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Basic Syntax and Commands
PHP syntax will be very familiar to anyone with an understanding ofC, C++, Java, JavaScript, Perl, or any other C-derived language. A PHP script
consists of a series of commands, or statements, each of which is an instruction
that the Web server must follow before it can proceed to the next. PHP statements,
like those in the above-mentioned languages, are always terminated by a semicolon
(;).This is a typical PHP statement:
echo( "This is a <b>test</b>!" );
This statement invokes a built-in function called echo and
passes it a string of text: This is a <b>test</b>!
Built-in functions can be thought of as things that PHP knows
how to do without us having to spell out the details. PHP has a lot of built-in
functions that let us do everything from sending email, to working with information
that's stored in various types of databases. The echo function, however, simply takes
the text that it's given, and places it into the HTML code of the page at
the current location. Consider the following (echo.php in
the code package):
<html>
<head>
<title> Simple PHP Example </title>
</head>
<body>
<p><?php echo('This is a <b>test</b>!'); ?></p>
</body>
</html>
If you paste this code into a file called echo.php and
place it on your Web server, a browser that views the page will see this:
<html>
<head>
<title> Simple PHP Example </title>
</head>
<body>
<p>This is a <b>test</b>!</p>
</body>
</html>
Notice that the string of text contained HTML tags (<b> and </b>),
which is perfectly acceptable.You may wonder why we need to surround the string of text with both
parentheses (()) and single quotes ('').
Quotes are used to mark the beginning and
end of strings of text in PHP, so their presence is fully justified. The parentheses serve a dual purpose. First, they indicate that echo is
a function that you want to call. Second, they mark the beginning and end
of a list of parameters that you wish to provide, in
order to tell the function what to do. In the case of the echo function,
you need only provide the string of text that you want to appear on the page.
Later on, we'll look at functions that take more than one parameter, and we'll
separate those parameters with commas. We'll also consider functions that
take no parameters at all, for which we'll still need the parentheses, though
we won't type anything between them.
