Jan 072000

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 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 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)
use CGI;
$query = new CGI;
print $query->header('text/html');
print `uptime`


Here is the HTML which uses the above script:
<p>click here for our <a href="cgi-bin/uptime.pl">uptime</a></p>


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 ""

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:

print "Content-Type: text/plain\n\n", `uptime`;

Here are some benchmarks from Kanji’s P100:



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:


And a php example using passthru

Marc Silver wrote in with this example using php3:
   $uptime = passthru ("/usr/bin/uptime");
   echo "<font face=\"Tahoma\" SIZE=\"1\">$uptime</font></p>";


Well, I told you that would be easy!