A Brief PHP Tutorial

by John Fortman: http://faub.keenspace.com/
October 09, 2003

First: PHP Manual (or here if your language of choice is not English.)
I do not own any PHP books because I have not seen a point in doing so. The manual on the PHP site is an excellent reference.

Terotrous and Phalanx started me writing this page. It seems that mastery of PHP-fu is not as common as one could hope. Tagboard.net started all this with their fun little web utility. The basic idea was that anyone viewing your site could leave a short message (200 characters), their name and maybe an email address or link. Useful for bloggers and webcomics alike. I had one for about a month and a half. The problem was, I got the free version. Tagboard.net is so popular that it's having bandwidth problems so, my tagboard would disappear right at about the time I was doing the whole newbie dying for attention thing. The end result, I wrote one and put it on my freeshell site. Lonestar.org is a free BSD shell account with 100 megs of webspace. They run an Apache server with mod_php among other things. In other words, I can host my PHP scripts here, edit and test them online.

For those not fortunate enough to have either a school unix account (my MU account also serves PHP scripts) or another host that serves PHP, I suggest dual booting Linux. You can install a webserver with PHP in less than 200megs if you're very careful and don't install X. I will not get into how to install Linux and PHP on your machine. There are many other sites more qualified to to that than I am: The Linux Documentation Project, Linux Questions, and others I can't find at the moment.

Okay, done with the lead in. Finally.

The Tagboard

Get the Code
It's on the web. You may as well have a look at it. I don't consider it to be anything special and it certainly doesn't have all the features of the tagboard.net utility.
This isn't a GPL release or anything official like that. I can and probably won't take the code down at any time. I wrote it, even if I did steal the ideas from anywhere I could find them so, please please please keep the copyright info around. I would like to get some credit for this somehow. You're not restricted from using the code but it's not really that safe. If you break your system with it, don't bother me about it.

That said. . .

The Tutorial

Question: Does my web host serve PHP?

No idea. However, you can check very easily. Create a short PHP program named phpcheck.php or something similar. Notice the ".php" extension. Technically this could be ".php2" or ".php3" or ".php" depending on the version of PHP that is active. You might test these as well. The different versions of PHP do have different capabilities so be careful.

<?php
phpinfo();
?>

Save this to your server and call it up like you would a regular HTML page. If you get something like this, then you're good to go. Otherwise, continue testing extensions or find a server that will host PHP.

Question: I don't know how to program. Can I still use PHP? Are there any script generators out there to help me?

Sorry, despite what the Visual Basic world would have you believe, you really do need some coding experience to get things done on the web. PHP in specific was written by scary developers on archane text editors like vi or emacs and their powers are great. They have no time for silly interfaces with bells and dropdowns. In other words, I don't really know. I've never looked.
Still, if you want something done in PHP, Perl, Javascript or whatever, somebody else has probably had the same idea. Search Google and most likely you'll find a pregenerated script.

Question: I want to make a website with the same menu/title bar/footer on every page but I don't want to use frames.

My first PHP site did this very thing. It's fairly simple really.

Problem: Your PHP code freaked when I tried to include my header.block. What's the deal?

At the top of your header.block file, you probably have something like:
<? xml version="1.0" encoding="iso-8859-1"?>
Notice that PHP also uses <? ?> to denote blocks of executable code. You can either remove the xml declaration and live without it or you can write it out using PHP:

<?php
echo "<" . "? xml version=\"1.0\"" .
"encoding=\"iso-8859-1\"?" . ">\n";
include("header.block");
include("body.block");
include("footer.block");
?>

Notice the < and ? are separated. PHP's write command is "echo" just like a bash shell script. Several other commands work as well: "print" (as in perl) and others. Check the docs for more info. The "." operator is actually string contatenation. Don't ask me, I didn't write the thing. Also notice that the quotes are switched out (\") just like Javascript or C.

Problem: This is great and all, but it only works for one page.

Now PHP gets interesting. CGI stands for Common Gateway Interface. It's the method that websites use to handle form data such as the tagboard above (when it's not being taken care of locally with Javascript). What we want to do with PHP is pass some parameters to the script that will make it decide which page to load.
First, some good CGI variables:

PHP references these variables with a couple global variables: $_GET, $_POST and $_SERVER. The first two describe the form method parameter. (ex. <form method="post") The third gives PHP direct access to the CGI variables listed above. (ex. $_SERVER['HTTP_USER_AGENT'])

It is possible to fake a GET form query using a hyperlink:
<a href="combine.php?loadpage=body.block">Body</a>
So now our PHP code will look like this:

<?php
$page = $_GET['loadpage'];
if( strlen( $page ) == 0 ) $page = "body.block";
echo "<" . "? xml version=\"1.0\"" .
"encoding=\"iso-8859-1\"?" . ">\n";
include("header.block");
include( $page );
include("footer.block");
?>

A large amount of error checking code can go in here. The above code is NOT SECURE IN ANY SENSE OF THE WORD!!! Do not use it. This code allows an unscrupulous individual to include /etc/passwd as the body of the HTML page. That's a bad thing.

