正则表达式为十进制值和可选字符串

Question

I'm looking for a Regex to validate a rating (1-10) + optional text. Rating is a decimal, with 1 point, which can use both dot or comma separator. Followed by an optional space + string.

Valid

• 7
• 7,5
• 7.5
• 7,5 This is my string
• 7.5 Hello

Invalid

• 7,75
• 11
• 7This is my string
• 7.This is my string
• 10.5 string

I've got this for getting the decimal values, but I'm not sure how to get the optional text behind it.

^(10|\d)([\.\,]\d{1,1})?$

Answer 1

Judging by your examples, the space after the initial number is not optional. Thus, the pattern you may use is

^(?:10|[1-9](?:[.,][0-9])?)(?:\s.*)?$

or - since a partial match with Regex.IsMatch is enough to validate the string - replace (?:\\s.*)?$ with a negative lookahead (?!\\S) that will require a whitespace or end of string after the number:

^(?:10|[1-9](?:[.,][0-9])?)(?!\S)
                           ^^^^^^^

See the regex demo

Details :

• ^ - start of a string
• (?:10|[1-9](?:[.,][0-9])?) - either 10 or a digit from 1 to 9 followed with an optional sequence of a , or . and any single digit and then...
• (?:\\s.*)?$ - an optional sequence of any whitespace followed with any chars up to the end of string - OR -
• (?!\\S) - a negative lookahead that fails the match if there is no non-whitespace char immediately to the right of the current position.

C# test :

var strs = new List<string> { "7","7,5","7.5","7,5 This is my string","7.5 Hello","7,75","11","7This is my string","7.This is my string","10.5 string"};
var pattern = @"^(?:10|[1-9](?:[.,][0-9])?)(?:\s.*)?$";
foreach (var s in strs)
    if (Regex.IsMatch(s, pattern))
        Console.WriteLine("{0} is correct.", s);
    else
        Console.WriteLine("{0} is invalid.", s);

Output:

7 is correct.
7,5 is correct.
7.5 is correct.
7,5 This is my string is correct.
7.5 Hello is correct.
7,75 is invalid.
11 is invalid.
7This is my string is invalid.
7.This is my string is invalid.
10.5 string is invalid.