PHP I

How does a Web Server Work

  • Up until now we have been using a webserver to perform two simple tasks
    • Convert the URL to the local file and retrieve it
    • Control access to the website
  • Both of these require no processing of the pages themselves
    • Commonly known as serving static pages
  • You don't even need a webserver to do this
    • HTML can be viewed just fine in a browser

Diagram depicting a request to a webserver, the webserver getting the file with no processing, and returning the file to the client Image from https://developer.mozilla.org/en-US/docs/Learn/Server-side/First_steps/Introduction

Dynamic Webserver

  • Web servers are capable of much more, including
    • Executing code prior to returing a request
    • Compressing files before sending them
    • Running SSL for HTTPs and everything that goes with it
    • Logging

Diagram showing how a dynamic webserver works. After recieving the request, the data is passed of to a web application, with may interact with files, a database, etc, and which will return to the webserver HTML to be sent back to the client Image from https://developer.mozilla.org/en-US/docs/Learn/Server-side/First_steps/Introduction

CGI vs Embedded

  • Prior to PHP, most web applications used an API known as the Common Gateway Interface (CGI)
    • Perls support of CGI was one of the big reasons for its popularity
    • CGI scripts are forked from the webserver
      • Can be safer (runs in a separate process)
      • Can be much more dangerous (is running as any script file would)
  • PHP, and many other languages that have come after it, run inside the webserver, in what is known as embedded mode
    • Is generally safer for beginning programmers, as the webserver offers many protections
    • Has access to the server API

PHP History

  • Invented in 1994 by Rasmus Lerdorf
  • Stands for PHP HyperText Processor
    • Orginally stood for Personal Home Page
  • Primarily used on server-side -Can be used in both command-line and GUI scripting as well

PHP Versions

  • PHP 4 reached end of life in 2008, any website using it is very insecure!!
  • PHP 5 came out in 2004, PHP 5.6 came out in 2014
    • GL has PHP 5.4 in the SWE environment
  • PHP 6 never came out, delayed over and over and over
  • PHP 7 released in 2015, 7.2 comes out the end of this month
    • Supported in most webhost now

Major Users of PHP

  • Facebook
  • Wikipedia (and all sites running MediaWiki)
  • Wordpress and Drupal
  • Baidu
  • Many, many more
    • up to 80% of all sites by some estimates

Embedding PHP in HTML

  • PHP is often found interspersed within an HTML document
    • PHP can be written without any HTML
  • The webserver pre-processes all files ending with *.php
    • Any code between the PHP tags is run, and output is placed directly into the HTML page
    • The page is sent to the client with no PHP in it, only the results of executing the PHP

PHP Tags

  • To indicate a section of PHP code, a PHP tag is needed
  • There are many different styles but you should only use <?php
    • This is the only one garunteed to always work!!
  • Others you may see
    • <?
    • <%

Running at https://www.csee.umbc.edu/~bwilk1/433/php_examples/simple.php

<!DOCTYPE html>
<?php $color = "#057f14" ?>
<html>
    <head>
    <style>
        #example1{background-color: 
             <?php echo $color; ?>}
    </style>
    </head>
    <body>
        <p id="example1">My background is 
        <?php echo $color; ?></p>
    </body>
</html>

Comments in PHP

Comments in PHP can either be

  • C/C++ Style
    • // for single line
    • /* */ for multiline
  • Scripting Language Style
    • # for single line
In [1]:
//This is a comment, nothing will happen
/*
 This is also a comment
 echo "HELLO"
 won't print
*/ 
 # This is a comment too
echo "HI"
Out[1]:
HI

Variables

  • All variables in PHP must start with $ (dollar sign)
    • Dollar signs can be stacked to use the value of one variable as the name of another (variable variables)
  • The first character after the dollar sign cannot be a number
  • The variables scope is
    • global if not declared in a function
    • the function if declared in one
In [2]:
$a = "var";
$$a = "value";
$$$a = "whaaat";
echo $a;
echo $$a , $var;
echo $$$a, $$var, $value;
Out[2]:
var
Out[2]:
value
Out[2]:
value
Out[2]:
whaaat
Out[2]:
whaaat
Out[2]:
whaaat

