How do I match number from 0 to 255 using regex in PHP?

Question

/[0-9]+/ will also match those out of range,like 999

How to write an regex that matches exactly numbers between 0~255 ?

Answer 1

Have a look here:

000..255:       ^([01][0-9][0-9]|2[0-4][0-9]|25[0-5])$ 
0 or 000..255:  ^([01]?[0-9]?[0-9]|2[0-4][0-9]|25[0-5])$

Answer 2

In reality, you should just match 0-999 and normalise the values afterwards, but...

/(25[0-5])|(2[0-4][0-9])|(1[0-9][0-9])|([0-9][0-9])|([0-9]))/

Answer 3

I would do:

$n >= 0 && $n <= 255

Regex are good but they can be avoided in cases like these.

Answer 4

first group matches 0-99, second one 100-199, third 200-249, fourth 250-255

/[0-9]{1,2}|1[0-9]{2}|2[0-4][0-9]|25[0-5]/

Answer 5

first group matches 0-99, second one 100-199, third 200-249, fourth 250-255

/[0-9]{1,2}|1[0-9]{2}|2[0-4][0-9]|25[0-5]/