A variable is simply a container that’s used to store both numeric and non-numeric information. And just as with any container, you can move it from place to place, add stuff to it, or empty it out on the floor in a pile and fill it with something completely different.
PHP has some simple rules for naming variables. Every variable name must be preceded with dollar($) symbol and must begin with a letter or underscore character, optionally followed by more letters, numbers, or underscore character. Common punctuation characters, such as commas, quotation marks, or periods, are not permitted variable names; neither are spaces. So, for example, $root, $_num and $query are all valid variable names, while $58%, $1day, and email are all invalid variable names.
Assigning Values to Variables
Assigning value to a variables in PHP is quite easy: use the equality(=) symbol, which also happens to be PHP’s assignment operator. This assigns the value on the right side of the equation to the variable on the left.
To use a variable in a script, simply call it by name in an expression and PHP will replace it with its value when the script is executed. Here’s an example:
<!DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Transitional//EN” “DTD/xhtml1-transitional.dtd”> <html xmlns=http://www.w3.org/1999/xhtml xml:lang=”en” lang=”en”> <head><title/></head> <body> <?php // assign value to variable $name= ’Anuj’; ?> <h2> Welcome to<? Php echo $name; ?>’s Blog!</h2> </body> </html>
In this example, the variables $name is assigned the value ‘Simon’. The echo statement is then used to print the value of this variable to the Web page.
You can also assign a variable the value of another variable, or the result of calculation.
The following example demonstrates both these situations:
<?php //assign value to variable $now=2008; // assign value to another variable $currentYear = $now; //perform calculation $lastYear = $currentYear-1; //output: ‘2007 has ended. Welcome to 2008!’ echo “$lastYear has ended. Welcome to $currentYear”; ?>
To destroy a variable, pass the variable to PHP’s aptly named unset() function, as in the following example:
<?php //assign value to variable $car = ‘Porsche’ //print variable value //output: ‘Before unset(), my car is a Porsche’ Echo “Before unset(), my car is a $car”; //destroy variable unset($car); //print variable vale //this will generate an ‘undefined variable’ error //output: ‘After unset(), my car is a’ echo “After unset(), my car is a $car; ?>
Inspecting Variable Content
PHP offers the var_dump() function, which accepts a variable and X-ray it for you.
<?php //define variables $name = ‘Fiona’; $age = 28; //display variable contents var_dump($name); var_dump($age); ?>