Original content restored by GrandFather below

file.txt
--------------
object-group network HOSTNAME_1ST
 network-object host 10.1.1.1

object-group service WEB_TCP tcp
 port-object eq 80
--------------
[download]

use strict;
use warnings;

my $iphostname;

my $filename = 'file.txt';
open(my $fh, '<:encoding(UTF-8)', $filename)
  or die "Could not open file '$filename' $!";

for $iphostname ($fh) {
  print $iphostname if (/^object-group/ ... /(\d{1,3})\.(\d{1,3})\.(\d
+{1,3})\.(\d{1,3})$/);
}
[download]

To read from a file handle, use the appropriate operator. To match a variable against a regex, you need to tell Perl what variable to match:

while (my $iphostname = <$fh>) {
    print $iphostname if $iphostname =~ /^object-group/ .. $iphostname
+ =~ /.../;
[download]

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]

Thank you. That helped.

What choroba is showing is called the "flip flop" operator. Have a look at this Flipin good, or a total flop? in the tutorials section.

Other techniques could possibly be applicable, but I don't know enough about what you are doing to make a suggestion. As always, showing some actual code that you are having trouble with is the best way to get quality advice.

At the time I was replying, the parent node contained a code sample, something like

for $iphostname ($fh) {
    print $iphostname if /^object-group/ .. /\d{4}:\d{4,6}:\d{3}/;
}
[download]

Someone has edited their node without notification. They should check How do I change/delete my post?.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]

There are a number of ways to implement this code.
One is shown below.
Basically, keep track of the last hostname found. When you find a valid ip, and that ip is the one that you are looking for, then that goes with the most previous hostname.

#!usr/bin/perl
use warnings;
use strict;


my $file =<<END;
object-group network HOSTNAME_1ST
 network-object host 10.1.1.1
 
object-group network HOSTNAME_2nd
 network-object host 10.3.1.1
 
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) and $ip eq '10.3.1.1')
  {
     print "ip $ip goes with host name $hostname\n";  
  }
}
__END__
ip 10.3.1.1 goes with host name HOSTNAME_2nd
[download]

I tried to replace the following line-

open my $fh, '<', \$file or die "unable to open read file $!";
[download]

with -

my $filename = 'file.txt';
open(my $fh, '<:encoding(UTF-8)', $filename)
  or die "Could not open file '$filename' $!";
[download]

and it doesn't give an output or any error. Any clue? --------------------------------------------------------------- oh, never mind... had to use chomp. chomp($line);