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

I'm trying to automate our net abuse report and am having a tough time extracting a list of IP addresses from a file. All I want to do is go though the file and build a list of every IP address contained within. I've worked out the regex to match lines containing ip addresses, but am having some trouble finding a way to actually obtain the IP numbers that it matches. The $1, $2 business is turning out to be a bit confusing. Can anyone help me out with a code example? Thanks a lot! Brian

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Re: Extracting IP addresses from a file...
by the_slycer (Chaplain) on Jul 04, 2001 at 23:46 UTC
Re: Extracting IP addresses from a file...
by damian1301 (Curate) on Jul 04, 2001 at 23:38 UTC
    foreach($data=~ /(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})/g){ push @ips, $1; }
    Should do it. (or some re like that.)

    $_.=($=+(6<<1));print(chr(my$a=$_));$^H=$_+$_;$_=$^H; print chr($_-39); # Easy but its ok.

      You can't use foreach like this - you need to use while to make your code work. See the code below for a demo:

      $data = <<'DATA'; foo foo bar bar baz 333.333.333.333 baz DATA # this is *wrong* foreach($data=~ /(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})/g){ push @ips, $1; } print "Foreach fails and gives:\n"; print "$_\n" for @ips; @ips = (); # this is right while($data=~ /(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})/g){ push @ips, $1; } print "While works and gives:\n"; print "$_\n" for @ips;

      For an explanation of why the for loop generates three copies of the last IP address you need to consider what has happened. A /g type regex will return an array of matches. So as it is called in array context it returns an array (this actually contains the three addresses) however $1 now contains the last address matched as we had to match all occurences to generate the array. We then iterate over this array and push $1 (the last IP address) into our array three times. To fix this we either use while or push $_ (not $1) into our IP array like this:

      $data = <<'DATA'; foo foo bar bar baz 333.333.333.333 baz DATA foreach($data=~ /(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})/g){ push @ips, $_; } print "Foreach now gives:\n"; print "$_\n" for @ips;

      Oh you can slurp up the file into a variable $data like this:

      open FILE, "<path/to/file" or die "Oops, Perl says: $!"; { local $/; $data = <FILE>; } close FILE;




Re: Extracting IP addresses from a file...
by rrwo (Friar) on Jul 04, 2001 at 23:43 UTC

    Can you be more specific about this file? Is it a web server log? They are usually standard formats and easy to parse, often separated by a spaces.... Usually the IP address is a separate field.

    Also, what regular expression are you using?