay for me" as well as "SpecialDay," and "SpecialDay.".

edited Dec 17 '18 at 09:08

Mikael Dúi Bolinder

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answered Dec 17 '18 at 09:01

Dmitry Bychenko

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OP asked specifically for *no regex* – marsze Dec 17 '18 at 09:10
Using `\b` also matches "SpecialDay-forMe" and in Swedish in that case "-" wouldn't count as a word boundary - so, it might have to be localized. – Mikael Dúi Bolinder Feb 15 '19 at 13:43

C# string replace if exact match is found

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