php - What regex can I use to validate a number between 0 and 255?

Question

I want to validate number in range of 0-255

I have this expression

'/^([0-1]?[0-9]?[0-9])|([2][0-4][0-9])|(25[0-5])$/'

But this accepts any number... And this works:

'/(^[0-1]?[0-9]?[0-9]$)|(^[2][0-4][0-9]$)|(^25[0-5]$)/'

why do I have to have ^ and $ for each option?

edit: I have it, but I cannot answer my question, so - ^ and $ have higher priority than |, so /^(...)$/ helped

Answer 1

Note: @alex's answer is the way to go. Validating a number range with regex is like using a jackhammer to catch a fly.

But nevertheless I wanted to provide an explanation for this "problem".

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You don't have to, you just have to group it correctly, which means you have to group the alternation:

'/^(([0-1]?[0-9]?[0-9])|([2][0-4][0-9])|(25[0-5]))$/'
// ^                                             ^

Otherwise the expression will be interpreted as follows (logically)

(^number) OR (number) OR (number$)

With the brackets, it will be

^(number OR number OR number)$