Starting to make php's first Script.

Starting to make php's first Script. A First Script

Overview

Having installed and configured PHP, it is now time to put it to the test. In this hour,

you will create your first script and spend a little time analyzing its syntax. By the

end of the hour, you should be ready to create documents that in clude both HTML

and PHP.

In this hour, you will learn

How to create, upload, and run a PHP script

How to incorporate HTML and PHP in the same document

How to make your code clearer with comments

Our First Script

Let's jump straight in with a PHP script. T o begin, open your favorite text editor. Like

HTML documents, PHP files are made up of plain text. You can create them with any

text editor, such as Notepad on Windows, Simple Text and BBEdit on MacOS, or VI

and Emacs on UNIX operating systems. Most popular HTML editors provide at least

some support for PHP.

Type in the example in  Listing 3.1 and save the file, calling it something like

first.php.

Listing 3.1: A First PHP Script

1: <?php

2:     print "Hello Web!";

3: ?>

Figure 3.1 shows the script created in Listing 3.1 as typed into the BBEdit text editor

for MacOS.

41

Figure 3.1:

Your first script as created in the BBEdit text editor.

The extension to the PHP document is important because it tells the server to treat

the file as PHP code and invoke the interpreter. The default PHP extension for a PHP

4 document is  .php. This can be changed, however, by altering the server's

configuration. You saw how to do this in Hour 2, "Installing PHP."

If you are not working directly on the machine that will be serving your PHP script,

you will probably need to use an FTP client, such as WS-FTP for Windows or Fetch for

MacOS to upload your saved document to the server.

After the document is in place, you should be able to access it via your browser. If

all has gone well, you should see the script's output. Figure 3.2 shows the output

from the first.php script.

Figure 3.2:

Success: the output from Listing 3.1.

If PHP is not installed on your server or your file's extension is not recognized, you

may not see the output shown in Figure 3.2. In these cases, you probably will see

the source code created in  Listing 3.1. Figure 3.3 shows what happens when an

unknown extension is encountered.

42

Figure 3.3:

Failure: the extension is not recognized.

If this happens, first check the extension with which you saved your PHP script. In

Figure 3.3, the document was accidentally called first.nphp. If the file extension is

as it should be, you may need to check that PHP has been installed properly and that

your server is configured to work with the  extension that you have used for your

script. You can read more about installing and configuring PHP in Hour 2.

Now that you have uploaded and tested your script, you can take a look at the code

in a little more detail.

Beginning and Ending a Block of PHP Statements

When writing PHP, you need to inform the interpreter that you want it to execute

your commands. If you don't do this, the code you write will be mistaken for HTML

and will be output to the browser. Table 3.1 shows the four ways of enclosing PHP

code.

Table 3.1: PHP Start and End Tags

Tag Style

Start Tag

End Tag

Standard

<?php    ?>

tags

Short tags  <?    ?>

ASP tags  <%    %>

Script tags  <SCRIPT

</SCRIPT>

LANGUAGE="php"

>

43

Of the tags in Table 3.1, only the standard and the script tags can be guaranteed to

work on any configuration. The short and ASP style tags must be explicitly enabled

in your php.ini. You examined the php.ini file in Hour 2.

To activate recognition for short tags, you must make sure that the short_open_tag

switch is set to "On" in php.ini:

short_open_tag = On;

Short tags are enabled by default, so you would only need to edit php.ini if you want

to disable these.

To activate recognition for the ASP style tags, you must enable the  asp_tags

setting:

asp_tags = On;

After you have edited php.ini, you should be able to choose from any of the four

styles for use in your scripts. This is largely a matter of preference, although if you

intend to work with XML, you should disable the short tags (<? ?>) and work with

the standard tags (<?php ?>).

Let's run through some of the ways in which you can legally write the code in Listing

3.1. You could use any of the four PHP start and end tags that you have seen:

<?

print("Hello Web!");

?>

<?php

print("Hello Web!");

?>

<%

print("Hello Web!");

%>

<SCRIPT LANGUAGE="php">

print("Hello Web!");

</SCRIPT>

Single lines of code in PHP also can be presented on the same line as the PHP start

and end tags:

44

<? print("Hello Web!"); ?>

Now that you know how to define a block of PHP code, take a closer look at the code

in Listing 3.1 itself.

The print() Function

print() is a function that outputs data. In most cases, anything output by print()

ends up in the browser window. A

function

is a command that performs an action,

usually modified in some way by data provided for it. Data sent to a function is

almost always placed in parentheses after the function name. In this case, you sent

the print() function a collection of characters, or string. Strings must always be

enclosed by quotation marks, either single or double.