Question: That's great but how did you make the tagboard?

First we need to discuss some file system issues. The tagboard will not work unless you have write access to at least one file on the website. If you don't have shell access to the server, ftp might work. The trick is that your FTP needs to have a chmod function that will change the permissions of a file on the web host. The linux command-line ftp client can do this (1st column, fourth from the bottom): 

ftp> ?
Commands may be abbreviated.  Commands are:

!		debug		mdir		sendport	site
$		dir		mget		put		size
account		disconnect	mkdir		pwd		status
append		exit		mls		quit		struct
ascii		form		mode		quote		system
bell		get		modtime		recv		sunique
binary		glob		mput		reget		tenex
bye		hash		newer		rstatus		tick
case		help		nmap		rhelp		trace
cd		idle		nlist		rename		type
cdup		image		ntrans		reset		user
chmod		lcd		open		restart		umask
close		ls		prompt		rmdir		verbose
cr		macdef		passive		runique		?
delete		mdelete		proxy		send
ftp> put tagboard.dumpfile
* FTP stuff ...
ftp> chmod 666 tagboard.dumpfile
* Now you know this is a bad thing 8)
ftp> bye

The Windows ftp client cannot. I do not use any GUI ftp clients so it's up to you to check those.

The basic idea is to set global write access to the file you want to save the tags to. Okay, warning bells and sirens should be going off in your head right about now. Global write access on a public website is a BAD thing. There has to be a better way to do it, but I haven't found it yet. The reason we need global write access is because PHP scripts execute as the user: nobody:nouser. This user has almost no permissions to do anything with any of the files on your site except read them. This is a good thing. It would be best to keep it that way, but that is completely impossible if we want to save information to the web.

Another (much better) option would be to use a database to store the tags. A simple query would be enough to build the contents of the tagboard:
SELECT TOP 10 FROM tagboard ORDER BY date DESC
A database is great but not always readily available. You generally need to request one and it's particularly difficult to maintain if you don't have access to the server. Try backing it up for example.

A simpler method is to use a flat text file as your database. PHP has enough power to parse the socks off a text file and that is why we need global write access.

PHP code to read and write a file looks a lot like C. There are other ways to read and write a file with PHP but I started with C so that's what I use:

function LogFile( $log, $data ) {
/* Simply appends the text $data to the end of the file $log.
* Nothing special.
*/
    $exists = file_exists( $log );
    $fd = fopen( $log, "a" );
    if( $fd ) {
        fwrite( $fd, $data, strlen( $data ));
        fflush( $fd );
        fclose( $fd );
        return true;
    } else {
        return false;
   }
}

This block of code points out several things about PHP code that one should keep in mind:

Notice that the function above would be all you needed if you wanted to add tags to the BOTTOM of the list. It's a nice, quick and easy function but it doesn't do what we want.
The real trick here is to read all the data in the file to memory, write the new tag block, then write all the original data. That's a pain to code and highly inefficient in terms of stress on the server. Luckily, a tagboard isn't meant to handle a couple thousand posts a minute. If it comes to that, this tagboard is getting taken down and I'm getting a real forum.
I'm not going to list the code to reverse the order of the tags. It's in the .tgz file I linked at the top of this list.

Basically, we're done. That's it. You don't need that much more code to produce the tagboard. The only other code you need is for error checking the data as it comes in. Believe it or not, the form itself does a lot of the work.

Hey! You didn't mention anything about the tag data itself. What does that look like?

Simple:

<div class="comment" title="Oct 09 2003 09:06:28 pm">
<span class="user"><a href="mailto:jfortman@hotmail.com">faub</a></span>:
<span class="message">I might be able to write up something. If you have a background in C or perl, you should be fine with PHP, though.</span>
</div>

The trick is to define a structure that is easy to parse.

Closing Comments

It's like 2:00am so I'm going to stop here. A lot of what you need to know about PHP can be discovered through experimentation. If you don't know how to do something, browse the manual. Most likely, you'll find something interesting there.

Good luck.

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This tagboard is from http://faub.keenspace.com/.