How to formulate Regular expression for given example

Question

I'm not very well versed with regular expressions. I've had to use them, maybe once every few years, and that was mostly for course work. Anyways, the following question should be a fairly straight forward question/answer for anyone familiar with regular expressions.

I need to ensure that the text entered into a field follows the following format:

x y z

or

x,y,z

or

x y z / <same pattern can repeat for almost unlimited length>

or

x,y,z / <...> // Spaces after the comma are ok

where x, y and z can only be integers. The patterns cannot be intermixed, so you cannot have

x, y, z / x y z / ...

I've tried the following

([1-9] [1-9] [1-9])

to get the x y z part, but I don't know how to include the '/' nor the ','

Any suggestions?

Answer 1

Try to break your regular expression down into pieces. Then try to combine them.

For example, an integer like 1024 is a sequence of one ore more digits, i.e. [0-9]+. Etc.

Grammar:

digit     ::= [0-9]
space     ::= [ ]
slash     ::= [/]
comma     ::= [,]

integer   ::= digit+
separator ::= space | comma
group     ::= integer separator integer separator integer
group-sep ::= space slash space
groups    ::= group ( group-sep group )*

Regex:

([0-9]+[ ,][0-9]+[ ,][0-9]+)([ ][/][ ][0-9]+[ ,][0-9]+[ ,][0-9]+)*

Answer 2

I guess you can use

Regex r = new Regex("^([0-9]+([ ,]|, )[0-9]+(\\2)[0-9]+)( [/] ([0-9]+(\\2)[0-9]+(\\2)[0-9]+)+)*$");

var x1 = r.IsMatch("1,2 3");         // false
var x2 = r.IsMatch("1 3 2 / 1 2 3"); // true
var x3 = r.IsMatch("1,3,2");         // true
var x4 = r.IsMatch("1 3 2 / 1");     // false

Console.WriteLine((x1 == false) ? "Correct" : "Error");
Console.WriteLine((x2 == true) ? "Correct" : "Error");
Console.WriteLine((x3 == true) ? "Correct" : "Error");
Console.WriteLine((x4 == false) ? "Correct" : "Error");
Console.ReadLine();

Spliting in smaller pieces

[0-9]+  matches any number, even 0. If it can't start with 0
        you will have to change it
[ ,]    the separator allows a space or a comma
\\2     matches the same thing the second group matched (space or comma)

The second big parenthesis matches or not more iterations of this sequence if started by /.

If all separator needs to be exactly the same, replace them by \\2 (just don't replace the first, that is what it is going to match for the group 2).