PHP is a web language based on scripts that allows developers to dynamically create generated web pages.
PHP means PHP: Hypertext Preprocessor.
PHP syntax resembles Perl and C
PEAR means “PHP Extension and Application Repository”. it extends PHP and provides a higher level of programming for web developers.
Version 5 is the actually used version of PHP.
The two most  common ways to start and finish a PHP script are:
To be able to display the output directly to the browser, we have to use the special tags <?= and ?>.
PHP 5 presents many additional OOP (Object Oriented Programming) features.
PHP includes only single inheritance, it means that a class can be extended from only one single class using the keyword ‘extended’.
‘final’ is introduced in PHP5. Final class means that this class cannot be extended and a final method cannot be overrided.
We use the operator ‘==’ to test is two object are instanced from the same class and have same attributes and equal values. We can test if two object are refering to the same instance of the same class by the use of the identity operator ‘===’.
It is possible to generate HTML through PHP scripts, and it is possible to pass informations from HTML to PHP.
If we would like to pass values througn a form or an URL then we need to encode and to decode them using htmlspecialchars() and urlencode().
PHP and Javascript cannot directly interacts since PHP is a server side language and Javascript is a client side language. However we can exchange variables since PHP is able to generate Javascript code to be executed by the browser and it is possible to pass specific variables back to PHP via the URL.
GD library is needed to be able execute image functions.
imagetypes() gives the image format and types supported by the current version of GD-PHP.
The functions are getimagesize() for size, imagesx() for width and imagesy() for height.
If the function require() cannot access to the file then it ends with a fatal error. However, the include() function gives a warning and the PHP script continues to execute.
require() and require_once() perform the same task except that the second function checks if the PHP script is already included or not before executing it.</p><p>(same for include_once() and include())
To be able to display a human-readable result we use print_r().
The set_time_limit(0) added at the beginning of a script sets to infinite the time of execution to not have the PHP error ‘maximum execution time exceeded’.It is also possible to specify this in the php.ini file.
This is a PHP syntax error expressing that a mistake at the line x stops parsing and executing the program.
The most common and used way is to get data into a format supported by Excel. For example, it is possible to write a .csv file, to choose for example comma as separator between fields and then to open the file with Excel.
file_get_contents() lets reading a file and storing it in a string variable.
mysql_pconnect() ensure a persistent connection to the database, it means that the connection do not close when the the PHP script ends.
The result set can be handled using mysql_fetch_array, mysql_fetch_assoc, mysql_fetch_object or mysql_fetch_row.
The function mysql_num_rows() returns the number of rows in a result set.
mysql_affected_rows() return the number of entries affected by an SQL query.
The mysql_fetch_object() function collects the first single matching record where mysql_fetch_array() collects all matching records from the table in an array.
In order to access the data sent via the GET method, we you use $_GET array like this:</p><p><br> $variable = $_GET[“var”]; this will now contain ‘value’
To access the data sent this way, you use the $_POST array.</p><p>Imagine you have a form field called ‘var’ on the form, when the user clicks submit to the post form, you can then access the value like this:</p><p>$_POST[“var”];
It is possible to use the dedicated function, is_numeric() to check whether it is a number or not.
It is possible to use the dedicated function, ctype_alnum&nbsp;to check whether it is an alphanumeric value or not.
If we want to check whether a variable has a value or not, it is possible to use the empty() function.
The unlink() function is dedicated for file system handling. It simply deletes the file given as entry.
The unset() function is dedicated for variable management. It will make a variable undefined.
addslashes function enables us to escape data before storage into the database.
The stripslashes function enables us to remove the escape characters before apostrophes in a string.
We have to enable the Magic quotes entry in the configuration file of PHP.
The function get_magic_quotes_gpc() tells us whether the magic quotes is switched on or no.
The strip_tags() function enables us to clean a string from the HTML tags.
This feature is possible using the global keyword.
A function returns a value using the instruction ‘return $value;’.
It is preferable to use crypt() which natively supports several hashing algorithms or the function hash() which supports more variants than crypt() rather than using the common hashing algorithms such as md5, sha1 or sha256 because they are conceived to be fast. hence, hashing passwords with these algorithms can vulnerability.
The PHP-openssl extension provides several cryptographic operations including generation and verification of digital signatures.
The define() directive lets us defining a constant as follows:</p><p>define (“ACONSTANT”, 123);
To be able to pass a variable by reference, we use an ampersand in front of it, as follows $var1 = &amp;$var2
“13” and 12 can be compared in PHP since it casts everything to the integer type.
The name of the output type have to be specified in parentheses before the variable which is to be cast as follows:</p><p>* (int), (integer) – cast to integer</p><p>* (bool), (boolean) – cast to boolean</p><p>* (float), (double), (real) – cast to float</p><p>* (string) – cast to string</p><p>* (array) – cast to array</p><p>* (object) – cast to object
When the original if was followed by : and then the code block without braces.
