Php Tutorials for Beginners

PHP Introduction to Server-Side Programming Charles Liu

Request to a Static Site You (client) Web server IP: 72.26.203.99 HTTP Request: GET www.xkcd.com HTTP Response: web content (HTML file) Client-side code: HTML, CSS, JavaScript Server: 1. Homepage lookup 2. Send as HTTP Response

Request to a Dynamic Site  The server must respond dynamically if it needs to provide different client-side code depending on the situation  Date and time  Specifics of the user’s request  Database contents – forms and authentication You (client) Web server HTTP Request: GET www.facebook.com HTTP Response: web content (HTML file) Client-side code: HTML, CSS, JavaScript (dynamically generated by server) Server: 1. Look up things that go on user’s profile, such as wall posts and friends  caches, database lookups 2. Generate client-side code containing these things 3. Send as HTTP response

PHP Introduction and Basic Syntax Charles Liu

What is PHP?  PHP = PHP: Hypertext Preprocessor  Server-side scripting language that may be embedded into HTML  Ultimate goal is to get PHP files to generate client- side code  must end up with HTML, CSS, JavaScript, other client- side code!

Side-by-side PHP File: <html> <head> <title> PHP Introduction </title> </head> <body> This is HTML! <br /> <?php echo 'This is PHP! <br />'; ?> </body> </html> Output: resulting HTML <html> <head> <title> PHP Introduction </title> </head> <body> This is HTML! <br /> This is PHP! <br /></body> </html>

A closer look  PHP tags: <?php and ?>  The echo command  Single line comment ( // )  Multiple line comment (/* and */) <html> <head> <title> PHP Introduction </title> </head> <body> This is HTML! <br /> <?php echo 'This is PHP! <br />'; // prints to screen /* Here's a longer comment that spans multiple lines. */ ?> </body> </html>

Viewing PHP files  PHP files executed on the web server  Therefore we cannot save them anywhere and view them, as with HTML files  Must save .php files in subdirectory of web server  /var/www/ on many Linux configurations  www directory of your user directory on Athena  Make call to web server via domain name (google.com), IP address (72.26.203.99), or localhost if on your own computer

PHP Syntax: Variables, Operators, and Strings Charles Liu

Variables  Store values for future reference, use variable name to refer to the value stored in it  PHP is a loosely-typed language  Do not need to declare the type of a variable  Type can change throughout the program $x = 42; // store the value 42 in $x echo $x; // prints 42 echo $x+1; // prints 43, value of $x is still 42 $x = ‘hello!’ // type of $x can change

Operators  Arithmetic operators  +, -, *, /, % (modulus – remainder after division)  Logical AND (&&), OR (||), NOT (!)  Assignment operators  Shorthand for assignment operators:  $x += $y equivalent to $x = $x + $y  Also works with subtraction, multiplication, division, modulus, and string concatenation

== versus ===  Two “equality” operators  == tests for “equality” in value but not necessarily type  === tests for “identity” in value AND type  == ignores the distinction between:  Integers, floating point numbers, and strings containing the same numerical value  Nonzero numbers and boolean TRUE  Zero and boolean FALSE  Empty string, the string ‘0’ and boolean FALSE  Any other non-empty string and boolean TRUE

Strings  A sequence of characters  Single and double quotes:  Suppose $str = 42;  echo ‘With single quotes, str is $str’;  output: With single quotes, str is $str  echo “With double quotes, str is $str”;  output: With double quotes, str is 42

Strings  Concatenation of strings – the . operator  String functions  Length: strlen()  Position of substring: strpos()  More on string functions: http://www.w3schools.com/php/php_ref_string.asp $a = ‘hello’; $b = ‘world’; echo $a . ‘ ‘ . $b . ‘!’; // prints ‘hello world!’

PHP Syntax: Conditional and Looping Statements Charles Liu

Conditional Statements if (condition / boolean expression) { statements } else if (another condition) { statements } // there may be more than one else if block else { statements } $x = 5; if ($x == 5) { echo ‘The variable x has value 5!’; }

The while loop while (condition) { statements } $x = 2; while ($x < 1000) { echo $x . “n”; // n is newline character $x = $x * $x; } Value of $x $x < 1000? Result 2 TRUE prints 2 4 TRUE prints 4 16 TRUE prints 16 256 TRUE prints 256 65536 FALSE exits loop

The do-while loop  The code within the loop is executed at least once, regardless of whether the condition is true do { statements } while (condition); equivalent to: statements while (condition) { statements }

The for loop for (init; condition; increment) { statements } equivalent to: init while (condition) { statements increment } Prints the first 10 positive integers and their squares: for ($i = 1; $i <= 10; $i++) { echo $i . “:” . ($i * $i) . “n”; }

PHP Syntax: Functions and Global Variables Charles Liu

Defining your own functions Example: a simple multiply function function function_name ($arg1, $arg2) { function code return $var // optional } function parameters function multiply($x, $y) { echo $x * $y; echo “n”; } multiply(5, 1.2);  prints 6 $a = 5; $b = 1.2; multiply($a, $b);  prints 6 $a = array(1,2,3); multiply($a, $b);  error $a = “string” multiply($a, $b);  prints 0 (?!)

