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PHP

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PHP Hypertext Preprocessor Language is a server side interpreted language written in C that runs primarily on Linux environments. PHP scripts can be run directly or served as webpages.

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Development Environment

PHP CLI

Xochipilli says
Many Linux distributions package the PHP CLI separately
  • php -l check syntax
  • php -v version
  • php -e oneliner

Pear/Pecl

Your first application

Variables

A variable is how you store a value such as a string or integer. An example where a variable would be used is if you wanted to handle a string multiple times throughout your application. Here is an example of a variable and how it can be used: 

 
$variable = "Blackhat Academy ";
$variable1 = "Rules!";
echo "$variable $variable1";
 

This snippet of code will display the following: 

 Blackhat Academy Rules!

data types

PHP is a dynamically-typed language, consisting of integers, arrays, associative arrays, strings, and classes.

Boolean Logic

Ternary Conditionals

In PHP, if else statements typically look like this: 

 
if( $a == $b ) {
    print "Equal!";
}
else {
    print "Not Equal!";
}
 

However, there is shorthand for this called a Ternary conditional. We can write the same if else statement like this: 

 
($a == $b) ? print "Equal!" : print "Not Equal!";
 

Where the general form is: 

 
(condition) ? if condition is true : if condition is false;
 

Loops

PHP has four main types of loops.

for

This loop is good for performing a set of instructions a set number of times. For example: 

 
for($i=0; $i<5; $i++) {
    print "i = " . $i . "\n";
}
 

The above will print the value of i 5 times and the values will be: 

   i = 0
   i = 1
   i = 2
   i = 3
   i = 4

foreach

This is probably the most common loop in all of PHP. It makes going through the elements of an array really easy. For example: 

 
$names = array("Jack", "Jill", "Mike", "Sally", "Steve");
 
foreach($names as $name) {
    print $name . "\n";
}
 
 

The output of this code will be 

   Jack 
   Jill
   Mike
   Sally
   Steve

Another really neat thing you could have done with this is the following: 

 
$names = array("Jack", "Jill", "Mike", "Sally", "Steve");
 
foreach($names as $key => $name) {
    print "Entry #: " . $key . " Name = " . $name . "\n";
}
 
 

The output will be: 

   Entry #: 0 Name = Jack 
   Entry #: 1 Name = Jill
   Entry #: 2 Name = Mike
   Entry #: 3 Name = Sally
   Entry #: 4 Name = Steve

Notice that in this example we define a $key. This key tells us what index of the array we are on. This is especially powerful when you use associative arrays like this: 

 
$names = array("Manager" => "Jack", "Sales" => "Jill", "Accounting" => "Mike", "HR" => "Sally", "CEO" => "Steve");
 
foreach($names as $key => $name) {
    print "Position: " . $key . " Name = " . $name . "\n";
}
 
 
   Position: Manager Name = Jack
   Position: Sales Name = Jill 
   Position: Accounting Name = Mike
   Position: HR Name = Sally
   Position: CEO Name = Steve

while

The while loop is probably the most simple of them all. In it's most basic form: 

 
while( true statement ) {
   ...
}
 

In this case, while "true statement" remains true, we will keep looping. For example: 

 
$i = 5;
while( $i < 10 ) {
   $i = $i + 1; // This could be shortened to $i++; But I'm being intentionally verbose.
}
 

The above code will continue to add 1 to $i until $i = 10, at which point the loop will stop. $i will retain it's value of 10.

do-while

This loop is very similar to the while loop. Example: 

 
$a = 0;
do {
    print "Hello: " . $a . "\n";
    $a = $a + 1;
} while( $a < 5);
 

The output of this will be: 

   Hello: 0
   Hello: 1
   Hello: 2
   Hello: 3
   Hello: 4


There is one major difference between the while and the do-while: The condition is evaluated AFTER the code is run. In a normal while loop, the condition is evaluated BEFORE the code in the { } is run. So for example

With a normal while loop: 

 
while( 1 == 0) {
    print "Hello!";
}
 
 

In this case "Hello" never gets printed because "1 == 0" gets evaluated BEFORE the code within the braces gets executed.

However, this changes in the following do-while example: 


 
 
do {
    print "Hello!";
} while( 1 == 0);
 
 

The word "Hello" will get executed exactly once because the condition "1 == 0" gets executed AFTER the code between the braces is executed.

Operators

Operators are used to compare variables, mathematics, and more. For example, you can set a variable equal to another variable using the '=' operator.

  • List of operators:
 + - Addition
 - - Subtraction
 * - Multiplication
 / - Division
 % - Modulus

 
$add = 1 + 1;
$subtract = 5 - 2;
$multiply = 6 * 5;
$divide = 14/7;
$modulus = 5 % 2;
 
echo "1 + 1 = $add";
echo "5 - 2 = $subtract";
echo "6 * 5 = $multiply";
echo "14 / 7 = $divide";
echo "5 % 2 = $modulus";
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Comparison operators are used to evaluate true or false when comparing variables and/or values
 
*List of comparison operators:
  == - Equal To
  != - Not Equal To
  < - Less than
  > - Greater than
  <= - Less Than or Equal To
  >= - Greater Than or Equal To
 
=User Input=
=User-Defined Functions=
 
Defining functions in [[PHP]] is accomplished using the function keyword, followed by the function name and comma delimited arguments, surrounded by parenthesis:
 
{{code
|text=
<source lang="php">
function myFunction(arg1, arg2) {
...
}
 

If the function is encapsulated in an object, you may specify the visibility of the function, public, protected or private. 

 
class MyClass
{
    public function myFunction(arg1, arg2) {
    ...
    }
...
}
 

Unlike some programming languages, like Perl or Python, PHP member functions implicitly extract their parent into the $this variable.

Security

code

Dangerous functions

  • include()
  • eval()
  • mysql_query()
  • pgsql_query()
  • phpinfo()
  • system()

Dangerous practices

  • include()
  • echo(), print(), sprintf()
  • string sanitizing using non-recursive string replacement
  • improper type handling

Best practices

The Golden Rule: Treat all user input as if it's malicious. Anything that gets transferred from the browser to the server (session variable especially) is a new vector for attacking your web app.

  • File inclusion
  • Type Handling
 
$clean_int = (int)$dangerous_int;
 
  • XSS
  • SQL Injection

Preventing SQL injection in PHP applications is relatively simple, so long as you are thorough. String input, surrounded by single quotes can be sanitized with mysql_real_escape_string(), which will escape dangerous characters such as single quotes (as well as \, so that you cannot escape the escapes!). Sanitizing integer input can be done simply by casting the input to integer.

php.ini

See Also : PHP Patching

PHP is part of a series on programming.
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