I am trying to construct a regular expression for a string which can have 0 upto 4 characters. The characters can only be 0 to 9 or a to z or A to Z.
I have the following expression, it works but I dont know how to set it so that only maximum of 4 characters are accepted. In this expression, 0 to infinity characters that match the pattern are accepted.
'([0-9a-zA-Z\s]*)'
分享 If you want to match a string that consists entirely of zero to four of those characters, you need to anchor the regex at both ends:
'(^[0-9a-zA-Z]{0,4}$)'
I took the liberty of removing the \s because it doesn't fit your problem description. Also, I don't know if you're aware of this, but those parentheses do not form a group, capturing or otherwise. They're not even part of the regex; PHP is using them as regex delimiters. Your regex is equivalent to:
'/^[0-9a-zA-Z]{0,4}$/'
If you really want to capture the whole match in group #1, you should add parentheses inside the delimiters:
'/(^[0-9a-zA-Z]{0,4}$)/'
... but I don't see why you would want to; the whole match is always captured in group #0 automatically.
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