asp net regular expression for not allowing blank spaces

Question

I want my validator to not allowing the user to enter more then 1 blank space since my application will crash. And a maximum of 25 characters, what is the regex for this?

<asp:RegularExpressionValidator ValidationGroup="grpSearch" ID="valSearch" ControlToValidate="txtSearchFor" ValidationExpression="^[a-zA-Z0-9][a-zA-Z0-9 ]+$" runat="server" ForeColor="Red"/>

The expression I have tried there does not work.

Answer 1

You may use

ValidationExpression="^(?!.{26})[a-zA-Z0-9]+( [a-zA-Z0-9]*)?$"

See the regex demo .

Details :

• ^ - start of string
• (?!.{26}) - no 26 chars allowed (25 and fewer only)
• [a-zA-Z0-9]+ - 1+ alphanumeric chars
• ( [a-zA-Z0-9]*)? - optional group matching a space and 0+ alphanumeric chars
• $ - end of string

Just in case it is of interest: to disallow the space at the end of string, the * quantifier ( zero or more occurrences) should be replaced with the + quantifier ( one or more occurrences).

Answer 2

Try this:

^[^ ]+ [^ ]+$

This is of a similar theme, but asserts your requirement for alpha-numeric characters only:

^(A-Za-z0-9|[^ ])+ (A-Za-z0-9|[^ ])+$

Tested here: https://regex101.com/r/3w6B6h/3