Extract the host, domain and subdomain name from a fully-qualified host name, assumed to be in $sbFQDN. For an application (from which this came from) see how to Reduce email address to its minimum expression. 
# Assuming $sbFQDN is "host.subdomain.domain.edu", then
#   $sbHost = host.subdomain.domain.edu
#   $sbSubdomain = subdomain.domain.edu
#   $sbDomain = domain.edu
#   $sub = subdomain
#   $host = host
# Assuming $sbFQDN is "host.domain.edu", then
#   $sbHost = host.domain.edu
#   $sbSubdomain = domain.edu
#   $sbDomain = domain.edu
#   $sub = ""
#   $host = host
($sbHost, $sbSubdomain, $sbDomain)=
  ($sbFQDN=~/^([^.]+\.((?:[^.]+\.)?([^.]+\.[^.]+)))$/);
die "Could not obtain the local domain from hostname '$sbFQDN'\n"
    unless $sbDomain;
$sbSubdomain=$sbDomain unless $sbSubdomain;
($sub=$sbSubdomain)=~s/\.?$sbDomain$//;
($host=$sbHost)=~s/\.?$sbSubdomain//;

[download]

In reply to Getting hostname, domainname and subdomainname by ZZamboni

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.