Data Types

  • PHP has 8 data types
  • Primitives/Scalars
    • boolean
    • integer
    • float
    • string
  • Other types
    • Arrays
    • Objects
    • Resources (files, etc.)
    • NULL
In [3]:
2001
Out[3]:
2001
In [4]:
-309
Out[4]:
-309
In [5]:
+33
Out[5]:
33
In [6]:
0755
Out[6]:
493
In [7]:
+010
Out[7]:
8
In [8]:
0xFF
Out[8]:
255
In [9]:
0xcc
Out[9]:
204
In [10]:
3.14
Out[10]:
3.14
In [11]:
0.016
Out[11]:
0.016
In [12]:
0.314E1
Out[12]:
3.14
In [13]:
16.0e-3
Out[13]:
0.016
In [14]:
'This is a string'
Out[14]:
"This is a string"
In [15]:
"This is also a string"
Out[15]:
"This is also a string"
In [16]:
false
Out[16]:
false
In [17]:
true
Out[17]:
true
In [18]:
0?'T':'F'
Out[18]:
"F"
In [19]:
0.0?'T':'F'
Out[19]:
"F"
In [20]:
516?'T':'F'
Out[20]:
"T"
In [21]:
"0"?'T':'F'
Out[21]:
"F"
In [25]:
"0.0"?'T':'F';
Out[25]:
"T"
In [23]:
""?'T':'F'
Out[23]:
"F"
In [26]:
(array())?'T':'F'
Out[26]:
"F"
In [27]:
NULL?'T':'F'
Out[27]:
"F"

Casting

  • PHP is weakly typed and will coerce data types when possible
  • To force casting to another datatype, use 
    (datatype) $var;
In [28]:
"5" * 2
Out[28]:
10
In [29]:
'3.14' + 5
Out[29]:
8.14
In [30]:
(int) "5"
Out[30]:
5
In [33]:
(int) "4+16"
Out[33]:
4
In [34]:
(int) "3.14"
Out[34]:
3
In [35]:
(int) "19.99"
Out[35]:
19
In [36]:
(float)"3.14"
Out[36]:
3.14
In [37]:
(float) "3.14 is pi"
Out[37]:
3.14
In [38]:
(string) 1
Out[38]:
"1"
In [39]:
(string) true
Out[39]:
"1"
In [40]:
(string) false
Out[40]:
""
In [41]:
(bool) 0
Out[41]:
false
In [42]:
(bool)3.14
Out[42]:
true
In [43]:
(bool)1
Out[43]:
true
In [44]:
(bool)""
Out[44]:
false
In [45]:
(bool)"NO"
Out[45]:
true

Constants

  • Constants are created by calling the define function, passing in a constant name and value
    • Constant names don't start with $
      define("NAME",value);
  • There are numerous predefined constants that are useful for introspection
    • __LINE__ gives the current line of the file
    • __FILE__ gives the file currently being executed
    • __FUNCTION__ provides the function name
    • __CLASS__ provides the class name
In [46]:
define("PI",3.14);
define("TU", "TUESDAY");
echo "Sometimes " . PI . " day is on a " . TU;
echo "I am running from " . __LINE__;
Out[46]:
Sometimes 3.14 day is on a TUESDAY
Out[46]:
I am running from 4

Selection Structures

  • PHP has 3 selection structures
    • If/Then/Else
    • Switch
    • Ternary Operator
  • These behave mostly like other langugaes, but can be mixed with HTML to produce efficent custom HTML pages
In [47]:
$today = "Tuesday";
if($today == "Monday"){
    echo "Happy Monday!";
}
else if($today == "Tuesday"){
    echo "One Day Down!";
}
else{
    echo "Start Counting Down Towards the Weekend!";
}
Out[47]:
One Day Down!
In [50]:
$today = "Tuesday";
if($today == "Monday"){
    echo "Happy Monday!";
}
elseif($today == "Tuesday"){
    echo "One Day Down!";
}
else{
    echo "Start Counting Down Towards the Weekend!";
}
Out[50]:
One Day Down!
In [51]:
$today = "Tuesday";
$mon = "Monday";

switch($today){
    case $mon:
        echo "Happy Monday!";
        break;
    case "Tuesday":
        echo "One Day Down!";
        break;
    default:
        echo "Start Counting Down Towards the Weekend!"; 
}
Out[51]:
One Day Down!

