Php introduction with history of php

PHP
Most of this is from the PHP manual
online at: http://www.php.net/manual/

What we'll cover
• A short history of php
• Parsing
• Variables
• Arrays
• Operators
• Functions
• Control Structures
• External Data Files

Background
• PHP is server side scripting system
• PHP stands for "PHP: Hypertext Preprocessor"
• Syntax based on Perl, Java, and C
• Very good for creating dynamic content
• Powerful, but somewhat risky!
• If you want to focus on one system for dynamic
content, this is a good one to choose

History
• Started as a Perl hack in 1994 by Rasmus Lerdorf
(to handle his resume), developed to PHP/FI 2.0
• By 1997 up to PHP 3.0 with a new parser engine
by Zeev Suraski and Andi Gutmans
• Version 5.2.4 is current version, rewritten by Zend
(www.zend.com) to include a number of features,
such as an object model
• Current is version 5
• php is one of the premier examples of what an
open source project can be

About Zend
• A Commercial Enterprise
• Zend provides Zend engine for PHP for free
• They provide other products and services for a fee
• Server side caching and other optimizations
• Encoding in Zend's intermediate format to protect
source code
• IDE-a developer's package with tools to make life
easier
• Support and training services
• Zend's web site is a great resource

PHP 5 Architecture
• Zend engine as parser (Andi Gutmans and Zeev Suraski)
• SAPI is a web server abstraction layer
• PHP components now self contained (ODBC, Java,
LDAP, etc.)
• This structure is a good general design for software
(compare to OSI model, and middleware applications)
image from http://www.zend.com/zend/art/intro.php

PHP Scripts
• Typically file ends in .php--this is set by the web
server configuration
• Separated in files with the <?php ?> tag
• php commands can make up an entire file, or can
be contained in html--this is a choice….
• Program lines end in ";" or you get an error
• Server recognizes embedded script and executes
• Result is passed to browser, source isn't visible

<?php $myvar = "Hello World!";
echo $myvar;
?>

Parsing
• We've talk about how the browser can read a text
file and process it, that's a basic parsing method
• Parsing involves acting on relevant portions of a
file and ignoring others
• Browsers parse web pages as they load
• Web servers with server side technologies like php
parse web pages as they are being passed out to
the browser
• Parsing does represent work, so there is a cost

Two Ways
• You can embed sections of php inside html:
• Or you can call html from php:
<BODY>

<?php $myvar = "Hello World!";
echo $myvar;
</BODY>
<?php
echo "<html><head><title>Howdy</title>
…
?>

What do we know already?
• Much of what we learned about javascript
holds true in php (but not all!), and other
languages as well
$name = "bil";
echo "Howdy, my name is $name";
echo "What will $name be in this line?";
echo 'What will $name be in this line?';
echo 'What's wrong with this line?';
if ($name == "bil")
{
// Hey, what's this?
echo "got a match!";
}

Variables
• Typed by context (but one can force type), so it's
loose
• Begin with "$" (unlike javascript!)
• Assigned by value
• $foo = "Bob"; $bar = $foo;
• Assigned by reference, this links vars
• $bar = &$foo;
• Some are preassigned, server and env vars
• For example, there are PHP vars, eg. PHP_SELF,
HTTP_GET_VARS 00

phpinfo()
• The phpinfo() function shows the php
environment
• Use this to read system and server variables,
setting stored in php.ini, versions, and
modules
• Notice that many of these data are in arrays
• This is the first script you should write…
00_phpinfo.php00_phpinfo.php

Variable Variables
• Using the value of a variable as the name of
a second variable)
$a = "hello";
$$a = "world";
• Thus:
echo "$a ${$a}";
• Is the same as:
echo "$a $hello";
• But $$a echoes as "$hello"….
00_hello_world.php00_hello_world.php

Operators
• Arithmetic (+, -, *, /, %) and String (.)Arithmetic (+, -, *, /, %) and String (.)
• Assignment (=) and combined assignmentAssignment (=) and combined assignment
$a = 3;
$a += 5; // sets $a to 8;
$b = "Hello ";
$b .= "There!"; // sets $b to "Hello There!";
• Bitwise (&, |, ^, ~, <<, >>)Bitwise (&, |, ^, ~, <<, >>)
• $a ^ $b(Xor: Bits that are set in $a or $b but not
both are set.)
• ~ $a (Not: Bits that are set in $a are not set,
and vice versa.)
• Comparison (==, ===, !=, !==, <, >, <=, >=)Comparison (==, ===, !=, !==, <, >, <=, >=)

