Introduction to PHP

Introduction to PHP

What is this “PHP” thing? • Official description: “PHP, which stands for "PHP: Hypertext Preprocessor" is a widely-used Open Source general-purpose scripting language that is especially suited for Web development and can be embedded into HTML. Its syntax draws upon C, Java, and Perl, and is easy to learn.

What does PHP do? • Most commonly: used inside a web server to parse pages and dynamically generate content. • Differs from a language like Javascript in that it is Server Side (processed on the server)

Normal HTML Document • Requires only a web browser to read • Can be read off local disk, or transferred from server via HTTP

PHP Document • In order to be correctly read and processed, must be parsed through a server capable of parsing PHP code. • Server processes code: formats a standard HTML document out of the PHP code, then transfers via HTTP to client browser. No client software required (other than web browser).

Simple Transfer of Normal HTML Server Client Web Server Application (Apache) Client’s Browser (MSIE, Netscape, Etc) .HTML File HTML HTML

Simple Transfer of PHP Server Client PHP Parsing Module Web Server Application (Apache) Client’s Browser (MSIE, Netscape, Etc) .PHP File PHP & HTML HTML HTML

What does a PHP file look like? <html> <p>Hello <?php echo “world!”; ?> </p> </html>

More… • A PHP file is just a HTML file with PHP code inserted where needed! • To designate PHP code, we use the <?php and ?> tags to indicate the start and end of code to be parsed.

Parsing… <html> <p>Hello <?php echo “world!”; ?> </p> </html> <html> <p>Hello world </p> </html>

Our First Command! Echo! • echo <string>; • Example: echo “Hello!”;Result: Hello! • Example: echo “I love PHP!”;Result: I love PHP!

What is this String? • echo <string>; • But what is a string? • A string is any sequence of characters. This also includes a sequence of no characters.

These are Strings • “Hi” • “I love PHP!” • “5” • “” • Note that saying “5” is NOT the same as saying just 5.

Processing • Just like HTML is processed sequentially (in order), so is PHP code. • <?php echo “Hello “; echo “world!”;?> • Results in Hello world!.

General Syntax • After typing a command, you should always put a semicolon (;) after it. • It is good practice to indent your code one tab after the <?php tag • Another good practice is to put each command on its own line. • Ex: • <?php echo “Hello “; echo “world!”;?>

More Fun With Echo • echo <string>; • We can put in numeric values in too! • echo “5”; and echo 5; both display 5. • This is because PHP can convert a number to a string automatically!

Data Types • Data is categorized by Data Types • PHP is not a strongly typed language, doesn’t require you to define types • string – text data – “Hello world”, “My password is 12345”, “12345” • double – number data – -5, 0, 11, 11.5, 13 • int – number data, but won’t remember decimals - -5, 0, 11, 13 • boolean – true or false? – true, false • Categorize these: • -5.51, “-5.51”, true, 5 • double, string, bool, int OR double!

Simple Math • We can do math! • <?php echo “If I add one to one, it is “; echo (1+1);?> • Displays If I add one to one it is 2

Example • <?php echo “I love PHP! “; echo “<BR>”; echo “PHP can do math: “; echo (8*10);?> • Displays:I love PHP!PHP can do math: 80

String Concatenation • We can add numbers: 2+2 • How do we add strings? • We use the . Operator (concatenation) • Echo “5 plus 5 is “ . (5+5); • Displays 5 plus 5 is 10

Example • <?php echo “I love PHP! “ . “<BR>” . “PHP can do math: “ . (8*10);?> • Displays:I love PHP!PHP can do math: 80

Comments • You can add human-readable text to your programs: • // will tell PHP to ignore the rest of the line • <?php // I love PHP! :) echo (8*10); // I can’t add :(?> • Displays: 80

Comments • Multiple lines are possible, just start a comment with /* and end with */ • <?php /* I love PHP! :) PHP Programming is fun! */ echo (8*10); /* I can’t add */?> • Displays: 80

Variables! • Variables let you save a value to use/modify later on. • In PHP to make a variable, assign it a value. Precede variable names with a $ sign to indicate that it’s a variable. • $foo = 5+5; // $foo is 10 • $bar = 5+$foo; // $bar is 15

Valid Variable Names • Variable names start with a letter or underscore • Then followed by any number of letters, numbers, or underscores • Names are case-sensitive ($a is not $A) • $asdf = valid • $_5asdf = valid • $5asdf = NOT valid • $asdf != $aSdF

Reserved Names • Some variable names are reserved by PHP • $GLOBALS • $_SERVER • $_GET • $_POST • $_COOKIE • $_FILES • $_ENV • $_REQUEST • $_SESSION

Using Variables • As shown, we can do assignment and such: • $foo = 5; $bar = $foo + 1; • Other ways of doing assignment: • $foo++; // Increases foo by one • $foo+=2; // Increases foo by two • $foo*=2; // Multiples foo by two • $foo /=2; // Divides foo by two • $foo -=2; // Subtracts foo by two