It is composed of three expressions: a condition, and two operands describing what instruction should be performed when the specified condition is true or false as follows:</p><p>Expression_1 ? Expression_2 : Expression_3;
The function func_num_args() is used to give the number of parameters passed into a function.
$$var2 contains the value 10.
:: is used to access static methods that do not require object initialization.
In PHP, objects passed by value.
No, a parent constructor have to be called explicitly as follows:</p><p>parent::constructor($value)
__sleep returns the array of all the variables that need to be saved, while __wakeup retrieves them.
1- Combining two variables as follows:</p><p>$variable1 = ‘Hello ‘;</p><p>$variable2 = ‘World’;</p><p>$variable3 = $variable1.$variable2;</p><p>Or</p><p>2- $variable3 = “$variable1$variable2”;</p><p>$variable3 will contain “Hello World”. The first code is faster than the second code especially for large large sets of data.
A session is a logical object enabling us to preserve temporary data across multiple PHP pages.
The use of the function session_start() lets us activating a session.
It is possible to propagate a session id via cookies or URL parameters.
A persistent cookie is permanently stored in a cookie file on the browser’s computer. By default, cookies are temporary and are erased if we close the browser.
Sessions automatically ends when the PHP script finishs executing, but can be manually ended using the session_write_close().
The session_unregister() function unregister a global variable from the current session and the session_unset() function free all session variables.
$GLOBALS is associative array including references to all variables which are currently defined in the global scope of the script.
$_SERVER is an array including information created by the web server such as paths, headers, and script locations.
$_FILES is an associative array composed of items sent to the current script via the HTTP POST method.
$_FILES[‘userfile’][‘error’] contains the error code associated with the uploaded file.
We can change the maximum size of files to be uploaded by changing upload_max_filesize in php.ini.
$_ENV is an associative array of variables sent to the current PHP script via the environment method.
$_COOKIE is an associative array of variables sent to the current PHP script using the HTTP Cookies.
The scope of a variable is the context within which it is defined. For the most part all PHP variables only have a single scope. This single scope spans included and required files as well.
$a and $b:&nbsp;&nbsp;&nbsp; TRUE if both $a and $b are TRUE.</p><p>$a &amp; $b:&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Bits that are set in both $a and $b are set.
The first is the concatenation operator (‘.’), which returns the concatenation of its right and left arguments. The second is (‘.=’), which appends the argument on the right to the argument on the left.
$a === $b TRUE if $a and $b have the same key/value pairs in the same order and of the same types.
!= means inequality (TRUE if $a is not equal to $b) and !== means non-identity (TRUE if $a is not identical to $b).
To be able to verify whether a PHP variable is an instantiated object of a certain class we use instanceof.
The goto statement can be placed to enable jumping inside the PHP program. The target is pointed by a label followed by a colon, and the instruction is specified as a goto statement followed by the desired target label.
Exception::getMessage lets us getting the Exception message and Exception::getLine lets us getting the line in which the exception occurred.
Exception::__toString gives the String representation of the exception.
The function parse_ini_file() enables us to load in the ini file specified in filename, and returns the settings in it in an associative array.
The boolean function isset determines if a variable is set and is not NULL.
The string function strstr(string allString, string occ) returns part of allString from the first occurrence of occ to the end of allString. This function is case-sensitive. stristr() is identical to strstr() except that it is case insensitive.
for is expressed as follows:</p><p>for (expr1; expr2; expr3)</p><p>statement</p><p>The first expression is executed once at the beginning. In each iteration, expr2 is evaluated. If it is TRUE, the loop continues and the statements inside for are executed. If it evaluates to FALSE, the execution of the loop ends. expr3 is tested at the end of each iteration.</p><p>However, foreach provides an easy way to iterate over arrays and it is only used with arrays and objects.
It is possible to use the document.form.submit() function to submit the form. For example: &lt;input type=button value=”SUBMIT” onClick=”document.form.submit()”&gt;
The function eregi_replace() is identical to the function ereg_replace() except that it ignores case distinction when matching alphabetic characters.
Yes, we use the urlencode() function to be able to protect special characters.
The three basic classes of errors are notices (non-critical), warnings (serious errors) and fatal errors (critical errors).
34 is octal 34 and x34 is hex 34.
It is possible to pass the variables between the PHP pages using sessions, cookies or hidden form fields.
The use of the set_time_limit(int seconds) enables us to extend the execution time of a php script. The default limit is 30 seconds.
Yes, it is possible by setting the cookie with a past expiration time.
The default session time in php is until closing of browser
Yes, it’s possible to integrate (Distributed) Component Object Model components ((D)COM) in PHP scripts which is provided as a framework.