Return values  A function can return a value after it is done  Use this value in future computation, use like a variable, assign value to a variable  A modified multiply function function multiply($x, $y) { return $x * $y; } multiply(2,3);  prints nothing! returns value, but we don’t store anywhere echo multiply(2,3);  prints 6 $a = multiply(2,3);  assigns the value 6 to the variable $a $b = multiply(multiply(2,3), multiply(3,4));  assigns the value 72 to the variable $b

Return values  A function can return at most once, and it can only return one value  If it does not return anything, assignments will result in NULL  A function ends after it returns, even if there is code following the return statement function do_stuff($x) { if ($x % 2 == 0) { // if even return $x/2 // exits function at this point } // this is ONLY executed if x is odd $x += 5; if ($x < 10) { $x += 3; } return x; }

Making function calls  Code inside of a function is not executed unless the function is called.  Code outside of functions is executed whenever the program is executed. <?php … // some code function1(); // makes function call to function1(), which // in turn calls function3() function function1() { … // some code function3(); // makes function call to function3() } function function2() { // this function is never called! … // some code } function function3() { … // some code } ?>

Variable scope  Variables declared within a function have local scope  Can only be accessed from within the function <?php function function1() { … // some code $local_var = 5; // this variable is LOCAL to // function1() echo $local_var + 3; // prints 8 } … // some code function1(); echo $local_var; // does nothing, since $local_var is // out of scope ?>

Global variable scope  Variables declared outside a function have global scope  Must use global keyword to gain access within functions <?php function function1() { echo $a; // does nothing, $a is out of scope global $a; // gain access to $a within function echo $a; // prints 4 } … // some code $a = 4; // $a is a global variable function1(); ?>

PHP Syntax: Arrays Charles Liu

Arrays as a list of elements  Use arrays to keep track of a list of elements using the same variable name, identifying each element by its index, starting with 0 $colors = array(‘red’, ‘blue’, ‘green’, ‘black’, ‘yellow’);  To add an element to the array: $colors[] = ‘purple’;  To remove an element from the array: unset($colors[2]); $colors = array_values($colors);

Arrays as key-value mappings  Use arrays to keep track of a set of unique keys and the values that they map to – called an associative array $favorite_colors = array(‘Joe’ => ‘blue’, ‘Elena’ => ‘green’, ‘Mark’ => ‘brown’, ‘Adrian’ => ‘black’, ‘Charles’ => ‘red’);  To add an element to the array: $favorite_colors[‘Bob’] = ‘purple’;  To remove an element from the array: unset($favorite_colors[‘Charles’]);  Keys must be unique: $favorite_colors[‘Joe’] = ‘purple’ overwrites ‘blue’

Recap: arrays  print_r($array_name) function lets you easily view the contents of an array  PHP arrays as a list  PHP arrays as a map $favorite_colors = array(‘Joe’ => ‘blue’, ‘Elena’ => ‘green’, ‘Mark’ => ‘brown’, ‘Adrian’ => ‘black’, ‘Charles’ => ‘red’); $colors[‘random person’] = ‘white’; unset($colors[‘Adrian’]); $colors = array(‘red’, ‘blue’, ‘green’, ‘black’, ‘yellow’); $colors[] = purple; // add to the list //remove ‘blue’ from list unset($colors[1]); $colors = array_values($colors);

PHP More about arrays and the for-each loop Charles Liu

All arrays are associative  Take our example of a list:  print_r($colors) gives: Array( [0] => red [1] => blue [2] => green [3] => black [4] => yellow )  Turns out all arrays in PHP are associative arrays  In the example above, keys were simply the index into the list  Each element in an array will have a unique key, whether you specify it or not. $colors = array(‘red’, ‘blue’, ‘green’, ‘black’, ‘yellow’);

