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PHP is a server side scripting language.

My notes originate from these books and PHP site:

  • Build Your Own Database Driven Website Using PHP & MySQL 2nd Edition by Kevin Yank
  • PHP and MySQL for Dynamic Web Sites 4th Edition by Larry Ullman

For MySQL information.

Useful sites

A collection of sites I have found useful

PHP Master

Virendra's TechTalk discussing "PHP isset() vs empty() vs is_null()"

Multidimensional arrays and array functions

Lots of Code

Basic Syntax & Commands

PHP statements are always terminated with semicolon (;).

Single quotes are used to mark start and end of text (' ')

All variable names in PHP start with dollar sign ($).

PHP is a loosely typed language. Variables may contain any type of data.


$variable_name = "Semper Fidelis";

Equal sign is called the assignment operator since it assigns values to variables.

Three ways to create comments. None of these are viewable to users via web browser.

  • //
  • /* */
  • #

arithmetic operators enable you to add, subtract, multiply, & divide.


The concatenation operator, the period "." allows you to add strings of text.


$variable_name = "Hello" . " there" . " world!";

Assigns value of "Hello there world!" without quotes.


variable comment
$var1 = 'PHP'; Assigns value of "PHP" to var1
$var2 = 5; Assigns value of 5 to $var2
$var3 = $var2 + 1; Assigns value of 6 to $var3
$var2 = $var1; Assigns value of "PHP" to $var2
echo($var1); Outputs "PHP"
echo($var2); Outputs "PHP"
echo($var3); Outputs 6
echo($var1 . ' rules!'); Outputs "PHP rules!"
echo("var1 rules!"); Outputs "PHP rules!"
echo('var1 rules!'); Outputs '$var1 rules!'
\ Escape character. Tells PHP to treat next character as text.

NOTE: Double quotes around text enables the variable name to be inserted & value is displayed. This is called variable interpolation. Single quotes will not interpolate the variable name.

Some of PHP Built-In Functions

echo( "add_text" );

passes a string

Variable interpolation = process of converting variable names to their values

Example: $variable1 = 'PHP4'; // assigns variable1 the value "PHP4" echo("$variable1 rocks!"); // output "PHP4 rocks!" echo('$variable1 rocks!"); // output '$variable1 rocks!'

Arrays: $variable = array('string1','string2',integer);

Integer indexes start from 0 and used to reference contents of array.

Examples: echo($variable[0]); // output "string1" echo($variable[1]); // output "string2" echo($variable[2]); // output "integer" $variable[3] = 95; // assigns 95 to 4th index (n-1) $variable[0] = 'string0'; // assigns string0 to index 0. $variable[] = 55; // assigns 55 to end of array

Associative array: Use a string as the index. Associate the value with index. $phone['Joe'] = '555-1212'; $phone['Mike'] = '555-1313';

Example: echo('Mikes phone number is ' . $phone['Mike']);

Predefined Variables

variable comment
$_GET is an associative array that PHP will automatically create so values

passed through a URL query string can be accessed.

$_SERVER is an array variable that contains information provided by the users

web browser

Examples of using predefined variables

Example $_SERVER use comment
$_SERVER['PHP_SELF'] Identifies the name of script being run. You can use to set browser to reference itself.
$_SERVER['HTTP_USER_AGENT'] Identifies web browser and operating system accessing script
$_SERVER['REMOTE_ADDR'] Identifies the IP address of the computer accessing script

urlencode(); will convert special characters within input sting to special codes in order to appear query string

isset(); outputs a true value if variable provided has been assigned a value

exit(); causes PHP to stop reading contents

die(); acts like echo(); immediately followed by exit();



Constants are a specific data type in PHP that retain their original value throughout the execution of a script.

To create a constant use define() function. Example syntax:

define ('CONSTANT_NAME', 'value');

Constants require special echo syntax for printing.


Foreach loop


A special variable that contains multiple values.

Simple format:

$array_name = array('test1', 'test2', 69);

To retrieve a value stored in an array you need the index.

Generally, arrays use incrementing integers that start with zero as their indices. Indices act as pointers to precisely locate a value in an array.

