I want my domain name to not contain more than one consecutive (.), '/' or any other special characters. But it can contain IDN Characters such as Á, ś, etc... I can achieve all requirements (except IDN) by using this regex:
@"^(?:[a-zA-Z0-9][a-zA-Z0-9-_]*\.)+[a-zA-Z0-9]{2,}$";
Problem is that this regex denies IDN charaters too. I want a regex which will allow IDN characters. I did a lof of research but I cant figure it out.
Regex contains a character class that allows you to specify Unicode general categories \p{}. The MSDN regex documentation contains the following:
\p{ name }Matches any single character in the Unicode general category or named block specified by name.
Also, as a sidenote, I noticed your regex contains an unescaped .. In regex the dot character . has a special meaning of any character (except newline unless otherwise specified). You may need to change this to \. to ensure proper functionality.
Editing your existing code to include Unicode character classes instead of simply the ASCII letters, you should attain the following:
^(?:[\p{L}\p{N}][\p{L}\p{N}-_]*.)+[\p{L}\p{N}]{2,}$
\p{L} Represents the Unicode character class for any letter in any language/script\p{N} Represents the Unicode character class for any number in any language/script (based on your character samples, you can probably keep 0-9, but I figured I would show you the general concept and give you slightly additional information)This site gives a quick and general overview of the most used Unicode categories.
\p{L}or\p{Letter}: any kind of letter from any language.
\p{Ll}or\p{Lowercase_Letter}: a lowercase letter that has an uppercase variant.\p{Lu}or\p{Uppercase_Letter}: an uppercase letter that has a lowercase variant.\p{Lt}or\p{Titlecase_Letter}: a letter that appears at the start of a word when only the first letter of the word is capitalized.\p{L&}or\p{Cased_Letter}: a letter that exists in lowercase and uppercase variants (combination of Ll, Lu and Lt).\p{Lm}or\p{Modifier_Letter}: a special character that is used like a letter.\p{Lo}or\p{Other_Letter}: a letter or ideograph that does not have lowercase and uppercase variants.\p{M}or\p{Mark}: a character intended to be combined with another character (e.g. accents, umlauts, enclosing boxes, etc.).
\p{Mn}or\p{Non_Spacing_Mark}: a character intended to be combined with another character without taking up extra space (e.g. accents, umlauts, etc.).\p{Mc}or\p{Spacing_Combining_Mark}: a character intended to be combined with another character that takes up extra space (vowel signs in many Eastern languages).\p{Me}or\p{Enclosing_Mark}: a character that encloses the character is is combined with (circle, square, keycap, etc.).\p{Z}or\p{Separator}: any kind of whitespace or invisible separator.
\p{Zs}or\p{Space_Separator}: a whitespace character that is invisible, but does take up space.\p{Zl}or\p{Line_Separator}: line separator character U+2028.\p{Zp}or\p{Paragraph_Separator}: paragraph separator character U+2029.\p{S}or\p{Symbol}: math symbols, currency signs, dingbats, box-drawing characters, etc.
\p{Sm}or\p{Math_Symbol}: any mathematical symbol.\p{Sc}or\p{Currency_Symbol}: any currency sign.\p{Sk}or\p{Modifier_Symbol}: a combining character (mark) as a full character on its own.\p{So}or\p{Other_Symbol}: various symbols that are not math symbols, currency signs, or combining characters.\p{N}or\p{Number}: any kind of numeric character in any script.
\p{Nd}or\p{Decimal_Digit_Number}: a digit zero through nine in any script except ideographic scripts.\p{Nl}or\p{Letter_Number}: a number that looks like a letter, such as a Roman numeral.\p{No}or\p{Other_Number}: a superscript or subscript digit, or a number that is not a digit 0–9 (excluding numbers from ideographic scripts).\p{P}or\p{Punctuation}: any kind of punctuation character.
\p{Pd}or\p{Dash_Punctuation}: any kind of hyphen or dash.\p{Ps}or\p{Open_Punctuation}: any kind of opening bracket.\p{Pe}or\p{Close_Punctuation}: any kind of closing bracket.\p{Pi}or\p{Initial_Punctuation}: any kind of opening quote.\p{Pf}or\p{Final_Punctuation}: any kind of closing quote.\p{Pc}or\p{Connector_Punctuation}: a punctuation character such as an underscore that connects words.\p{Po}or\p{Other_Punctuation}: any kind of punctuation character that is not a dash, bracket, quote or connector.\p{C}or\p{Other}: invisible control characters and unused code points.
\p{Cc}or\p{Control}: an ASCII or Latin-1 control character: 0x00–0x1F and 0x7F–0x9F.\p{Cf}or\p{Format}: invisible formatting indicator.\p{Co}or\p{Private_Use}: any code point reserved for private use.\p{Cs}or\p{Surrogate}: one half of a surrogate pair in UTF-16 encoding.\p{Cn}or\p{Unassigned}: any code point to which no character has been assigned.