Question

I have an asp.net regularexpressionvalidator that I need to match on a textbox. If there is any text, logically the rules are as follows:

The text must be at least three characters, after any trimming to remove spaces.
Characters allowed are a-zA-Z0-9-‘ /\&.

I’m having major pain trying to construct an expression that will allow a space as the thrid character only if there is a fourth non-space character.

Can anyone suggest an expression? My last attempt was:

^[a-zA-Z0-9-'/\\&\.](([a-zA-Z0-9-'/\\&\.][a-zA-Z0-9-' /\\&\.])|([a-zA-Z0-9-' /\\&\.][a-zA-Z0-9-'/\\&\.]))[a-zA-Z0-9-' /\\&\.]{0,}$

but that does not match on ‘a  a’.

Thanks.

Answer 1

OK, now this is all in one regex:

^\s*(?=[a-zA-Z0-9'/\\&.-])([a-zA-Z0-9'/\\&.\s-]{3,})(?<=\S)\s*$

Explanation:

^                      # Start of string
\s*                    # Optional leading whitespace, don't capture that.
(?=                    # Assert that...
 [a-zA-Z0-9'/\\&.-]    # the next character is allowed and non-space
)
(                      # Match and capture...
 [a-zA-Z0-9'/\\&.\s-]{3,} # three or more allowed characters, including space
)
(?<=\S)                # Assert that the previous character is not a space
\s*                    # Optional trailing whitespace, don't capture that.
$                      # End of string

This matches

abc
aZ- &//
a  ab  abc   x
    aaa
a a

and doesn’t match

aa
abc!
     a&