How to make this simple regexp?

I need to make a string starts and ends with alphanumeric range between 5 to 20 characters and it could have a space or n开发者_C百科one between characters. /^[a-z\s?A-Z0-9]{5,20}$/ but this is not working.

EDIT

test test -should pass

testtest -should pass

test test test -should not pass

You can't do this with traditional regex without writing a ridiculously long expression, so you need to use a look-ahead:

/^(?=(\w| ){15,20}$)\w+ ?\w+$/

This says, make sure there are between 15 and 20 characters in the match, then match /\w+ \w+/

Note I used \w for simplification. It is the same as your character class above except it also accepts underscores. If you don't want to match them you have to do:

/^(?=[a-zA-Z0-9 ]{15,20}$)[a-zA-Z0-9]+ ?[a-zA-Z0-9]+$/

You can't put a ? inside of [...]. [...] is used to specify a set of characters precisely, you can't maybe (?) have a character inside a set of characters. The occurrence of any specific characters is already optional, the ? is meaningless.

If you allow any number of spaces inside your match, just remove the question mark. If you want to allow a single space but no more, then regular expressions alone can't do that for you, you'd need something like

if (myString.match(/^[a-z\sA-Z0-9]{5,20}$/ && myString.match(/\s/g).length <= 1)

You couldn't do this with a single traditional regex without it being dozens of lines long; regexes are meant for matching more simpler patterns than this.

If you only want to use regexes, you could use two instead of one. The first matches the general pattern, the second ensures that only one non-space characters is found.

if (myString.match(/^[a-z\sA-Z0-9]{5,20}$/ && myString.match(/^[^\s]*\s?[^\s]*$/))) {

Example Usage

inputs = ["test test", "testtest", "test test test"];

for (index in inputs) {
    var myString = inputs[index];
    if (myString.match(/^[a-z\sA-Z0-9]{5,20}$/ && myString.match(/^[^\s]*\s?[^\s]*$/))) {
        console.log(myString + " matches.")
    } else {
        console.log(myString + " does not match.")
    }
}

This produces the output specified in your question.

Meh , So here's the ridiculously long traditional regex for the same

(?i)[a-z0-9]+( [a-z0-9]+)?{5,12}

js vesrion (w/o the nested quantifier)

/^([a-z0-9]( [a-z0-9])?){5,12}$/i