C# – case insensitive regex

.netc++regex

I want to validate an email address with Regex in C#.

I'm using this pattern:

^[A-Z0-9._%-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$

This pattern only matches upper case letters. For example:

"example@gmail.com" –> returns false.
"EXAMPLE@GMAIL.COM" –> returns true.

I obviously would like that the first example will also return true.

NOTE: I DON'T want to use the RegexOptions.IgnoreCase flag.

I would like to change the pattern itself to match the first example. I think that I can add a "/i" in the end of the pattern or something like this but it doesn't seems to work.
I prefer not to use the "?i" in the beginning as well.

How can i achieve this?

(If you could rewrite the whole pattern for me, it would be great!).

Thanks.

Best Solution

Instead of just [A-Z], use [A-Za-z].

But watch out: there are e-mail addresses that end in top-level domains like .travel, that are forbidden according to your regex!

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Regex – Can you make just part of a regex case-insensitive

Perl lets you make part of your regular expression case-insensitive by using the (?i:) pattern modifier.

Modern regex flavors allow you to apply modifiers to only part of the regular expression. If you insert the modifier (?ism) in the middle of the regex, the modifier only applies to the part of the regex to the right of the modifier. You can turn off modes by preceding them with a minus sign. All modes after the minus sign will be turned off. E.g. (?i-sm) turns on case insensitivity, and turns off both single-line mode and multi-line mode.

Not all regex flavors support this. JavaScript and Python apply all mode modifiers to the entire regular expression. They don't support the (?-ismx) syntax, since turning off an option is pointless when mode modifiers apply to the whole regular expressions. All options are off by default.

You can quickly test how the regex flavor you're using handles mode modifiers. The regex (?i)te(?-i)st should match test and TEst, but not teST or TEST.

Source

Regex – How to validate phone numbers using regex

Better option... just strip all non-digit characters on input (except 'x' and leading '+' signs), taking care because of the British tendency to write numbers in the non-standard form +44 (0) ... when asked to use the international prefix (in that specific case, you should discard the (0) entirely).

Then, you end up with values like:

 12345678901
 12345678901x1234
 345678901x1234
 12344678901
 12345678901
 12345678901
 12345678901
 +4112345678
 +441234567890

Then when you display, reformat to your hearts content. e.g.

  1 (234) 567-8901
  1 (234) 567-8901 x1234

Best Solution

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Regex – Can you make just part of a regex case-insensitive

Regex – How to validate phone numbers using regex

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