How to accept numbers and specific words? - regex

Question

i have validating a clothes size field, and want it to accept only numbers and specific "words" like S, M, XL, XXL etc. But i am unsure how to add the words to the pattern. For example, i want it to match something like "2, 5, 23, S, XXXL" which are valid sizes, but not random combinations of letters like "2X3, SLX"
Ok since people are not suggesting regexp solutions i guess i should say that this is part of a larger method of validation which uses regexp. For convenience and code consistency i want to do this with regexp.
Thanks

Answer 1

If they're a known set of values, I am not sure a regex is the best way to do it. But here is one regex that is basically a brute-force match of your values, each with a \b (word boundary) anchor
\b2\b|\b5\b|\b23\b|\bXXXL\b|\bXL\b|\bM\b|\bS\b

Answer 2

Sorry for not giving you a straight answer. regexp might be overkill in your case. A solution without it could, depending on your needs, be more maintainable.
I don't know which language you use so I will just pick one randomly. You could treat it as a piece of pseudo code.
In PHP:
function isValidSize($size) {
$validSizeTags = array("S", "M", "XL", "XXL");
$minimumSize = 2;
$maximumSize = 23;
if(ctype_digit(strval($size))) { // explanation for not using is_numeric/is_int below
if($size >= $minimumSize && $size <= $maxiumSize) {
return true;
}
} else if(in_array($size, $validSizeTags)) {
return true;
} else {
return false;
}
}
$size = "XS";
$isValid = isValidSize($size); // true
$size = 23;
$isValid = isValidSize($size); // true
$size = "23";
$isValid = isValidSize($size); // true, is_int would return false here
$size = 50;
$isValid = isValidSize($size); // false
$size = 15.5;
$isValid = isValidSize($size); // false, is_numeric would return true here
$size = "diadjsa";
$isValid = isValidSize($size); // false
(The reason for using ctype_digit(strval($size)) instead of is_int or is_numeric is that the first one will only return true for real integers, not strings like "15". And the second one will return true for all numeric values not just integers. ctype_digit will however return true for strings containing numeric characters, but return false for integers. So we convert the value to a string using strval before sending it to ctype_digits. Welcome to the world of PHP.)
With this logic in place you can easily inject validSizeTags, maximumSize and minimumSize from a configuration file or a database where you store all valid sizes for this specific product. That would get much messier using regular expressions.

Answer 3

Here is an example in JavaScript:
var patt = /^(?:\d{1,2}|X{0,3}[SML])$/i;
patt.test("2"); // true
patt.test("23"); // true
patt.test("XXXL"); // true
patt.test("S"); // true
patt.test("SLX"); // false

Answer 4

Use Array Membership Instead of Regular Expressions
Some problems are easier to deal with by using a different approach to representing your data. While regular expressions can be powerful, you might be better off with an array membership test if you are primarily interested in well-defined fixed values. For example, using Ruby:
sizes = %w[2 5 23 S XXXL].map(&:upcase)
size = 'XXXL'
sizes.include? size.to_s.upcase # => true
size = 'XL'
sizes.include? size.to_s.upcase # => false

Answer 5

seeing as it is being harder than i had thought, i am thinking to store the individual matched values in an array and match those individually against accepted values. i will use something like
[0-9]+|s|m|l|xl|xxl
and store the matches in the array
then i will check each array element against [0-9]+ and s|m|l|xl|xxl and if it matches any of these, it's valid. maybe there is a better way but i can't dwell on this for too long
thanks for your help

Answer 6

This will accept the alternatives one or more times, separated by whitespace or punctuation. It should be easy enough to expand the separator character class if you think you need to.
^([Xx]{0,3}[SsMmLl]|[0-9]+)([ ,:;-]+([Xx]{0,3}[SsMmLl]))*$
If you can interpolate the accepted pattern into a string before using it as a regex, you can reduce the code duplication.
This is a regular egrep pattern. Regex dialects differ between languages, so you might need to tweak something in order to adapt it to your language of choice (PHP? It's good form to include this information in the question).