Regular Expression for IP address?

[Anon]

Hi!

Does anyone have a regular expression for checking an IP address?

And BTW: Is there something like a code library for regular expressions?

Thanks,
Malte

[yelvington]

Slightly more compact expression of the same thing:
"([0-9]{1,3}).([0-9]{1,3}).([0-9]{1,3}).([0-9]{1,3})"

[[deleted]]

But... doesn't this allow for 999.999.999.999 too?

[Anon]

Hi!

Actually, the one by Jose' L. Landivar would allow that, too.

Malte

[[deleted]]

I feel a complex regexp comping on.
I think it would be a lot easier (not faster maybe, but easier) to use the before mentioned regexps to find out if something "looks like" an IP address,
and then explode() the string into four numbers and using a simple IF or a for loop to see if all four numbers are 0>=number>=255.
And then the first number may not be 0.

[yelvington]

You're right, Vincent. I don't see a way that a regular expression can do the math to validate an IP address, do you?

Perhaps you could build a horrendous collection of string branches, listing every legal value from 0 to 256. Ick.

It would be easier to use the above regex to pull the values out, then (externally) test them to see if they fall within the legal range. There is some code in the user-contributed notes here:

http://www.php.net/manual/en/function.ip2long.php

... that appears to work that way.

[[deleted]]

Hmmm.... "all you have to do" is set the limits for what is valid

Valid values are:
single [1-9] for the first set, or [0-9] for the other three
or two times [0-9]
or [0-1] with two times [0-9]
or 2 with [0-4] and [0-9]
or 25 with [0-5]

So, this would do it. (it does in my small test, nicely rejecting 0.1.1.1 and 234.300.34.4)
(This is all one line)

preg_match('/^{(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[1-9]).(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9}
]{1}|[0-9]).(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[0-9]).(25[0-5]|2[0-4][0-9]|[0-1]{1}[0-9]{2}|[1-9]{1}[0-9]{1}|[
0-9])$/',$ip_string)

[Anon]

I think this would do the trick mutch better:

^{(25[0-5]|2[0-4][0-9]|1[0-9]{2}|0?[1-9][0-9]|0?0?[1-9])(.(25[0-5]|2[0-4][0-9]|[0-1][0-9]{2}|[0-9]{1,2})){3}$}

[Anon]

When using the regex I just posted in the Internet Explorer 6.0 RegEx engine (javascript). It seems to fail interpretating the "." correct. Instead I use "[.]" that should work great in PHP also.

The regex then looks like this:
^{(25[0-5]|2[0-4][0-9]|1[0-9]{2}|0?[1-9][0-9]|0?0?[1-9])(.){3}$}

[[deleted]]

Have you tested this at all? I can't get it to work in PHP, it always gives false.

But more importantly, your regex does not account for the fact that the middle two octets are allowed to be zero.

You may a good point about the possible leading zero's though, I forgot about those.

[[deleted]]

er.. no actually I didn't forget about the leading zeros, I just implemented them differently 🙂

[Anon]

When I use this code my regex works fine...

<?php

$ips = array("1.0.0.0", "0.0.0.0", "255.255.2", "999.999.999.999", "0.1.1.1", "1.1.1.", "123.123.123.123", "255.255.255.255", "001.000.000.000");
$regex = "^{(25[0-5]|2[0-4][0-9]|1[0-9]{2}|0?[1-9][0-9]|0?0?[1-9])(.){3}$";}

foreach($ips as $ip) {
print("Testing <b>" . $ip . "</b>: ");
if(preg_match("/" . $regex . "/i", $ip))
print("valid");
else
print("not valid");
print("<br />\n");
}

?>

And by the way... it should alow the middle two octets to be zero... or am I missing someting here?

[[deleted]]

Ah... forgot the slashes... DOH!

You regex does indeed allow the middle ones to be zero, but it also allowes the last octet to be zero, which is not valid as far as I know.

[Anon]

Sorry for the delay... and yes you are absolutely right. The last octet may not be 0. To that I will add that it cannot be 255 either.

So the regex should look like this:
^{(25[0-5]|2[0-4][0-9]|1[0-9]{2}|0?[1-9][0-9]|0?0?[1-9])(.){2}.$}

/watson

[[deleted]]

To quote Col. Smith from the A-team:"nice"

[Anon]

Actually, an IP address can have a trailing byte being either 0 or 255 depending on the subnet mask. i.e. 1.0.4.0 and 1.0.3.255 are valid for a mask of 255.255.254.0 (leaving the obvious statement that the netaddress and the broadcast address are valid themselves anyway).

The cleanest regex I have seen to date is:
^{([01]?\d\d?|2[0-4]\d|25[0-5]).([01]?\d\d?|2[0-4]\d|25[0-5]).([01]?\d\d?|2[0-4]\d|25[0-5]).([01]?\d\d?|2[0-4]\d|25[0-5])$}

This lets 0.0.0.0 pass, which is unfortunate...