Match a specific expression across multiple lines with RegularExpressionValidator

I’m trying to build a regular expression to match the text typed by a user in a multineline input

The text should be on that shape:

Class 1: Exemple1 
Class 2: Exemple2
....

Every line must respect that syntax.

I managed to create the regex for a single line but i can’t find a proper solution to extend it to a multilines version

<asp:RegularExpressionValidator ID="RegularExpressionValidator" runat="server"
 ErrorMessage="This is wrong!" ValidationExpression="^[Class]+s[0-9]+:+s+[a-zA-Z]+$"
ControlToValidate="txtUserInput"></asp:RegularExpressionValidator><br />

Thank you in advance for your help

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Answers:

Method 1

Answers:

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Method 1

You may use

^Class[ t]+[0-9]+:[ t]+w+(?:r?nClass[ t]+[0-9]+:[ t]+w+)*$

Or, if the line breaks may be just CR:

^Class[ t]+[0-9]+:[ t]+w+(?:(?:rn?|n)Class[ t]+[0-9]+:[ t]+w+)*$

Or, a more line break sequence agnostic version (where r?n is replaced with [rn]+, but it may match empty lines in between valid lines):

^Class[ t]+[0-9]+:[ t]+w+(?:[rn]+Class[ t]+[0-9]+:[ t]+w+)*$

See the regex demo

I suggest using [ t] instead of s to match horizontal whitespace (it will work both on server- and client-side) and replace [a-zA-Z] with w that matches letters, digits and underscores, not just letters (since your example contains digits, too).

The main difference is the (?:r?nYOUR_SINGLE_LINE_PATTERN)* part, that matches all subsequent lines in the desired format, if any.

Details

^ – start of string
Class – a char sequence
[ t]+ – 1 or more tabs or spaces
[0-9]+ – 1 or more digits
: – a colon
[ t]+ – 1 or more tabs or spaces
w+ – one or more word chars
(?:r?nClass[ t]+[0-9]+:[ t]+w+)* – 0 or more repetitions of an optional CR (vbCr) followed with a required newline char (vbLf) (or, if [rn]+ is used, just one or more CR or/and LF chars, or if (?:rn?|n) is used, a CRLF, CR or LF line break) and the pattern of the first line
$ – end of string.

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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