Specifying the key/index  Thus, we can add to a list of elements with any arbitrary index  Using an index that already exists will overwrite the value $colors = array(‘red’, ‘blue’, ‘green’, ‘black’, ‘yellow’); $colors[5] = ‘gray’; // the next element is gray $colors[8] = ‘pink’;// not the next index, works anyways $colors[7] = ‘orange’ // out of order works as well

Array functions  isset($array_name[$key_value]) tells whether a mapping exists AND is non-null  unset($array_name[$key_value]) removes the key-value mapping associated with $key_value in the array  The unset() function does not “re-index” and will leave gaps in the indices of a list of elements since it simply removes the key-value pairing without touching any other elements  array_keys($array_name) and array_values($array_name) returns lists of the keys and values of the array

Adding elements without specifying the key  Recall that we did not specify the key when adding to a list of elements: $colors = array('red', 'blue', 'green', 'black', 'yellow'); $colors[] = 'purple';  PHP automatically takes the largest integer key that has ever been in the array, and adds 1 to get the new key $favorite_colors = array(“Joe” => “blue”, “Elena” => “green”, “Mark” => “brown”, “Adrian” => “black”, “Charles” => “red”); $favorite_colors[] = 'new color 1'; // key is 0 $favorite_colors[7] = 'another new color'; $favorite_colors[] = 'yet another color'; // key is 8 unset($favorite_colors[8]); $favorite_colors[] = 'color nine'; // key is 9, the old // maximum is 8 even though it no longer exists!

The for-each loop  The for-each loops allow for easy iteration over all elements of an array. foreach ($array_name as $value) { code here } foreach ($array_name as $key => $value) { code here } foreach ($colors as $color) { echo $color; // simply prints each color } foreach ($colors as $number => color) { echo “$number => $color”; // prints color with index // to change an element: // $colors[$number] = $new_color;

PHP HTTP Requests and Forms Charles Liu

Superglobals  A few special associative arrays that can be accessed from anywhere in a PHP file  Always $_ALLCAPS  The $_SERVER superglobal gives information about server and client  $_SERVER[‘SERVER_ADDR’]  server IP  $_SERVER[‘REMOTE_ADDR’]  client IP  $_SERVER[‘HTTP_USER_AGENT’]  client OS and browser

Passing information to the server  Sometimes, we require additional values be passed from client to server  Login: username and password  Form information to be stored on server  GET request: pass information via the URL  http://www.yourdomain.com/yourpage.php?firstparam =firstvalue&secondparam=secondvalue  Access values server-side using $_GET superglobal  $_GET[‘firstparam’] => ‘firstvalue’  $_GET[‘secondparam’] => ‘secondvalue’

When to use $_GET vs. $_POST  GET requests are sent via the URL, and can thus be cached, bookmarked, shared, etc  GET requests are limited by the length of the URL  POST requests are not exposed in the URL and should be used for sensitive data  There is no limit to the amount of information passed via POST

Dealing with forms  Forms are generally used to collect data, whether the data needs to be stored on the server (registration) or checked against the server (login)  2 components to a form:  The HTML generating the form itself  The server-side script that the form data is sent to (via GET or POST), taking care of the processing involved  Server should respond appropriately, redirecting the user to the appropriate destination or generating the appropriate page

Forms: client-side  form action – where to send the form data  method – how to send the data (GET or POST)  Name attributes become the keys used to access the corresponding fields in the $_GET or $_POST arrays <html> <head> <title> A Form Example </title> </head><body> <form action="welcome.php" method="post"> Name: <br /> <input type="text" name="name" /><br /> Phone Number: <br /> <input type="text" name="phone" /><br /> <input type="submit" value="Submit"> </form> </body> </html>

Forms: server-side  A simple PHP file that displays what was entered into the form  Can do many other things server-side depending on the situation  Note the use of $_POST <html> <head><title>This is welcome.php</title></head> <body> The name that was submitted was:   <?php echo $_POST['name']; ?><br /> The phone number that was submitted was:   <?php echo $_POST['phone']; ?><br /> </body> </html>

PHP Cookies and Sessions Charles Liu

Cookies and sessions  HTTP is stateless – it does not keep track of the client between requests  But sometimes we need to keep track of this information  Shopping cart  “Remember me” on login sites  2 solutions to this issue  Cookies – small file stored client-side  Sessions – relevant data stored on the server

Cookies  Cookies are stored on the user’s browser, and are sent to the server on every relevant request  The $_COOKIE superglobal makes a cookie a key- value pairing  Store user information as a value with a known key  Never assume a cookie has been set. Always check with isset($_COOKIE[$cookie_name]) before trying to use the cookie’s value

