how to use regex replace in C#

Question

I have a string, shown below

A123459922

I want to remove A and add B with Regex to the end of it. How can I do it using regex

Regex.Replace("A123459922","(\w{1})(\d*)");

I don't know exactly how can I remove the first character and Add 'B' to the end of it? to ended up something like this

123459922B

Is B needed to be added only when there's an A in the beginning? Or always regardless? — Sina Iravanian
– Sina Iravanian, Commented Feb 26, 2013 at 9:27
I see , but just keen to know how regex can apply to this issue — wikinevis
– wikinevis, Commented Feb 26, 2013 at 9:28
So long as you don't care about any A, you can also use string.Replace which is faster but will also match any and all A even the ones you might want to keep. — Nolonar
– Nolonar, Commented Feb 26, 2013 at 9:28

Oscar Mederos · Accepted Answer · 2013-02-26 09:31:52Z

2

I'll use the same regex of your question.

You could look at this (for more complex situations)

Regex.Replace("A123459922",@"(\w{1})(\d*)", m => m.Groups[2].Value + "B");

See the 3rd parameter of the Replace method. It is a MatchEvaluator, which receives a Match and returns the replacement string. The above expressions is equivalent to:

private static void Main()
{
    Regex.Replace("A123459922",@"(\w{1})(\d*)", Evaluator);
}

private static string Evaluator(Match m) {
    return m.Groups[2].Value + "B";
}

You're basically saying: I want to replace the entire match by the 2nd group + the B character

edited Feb 26, 2013 at 9:31

answered Feb 26, 2013 at 9:26

Oscar Mederos

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1 Comment

Jon Over a year ago

The question, while unclear, does mention "the first character". Shouldn't answers take this into account?

Mitch Wheat · Accepted Answer · 2013-02-26 09:35:55Z

2

According to your given input and output string example, you can do this simply with Substring():

var newString = myString.Substring(1) + "B";

edited Feb 26, 2013 at 9:35

answered Feb 26, 2013 at 9:28

Mitch Wheat

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Comments

Aziz Shaikh · Accepted Answer · 2013-02-26 09:30:51Z

1

Try using this regex:

Regex.Replace("A123459922", @"\w(.*)", "$1B");

answered Feb 26, 2013 at 9:30

Aziz Shaikh

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