Expanding on simple format:

code comment
echo($array_name[0]); Outputs 'test1'
echo($array_name[1]); Outputs 'test2'
echo($array_name[2]); Outputs 69
$array_name[1] = 'wiki1'; Assign a new value
$array_name[3] = 'wiki2'; Create a new element
$array_name[] = 'transformers'; Add element to end of array.
echo($array_name[4]); Outputs "transformers"

Arrays can use strings for indices. This is called an associative array because we can associate values with meaningful indices.


$weight['robert'] = 225;

$weight['gene'] = 180;

$weight['julie'] = 103;

Array Variables

Array variables useful to HTML

Array variable comment
$_FILES Using HTML to upload files automatically creates this PHP array. Information about the uploaded files is in the $_FILES array.
blah blah


Functions are good for your health.

function syntax description
echo outputs data to browser
urlencode takes any special characters in a string (like spaces) & converts them into special codes to appear in php query strings
mysql_connect Enables connection to MySQL database, returns a number that identifies the connection that has been established
mysql_select_db Selects database table that PHP will use.
mysql_query Enables PHP to send MySQL queries to MySQL db
exit( ); Commands PHP to stop reading page.
mysql_affected_rows Returns number of rows affected for DELETE, INSERT, and UPDATE queries. MySQL tracks the number of rows that were affected.
isset returns a value of true if the identified variable has a value
mysql_fetch_array Accepts a result as a parameter and returns the next row in the result set as an array. No row returns a false.
CURDATE() returns current date
split takes a regular expression string of text and breaks it into an array based on char matches
spliti same as split except ignores case
blah blah

mysql_connect example

Example code:

$dbc = @mysql_connect ('db_hostname', 'db_user_name', 'db_user_password');

if (!$dbc) {

echo ( '<p>Unable to connect to the ' .

'database server at this time.</p>' );

exit ();

  • The '@' symbol tells the function to fail silently which enables the coder to display your own message.
  • The '!' symbol flips the $dbcnx value. A returned number for $dbcnx is true (your code successfully connected to MySQL db. !$dbcnx means a successful db connection results in false and the if statement would not execute. !$dbcnx means a failed db connection results in true and the if statement would execute (print the custom error message).
  • exit() function causes php to stop reading the page

Example testing connection to db

// Connect to database:


// Check db connection

if (!$dbc) {
  die('Connect Error (' . mysqli_connect_errno() . ') '
        . mysqli_connect_error());

echo 'Success... ' . mysqli_get_host_info($dbc) . "\n";

mysql_select_db example

After your code successfully connects to the MySQL db you must tell PHP which db table to use.

Example basic code:

mysql_select_db ('db_name', $dbcnx );

  • The function contains the db identifier $dbcnx. This parameter is optional but I will use it for completeness. The function will default to the last connection opened.
  • Function returns true when it's successful and false if an error occurs.

Example basic code with error handling:

if (! @mysql_select_db('db_name', $dbcnx) ) {
die ( '<p>Unable to locate the db_name ' .
'database at this time.</p>' );

  • die function works like echo except the script exits after
  • Executing die is equivalent to echo followed by exit

mysql_query example

Example code:

mysql_query ( query, connection_id ) ;

  • query is a string that contains the SQL command we want to execute
  • connection_id is optional parameter
  • Returns true (success) or false (failure) for most SQL queries. SELECT queries view data in db so it requires more than true or false.
  • With SELECT query mysql_query returns a number that identifies a result set which contains a list of all the rows (entries) returned from the query.
  • False is always returned if query fails.

mysql_query debugging

Some examples to debug code:

$r = mysqli_query ($dbc, $q);
	// Debugging
	if ($r == FALSE) {
		echo '<p>$r is FALSE so myqli_query failed error: ' . mysqli_error($dbc) . '</p>';
	// debugging end

$result = @mysql_query ('SELECT column_name0, column_name1, ... FROM table_name');

if ( !$result )  {

die ('<p>Error performing query: ' . mysql_error() .


