My first CGI script (uptime.pl)

This article is about my first CGI script. That may not sound like much, but I
found it was pretty exciting. Everything I’d written today on my websites had been
static. This script shows you some dynamic content.

If you’ve never done CGI
scripts before, you’re going to be amazed at how simple it is.

Since first writing this article, I’ve been told how you can use a shell
script instead of a perl script.

CGI

CGI means Common Gateway Interface. CGI is the standard for running external
programs from an http server. With a CGI script, you can access information in a
database, or run a perl script (which is what I did). It is the most common method
used to provide dynamic information on a webpage (most of which are static).

Most web
pages are static. What you type is what you see. Every time you see it.
But with a CGI script, you can put anything you want in your HTML script. I used uptime
as my example.

uptime

uptime is the utility which displays the length of time the system has been
up (as if you didn’t know). Here’s an example output:

$ uptime
1:53PM up 99 days, 5:49, 1 user, load averages: 1.28, 1.11, 1.09
The load averages shown are high because I’m running RC5/DES. Otherwise they’d be
much closer to zero.

The script

Here’s the uptime.pl script which is located in my cgi-bin directory under
the root directory of my webpage (see below for a faster perl version)

#!/usr/bin/perl
use CGI;
$query = new CGI;
print $query->header('text/html');
print `uptime`

The HTML

Here is the HTML which uses the above script:

<p>click here for our <a href="cgi-bin/uptime.pl">uptime</a></p>

Problems

I did encounter one problem when setting this up. If you wind up
seeing the uptime script in your browsers, then you have a problem with your virtual
hosts. You may want to see Perl scripts that appear in
your browser.

But you don’t have to use perl!

This option was pointed out to me by Kanji T Bates. Thanks.

You
don’t have to use perl to do this. In fact, you can just use a plain old shell
script. It turns out to be much faster. I don’t have mod_perl installed with
my apache, but I’m told that will make perl as fast as the shell script..

But be warned. Something simple like this script is pretty low risk, from a
security point of view. But be careful with any script you write.

#!/bin/sh -
echo "Content-Type: text/plain"
echo ""
/usr/bin/uptime

Not only is this script smaller, it executes faster. As always, comments are welcome.

A faster perl version

Kanji T Bates bates@jurai.net wrote in with this
faster version of my original script. Kanji wrote:

The reason the shell is much faster is two-fold: you’re not firing off a Perl instance
to interpret and run your code, and — more importantly — you’re not including 200K of
code (6481 lines or so) that follows CGI.pm around.

Kanji also supplied this lean and mean perl script:

#!/usr/bin/perl
print "Content-Type: text/plain\n\n", `uptime`;

Here are some benchmarks from Kanji’s P100:

Script

Time
uptime.sh
0.040s
uptime.pl
0.082s
uptime.cgi
1.031s

A working example

Here’s the webpage which puts all of the above together:

http://test.freebsddiary.org/

And a php example using passthru

Marc Silver wrote in with this example using php3:

<?php 
   $uptime = passthru ("/usr/bin/uptime");
   echo "<font face=\"Tahoma\" SIZE=\"1\">$uptime</font></p>";
?>

Wow

Well, I told you that would be easy!