Running at https://www.csee.umbc.edu/~bwilk1/433/php_examples/if.php

<?php
if(date('s') % 2 == 0){
?>
<p>You opened this page during an <strong>even</strong> second.
<?php
}
else{ ?>
<p>You opened this page during an <strong>odd</strong> second.
<?php } ?>

Selection Structures and HTML Practice

  • Write a simple PHP page that intermixes PHP and HTML
    • Get a random number using the PHP function rand()
    • If the number is even, display a blue h1 tag with the words "It's Even!"
    • If the number is odd, display a green h2 tag with the words "It's Odd!"

Quoting

  • In PHP, strings can be declared using
    • single quotes
    • double quotes
    • HERE docs
  • Variables are interpolated in both double quoted string and here docs
    • They are not interpolated in a single quoted string
    • Can use ${} notation like in bash
In [52]:
$lyric = "Teapot";
echo 'I\'m a little $lyric';
Out[52]:
I'm a little $lyric
In [53]:
$lyric = "Teapot";
echo "I'm a little $lyric";
Out[53]:
I'm a little Teapot

HERE Docs

  • HERE Docs are used to make multi-line strings more conviently
  • A HERE doc starts with three less-than symbols (<<<) followed by an identifier
  • It ends when the indentifier is repeated, and is the only thing on the line besides as semicolon
In [54]:
$var = "this";
$a_long_string = <<<HERE
This string is like a quoted
string, it will interpolate all
variables in it, like $var.
It only ends when HERE is on a
line of it's own
HERE;
echo $a_long_string;
Out[54]:
This string is like a quoted
string, it will interpolate all
variables in it, like this.
It only ends when HERE is on a
line of it's own

String Operators

  • The concatenation operator in PHP is the dot (.)
    • This can be combined with the assignment operator (.=)
  • Strings can be compared using the standard operators
    • == Compares equality and coerces if needed
    • === Compares equality, but never coerces
    • <,<=,>,>= compare for lexicographic order, coerce if necessary
In [55]:
$alphabet = "a" . 'b' . 'c' . 'd';
echo $alphabet;
$alphabet .= 'e';
echo $alphabet;
Out[55]:
abcd
Out[55]:
abcde
In [56]:
"3" == 3;
Out[56]:
true
In [57]:
"3" === 3;
Out[57]:
false
In [65]:
"3" <= 4;
Out[65]:
true

String Practice

  • Using concatenation, conversion, and interpolation, use the following variables to print the string "Today is the 20th day of class"
In [69]:
$num1 = "15";
$num2 = 5;
$rest = "day of class";
$num = $num1 + $num2;
echo "Today is the ${num}th ".  $rest;
Out[69]:
Today is the 20th day of class