More uses • We can use variables in functions:$foo = 5;echo “Foo is $foo”; • Same thing as:$foo = 5;echo “Foo is “ . $foo; • Echo automatically converts $foo to its value when using double quotes (“), when using single quotes, do string concatenation • $foo = 5;echo ‘Foo is ‘ . $foo;

What does this program do? • $foo = 5;$foo++;echo “Foo is $foo”; • Displays: Foo is 6

What does this program do? • $_BAR = 1;$_bar = 2;echo “Bar is $_BAR”; • Displays: Bar is 1

A little about ++ • The ++ operator is neat in that not only does it increase the variable, it can be used inside of commands! • ++ before a variable: increases variable, and function is given NEW value • ++ after a variable: increases a variable, and function is given OLD value • $foo = 2; $bar = 2;echo “Foo is: “ . $foo++;echo “ - Bar is: “ . ++$bar;// Now Foo and Bar are both 3 in memory • Outputs Foo is: 2 – Bar is: 3

What does this program do? • $1var = 1;$2var = $1var++;echo “2var is $2var”; • Displays: PARSE ERROR! (Haha!) • $a = 1;$b = $a++;echo “b is $b”; • Displays: b is 1

Conditionals • if (conditional) { result }; • Evaluates conditional, and if TRUE, then does result commands. • We use conditional operators, such as: • == for equals • != for not equals • > for greater • < for less than • >= for greater than or equal • <= for less than or equal

Example • $bar = 2; if ($bar == 2) { echo “Bar is 2, yay! ”; echo “w00t!”; } Displays: Bar is 2, yay! w00t!

Another Example • $foo = 3;$bar = 300;if ($foo > $bar){ echo “foo is big!”;} • Displays nothing.

Only one command? • $foo = 3;$bar = 300;if ($foo > $bar) echo “foo is big!”; • You may omit the { and } if you only have one command. Don’t forget to use them when you have two commands or more!

Another Example • $foo = 2;if ($foo != 2) echo “Foo is not two ”; echo “Foo is still not two”; • Displays Foo is still not two • Be careful not to forget brackets. Tabbing your code will help you find these logic errors!

Else • You can also specify what to do if the If conditional is FALSE • if (condition) { result } else { result } • $foo = 5;if ($foo != 5){ echo “Foo isn’t five!”;} else { echo “Foo IS five!”;} • Displays: Foo IS five!

Another If/Then/Else example • $a = 0;if ($a == 1) $a++;else $a--;echo $a; • Displays -1

Arrays • In PHP, Arrays are actually quite easy to use, and very powerful (you’ll see why in a minute!) • We map keys to values. array( [key =>] value, ... ) • key may be an integer or string • value may be any value

Array Example • $arr = array("foo" => "bar", 12 => true);echo $arr["foo"]; // barecho $arr[12]; // true • So we see that arrays are just like variables, except that they also contain a collection of variables themselves. (Arrays can even have arrays in them!)

More Array Examples • $arr = array(5 => 1);$arr[5]++;echo $arr[5]; // 2$arr[5] = 10;echo $arr[5]; // 10$arr[“foo”] = 5; // New entry!echo $arr[“foo”]; // 5

Deleting from Array • Use unset() to delete from array • $arr =array(0=>“foo”, 1=>“bar”);echo $arr[0]; // fooecho $arr[1]; // barunset($arr[0]); // deletes 0=>”foo”unset($arr); // deletes entire array

Auto-numbering • If you don’t specify a key, PHP assumes the largest key used + 1 (or zero if the largest + 1 is negative) Example: array(5 => 43, 6 => 32, 7 => 56, "b" => 12); array(5 => 43, 32, 56, "b" => 12); • These are identical!

More Auto-Numbering $array = array(0, 1, 2, 3, 4); $array[] = 5; Now [0] => 0, [1] => 1, etc (including 5) • Tip: Use print_r($array); command to display an array in human-readable form. • Note: Even if you were to delete 0-5, the next key automatically assigned would still be 6. To fix this, use array_values($array)

Forms (User Input) • Often times we want to get user input from HTML forms. Here’s an example of a simple form: • <form name=“testform” method=“get” action=“test.php”>What is your name:<input type=“text” name=“username”><input type=“submit” value=“Go!”></form> • Should result in a form with a textbox to enter your name and a “Go!” button.

Post & Get Refresher • Remember: POST method puts data into the browser’s request • Transparent to user • GET method puts form data into browser string • Urls look like this: • Pagename.php?key1=value1&key2=value2 • For our form, we use GET, so if a user enters “Palazzo” at the prompt: • Test.php?username=Palazzo

Web ServersIntroduction to Apache

What does a web server do? • A web server serves files to clients (such as the browser) • Files may be HTML, GIFs, video, PDF • Serves multiple clients at the same time • Transfer protocol: HTTP

Apache model • Provides multiple processes to handle simultaneous requests • Throttles the number of child processes • Crashing a child process doesn’t crash the server; the parent is very stable • Memory leaks don’t take down the machine; memory freed when child exits

Introduction to PHP