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Starting out with expressions

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so i am not a huge fan of these snippets, but i need some help creating one.

string requirements:
-minimum length of 3.
-maximum length of 28.
-can only contain letters (both capital and none) and numbers.
-string can contain - (normal dash), they can not be at the very beginning/end of the string.
--> also, the dash can not be concurrent, string can not be 'asd--asd', but only 'asd-asd' or 'as-d-as-d'

this is what i have, i only have an issue with the dash.

function isValidDisplayName($displayName){
    return preg_match('/[a-zA-Z0-9-]{3,28}/',$displayName);

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Checking the string length is the job of strlen(), so forget about that when you write the regex.


There are three logical steps here:

  • Write a pattern for an alphanumerical sequence without a dash. That's the prefix.
  • Write a second pattern for an alphanumerical sequence preceded by a dash.
  • Put the two together and repeat the second with the * quantifier.

And learn what anchors are. Right now, you're merely doing a substring search.

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