LIS651 lecture 1 PHP basics

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LIS651 lecture 3taming PHP with custom
functions, sessions and includes
Thomas Krichel 2009-04-05
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functions

• The PHP function reference is available on its
  web site http//php.net/quickref.php. It shows
  the impressive array of functions within PHP.
• But one of the strengths of PHP is that you can
  create your own functions as you please.
• If you recreate one of the built-in functions,
  your own function will have no effect.

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simplest function
function beer_print print
"beer\n" beer_print() // prints beer and
newline
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A more practical example

• Stephanie Rubino was an English teacher and
  objects to sentences like
• You have ordered 1 bottles of Grosswald Pils.
• Let us define a function rubino_print(). It will
  take three arguments
• a number to check for plural or singular
• a word for the singular
• a word for the plural

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a function and its arguments

• declare the arguments to the function in
  parenthesis
• function rubino_print (number,
  singular,plural)
• if(number 1)
• print "one singular"
• else
• print "number plural"
• rubino_print(3,'woman','women') // prints 3
  women

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default arguments

• Sometimes you want to allow a function to be
  called without giving all its arguments. You can
  do this by declaring a default value, using an
  equal sign in the function list
• function thomas_need(thing'beer')
• print "Thomas needs thing.\n"
• thomas_need() // prints Thomas needs beer.
• thomas_need('vodka') // prints Thomas needs
  vodka.

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rubino_print using common plurals
function rubino_print (num, sing,plur1)
if(num 1) print "one sing"
elseif(plur 1) print "num
sing"."s" else print "num
plur" rubino_print(6,'beer') //
prints 6 beers
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return value

• Up until now we have just looked at the side
  effect of a function.
• "return" is a special command that returns a
  value.
• It takes the return value as a parameter
• return result
• When return is used, the function is left.
  Example
• function good_beer ()
• return 'Festbock'
• beergood_beer()
• print beer // prints Festbock.

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rubino_print with return
function rubino_print (number,
singular,plural) if(number 1)
return "one singular" return "number
plural" orderrubino_print(2,"beer","beers")
print "you ordered order\n" // prints you
ordered 2 beers.
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visibility of variables

• Variables used inside a function are not visible
  from the outside. Example
• beer"Karlsberg"
• function yankeefy (name'Sam Adams')
• beername
• yankeefy()
• print beer // prints Karlsberg
• The variable inside the function is something
  different than the variables outside.

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accessing global variables.

• There are two ways to change a global variable,
  i.e. one that is defined in the main script.
• One is just to call it as GLOBAL'name' where
  name is the name of the global variable.
• function yankeefy (name"Sam Adams")
• GLOBALS'beer'name
• The other is to change it outside a function
  definition.
• Example in brewer_quiz.php

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working with many source files

• Many times it is useful to split a PHP script
  into several files.
• PHP has two mechanisms.
• require(file) requires the file file to be
  included. If the file is not there, PHP exits
  with an error.
• include(file) includes the file. If the file is
  not there no error is reported.

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require() and include()?

• Both assume that you leave PHP. Thus within your
  included file you can write simple HTML.
• If you want to include PHP in your included file,
  you have to surround it by lt?php and ?gt, just
  like in a PHP script.
• Here is an example to use include to build the
  basic web page.
• Included files are customarily give the extension
  .inc.

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top.inc
lt!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0
Strict//EN" "http//www.w3.org/TR/xhtml1/DTD/xhtml
1-strict.dtd"gt lthtmlgt ltheadgtlttitlegttitlelt/titlegt
ltmeta http-equiv"content-type"
content"text/html charsetUTF-8"/gt ltlink
rel"stylesheet" type"text/css"
href"main.css"/gt lt/headgt ltbodygt
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bottom.inc
ltp id"validator"gt lta href"http//validator.w3.or
g/check?urireferer"gtltimg style"border
0pt" src"http//wotan.liu.edu/valid-xhtml10.p
ng" alt"Valid XHTML 1.0!" height"31"
width"88" /gtlt/agt lt/pgt lt/bodygt lt/htmlgt
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trouble

• title in the top.html is not understood as the
  title. It reads as title, which means "idiot"
  for your web user.
• Even if you replace title with
• lt?php title ?gt
• title is empty. The definition from the
  outer file is not seen in the included file.
• So you have to split into three files, and print
  the title in the main file. I leave that to you
  to figure out.

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login.php create_account.php

• Both require a database that has three fields
• id which is an auto_increment int acting as a
  handle
• username is the username of the account. it must
  be unique and this is enforced by mySQL
• password is a varchar(41) because the sha1 of the
  password is stored. This is 40 chars long.

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sessions

• You will recall that HTTP is a stateless
  protocol. Each request/response is
  self-contained.
• Statefulness is crucial in Web applications.
  Otherwise users have to authenticate every time
  they access a new page.
• Traditionally, one way to create statefulness is
  to use cookies.
• PHP uses cookies to create a concept of its own,
  sessions, that makes it all very easy.

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cookies

• A cookie is a piece of attribute/value data. A
  server can send cookies as value of a HTTP header
  Set-Cookie. Multiple headers may be sent.
• When the client visits the web site again, it
  will send the cookie back to the server with a
  HTTP header Cookie

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Set-Cookie

• Set-Cookie namevalue expires date
  pathpath domaindomain secure
• where indicates optional components and
• name is the variable name set in the cookie
• value is the variable's value
• date is a date when the cookie expires
• path restricts the cookie to be sent only when
  requests to a path starting with path are made
• domain restricts the sending of the cookie to a
  certain domain
• secure restricts transmission to https

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Cookies

• The browser compares the request it wants to make
  with the URL and the domain that sent the cookie.
• If the path is not set the cookie will only be
  sent to a request with the originating URL.
• If the cookie matches the request a request
  header of the form
• Cookie name1value1 name2value2
• is sent.

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sessions

• Sessions are a feature of PHP. PHP remembers a
  session through a special cookie PHPSESSID.
• To activate the sessions, include
  session_start() at the beginning of your script,
  before any printing has been done.
• One a session is active, you have a special
  super-global variable _SESSION. Session data is
  stored in special files on wotan.

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_SESSION

• This is an array where you can read and set
  variables that you want to keep during the
  session.
• if(_SESSION'user_name)
• print "welcome " . _SESSION'user_name
• else
• // show users login form
• print login_form()

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ending sessions

• At 9 and 39 past each hour, wotan deletes all
  session files that have not been changed for 24
  minutes or more.
• If you want to remove a session yourself, you can
  call session_destroy() in your script.
• An example is in visit.php.

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