Getting an IP out of a string

the_slycer has asked for the wisdom of the Perl Monks concerning the following question:

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Re: Getting an IP out of a string by Cirollo (Friar) on Aug 16, 2000 at 20:47 UTC
Check out the nodes at Matching an IP Address.	[reply]
RE: Getting an IP out of a string by merlyn (Sage) on Aug 16, 2000 at 20:47 UTC
First off, that's not legal HTML. Are you really parsing something that is that broken? Second, if it's general HTML to parse, use a general HTML parser {grin}. See HTML::Parser. -- Randal L. Schwartz, Perl hacker	[reply]
RE: Getting an IP out of a string by knight (Friar) on Aug 16, 2000 at 21:07 UTC
Don't try to search for the form of the IP address in the string, use the "http:" and URL delimiters in the regex: `$host = m#http://([^/]+)*#;` [download] That will also select a hostname if the URL is something like "http://foo.bar.com/foo". HTML::Parser is a better solution, but the above would still work if you're forced into parsing non-conformant HTML.	[reply] [d/l]
RE: RE: Getting an IP out of a string by the_slycer (Chaplain) on Aug 16, 2000 at 21:34 UTC
Problem is it's not always going to be http://ipaddress in front - IE it's not always a link :-) Sometimes it will be surrounded by formatting tags, other times by link tags.. basically looking through an HTML file for any IP address. Can do that no problem using hints from node mentioned above, but that returns the whole line - now need to strip anything but the IP :-) Sorry if I wasn't clearer to start out with, starting to play with HTML::Parser now..	[reply]
RE: RE: RE: Getting an IP out of a string by knight (Friar) on Aug 17, 2000 at 00:15 UTC
The problem is that what is or is not an IP address really depends on the file semantics, not just on what an IP address "looks like." A simple regex match for dotted-quad "IP addresses" in arbitrary text will give you false positives. In the HTML source for one site I maintain, for example, such a regex would match the following: `1.41.1.1` [download] Is it an IP address? Nope, it's an RCS version number, and blindly assuming it's an IP address would be wrong at best and dangerous at worst. That said, `@ip_addrs = m/{regex to match IP}/g;` [download] will select only the "IP address" texts from $_ for whatever regex you choose, without the danger of relying on $1.	[reply] [d/l] [select]
RE: RE: RE: RE: Getting an IP out of a string by the_slycer (Chaplain) on Aug 17, 2000 at 19:33 UTC
Re: Getting an IP out of a string by raflach (Pilgrim) on Aug 16, 2000 at 21:40 UTC
`m/(regex to match IP)/; print $1;` [download] surround the regex to match the IP with parens, and then use the $1 variable to grab what was matched	[reply] [d/l]
RE: Re: Getting an IP out of a string by merlyn (Sage) on Aug 16, 2000 at 22:14 UTC
Danger will robinson! Never use $1 unless it's in the context of a conditional based on the success of the match. Otherwise, you get the previous success $1, and that's gonna bring you to tears while you're trying to debug it. -- Randal L. Schwartz, Perl hacker	[reply]
RE: RE: Re: Getting an IP out of a string by bliz (Acolyte) on Aug 16, 2000 at 22:48 UTC
always the wise one.. :) ++merlyn	[reply]
(Kozz)RE: RE: Re: Getting an IP out of a string by Kozz (Friar) on Aug 17, 2000 at 01:10 UTC
Most people will tell you to learn from your mistakes, but I always think it's 100% better if you can learn from someone else's mistakes. This is actually one of the great reasons I visit Perlmonks -- the cooperative learning can't be beat! p.s. no offense intended to raflach: I might have made the same mistake.	[reply]


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