Wednesday, June 18, 2008

Pinging And Checking Port Status With Perl CGI On Linux And Unix


To change things up a bit today, we're going to go back to some Perl scripting. It seems like it's been a while, but that may just be my distorted sense of space and time. In any event, since this blog covers many many things related to Linux and Unix (which my probable life-span wouldn't allow me to script out or write about ;), today seems a good a day as any to get back to putting out some script work.

Today's Perl script is very simply written and, although a bit lengthy, fairly limited in what it does. Of course, it should also be fairly simple to expand upon and make do much more work than would normally be commensurate with a general breakdown of the keystroke/output-usefulness ratio.

This script closely echoes previous scripts we put out to check on web server status and check on network server port-health insofar as the end result is concerned. It should run fairly simply, too (you'll probably just need to change the target host, target port and, possibly, the location of the ping command, and its arguments, to suit your taste - or have those all fed to the script from the command line using the @ARGV array):

host # ./

This version, however, is a bit more complex (or convoluted, depending on how you look at it ;) to highlight a few other concept-based posts that we've put out in the interim. For instance, this Perl script (while it's not absolutely necessary, given the abundance of variable names we could have used to get-around) makes use of variable scoping within subroutines. This is something, actually, that we're building toward in our ever-expanding series on porting code between shell, Perl and awk. And the final thing we highlight, somewhat, in this particular script (that my green-screen-addled brain can still discern ;) is signal trapping and handling with Perl.

Whether or not you have any use for it, I hope you can find something in its over-production that sparks some interest or gets you thinking more about the many different ways you can use Perl to do many different things. Basically, this script does a ping, a port check and then puts up a CGI web page. But, sometimes, the lessons (good or bad) are found more in the context than in the message :)


Creative Commons License

This work is licensed under a
Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License


# - Ping a Port and Check Another One Just for kicks.
# 2008 - Mike Golvach -
# Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License

use Socket;
use CGI;

$socketpinger = new CGI;
$pingee = "";
system("ping $pingee 1 1 2>/dev/null 1>/dev/null");
$pingyn = $? >> 8;

print $socketpinger->header();
print "<html><head><title>Caps Checker</title></head>\n";
print "<body>\n";
if ( $pingyn ) {
print "<center><h3>Result of ping to $pingee:</3></center> <center><h2>N
o Answer</h2></center>\n";
} else {
print "<center><h3>Result of ping to $pingee:</h3></center> <center><h2>
$pingee is alive!</h2></center>\n";

print "<center><h3>Result of tcp connect to port 443:</h3></center>\n";

print $socketpinger->end_html();
sub Timer { die "Alarm Clock\n"; }

sub checkhost {
local($host,$port) = @_;
undef @fdata;
$sockaddr = 'S n a4 x8';
($t,$t,$t,$t,@var) = gethostbyname($host);
$ip = $var[0];

$down = 0;
$this = pack($sockaddr, $AF_INET, 0, "\0\0\0\0");
$serveraddr = pack($sockaddr, $AF_INET, $port, $ip);
eval 'socket(RS, $PF_INET, $SOCK_STREAM, $IPPROTO_TCP)|| die "socket: $!"';
if ($@) {
socket(RS, $PF_INET, $SOCK_STREAM, $IPPROTO_TCP) || die print "socket: $
bind(RS, $this) || ($down = 1);
if ($down) {
print "<center><h2>$host at port $port is down.</h2></center>\n";
$SIG{'ALRM'} = 'Timer';
eval {
connect(RS, $serveraddr) || die ($down = 1);
if ($down || $@ =~ /Alarm Clock/) {
print "<center><h2>$host at port $port is down.</h2></center>\n";
$up[$num] = 1;
print "<center><h2>Connection to $host at port $port successful.</h2></cente

, Mike