ip address REGEX
 

could someone give a regex that detects a VALID ip address:

note: 255.255.255.255 is valid in my book


i cant seem to write one.

i'm trying to parse a file of valid and invalid IP's and print the good ones, it's using egrep and there is 1 ip per line.

i had to do this in school once before but never got the answer.

dunno, in perl maybe something like this;

#IP is in $ip
@ip_bits = split(/\./,$ip);

die if(scalar(@ip_bits)<4);

foreach(@ip_bits)
{
$_ =~ s/\D//g;
die if($_ > 255 || $_ < 0);
}

Again, I am not too great with perl, but I think that does it... though it isn't a one-off regexp

perl...so cryptic looking, i dont know any perl but thanks.

wait, i can tell what that does.

im guessing split splits the ip with a "." delimitor and then tests each part to see if it is greater than 255. took a minute but i get it now.

Python:

If you really want to use egrep:
This assumes there only an IP-address on each line, nothing else, except leading and trailing spaces.

Also note that it accepts zero-padding, i.e. 001.002.003.004 will be valid. but this actually is a valid IP-address.

I just did this the other day, try it out (perl):

1) Make some variables for the regex pattern (let me know if it breaks ;)
2) use whatever you like for matching, maybe something like:

The problem is that that matches 999.999.999.999 as a valid IP, which it isn't :)

thanks guys. the egrep example is the one i really needed.

im not using perl or python so i needed just a plain ole regex, but i will save all of the example becuase you never know. i will have to use python later on tho....have to learn it to teach it to my girlfriend because she has to take a class that uses it. i get to learn it for the sake of helping her out in the class (arent i a good boyfriend).

perl will do it great. the example posted was correct

the egrep one works also by the way....so that's atleast 2 that have been tested.

does the python example work? wouldnt 123.123.123.123.123 pass? i cant see where it checks for the number of octets.
<edit>also, how does int() treat characters, if someone entered 46.abc.123.87, what would int(abc) evaluate to? hopefully not 0 because if it did then it would pass.

but i have to say, not knowing python/perl and not being very good at regex, the python example was the only one i could read, and i wouldnt want to have to maintain the others.

Yeah, it would. You can add a check for that, of course.

It would raise an exception, as it should.

:D

Here's the modified version to check for number of octets as well.

Re: ip address REGEX
 

The answers above are all very well, but doesn't fully solve the problem :p

All fails to read in the file and to print out the result :D (Well, except maybe the egrep thing). Here's a solution in perl that includes a novel thing: indentation ;-) I wasn't sure if the ip-addresses were printed on the line without any noise except maybe whitespace. If this was the case, the 3rd line could be simply
@ipbits = split(/\./);

#!/usr/bin/perl -w
main: while(<>) {
@ipbits = /(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})?/; # pick out ip addresses
next unless (@ipbits); # verify pattern match
for (@ipbits) {
next main if ($_ <0 || $_>255); # verify ranges
}
print join('.',@ipbits)."\n"; # print valid numbers
}

The important things to know in order to read perl is:
1) Scalar variables are prefixed with $, arrays with @ and hashes with #
2) Many perl functions work implicitly on $_ if nothing else is stated.
3) one-line if are written in reverse. E.g.:
die if ($shot);

but he asked
so your post doesnt answer the question either. dont try to be a smart ass, you normally just end up being an ass.

thanks for the perl hints though.