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

i want validate number in range of 0-255

i have expression

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

but accepts number... , works:

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

why have have ^ , $ each option?

edit: have it, cannot answer question, - ^ , $ have higher priority |, /^(...)$/ helped

note: @alex's answer way go. validating number range regex using jackhammer catch fly.

but nevertheless wanted provide explanation "problem".

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you don't have to, have group correctly, means have group alternation:

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

otherwise expression interpreted follows (logically)

(^number) or (number) or (number$) 

with brackets, be

^(number or number or number)$