Regex.Replace not working

Question

I am having a strange issue with Regex.Replace

string test = "if the other party is in material breach of such contract and, after <span style=\"background-color:#ffff00;\">forty-five (45)</span> calendar days notice of such breach";
string final = Regex.Replace(test, "forty-five (45)", "forty-five (46)", RegexOptions.IgnoreCase);

the "final" string still shows "forty-five (45)". Any idea why? I am assuming it has to do something with the tag. How do I fix this?

Thanks

Did you really want to replace forty-five (45) with forty-five (46)? Looks like a typo. — Erik Philips
– Erik Philips, Commented Feb 5, 2014 at 0:36
I am assuming it is because of the special characters "(" and ")" — Mithil
– Mithil, Commented Feb 5, 2014 at 0:36
@ErikPhilips, this is just a test text. I know the text does not make sense but this is just a test scenario which is failing. — Mithil
– Mithil, Commented Feb 5, 2014 at 0:37

PearsonArtPhoto · Accepted Answer · 2014-02-05 00:51:39Z

6

Escape the parenthesis. Depending on the language, might require two back slashes.

string final = Regex.Replace(test, "forty-five \(45\)", "forty-five (46)", RegexOptions.IgnoreCase);

Basically, parenthesis are defined to mean something, and by escaping the characters, you are telling regex to use the parenthesis character, and not the meaning.

Better yet, why are you using a Regex to do this at all? Try just doing a normal string replacement.

string final = test.Replace("forty-five (45)", "forty-six (46)")

edited Feb 5, 2014 at 0:51

answered Feb 5, 2014 at 0:27

PearsonArtPhoto

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5 Comments

Mithil Over a year ago

I actually simplified the code for posting. The "search" and "replace" variables are dynamic. So I can't really escape anything.

Erik Philips Over a year ago

Why can't you escape ( and )? Those can be string replaced before regex replaced.

Mithil Over a year ago

@ErikPhilips the actual string might contain other special characters as well. So it won't be feasible to check on each special character.

PearsonArtPhoto Over a year ago

If that's the case, you probably want to do a replacement that doesn't involve regex. See my edit.

Erik Philips Over a year ago

It seems you don't have a clear understanding (or you haven't communicated it) of what your source and replacement values are. Escaping special characters isn't that hard, I don't see the issue.

Nicholas Carey · Accepted Answer · 2020-07-31 01:08:59Z

1

Parentheses are special in regular expressions. They delimit a group, to allow for things such as alternation. For example, the regular expression foo(bar|bat)baz matches:

foo, followed by
either bar OR bat, followed by
baz

So, a regular expression like foo(bar) will never match the literal string foo(bar). What it will match is the literal string foobar. Consequently, you need to escape the metacharacters. In C#, this should do you:

string final = Regex.Replace(test, @"forty-five \(45\)", "forty-five (46)", RegexOptions.IgnoreCase);

The @-quoted string helps avoid headaches from excessive backslashes. Without it, you'd have to write "forty-five \(45\)".

edited Jul 31, 2020 at 1:08

answered Feb 5, 2014 at 0:47

Nicholas Carey

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Comments

Vasili Syrakis · Accepted Answer · 2014-02-05 01:08:29Z

0

If you are unable to escape the parenthesis, put them in a character class:

forty-five [(]45[)]

answered Feb 5, 2014 at 1:08

Vasili Syrakis

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