File Functions

Functions to manipulate files

function syntax description
fopen opens file for modification
fclose closes file
fread read data from file
fwrite writes data from a PHP variable into a file
copy copy a file

Number Functions

function syntax description
round() Rounds a decimal to nearest integer. Specify the number of decimals to round by using format round($number, 3)
number_format() Converts number into commonly written version. Specify the number of decimals to round by using format number_format($number, 2)

Regular Expressions

A regular expression is a string of text that contains special codes. Enables use of a few PHP functions to search and manipulate other strings of text.

ereg - searches text for string match & is case sensitive.

eregi - like ereg except is not case sensitive.

$text = 'Be nice and respectful.';

if (ereg('nice', $text)){
  echo( '$text contains the string "nice".');
} else {
  echo( '$text does not contain the string "nice".');

ereg_replace - same as ereg plus it replaces every match of the regular expression with another string

eregi_replace - same except is not case sensitive.

$new_string = ereg_replace(regexp, replacewith, old_string);

special code comment
A caret " ^ " Marks start of text.
A dollar sign " $ " Marks end of text.
Backslash " \ " Prefix with a backslash to remove special meaning of a character.
Square brackets " [ ] " Matches any string with any character within brackets.
Question mark " ? " Trailing char is optional
Addition sign " + " one or more of the previous char
Asterisk " * " zero or more of the previous char
Period " . " Matches any string of one or more char with no line breaks.
Parentheses " ( ) " May be used to group string char together to apply ?, +, or * to them as a whole.


Example Result
[6789] Matches 6, 7, 8, 9, or any text with those characters.
[6-9] Same as [6789]
^[0-9]$ Matches any single number
^[a-z]$ Matches any single lower case letter
[0-9a-zA-Z] Matches any string with a letter or number
^[a-zA-Z]+$ Matches any string of one ore more letters.
bana?na Matches "banana" and "banna", but not "banaana".
bana+na Matches "banana" and "banaana", but not "banna".
bana*na Matches "banna", "banana", and "banaaana".
ba(na)+na Matches "banana" and "banananana", but not "bana" or "banaana".

Regular Expression Resources

Regex 101

Regular Expression Tutorials

10 Regular Expression Examples You Should Know

User Interaction & Forms

Formats, tips, and suggestions for user interaction & forms.

Variables can be separated in s query string by an ampersand (&). You may use the ampersand multiple times.

Web pages that can decide whether to display more than one pages is a multipurpose page.

Sample multipurpose page in the HTML body tags:

<?php if ( condition ) { ?>

HTML content to display if condition is true

<?php } else { ?>

HTML content to display if condition is false

<?php } ?>

Control Structures

if-else statement

if ( condition ) {

executed if condition is true

} else {

executed if condition false

while loop

while ( conditions ) {

statements execute if true, then repeat, until false


for loop

for ( initialize; condition; update ) {

statement(s) to execute repeatedly while condition is true



for ($i = 0; $i < 30; $i++) {
echo 'Iteration ' . $i;


operator meaning structure
and or && compares two conditions both must be true
or or || compares two and either must be true
! negation operator or not operator, reverses a returned value from true to false or vice versa
== equal-to operator
!= not equal
< less than
> greater than
<= less than or equal
>= greater than or equal
.= String concatenation operator - adds a new string on the end of another string
? Ternary operator evaluates to exprTrue if expr1 evaluates to TRUE & exprFalse if FALSE. expr1 ? exprTrue : exprFalse
? PHP version 5.3+ Ternary operator returns exprTrue if exprTrue evaluates to TRUE, & exprFalse otherwise. exprTrue ?: exprFalse

Useful URLs

Ternary examples

Arithmetic Operators

operator meaning
+ Addition
- Subtraction
* Multiplication
/ Division
% Modulus
++ Increment
-- Decrement


A useful PHPMailer tutorial that describes how to use PHPMailer and explains the use of the class functions by Tom Klingenberg.

Another PHPMailer tutorial on Dreamhost wiki.

Troubleshooting Tips

Web resources (leetspeak for eval) is an online shell that allows you to run your code on my server.

Print contents of an array

echo '<pre>';
echo '</pre><br />';