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

Monks, I am trying to modify the following code from Marshall, but it doesn't seem to work.
Trying to print the Hostname for the IP from the 2nd line. 
use warnings;
use strict;


my $file =<<END;
object-group network HOSTNAME-1A_1ST
 network-object host 10.1.1.1

object-group network HOSTNAME-1B_2ND
 network-object host 10.1.1.2

object-group network HOSTNAME-2A_1ST
 network-object host 10.3.1.1

object-group network HOSTNAME-2B_2ND
 network-object host 10.3.1.2

object-group service WEB_TCP tcp
 port-object eq 80
END

my $hostname;

open my $fh, '<', \$file or die "unable to open read file $!";
while (my $line = <$fh>)
{
  if (my ($name) = $line =~ /^object-group network (\w+)/)
  {
     $hostname = $name; # "last seen hostname"
  }

  my ($ip) = $line =~ /(\d+\.\d+\.\d+\.\d+)/;

  if (defined ($ip))
  {
     print "ip $ip goes with host name $hostname\n";
  }
}

[download]
It prints 
ip 10.1.1.1 goes with host name HOSTNAME
ip 10.1.1.2 goes with host name HOSTNAME
ip 10.3.1.1 goes with host name HOSTNAME
ip 10.3.1.2 goes with host name HOSTNAME

[download]
Please let me know.

Replies are listed 'Best First'.
Re: Match IP from 2nd line and Print Hostname from 1st line
by Corion (Patriarch) on Aug 01, 2016 at 12:52 UTC

    If you want to match the whole hostname, you will need to expand the regular expression matching its name. See perlre on what \w+ matches and also on how to include other characters in that matching.

[reply]
[d/l]
      It worked- 
      (\w+.+)

      [download]
      OUPUT 
      ip 10.1.1.1 goes with host name HOSTNAME-1A_1ST
ip 10.1.1.2 goes with host name HOSTNAME-1B_2ND
ip 10.3.1.1 goes with host name HOSTNAME-2A_1ST
ip 10.3.1.2 goes with host name HOSTNAME-2B_2ND

      [download]
      Thank you Corion.
[reply]
[d/l]
[select]
        In this case your modified expression works fine because there aren't any trailing blanks after the Hostname. If that happened, something like "HOSTNAME-1A_1ST   " your expression would also pick up those extra spaces. To prevent that, you could use a character set, like ([\w\-]+) That essentially adds "-" to the \w character set.

        Update: There is more than one way to write the regex. Another possibility would be (\S+) Changing one character (\w to \S) does a lot. That would match any non-whitespace character. So if some weirdo thing like "*" showed up, it would also be included. What you choose to implement depends both upon your actual data and personal preference.

[reply]
[d/l]
[select]

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