Note

Function calls generally require parentheses after their name whether or

not they demand that data be passed to them. print() is an exception,

and enclosing the data you want to print to the browser in parentheses is

optional. This is the more common syntax, so we will usually omit the

brackets in our examples.

You ended your only line of code in Listing 3.1 with a semicolon. The semicolon

informs the interpreter that you have completed a statement.

NEW

A

statement

represents an instruction to the interpreter. Broadly, it

TERM

is to PHP what a sentence is to written or spoken English. A

statement should usually end with a semicolon; a sentence should

end with a period. Exceptions to this include statements that

enclose other statements, and statements that end a block of code.

In most cases, however, failure to end a statement with a semicolon

will confuse the interpreter and result in an error.

Because the statement in Listing 3.1 is the final one in that block of code, the

semicolon is optional.

Combining HTML and PHP

The script in  Listing 3.1 is pure PHP. You can incorporate this into an HTML

document simply by adding HTML outside the PHP start and end tags, as shown in

Listing 3.2.

Listing 3.2: A PHP Script Including HTML

1: <html>

2: <head>

45

3:     <title>Listing 3.2 A PHP script including HTML</title>

4: </head>

5: <body>

6: <b>

7: <?php

8:     print "hello world";

9: ?>

10: </b>

11: </body>

12: </html>

As you can see, incorporating HTML into a PHP document is simply a matter of

typing in the code. The PHP interpreter ignores everything outside PHP open and

close tags. If you were to view Listing 3.2 with a browser, as shown in Figure 3.4,

you would see the string "hello world" in bold. If you were to view the document

source, as shown in Figure 3.5, the listing would look exactly like a normal HTML

document.

You can include as many blocks of PHP code as you need in a single document,

interspersing them with HTML as required. Although you can have multiple blocks of

code in a single document, they combine to form a single script. Anything defined in

the first block (variables, functions, or classes, for example) u sually will be available

to subsequent blocks.

Figure 3.4:

The output of Listing 3.2  as viewed in a browser.

46

Figure 3.5:

The output of Listing 3.2  as HTML source code.

Adding Comments to PHP Code

Code that seems clear at the time of writing, can seem like a hopeless tangle when

you come to amend it six months later. Adding comments to your cod e as you write

can save you time later on and make it easier for other programmers to work with

your code.

NEW

A

comment

is text in a script that is ignored by the interpreter.

TERM

Comments can be used to make code more readable, or to annotate a

script.

Single line comments begin with two forward slashes ( / /) or a single hash sign (#).

All text from either of these marks until either the end of the line or the PHP close tag

is ignored.

// this is a comment

#  this is another comment

*

Multiline comments begin with a forward slash followed by an asterisk (/

) and end

*

with an asterisk followed by a forward slash (

/).

*

/

this is a comment

none of this will

be parsed by the

interpreter

/

*

Summary

You should now have the tools at your disposal to run a simp le PHP script on a

properly configured server.

In this hour, you created your first PHP script. You learned how to use a text editor

to create and name a PHP document. You examined four sets of tags that you can

use to begin and end blocks of PHP code. You learned how to use the print() function

to send data to the browser, and you brought HTML and PHP together into the same

script. Finally, you learned about comments and how to add them to PHP

documents.

Q&A

Q Which are the best start and end tags to use?

A

It is largely a matter of preference. For the sake of portability the standard tags

(<?php ?>) are probably the safest bet. Short tags are enabled by default and have

the virtue of brevity.

Q What editors should I avoid when creating PHP code?

A

Do not use word processors that format text for printing (such as Word, for

example). Even if you save files created using this type of editor in plain text format,

hidden characters are likely to creep into your code.

Q When should I comment my code?

A

This is a matter of preference once again. Some short scripts will be

self-explanatory to you, even after a long interval. For scripts of any length or

complexity, you should comment your code. This often saves you time and

frustration in the long run.

Workshop

The Workshop provides quiz questions to help you solidify your understanding of the

material covered. Try to understand the quiz answers before continuing to the next

hour's lesson. Quiz answers are provided in Appendix A.

Quiz

Can a user read the source code of PHP script you have successfully installed?

What do the standard PHP delimiter tags look like?

What do the ASP PHP delimiter tags look like?

What do the script PHP delimiter tags look like?

What function would you use to output a string to the browser?

Activity

Familiarize yourself with the process of creating, uploading, and running PHP

scripts.