Coercion
• Just like javascript, php is loosely typed
• Coercion occurs the same way
• If you concatenate a number and string, the
number becomesa string
17_coercion.php17_coercion.php

Operators: The Movie
• Error Control (@)Error Control (@)
• When this precedes a command, errors generated are ignoredWhen this precedes a command, errors generated are ignored
(allows custom messages)(allows custom messages)
• Execution (` is similar to the shell_exec()Execution (` is similar to the shell_exec()
function)function)
• You can pass a string to the shell for execution:You can pass a string to the shell for execution:
$output = `ls -al`;$output = `ls -al`;
$output = shell_exec("ls -al");$output = shell_exec("ls -al");
• This is one reason to be careful about user set variables!This is one reason to be careful about user set variables!
• Incrementing/DecrementingIncrementing/Decrementing
++$a (Increments by one, then returns $a.)++$a (Increments by one, then returns $a.)
$a++ (Returns $a, then increments $a by one.)$a++ (Returns $a, then increments $a by one.)
--$a--$a (Decrements $a by one, then returns $a.)(Decrements $a by one, then returns $a.)
$a--$a-- (Returns $a, then decrements $a by one.)(Returns $a, then decrements $a by one.)

Son of the Valley of Operators
• Logical
$a and $b And True if both $a and $b are true.
$a or $b Or True if either $a or $b is true.
$a xor $b Xor True if either $a or $b is true,
but not both.
! $a Not True if $a is not true.
$a && $b And True if both $a and $b are true.
$a || $b Or True if either $a or $b is true.
• The two ands and ors have different
precedence rules, "and" and "or" are lower
precedence than "&&" and "||"
• Use parentheses to resolve precedence
problems or just to be clearer

Control Structures
• Wide Variety available
• if, else, elseif
• while, do-while
• for, foreach
• break, continue, switch
• require, include, require_once, include_once

Control Structures
• Mostly parallel to what we've covered
already in javascript
• if, elseif, else, while, for, foreach, break and
continue

Switch
• Switch, which we've seen, is very useful
• These two do the same
things….
example from http://us3.php.net/manual/en/control-structures.switch.php
if ($i == 0) {
echo "i equals 0";
} elseif ($i == 1) {
echo "i equals 1";
} elseif ($i == 2) {
echo "i equals 2";
}
switch ($i) {
case 0:
echo "i equals 0";
break;
case 1:
echo "i equals 1";
break;
case 2:
echo "i equals 2";
break;
}

Nesting Files
• require(), include(), include_once(), require_once() arerequire(), include(), include_once(), require_once() are
used to bring in an external fileused to bring in an external file
• This lets you use the same chunk of code in a numberThis lets you use the same chunk of code in a number
of pages, or read other kinds of files into your programof pages, or read other kinds of files into your program
• Be VERY careful of using these anywhere close to userBe VERY careful of using these anywhere close to user
input--if a hacker can specify the file to be included,input--if a hacker can specify the file to be included,
that file will execute within your script, with whateverthat file will execute within your script, with whatever
rights your script has (readfile is a good alternative ifrights your script has (readfile is a good alternative if
you just want the file, but don't need to execute it)you just want the file, but don't need to execute it)
• Yes, Virginia, remote files can be specifiedYes, Virginia, remote files can be specified

Example: A Dynamic Table
• I hate writing html tables
• You can build one in php
• This example uses pictures and builds a
table with pictures in one column, and
captions in another
• The captions are drawn from text files
• I'm using tables, but you could use css for
placement easily…

Arrays
• You can create an array with the array function, or use the
explode function (this is very useful when reading files into
web programs…)
$my_array = array(1, 2, 3, 4, 5);
$pizza = "piece1 piece2 piece3 piece4 piece5 piece6";
$pieces = explode(" ", $pizza);
• An array is simply a variable representing a keyed list
• A list of values or variables
• If a variable, that var can also be an array
• Each variable in the list has a key
• The key can be a number or a text label

• Arrays are lists, or lists of lists, or list of lists of
lists, you get the idea--Arrays can be multi-
dimensional
• Array elements can be addressed by either by
number or by name (strings)
• If you want to see the structure of an array, use the
print_r function to recursively print an array inside
of pre tags
Arrays

Text versus Keys
• Text keys work like number keys (well,
really, it's the other way around--number
keys are just labels)
• You assign and call them the same way,
except you have to assign the label to the
value or variables, eg:
echo "$my_text_array[third]";
$my_text_array = array(first=>1, second=>2, third=>3);
echo "<pre>";
print_r($my_text_array);
echo "</pre>";

