CODEWITHSUNDEEP
c#htmlregexwhitespace
user3313045
user3313045

Reputation: 23

Whitespace in a current regex

I'm currently using the following regex: ^[^&<>\"'/]*$ and I would like to also add a validation where a user can't just enter a space in the beginning of my textbox. Any ideas pls ? Note: Spaces are allowed but not as the first element

Upvotes: 2

Views: 70

Answers (2)

Wiktor Stribiżew
Wiktor Stribiżew

Reputation: 626950

Here is another option: you may allow typing any space (hard or regular one) by adding \p{Zs} Unicode category class to your regex.

To make sure you still can match an empty string, you need to use a look-ahead anchored at the beginning of the string (that is, you must use it right after ^ start-of-string anchor):

^(?!\p{Zs})[^&<>"'/]*$
//^^^^^^^^^

I strongly suggest using verbatim string literals in C# to declare regexes as you won't have to think about how many backslashes you need to use:

var rx = new Regex(@"^(?!\p{Zs})[^&<>""'/]*$");

Note that you need to double the quotation marks in these literals to declare a single double quote.

C# demo:

var rx = new Regex(@"^(?!\p{Zs})[^&<>""'/]*$");
Console.WriteLine(rx.IsMatch("")); // true - empty string
Console.WriteLine(rx.IsMatch(" sapceAtStart")); // false - space at start
Console.WriteLine(rx.IsMatch(" sapceAtStart")); // false - Hard space at start
Console.WriteLine(rx.IsMatch("space not at start")); // true - space not at start

Upvotes: 0

Shlomo
Shlomo

Reputation: 14350

A negative look-ahead is the way to go here: ^(?! )[^&<>\"'\/]*$

(?! ) means match only if the next character isn't a space. Since that is right after the ^ anchor, that essentially means match only if the first character isn't a space.

Upvotes: 1

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