in reply to Seeking guidance for more idiomatic way of (re)writing this script.
You've got 2 places where you send e-mail. If you do something twice, it's a good candidate for splitting out into a function. I'd probably write a function called "send_mail()" or something, and put all of your e-mail work there. You can call it with an option to tell it what type of e-mail it should send.
As someone else mentioned, if most of your code is in an else {} block, that's a red flag that you might want to refactor. Since the initial if {} block is basically just checking to make sure you opened the file, I'd probably do something like:
open(my $fh , "<" , $array_ip_list) or send_mail("ip_list_error"), die "IP List File - nas_array_ip_li +st.txt not found";Where send_mail() is the function mentioned earlier. The send_mail() function will check its argument, see "ip_list_error" and know what to do. This way, you either successfully open the file, or you send your e-mail and exit.
Definitely pull out any "global" settings and put them together at the front. That'll make it significantly easier to update later. As mentioned, a hash can be useful for this. You can use a single hash if you don't have too many things, or a couple of them if it makes logical sense.
Since you're deleting dmcheck.txt at the end and only using it as a temporary holding place for your e-mail, you'd be better off to use File::Temp. It's a standard module since 5.6.1, and gives you a safer way of using a temp file.
Minor style point: in my experience, most Perl programmers don't use parentheses around the conditional in a postfix if statement. For example:
next if /foo/;If you're doing anything much more complicated than that, you'll want to use parens as appropriate of course.
Other than that, you're off to a good start already, and there's a bunch of other good suggestions here, too.