String Functions

  • PHP provides many robust, built-in, string functions
  • Some common ones are:
    • explode - Similar to string_split in other languages
    • htmlentities - Encodes anything that needs to be encoded for HTML (e.g. <, >, etc.)
    • html_entity_decode - Converts HTML encoded characters back into their regular string values
    • join - Joins an array together (can also use implode)
    • parse_str - Turns a query string into an array
    • strip_tags - Removes all HTML and PHP tags from a string
    • trim - Removes whitespace from both ends of the string
  • A full list can be found at http://php.net/manual/en/ref.strings.php
In [70]:
echo print_r(explode(',', "John,Paul,George,Ringo"),true);
Out[70]:
Array
(
    [0] => John
    [1] => Paul
    [2] => George
    [3] => Ringo
)
In [71]:
$html = "This is an example of an HTML tag 3 < 4 <html>. It must be closed like this: </html>";
echo htmlentities($html);
Out[71]:
This is an example of an HTML tag 3 &lt; 4 &lt;html&gt;. It must be closed like this: &lt;/html&gt;
In [72]:
$html = "Some characters, like the amperstand, need to be escaped in HTML, like &amp;";
echo html_entity_decode($html);
Out[72]:
Some characters, like the amperstand, need to be escaped in HTML, like &
In [73]:
parse_str("key1=value1&key2=value2",$result);
echo print_r($result,true);
Out[73]:
Array
(
    [key1] => value1
    [key2] => value2
)
In [74]:
$wiki = <<<WIKI
<div class="thumbinner" style="width:302px;"><a href="/wiki/File:Manchester_Mark2.jpg" class="image"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/d/d8/Manchester_Mark2.jpg/300px-Manchester_Mark2.jpg" width="300" height="238" class="thumbimage" srcset="//upload.wikimedia.org/wikipedia/en/d/d8/Manchester_Mark2.jpg 1.5x" data-file-width="355" data-file-height="282" /></a>
<div class="thumbcaption">
<div class="magnify"><a href="/wiki/File:Manchester_Mark2.jpg" class="internal" title="Enlarge"></a></div>
The Manchester Mark 1 was one of the world's first stored-program computers.</div>
</div>
</div>
<p>The <b>Manchester Mark 1</b> was one of the earliest <a href="/wiki/Stored-program_computer" title="Stored-program computer">stored-program computers</a>, developed at the <a href="/wiki/Victoria_University_of_Manchester" title="Victoria University of Manchester">Victoria University of Manchester</a> from the <a href="/wiki/Manchester_Small-Scale_Experimental_Machine" title="Manchester Small-Scale Experimental Machine">Small-Scale Experimental Machine</a> (SSEM) or "Baby" (operational in June 1948). It was also called the <b>Manchester Automatic Digital Machine</b>, or <b>MADM</b>.<sup id="cite_ref-FOOTNOTELavington199820_1-0" class="reference"><a href="#cite_note-FOOTNOTELavington199820-1">[1]</a></sup> Work began in August 1948, and the first version was operational by April 1949; a program written to search for <a href="/wiki/Mersenne_primes" class="mw-redirect" title="Mersenne primes">Mersenne primes</a> ran error-free for nine hours on the night of 16/17 June 1949.</p>
<p>The machine's successful operation was widely reported in the British press, which used the phrase "electronic brain" in describing it to their readers. That description provoked a reaction from the head of the University of Manchester's Department of Neurosurgery, the start of a long-running debate as to whether an electronic computer could ever be truly creative.</p>
WIKI;
echo strip_tags($wiki);
Out[74]:


The Manchester Mark 1 was one of the world's first stored-program computers.


The Manchester Mark 1 was one of the earliest stored-program computers, developed at the Victoria University of Manchester from the Small-Scale Experimental Machine (SSEM) or "Baby" (operational in June 1948). It was also called the Manchester Automatic Digital Machine, or MADM.[1] Work began in August 1948, and the first version was operational by April 1949; a program written to search for Mersenne primes ran error-free for nine hours on the night of 16/17 June 1949.
The machine's successful operation was widely reported in the British press, which used the phrase "electronic brain" in describing it to their readers. That description provoked a reaction from the head of the University of Manchester's Department of Neurosurgery, the start of a long-running debate as to whether an electronic computer could ever be truly creative.
In [75]:
$evil_user = "I am going to try an run some code <?php echo 'Hi There';?>";
echo strip_tags($evil_user);
Out[75]:
I am going to try an run some code
In [76]:
$str_with_spaces = "             There are so many spaces on either side of me                 ";
echo trim($str_with_spaces);
Out[76]:
There are so many spaces on either side of me

PHP On GL

  • The PHP mod is already part of the Apache server running on GL,so no set up is needed
  • Pages must end with .php and be word-readable
    • chmod a+r
  • Can only use the <?php version of the tag

Getting Help with PHP

  • The PHP documentation is very well done and has information on every built-in PHP function
  • The comments below are usually quite helpful