The setcookie() function  To set a cookie in PHP: setcookie(name, value, expire, path, domain);  Name and value correspond to $_COOKIE[$name] = $value  Expiration – cookie will no longer be read after the expiration  Useful to use time in seconds relative to the present:  time() + time in seconds until expiration  Path and domain refer to where on the site the cookie is valid  Usually ‘/’ for path and the top-level domain (yoursitename.com)  To delete a cookie, set a new cookie with same arguments but expiration in the past

Setting cookies  Cookies are set via the HTTP header  Must be sent before the body – before any HTML, CSS, JS, etc.  This code will not work: if(isset($_COOKIE["6470"])) { $value = $_COOKIE['6470']; echo "Cookie is set to $value"; } else { $value = 0; } // after echo statement: will not work! setcookie("6470", $value+1, time()+60*60);?>

Example of cookie usage  First visit: form with a text field for user’s name  Subsequent visits: Welcome message with the name  Store the name field in a cookie:  Key: “name”; value: the user’s name input into the form  Remember: when a cookie is set (the setcookie function call is made), the cookie can only be accessed on the next request

Contents of the HTTP request/response HTTP request: GET cookie.php HTTP reponse: HTML form HTTP request: GET name=“username” HTTP response: set cookie HTTP request: cookie “name” = “username” HTTP response: updated cookie CLIENT SERVER isset($_COOKIE[“name”])? NO isset($_GET[“name”])? NO respond with HTML form isset($_COOKIE[“name”])? NO isset($_GET[“name”])? YES set cookie on client welcome message based on user input isset($_COOKIE[“name”])? YES isset($_GET[“name”])? NO update cookie on client welcome message based on cookie NO COOKIES COOKIES SET

Case 1: cookies already set if(isset($_COOKIE["name"])) { $cookie_exp = time()+60*60; // one hour $name = $_COOKIE["name"]; setcookie("name", $name, $cookie_exp); if (isset($_COOKIE["visits"])) { $num_visits = $_COOKIE["visits"]+1; setcookie("visits", $num_visits, $cookie_exp); } echo "Welcome $name! "; if (isset($_COOKIE["visits"])) { echo "You've visited $num_visits times"; } }

Cases 2&3: first and second visits // case 2: upon submission of form else if (isset($_GET["name"])) { $name = $_GET["name"]; setcookie("name", $name, $cookie_exp); setcookie("visits", 2, $cookie_exp); echo "Welcome $name! This is your second visit."; } // case 3: first visit: need to show form else { <form action="<?php $_SERVER["PHP_SELF"] ?>" method="get"> Enter your name here: <input type="text" name="name" /> <br /><input type="submit" /> </form> }

Sessions  Two main disadvantages of cookies  Limited in size by browser  Stored client-side  can be tampered with  Sessions store user data on the server  Limited only by server space  Cannot be modified by users  A potential downside to sessions is that they expire when the browser is closed  Sessions are identified by a session id: often a small cookie! But the rest of the data is still stored on the server

Using sessions  Call session_start() at top of every page to start session  Sets a cookie on the client: must follow same rules as cookies (before any HTML, CSS, JS, echo or print statements)  Access data using the $_SESSION superglobal, just like $_COOKIE, $_GET, or $_POST <?php session_start(); if (isset($_SESSION["count"])) { $_SESSION["count"] += 1; echo "You've visited here {$_SESSION['count']} times"; } else { $_SESSION["count"] = 1; echo "You've visited once"; } ?>

Removing sessions  Remove an individual element of the $_SESSION superglobal  unset($_SESSION[‘key_name’]);  The session still exists and can be modified.  Destroy the entire session, remove all data  Use the function session_destroy()  $_SESSION no longer valid  Will need to call session_start() to start a new session

Recap: a comparison COOKIES SESSIONS Where is data stored? Locally on client Remotely on server Expiration? Variable – determined when cookie is set Session is destroyed when the browser is closed Size limit? Depends on browser Depends only on server (practically no size limit) Accessing information? $_COOKIE $_SESSION General use? Remember small things about the user, such as login name. Remember things after re-opening browser Remembering varying amount of data about the user in one browsing “session”

Databases and MySQL  Recall the basic reason for server-side programming  We need to store client data or look up data stored on the server  Databases give us an easy way to issue “commands” to insert, select, organize, and remove data  MySQL: open-source database, relatively easy to set up, easy to use with PHP  Other SQL databases, as well as non-SQL options such as MongoDB

