String Formatting with Regex

My latest favorite trick with regular expressions is to shortcut string formatting. We’ve all written some code like this:

if (/* string is not formatted a certain way */)
    /* make it formatted that way */

Now, there’s nothing wrong with that code, but for simple examples you could do it all in one step with a regular expression!

Here are a few examples:

// remove "www." from a domain if one exists
//     ->
// ->
Regex.Replace(input, @"^(?:www.)?(.+)$", "$1");

// format phone number
// 1234567890       -> 123-456-7890
// (123) 456-7890   -> 123-456-7890
// (123) 456 - 7890 -> 123-456-7890
Regex.Replace(input, @"^\(?(\d{3})\)?\s*(\d{3})\s*-?\s*(\d{4})$", "$1-$2-$3");

Yay, regular expressions!


Author: Adam Prescott

I'm enthusiastic and passionate about creating intuitive, great-looking software. I strive to find the simplest solutions to complex problems, and I embrace agile principles and test-driven development.

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