C＃中接受下划线和空格的Alpha字符串的正则表达式

Question

I already gone through many post on SO . I didn't find what I needed for my specific scenario.

I need a regex for alpha numeric string. where following conditions should be matched

Valid string:

ameya123 (alphabets and numbers)
ameya (only alphabets)
AMeya12(Capital and normal alphabets and numbers)
Ameya_123 (alphabets and underscore and numbers)
Ameya_   123 (alphabets underscore and white speces)

Invalid string:

123 (only numbers)
_ (only underscore)
(only space) (only white spaces)
any special charecter other than underscore

what i tried till now:

(?=.*[a-zA-Z])(?=.*[0-9]*[\s]*[_]*)

the above regex is working in Regex online editor however not working in data annotation in c#

please suggest.

Answer 1

Based on your requirements and not your attempt, what you are in need of is this:

^(?!(?:\d+|_+| +)$)[\w ]+$

The negative lookahead looks for undesired matches to fail the whole process. Those are strings containing digits only, underscores only or spaces only. If they never happen we want to have a match for ^[\\w ]+$ which is nearly the same as ^[a-zA-Z0-9_ ]+$ .

See live demo here

Explanation :

• ^ Start of line / string
• (?! Start of negative lookahead
  • (?: Start of non-capturing group
    • \\d+ Match digits
    • | Or
    • _+ Match underscores
    • | Or
    • [ ]+ Match spaces
  • )$ End of non-capturing group immediately followed by end of line / string ( none of previous matches should be found )
• ) End of negative lookahead
• [\\w ]+$ Match a character inside the character set up to end of input string

Note: \\w is a shorthand for [a-zA-Z0-9_] unless u modifier is set.

Answer 2

If I understand your requirements correctly, you need to match one or more letters (uppercase or lowercase), and possibly zero or more of digits, whitespace, or underscore. This implies the following pattern:

^[A-Za-z0-9\s_]*[A-Za-z][A-Za-z0-9\s_]*$

Demo

In the demo, I have replaced \\s with \\t \\r , because \\s was matching across all lines.

Unlike the answers given by @revo and @wiktor, I don't have a fancy looking explanation to the regex. I am beautiful even without my makeup on. Honestly, if you don't understand the pattern I gave, you might want to review a good regex tutorial.

Answer 3

One problem with your regex is that in annotations, the regex must match and consume the entire string input, while your pattern only contains lookarounds that do not consume any text.

You may use

^(?!\d+$)(?![_\s]+$)[A-Za-z0-9\s_]+$

See the regex demo . Note that \\w (when used for a server-side validation, and thus parsed with the .NET regex engine) will also allow any Unicode letters, digits and some more stuff when validating on the server side, so I'd rather stick to [A-Za-z0-9_] to be consistent with both server- and client-side validation.

Details

• ^ - start of string (not necessary here, but good to have when debugging)
• (?!\\d+$) - a negative lookahead that fails the match if the whole string consists of digits
• (?![_\\s]+$) - a negative lookahead that fails the match if the whole string consists of underscores and/or whitespaces. NOTE : if you plan to only disallow ____ or " " like inputs, you need to split this lookahead into (?!_+$) and (?!\\s+$) )
• [A-Za-z0-9\\s_]+ - 1+ ASCII letters, digits, _ and whitespace chars
• $ - end of string (not necessary here, but still good to have).

Answer 4

This simple RegEx should do it:

[a-zA-Z]+[0-9_ ]*

One or more Alphabet, followed by zero or more numbers, underscore and Space.

Answer 5

这个应该不错：

[\w\s_]*[a-zA-Z]+[\w\s_]*