Connecting to MySQL  MySQL database server can contain many databases, each of which can contain many tables  Connecting to the server via PHP:  $db is a database resource type. We use this variable to refer to the connection created $db = mysql_connect(server, username, password); if (!$db) { // terminate and give error message die(mysql_error()); } mysql_select_db(database_name, $db);

Making SQL queries  PHP function for making queries: mysql_query(query_string, db_resource);  Queries that return information, such as SELECT: returns a resource $result = mysql_query(query_string, $db);  In this case, this resource is stored in the variable $result  Other queries, returns TRUE upon success.  All queries return FALSE on failure. Best practice is to handle the error (e.g. die(mysql_error()))

SQL injection  Attacker guesses the format of a query, then exploits  If the attacker is able to form a valid SQL query using one of the input fields, then there may be unintended results  Look at this code which simply displays the phone number given a correct username and password

SQL injection: example $db = mysql_connect("localhost", "6470user", "6470") or die(mysql_error()); mysql_select_db("6470example", $db) or die(mysql_error()); if (isset($_POST["username"]) && isset($_POST["password"])) { $user = $_POST["username"]; $pass = $_POST["password"]; $query = "SELECT PHONE FROM userinfo WHERE USER='$user' and PASSWORD='$pass'"; echo $query . "<br />"; $result = mysql_query($query, $db); $row = mysql_fetch_assoc($result); if ($row) { echo "Phone number is: {$row['PHONE']}"; } else { echo "Invalid user or password"; } }

SQL injection: example  The issue here is that we are “trusting” user input.  What if the user inserts the string randompass’ OR ‘1=1 as the password?  Resulting query: SELECT PHONE FROM userinfo WHERE USER=‘username’ and PASSWORD=‘randompass’ OR ‘1=1’  ‘1=1’ always true. We can get the server to give the phone number regardless of username/password!  Fix: must pass ALL user input through the function mysql_real_escape_string()

Retrieving information from a query  Loop over the returned $result resource, row by row  mysql_fetch_assoc() function: turns a row of the result into key-value pairs, where keys are the names of the fields and their values are the corresponding values in the table $result = mysql_query(query, $db); while ($row = mysql_fetch_assoc($result)) { $col1 = $row['column_1_name']; $col2 = $row['column_2_name']; // and so forth... }

A registration-login example  Login page  Check username and password  If already logged in (use sessions!), welcome the user by name  Link to register page  Register page  Form for registration  If registration is successful, confirm the username  Link back to login page  Complete code can be downloaded from the video lectures website

A shared database resource  Both login and register pages use the same database connection  Put database connection, select database code into the same file  Reference the connection resource ($db) in other files <?php $db = mysql_connect("localhost", "6470user", "6470") or die(mysql_error()); mysql_query("CREATE DATABASE IF NOT EXISTS 6470example") or die(mysql_error()); mysql_select_db("6470example", $db) or die(mysql_error()); mysql_query("CREATE TABLE IF NOT EXISTS users (USERNAME VARCHAR(2000), PASSWORD VARCHAR(2000))") or die(mysql_error()); ?>

The login page – handle login request if (isset($_POST["username"]) && isset($_POST["password"])) { require("db.php"); // establish DB connection $user = $_POST["username"]; $pass = $_POST["password"]; $query = "SELECT PASSWORD from users WHERE USERNAME='" . mysql_real_escape_string($user) . "'"; $result = mysql_query($query, $db) or die(mysql_error()); $row = mysql_fetch_assoc($result); if ($pass == $row["PASSWORD"]) { $_SESSION["username"] = $user; } else { echo "Invalid username or password <br />"; } }

The register page if (isset($_POST["username"]) && isset($_POST["password"])) { require("db.php"); $user = mysql_real_escape_string($_POST["username"]); $pass = mysql_real_escape_string($_POST["password"]); $query = "INSERT INTO users VALUES ('$user', '$pass')"; mysql_query($query, $db) or die(mysql_error()); echo "Registration for $user was successful <br /><br />"; // HTML login <a href> tag } else { // HTML form }

MySQL recap  Connecting to database  $db= mysql_connect(location, username, password)  mysql_select_db(db_name, $db)  Making a query  $result = mysql_query(query_string, $db)  Getting results of query  while($row = mysql_fetch_assoc($result))  Sanitizing user input  $username = mysql_real_escape_string($_POST[“username”])

What we’ve talked about…  Purpose of server-side programming  Basic PHP syntax, arrays, functions  Specifics to websites: cookies, sessions, HTTP requests and forms, MySQL  Other server-side solutions:  ASP.NET  Python  PHP’s extensive documentation: http://www.php.net/manual/en

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