asp validation for multiple spaces between strings

Question

I've a textbox for name field where I've used asp validation for proper name format. I want to validate multiple spaces between the strings. How can I do that? The leading and trail spaces are removed by trim() function but how can I validate multiple spaces between the strings? like

multiple    spaces

no   space

My validation code::

<label>
    <span>Full name</span>
    <input type="text" id="txt_name" runat="server" required="required"/>      
    <asp:RegularExpressionValidator ID="rev_txt_name" runat="server" ControlToValidate="txt_name" ForeColor="Red" 
    ErrorMessage="Invalid name!" SetFocusOnError="True" ValidationExpression="^[a-zA-Z'.\s]{2,50}"></asp:RegularExpressionValidator>

</label>

Do you need to limit the whole string to 50 chars? You mean "one two three" is valid and "one<SPACE><SPACE>two<SPACE><SPACE>three" is not? — Wiktor Stribiżew
– Wiktor Stribiżew, Commented May 25, 2017 at 10:13
Well, if it is optional, you may just use ^[a-zA-Z'.]+(?:\s[a-zA-Z'.]+)*$. If not, ^(?=.{2,50}$)[a-zA-Z'.]+(?:\s[a-zA-Z'.]+)*$. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented May 25, 2017 at 10:15
Thank You! what if I've to validate it using character count also. — user4221591
– user4221591, Commented May 25, 2017 at 10:16
@WiktorStribiżew Please can you provide the answer so that I can mark it as correct reply for future reference. Thank You! — user4221591
– user4221591, Commented May 25, 2017 at 10:18

Graham · Accepted Answer · 2017-09-24 05:36:56Z

1

The pattern you are using allows matching whitespace anywhere inside the string and any occurrences, consecutive or not, since it is part of a rather generic character class. You need to use a grouping and quantify it accordingly:

^(?=.{2,50}$)[a-zA-Z'.]+(?:\s[a-zA-Z'.]+)*$

Note that the (?=.{2,50}$) lookahead requires the whole line to be of 2 to 50 chars long.

See the regex demo.

Details:

^ - start of string
(?=.{2,50}$) - a positive lookahead requiring any 2 to 50 chars other than a newline up to the end of the string
[a-zA-Z'.]+ - 1+ letters, single quote or dot chars
(?: - a non-capturing group start:
- \s - 1 whitespace
- [a-zA-Z'.]+ - 1+ letters, single quote or dot chars
)* - zero or more (*) occurrences
$ - end of string

edited Sep 24, 2017 at 5:36

Graham

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answered May 25, 2017 at 10:21

Wiktor Stribiżew

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1 Comment

user4221591 Over a year ago

Thank You for the nice explanation. Your description will be help others to understand regular expression in future also. Thank You!!!

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