Fred Brack
Raleigh, NC

Introduction to PHP
by Fred Brack
Updated

It's February 2021, and I need to learn a little about PHP, the server-side scripting language that runs on most servers supporting web pages. My motivation for learning PHP was the need to create an HTML form from which I would gather visitor input and then send a message to myself. An example of this would be a comment form on a website. I document this as Using PHP to Send an Email from an HTML Form.

I'm documenting what I learn here for both myself and anyone else who might want an introduction to the language. That's just what I do ...

PHP is an acronym that is oddly self-inclusive, as it stands for "PHP: Hypertext Preprocessor." It runs on the server that supports your web page. Well, it can run there; you'll have to test it or ask to see if it is available to you, but it probably is. Test your own system for PHP support by clicking here.

The Basics

PHP language statements can exist on a web page by themselves or in concert with regular HTML.
If you have regular HTML and include some PHP statements, the PHP code generally returns HTML in-place to help build your web page.
A series of one or more PHP statements must begin with <?php and end with ?> . Example:
<?php echo "Hello World"; ?>
COMMENTS within PHP can be any of the following:
// the double slash starts a comment through end-of-line # a hash tag does the same thing /* this notation starts and ends a comment anywhere, even across lines */
PHP keywords, classes, and both system- and user-defined functions are NOT case-sensitive.
Here's the catch: Unless your system allows an exception, your page's filetype must be .php not .html.

Variables

Variable names ARE case-sensitive.
All variable names must begin with a dollar-sign ($) and be followed by a letter or an underscore.
Variable names must contain ONLY alpha-numeric characters or an underscore, no special characters other than the leading $.
No type declarations are required: just use a variable name, equal-sign, and value (quoted if text). Examples:
$n = 5; $text_message = "Hello World"; $camelCaseIsOK2 = "whatever...";
All PHP statements should end with a semicolon as shown above. (The final statement in a block of PHP code may omit the semicolon).

Variable Scope

When we come to functions, while we will see that variables outside a function are called global, they are not, in fact available inside any called functions by default.
Variables defined inside functions are called local, and their scope is solely within that function. They may optionally have the same name as global variables, and they "go away" at the end of the function by default.
To access a global variable inside a function, you must use the global keyword in the function (shown later -- we just wanted to let you know it is possible).
To save the value of a local variable for reuse later in the same function, declare it as static: static $count = 0;.

Variable Data Types

PHP supports the following data types:

String: $x = "Hello";
Integer: $n = 99;
Float (floating point numbers - also called double): $n = 99.1;
Boolean: $continue = true; // versus "false"
Array: $colors = array("red", "green", "blue");
Object: we'll give an example later
NULL: $x = null; // or NULL
Resource: not really a data type, but rather a reference to a function or external resource

Echo and Print

The echo and print keywords are nearly identical. They both output data to the screen (e.g., typically in the middle your HTML screen presentation). Because of the similarity, we will only discuss echo.

There's not much to discuss! The operand of echo can be straight text, text with HTML tags, or a calculation or other PHP statement. Parentheses are optional. Examples:



	echo("Hello"); // note: a space before the paren is optional
	echo "<h2>My Heading</h2>";
	$n = 5;
echo "The first value is " . $n + "<br>";
$m = 5;
echo 
	"Adding " . $m . " the sum is " . $n + $m . "<br>";

Note the use of the concatenation character (a period surrounded by blanks). Also note our use of "<br>". Without it, no new line break would occur between uses of echo.

String Functions

There are, of course, lots of built-in string functions. You can consult this PHP String Reference to see all of them. Here are some common examples:



	$mystring = "My name is Fred Brack.";
	echo strlen($mystring); // = 22
	echo str_word_count($mystring); // = 5
	echo strrev($mystring); // = .kcarB derF si eman yM
	echo strtoupper($mystring); // MY NAME IS FRED BRACK.

	  I know you guess what strtolower does ...
	echo strpos($mystring, "Fred"); // = 11
  (1) position counting 
	starts at 0;
  (2) the operands are in the reverse order from many other programming 
	languages; 
 
	(3) stripos does the same thing 
	case-insensitive
	echo str_replace("Fred", "Kathy", $mystring); // = My name is Kathy 
	Brack.
  NOTE that now the operands are in a more logical order ...
  
	And here's how you remove all blanks:  
	str_replace(" ","",$variable);
	echo substr($mystring,11,6); // = Fred B
  NOTE that if the 
	third parameter (length) is missing, it defaults to end of string
	echo strstr($mystring, "Fred"); // = Fred Brack.
  This returns 
	the string starting with the passed phrase

There are many interesting string functions, including ones that:

Substitute characters within a string
Convert to hex or back
Format numbers or currency or text for printing
Trim left, right, or in-between
Convert to or from an array
Parse a string into variables
Compare strings with numerous options
Translate characters in various ways

Date and Time

PHP offers extensive date and time functions, so we are only going to give one example of the most common format here, and you can consult the w3schools Date and Time Functions Reference page for details. Be sure to click on the date() function by itself on that page to see the myriad of options (like the l M j below, which don't exactly jump out in their meaning)!

date_default_timezone_set("America/New_York"); // this sets your local time zone date("l M j\, Y") . " at " . date("h:i a") // = (for example) "Friday Feb 12, 2021 at 11:00 am"

It is worth noting that PHP, like JavaScript and other languages, has an "escape" character, the backslash \, which means, "take the following character literally." So the comma in the operand to the date function is not separating two operands but is rather to be written out as a comma, which you see above after the 12. There is no confusion about the colon in the second date function, however, so it doesn't need the escape character.

Math Functions

PHP offers a variety of math functions. You can view the complete list at PHP Math Reference. They include functions like:

Min/Max
Rounding
Random number generator
PI
Conversion of one base to another (e.g., decimal to hex)
All the trigonometric functions

Miscellaneous Functions

Some of the miscellaneous functions available are as follows. See the complete list at Miscellaneous PHP Functions.

Exit with or without a message
Sleep for a given number of seconds
Define a constant
Evaluate a string as if it were PHP input
Validate a variable as an email address or website URL (caution from experience: trim the variable of all blanks first via str_replace(" ","",$address);)

PHP Mail

You can use PHP to initiate an email to yourself or anyone else, with or without a copy list or blind copy list. Typically this would be done after a user fills out a form with requested data. For example, you might wish to use a form for user requests for information from you, to assure yourself of gathering required data. To learn how to do this, see Using PHP to Send an Email from an HTML Form.

Resources

And Now ...

I will be adding to this document after I have reason to learn more about PHP myself or I just decide to continue my own learning process, which I will share with you!

Fred

Introduction to PHP by Fred Brack Updated document.write(document.lastModified.substr(0,10))