Assumptions:

• The mapping of IP addresses to Computer names is in a relatively small file named 'ip.dat'.
• You don't want to overwrite your data file.
• You trust Ovid's untested code :)

use strict;
use warnings;

my $ips      = 'ip.dat';
my $in_data  = 'DJB.dat';
my $out_data = 'DJB_new.dat';
my %ip_map;

# you should ask for a shared lock in case someone updates this
open IPS, "< $ips" or die "Couldn't open $ips for reading: $!";

while ( <IPS> ) {
    my ( $ip, $name ) = split /:/, $_, 2;
    warn "$ip is already mapped to $ip_map{$ip }" if exists $ip_map{ $
+ip };
    chomp $name;
    $ip_map{ $ip } = $name;
}

close IPS;

open IN_DATA, "< $in_data"   or die "Couldn't open $in_data for readin
+g: $!";
open OUT_DATA, "> $out_data" or die "Couldn't open $out_data for writi
+ng: $!";

while ( <IN_DATA> ) {
    my $replace;
    my $ip = '';
    ( $replace, $ip ) = ( /^\+([^:]+):([\d.]+)/ );
    if ( exists $ip_map{ $ip } ) {
        s/$replace/$ip_map{ $ip }/;
    }
    print OUT_DATA $_;
}

close OUT_DATA;
close IN_DATA;
[download]

Cheers,
Ovid

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