That was incredibly helpful. Thank you. This is not my cleanest work and needs better error checking. It does, however, work as expected.

#!/usr/bin/env perl
#------------------------------------------------

use strict;
use warnings;

#------------------------------------------------
# extras
my $DEBUG = 1;

use LWP::UserAgent;
use Time::HiRes qw(gettimeofday tv_interval);
use Date::Parse;

my $XYMON_SVR = "127.0.0.1";
my $XYMON_PORT = 1984;

my $WARN_DAYS = 30;

my @MONTH = qw(Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec);
#------------------------------------------------
# output formats

# month day, year hh:mm:ss zone
my $TIME_FMT = "%s %s, %s %s:%s:%s %s";

# output for http
my $HTTPFMT="status %s.%s %s %s

%s

%s

%s

%s seconds\n";

# output fro sslcert
my $SSLCERTFMT="status %s.%s %s %s

Certificate for %s expires in %d days

Expiration Date: %s\n";

#------------------------------------------------
# globals

## certificate info
my %g_certinfo = ();

#------------------------------------------------
# main
#------------------------------------------------
sub main {
  # get the site name
  my $site = $ARGV[0];

  return 1 unless $site;

  my $resp_line = "";
  my $resp_headers = "";

  # always start as green
  my $status_color = "green";

  # start the timer
  my $t0 = [gettimeofday];

  #----------------------------------------------
  # get site headers if it is reachable

  # create the agent
  my $ua = LWP::UserAgent->new (
    ssl_opts => {SSL_verify_callback => \&xtract_cert }
  );

  # define teh url
  my $url = "https://" . $site;

  # try to connect
  my $resp = $ua->get($url);

  # we don't care if the response code is a 200, 300, or 400 but 500 i
+s still a
  # bad thing

  if ($resp->code >= 500) {
    $resp_line = $resp->status_line ? $resp->status_line : "Unable to 
+connect to " . $site;

    $resp_headers = "";
    $status_color = "red";
  } else {
    $resp_line = $resp->protocol . " " . $resp->status_line;
    $resp_headers = $resp->headers_as_string;

    chomp($resp_headers);
  }

  # calculate Elapsed Time
  my $et = tv_interval ($t0);

  # time for status line
  my $time = localtime();

  # send https status to xymon
  my $httpout = sprintf $HTTPFMT, $site, "http", $status_color, $time,
+ $url, $resp_line, $resp_headers, $et;

  send_2_xymon($XYMON_SVR, $XYMON_PORT, $httpout);

  # convert time from LWP to seconds since epoch
  my $epoch_xpire = str2time( $g_certinfo{EndDate} );

  # if no epoch_xpire then there is a problem.
  return 1 unless ($epoch_xpire);

   # convert expiration time to human readable format
  my ($sec, $min, $hour, $mday, $mon, $year, $wday, $yday, $isdst) =  
+localtime($epoch_xpire);
  $year += 1900;

  my $tz = $isdst > 0 ? "PDT" : "PST";

  my $expire_date = sprintf $TIME_FMT, $MONTH[$mon], $mday, $year, $ho
+ur, $min, $sec, $tz;

  # current time since epoch
  my $epoch_now = time();

  # how much time is left on cert
  my $remain_sec = $epoch_xpire - $epoch_now;
  my $remain_day = int($remain_sec / 86400 + 0.5);

  if ($remain_sec > $WARN_DAYS * 86400) {
    $status_color = "green";
  } elsif ($remain_sec < 0) {
    $status_color = "red";
  } else {
    $status_color = "yellow";
  }

  my $sslcertout = sprintf $SSLCERTFMT, $site, "sslcert", $status_colo
+r, $time, $url, $remain_day, $expire_date;

  send_2_xymon($XYMON_SVR, $XYMON_PORT, $sslcertout);

  return 0;
}

#------------------------------------------------
# extract some certificate information
#------------------------------------------------
sub xtract_cert {
  my ($ok, $ctx_store) = @_;

  my $cert = Net::SSLeay::X509_STORE_CTX_get_current_cert($ctx_store);

  $g_certinfo{EndDate} = Net::SSLeay::P_ASN1_TIME_get_isotime(Net::SSL
+eay::X509_get_notAfter($cert));

  return $ok;
}

#------------------------------------------------
# send the data to xymon
#------------------------------------------------
sub send_2_xymon {
  use IO::Socket;

  my ($server,$port,$output) = @_;

  if ($DEBUG) {
    print $output, "\n";
    return "";
  }

  # open a socket
  my $socket = new IO::Socket::INET (
    PeerAddr => $server,
    PeerPort => $port,
    Proto => 'tcp',
  );

  return "Could not create socket: $!n" unless $socket;

  # send data over socket
  print $socket $output;

  # close socket
  close($socket);

  # return empty string on success
  return "";
}

exit main();
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