Set minimum and maximum characters in a regular expression

Question

I\'ve written a regular expression that matches any number of letters with any number of single spaces between the letters. I would like that regular expression to also enfo

Answer 1

you should use

[a-zA-Z ]{20}

[for allowed characters]{for limit of number of characters}

Answer 2

Yes

Just like + means one or more you can use {3,30} to match between 3 and 30

For example [a-z]{3,30} matches between 3 and 30 lowercase alphabet letters

From the documentation of the Pattern class

X{n,m}    X, at least n but not more than m times

In your case, matching 3-30 letters followed by spaces could be accomplished with:

([a-zA-Z]\s){3,30}

If you require trailing whitespace, if you don't you can use: (2-29 times letter+space, then letter)

([a-zA-Z]\s){2,29}[a-zA-Z]

If you'd like whitespaces to count as characters you need to divide that number by 2 to get

([a-zA-Z]\s){1,14}[a-zA-Z]

You can add \s? to that last one if the trailing whitespace is optional. These were all tested on RegexPlanet

If you'd like the entire string altogether to be between 3 and 30 characters you can use lookaheads adding (?=^.{3,30}$) at the beginning of the RegExp and removing the other size limitations

All that said, in all honestly I'd probably just test the String's .length property. It's more readable.

Answer 3

This is what you are looking for

^[a-zA-Z](\s?[a-zA-Z]){2,29}$

^ is the start of string

$ is the end of string

(\s?[a-zA-Z]){2,29} would match (\s?[a-zA-Z]) 2 to 29 times..

Answer 4

Actually Benjamin's answer will lead to the complete solution to the OP's question. Using lookaheads it is possible to restrict the total number of characters AND restrict the match to a set combination of letters and (optional) single spaces.

The regex that solves the entire problem would become

(?=^.{3,30}$)^([A-Za-z][\s]?)+$

This will match AAA, A A and also fail to match AA A since there are two consecutive spaces. I tested this at http://regexpal.com/ and it does the trick.