my @IPs = <DATA>;

foreach $confLine (<$in>) {
    if ($confLine =~ /ip4-address address=\"/) {
        foreach (@IPs) {
            my $ip = $_;
                if ($confLine =~ /ip4-address address=\"$ip/) {
                $confLine =~ s/\/>/update\"\/>/;
            }
        }
    }
    print $out $confLine;
}

___DATA___
1.2.3.4
1.2.3.5

##</code><code>##

INPUTLINE: foreach my $line (<<>>) {
    chomp $line;
    foreach my $pattern (@patterns) {
        $line =~ $pattern and do {
            say "$line matched $pattern!";
            next INPUTLINE;
        }
    }
}