正则表达式以确保在诸如“ 05123：12315”的字符串中，第一个数字小于第二个？

Question

I must have strings in the format x:y where x and y have to be five digits (zero padded) and x <= y .

Example:

00515:02152

What Regex will match this format?

If possible, please explain the solution briefly to help me learn.

EDIT: Why do I need Regex? I've written a generic tool that takes input and validates it according to a configuration file. An unexpected requirement popped up that would require me to validate a string in the format I've shown (using the configuration file). I was hoping to solve this problem using the existing configuration framework I've coded up, as splitting and parsing would be out of the scope of this tool. For an outstanding requirement such as this, I don't mind having some unorthodox/messy regex, as long as it's not 10000 lines long. Any intelligent solutions using Regex are appreciated! Thanks.

Answer 1

Description

This expression will validate that the first 5 digit number is smaller then the second 5 digit number where zero padded 5 digit numbers are in a : delimited string and is formatted as 01234:23456 .

^
(?:
(?=0....:[1-9]|1....:[2-9]|2....:[3-9]|3....:[4-9]|4....:[5-9]|5....:[6-9]|6....:[7-9]|7....:[8-9]|8....:[9])
|(?=(.)(?:0...:\1[1-9]|1...:\1[2-9]|2...:\1[3-9]|3...:\1[4-9]|4...:\1[5-9]|5...:\1[6-9]|6...:\1[7-9]|7...:\1[8-9]|8...:\1[9]))
|(?=(..)(?:0..:\2[1-9]|1..:\2[2-9]|2..:\2[3-9]|3..:\2[4-9]|4..:\2[5-9]|5..:\2[6-9]|6..:\2[7-9]|7..:\2[8-9]|8..:\2[9]))
|(?=(...)(?:0.:\3[1-9]|1.:\3[2-9]|2.:\3[3-9]|3.:\3[4-9]|4.:\3[5-9]|5.:\3[6-9]|6.:\3[7-9]|7.:\3[8-9]|8.:\3[9]))
|(?=(....)(?:0:\4[1-9]|1:\4[2-9]|2:\4[3-9]|3:\4[4-9]|4:\4[5-9]|5:\4[6-9]|6:\4[7-9]|7:\4[8-9]|8:\4[9]))
)
\d{5}:\d{5}$

Live demo: http://www.rubular.com/r/w1QLZhNoEa

Note that this is using the x option to ignore all white space and allow comments, if you use this without x then the expression will need to be all on one line

Answer 2

The language you want to recognize is finite , so the easiest thing to do is just list all the cases separated by "or". The regexp you want is:

(00000:[00000|00001| ... 99999])|  ...  |(99998:[99998|99999])|(99999:99999)

That regexp will be several billion characters long and take quite some time to execute, but it is what you asked for: a regular expression that matches the stated language.

Obviously that's impractical. Now is it clear why regular expressions are the wrong tool for this job? Use a regular expression to match 5 digits - colon - five digits, and then once you know you have that, split up the string and convert the two sets of digits to integers that you can compare.

Answer 3

x <= y.

Well, you are using wrong tool. Really, regex can't help you here. Or even if you get a solution, that will be too complex, and will be too difficult to expand.

Regex is a text-processing tool to match pattern in regular languages. It is very weak when it comes to semantics . It cannot identify meaning in the given string. Like in your given condition, to conform to x <= y condition, you need to have the knowledge of their numerical values.

For eg , it can match digits in a sequence, or a mix of digits and characters, but what it cannot do is the stuff like -

• match a number greater than 15 and less than 1245 , or
• match a pattern which is a date between given two dates .

So, where-ever matching a pattern, involves applying semantics to the matched string, Regex is not an option there.

The appropriate way here would be to split the string on colon , and then compare numbers. For leading zero, you can find some workaround.

Answer 4

You can't generally* do this with regex. You can use regex to match the pattern and extract the numbers, then compare the numbers in your code.

For example to match such format (without comparing the numbers) and get the numbers you could use:

^(\d{5}):(\d{5})\z

*) You probably could in this case (as the numbers are always 5 digits and zero padded, but it wouldn't be nice.

Answer 5

You should do something like this instead:

bool IsCorrect(string s)
{
    string[] split = s.split(':');
    int number1, number2;
    if (split.Length == 2 && split[0].Length == 5 && split[1].Length == 5)
    {
        if (int.TryParse(split[0], out number1) && int.TryParse(split[1], out number2) && number1 <= number2)
        {
            return true;
        }
    }
    return false;
}

With regex you can't make comparisons to see if a number is bigger than another number.

Answer 6

Let me show you a good example of why you shouldn't try to do this. This is a regex that (nearly) does the same job.

https://gist.github.com/anonymous/ad74e73f0350535d09c1

Raw file:

https://gist.github.com/anonymous/ad74e73f0350535d09c1/raw/03ea835b0e7bf7ac3c5fb6f9c7e934b83fb09d95/gistfile1.txt

Except it's just for 3 digits. For 4, the program that generates these fails with an OutOfMemoryException . With gcAllowVeryLargeObjects enabled. It went on until 5GB until it crashed. You don't want most of your app to be a Regex, right?

This is not a Regex's job.

Answer 7

This is a two step process because regex is a text parser and not analyzer. But with that said, Regex is perfect for validating that we have the 5:5 number pattern and this regex pattern will determine if we have that form factor \\d\\d\\d\\d\\d:\\d\\d\\d\\d\\d right. If that form factor is not found then a match fails and the whole validation fails. If it is valid, we can use regex/linq to parse out the numbers and then check for validity.

This code would be inside a method to do the check

var data = "00515:02151";
var pattern = @"
^               # starting from the beginning of the string...
(?=[\d:]{11})   # Is there is a string that is at least 11 characters long with only numbers and a ;, fail if not
(?=\d{5}:\d{5}) # Does it fall into our pattern? If not fail the match
((?<Values>[^:]+)(?::?)){2}  
";

// IgnorePatternWhitespace only allows us to comment the pattern, it does not affect the regex parsing
var result = Regex.Matches(data, pattern, RegexOptions.IgnorePatternWhitespace)
                  .OfType<Match>()
                  .Select (mt =>  mt.Groups["Values"].Captures
                                                .OfType<Capture>()
                                                .Select (cp => int.Parse(cp.Value)))
                  .FirstOrDefault();

// Two values at this point 515, 2151

bool valid = ((result != null) && (result.First () < result.Last ()));

Console.WriteLine (valid); // True

Answer 8

Using Javascript this can work.

    var string = "00515:02152";

    string.replace(/(\d{5})\:(\d{5})/, function($1,$2,$3){ 
         return (parseInt($2)<=parseInt($3))?$1:null;
    });

FIDDLE http://jsfiddle.net/VdzF7/