Walking Arrays
• Use a loop, eg a foreach loop to walk
through an array
• while loops also work for arrays with
numeric keys--just set a variable for the
loop, and make sure to increment that
variable within the loop
$colors = array('red', 'blue', 'green', 'yellow');
foreach ($colors as $color) {
echo "Do you like $color?n";
}
05_arrays.php05_arrays.php

05_arrays.php
• You can't echo an
array directly…
• You can walk through
an echo or print() line
by line
• You can use print_r(),
this will show you the
structure of complex
arrays--that output is
to the right, and it's
handy for learning the
structure of an array
Array
(
[1] => Array
(
[sku] => A13412
[quantity] => 10
[item] => Whirly Widgets
[price] => .50
)
[2] => Array
(
[sku] => A43214
[quantity] => 142
[item] => Widget Nuts
[price] => .05
)

Multidimensional Arrays
• A one dimensional array is a list, a spreadsheet or other columnar data
is two dimensional…
• Basically, you can make an array of arrays
$multiD = array
(
"fruits" => array("myfavorite" => "orange", "yuck" =>
"banana", "yum" => "apple"),
"numbers" => array(1, 2, 3, 4, 5, 6),
"holes" => array("first", 5 => "second", "third")
);
• The structure can be built array by array, or declared with a single
statement
• You can reference individual elements by nesting:
echo "Yes, we have no " . $multiD["fruits"]["yuck"] . "
(ok by me).";
01a_arrays.php01a_arrays.php

Getting Data into arrays
• You can directly read data into individual
array slots via a direct assignment:
$pieces[5] = "poulet resistance";
• From a file:
• Use the file command to read a delimited file
(the delimiter can be any unique char):
$pizza = file(./our_pizzas.txt)
• Use explode to create an array from a line
within a loop:
$pieces = explode(" ", $pizza);

The Surface
• The power of php lies partially in the wealth of
functions---for example, the 40+ array functions
• array_flip() swaps keys for values
• array_count_values() returns an associative array of all
values in an array, and their frequency
• array_rand() pulls a random element
• array_unique() removes duppies
• array_walk() applies a user defined function to each
element of an array (so you can dice all of a dataset)
• count() returns the number of elements in an array
• array_search() returns the key for the first match in an
array
08_array_fu.php08_array_fu.php

Using External Data
• You can build dynamic pages with just the
information in a php script
• But where php shines is in building pages
out of external data sources, so that the web
pages change when the data does
• Most of the time, people think of a database
like MySQL as the backend, but you can
also use text or other files, LDAP, pretty
much anything….

Standard data files
• Normally you'd use a tab delimited file, but you can
use pretty much anything as a delimiter
• Files get read as arrays, one line per slot
• Remember each line ends in n, you should clean
this up, and be careful about white space
• Once the file is read, you can use explode to break
the lines into fields, one at a time, in a loop….

Standard data files
• You can use trim() to clean white space and
returns instead of str_replace()
• Notice that this is building an array of arrays
$items=file("./mydata.txt");$items=file("./mydata.txt");
foreach ($items as $line)foreach ($items as $line)
{{
$line = str_replace("n", "", $line);$line = str_replace("n", "", $line);
$line = explode("t", $line);$line = explode("t", $line);
// do something with $line array// do something with $line array
}}

Useful string functions
• str_replace()
• trim(), ltrim(), rtrim()
• implode(), explode()
• addslashes(), stripslashes()
• htmlentities(), html_entity_decode(),
htmlspecialchars()
• striptags()

06_more_arrays.php
• This is a simple script to read and process a text
file
• The data file is tab delimited and has the column
titles as the first line of the file

How it works
• The script uses the first line to build text labels for
the subsequent lines, so that the array elements
can be called by the text label
• If you add a new column, this script
compensates
• Text based arrays are not position dependent…
• This script could be the basis of a nice function
• There are two version of this, calling two different
datafiles, but that's the only difference

06a_more_arrays.php
• This version shows how to dynamically build a table in the
html output

Alternative syntax
• Applies to if, while, for, foreach, and switch
• Change the opening brace to a colon
• Change the closing brace to an endxxx
statement
sample code from http://us3.php.net/manual/en/control-structures.alternative-syntax.php
<?php if ($a == 5): ?>
A is equal to 5
<?php endif; ?>
<?php
if ($a == 5):
echo "a equals 5";
echo "...";
else:
echo "a is not 5";
endif;
?> 07

Sources
• http://www.zend.com/zend/art/intro.php
• http://www.php.net/
• http://hotwired.lycos.com/webmonkey/prog
ramming/php/index.html

Php introduction with history of php

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