#!/usr/bin/perl -w
use strict;
use warnings;
my $file_name = "test.txt";
my @ip;
my $ip;

@ip = (qw/test test1/);
open(my $in,  '<', $file_name) || die "cannot open $file_name for read $!";
open(my $out, '>', "$file_name.tmp") || die "cannot open $file_name.tmp for write $!";

while( <$in>)
{
   foreach $ip(@ip) {
   print $out "#" if(/\b$ip\b/i && !/^#/); #only one # at front of line
   print $out $_;
        }
}
close ($in);
close ($out);
# save copy of original file
rename ($file_name,"$file_name.bak")  || die "problem with rename $!";
# replace original with the modified version
rename ("$file_name.tmp", $file_name) || die "problem with rename $!";

=for I/O files
#= file test.txt before running program
testing is requrired
see/for/test
test/data/istesting
testing/data/test1
data/data/test2
#= file test.txt after running program
testing is requrired
testing is requrired
#see/for/test
see/for/test
#test/data/istesting
test/data/istesting
#testing/data/test1
testing/data/test1
data/data/test2
data/data/test2
=cut