Synapseindia reviews sharing intro on php

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:
<BODY>

<?php $myvar = "Hello World!";
echo $myvar;
</BODY>
 Or you can call html from php:
<?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…
0000__pphhppiinnffoo..pphhpp

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"….

Operators
 AArriitthhmmeettiicc ((++,, --,, **,, //,, %%)) aanndd SSttrriinngg ((..))
 AAssssiiggnnmmeenntt ((==)) aanndd ccoommbbiinneedd aassssiiggnnmmeenntt
$a = 3;
$a += 5; // sets $a to 8;
$b = "Hello ";
$b .= "There!"; // sets $b to "Hello There!";
 BBiittwwiissee ((&&,, ||,, ^^,, ~~,, <<<<,, >>>>))
- $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.)
 CCoommppaarriissoonn ((====,, ======,, !==,, !====,, <<,, >>,, <<==,, >>==))

Coercion
 Just like javascript, php is loosely typed
 Coercion occurs the same way
 If you concatenate a number and string, the
number becomesa string
1177__ccooeerrcciioonn..pphhpp

Operators: The Movie
 EErrrroorr CCoonnttrrooll ((@@))
- WWhheenn tthhiiss pprreecceeddeess aa ccoommmmaanndd,, eerrrroorrss ggeenneerraatteedd aarree
iiggnnoorreedd ((aalllloowwss ccuussttoomm mmeessssaaggeess))
 EExxeeccuuttiioonn ((`` iiss ssiimmiillaarr ttoo tthhee sshheellll__eexxeecc(())
ffuunnccttiioonn))
- YYoouu ccaann ppaassss aa ssttrriinngg ttoo tthhee sshheellll ffoorr eexxeeccuuttiioonn::
$$oouuttppuutt == ``llss --aall``;;
$$oouuttppuutt == sshheellll__eexxeecc((""llss --aall""));;
- TThhiiss iiss oonnee rreeaassoonn ttoo bbee ccaarreeffuull aabboouutt uusseerr sseett vvaarriiaabblleess!
 IInnccrreemmeennttiinngg//DDeeccrreemmeennttiinngg
++++$$aa ((IInnccrreemmeennttss bbyy oonnee,, tthheenn rreettuurrnnss $$aa..))
$$aa++++ ((RReettuurrnnss $$aa,, tthheenn iinnccrreemmeennttss $$aa bbyy oonnee..))
----$$aa ((DDeeccrreemmeennttss $$aa bbyy oonnee,, tthheenn rreettuurrnnss $$aa..))
$$aa---- ((RReettuurrnnss $$aa,, tthheenn ddeeccrreemmeennttss $$aa bbyy oonnee..))

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….
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;
}
example from http://us3.php.net/manual/en/control-structures.switch.php

Nesting Files
 rreeqquuiirree(()),, iinncclluuddee(()),, iinncclluuddee__oonnccee(()),,
rreeqquuiirree__oonnccee(()) aarree uusseedd ttoo bbrriinngg iinn aann eexxtteerrnnaall
ffiillee
 TThhiiss lleettss yyoouu uussee tthhee ssaammee cchhuunnkk ooff ccooddee iinn aa
nnuummbbeerr ooff ppaaggeess,, oorr rreeaadd ootthheerr kkiinnddss ooff ffiilleess iinnttoo
yyoouurr pprrooggrraamm
 BBee VVEERRYY ccaarreeffuull ooff uussiinngg tthheessee aannyywwhheerree cclloossee
ttoo uusseerr iinnppuutt----iiff aa hhaacckkeerr ccaann ssppeecciiffyy tthhee ffiillee ttoo bbee
iinncclluuddeedd,, tthhaatt ffiillee wwiillll eexxeeccuuttee wwiitthhiinn yyoouurr ssccrriipptt,,
wwiitthh wwhhaatteevveerr rriigghhttss yyoouurr ssccrriipptt hhaass ((rreeaaddffiillee iiss aa
ggoooodd aalltteerrnnaattiivvee iiff yyoouu jjuusstt wwaanntt tthhee ffiillee,, bbuutt ddoonn''tt
nneeeedd ttoo eexxeeccuuttee iitt))

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
 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

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.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).";
 print_r() will show the entire structure, but don’t forget the pre
tags

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

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
$iitteemmss==ffiillee((""..//mmyyddaattaa..ttxxtt""));;
ffoorreeaacchh (($$iitteemmss aass $$lliinnee))
{{
$$lliinnee == ssttrr__rreeppllaaccee((""nn"",, """",, $$lliinnee));;
$$lliinnee == eexxppllooddee((""tt"",, $$lliinnee));;
//// ddoo ssoommeetthhiinngg wwiitthh $$lliinnee aarrrraayy
}}

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
<?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
sample code from http://us3.php.net/manual/en/control-structures.alternative-syntax.php

Synapseindia reviews sharing intro on php

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