PHP Tutorial - PHP Introduction

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PHP scripts are generally saved with the file extension .php.

Statement

The basic unit of PHP code is called a statement, which ends with a semicolon.

Usually one line of code contains just one statement, but we can have as many statements on one line as you want.

PHP Opening and Closing Code Islands

<?php and ?> marks the PHP code island.

The short tags version is <? and ?>.

<?="Hello, world!" ?>

Here is the equivalent, written using the standard open and closing tags:

<?php 
   print "Hello, world!";
?>

Example - PHP Statements

The following PHP code uses print statement to output message on to the screen.

<?php
        // option 1
        print "Hello, ";
        print "world!";

        // option 2
        print "Hello, "; print "world!";
?>

The code above generates the following result.

echo is another command we can use to output message. echo is more useful because you can pass it several parameters, like this:

<?php
        echo "This ", "is ", "a ", "test.";
?>

The code above generates the following result.

To do the same using print, you would need to use the concatenation operation (.) to join the strings together.

PHP Variables

A variable is a container holding a certain value.

Syntax

Variables in PHP beginning with $ followed by a letter or an underscore, then any combination of letters, numbers, and the underscore character.

Here are the rules we would follow to name variables.

• Variable names begin with a dollar sign ( $ )
• The first character after the dollar sign must be a letter or an underscore
• The remaining characters in the name may be letters, numbers, or underscores without a fixed limit

Example - Define PHP variables

We cannot start a variable with a number. A list of valid and invalid variable names is shown in the following table.

Variable	Description
$myvar	Correct
$Name	Correct
$_Age	Correct
$___AGE___	Correct
$Name91	Correct;
$1Name	Incorrect; starts with a number
$Name's	Incorrect; no symbols other than "_" are allowed

Variables are case-sensitive. $Foo is not the same variable as $foo.

Variable substitution

In PHP we can write variable name into a long string and PHP knows how to replace the variable with its value. Here is a script showing assigning and outputting data.

<?php
       $name = "java2s.com";
       print "Your name is $name\n";
       $name2 = $name;
       print 'Goodbye, $name2!\n';
?>

The code above generates the following result.

PHP will not perform variable substitution inside single-quoted strings, and won't replace most escape characters.

In the following example, we can see that:

• In double-quoted strings, PHP will replace $name with its value;
• In a single-quoted string, PHP will output the text $name just like that.

<?php
        $food = "grapefruit";
        print "These ${food}s aren't ripe yet.";
        print "These {$food}s aren't ripe yet.";
?>

The code above generates the following result.

The braces {} tells where the variable ends.

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