Introduction to PHP. PHP vs CGI/Perl.

Unix commands, installed Apache: post HTML documents. Static.
Program Apache: use Perl, CGI (Common Gateway Interface), CGI.pm. 
Main issue: keeping state. Why: HTTP is connectionless. 

We developed a pattern: the program starts and

0. setup 
1. read input (input and state) assumption is: you trust your user
2. is state empty? 
  2.1 if yes: initialize state 
  2.2 else:
      change state according to input
3. report state 
4. save state 
5. get ready for more input

state: 
  $message, $total, $good, $answer (a collection of variables)
PHP:
  same thing

setup:
  #!/usr/bin/perl

  use CGI; 

  $q = new CGI; 

PHP: 
  no need for a setup

retrieve state (input): 
  $message = $q->param('message'); 
  $total = $q->param('total'); 
PHP:
  happens automatically 

initialize state: 
  $message = "Welcome"; 
  $total = 0;
  $good = 0; 
PHP:
  same way 

update state based on input:
  basic algorithm specific to that problem
PHP: 
  same 

save state and ger ready for more input:
  print qq{
    <form>

      Type your answer here: <input type="text" name="userInput"> 
      Press <input type="submit" value="Proceed"> to continue. 

      <input type="hidden" name="message" value="$message">
      <input type="hidden" name="total" value="$total">
    </form>
  }; 
PHP: 
  basically same 

report state: 
  print $message; 
PHP:
  <? $message = "Welcome"; echo $message; ?> scriptlet 
  <? echo $message; ?> prints an expression same as <?=$message?>  

programs in CGI/Perl are stored in ~/apache/cgi-bin
PHP: programs in htdocs 

let's try an example:

#!/usr/bin/perl

use CGI; 

$q = new CGI; 

print $q->header, $q->start_html; 

$message = $q->param('message'); 
$secret = $q->param('secret'); 
$attempts = $q->param('attempts'); # state 

$userGuess = $q->param('userGuess'); # input 

if ($message) { # state is not empty 
  if ($userGuess == $secret) {
    $message = "That's right, you won."; 
  } elsif ($userGuess > $secret) {
    $message = "Nope, try lower."; 
    $attempts += 1; 
  } else {
    $message = "Nope, try higher."; 
    $attempts += 1;     
  }
  if ($attempts == 10) {
    $message = "You lost. The number was $secret."; 
  } 
} else { # initialize
  $secret = int(rand(100)); 
  $attempts = 0; 
  $message = "Welcome"; 
}

print qq{
  <form> 
    $message <p> 
    (The secret number is $secret, you have $attempts missed attempts thus far). <p> 

    Guess the number: <input type="text" name="userGuess"> <p> 
    Press <input type="submit" value="Proceed"> to move on. 

    <input type="hidden" name="message"  value="$message"> 
    <input type="hidden" name="secret"   value="$secret"> 
    <input type="hidden" name="attempts" value="$attempts"> 
  </form> 
}; 

print $q->end_html; 

Using the equivalences mentioned above we convert this to:

<? 

if ($message) { // state is not empty 
  if ($userGuess == $secret) {
    $message = "That's right, you won."; 
  } elseif ($userGuess > $secret) {
    $message = "Nope, try lower."; 
    $attempts += 1; 
  } else {
    $message = "Nope, try higher."; 
    $attempts += 1;     
  }
  if ($attempts == 10) {
    $message = "You lost. The number was $secret."; 
  } 
} else { // initialize
  $secret = rand(0, 100); 
  $attempts = 0; 
  $message = "Welcome"; 
}

?> 

  <form> 
    <?=$message?> <p> 
    (The secret number is <?=$secret?>, you have <?=$attempts?> missed attempts thus far). <p> 

    Guess the number: <input type="text" name="userGuess"> <p> 
    Press <input type="submit" value="Proceed"> to move on. 

    <input type="hidden" name="message"  value="<?=$message?>"> 
    <input type="hidden" name="secret"   value="<?=$secret?>"> 
    <input type="hidden" name="attempts" value="<?=$attempts?>"> 
  </form> 

minute paper: 
a) how comfortable are you with perl given the above
b) same question about cgi.pm the library
c) how do you feel about php, in anticipation for thu; do you
   need any url for any tutorial you want to look over for thu 
   or what do you think you need? (thu we discuss php by itself
   not by analogy like today and we should be able to discuss
   sessions as well).

--end of lecture