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In covering PHP we have mentioned the following aspects.
Variables have names, like in Perl, and these names are always
prefixed by the dollar sign ($).
So here's a simple PHP file:
<html>
<head>
<title>PHP variables</title>
</head>
<body bgcolor=white>
<? $i = 3; ?>
<p> I have set <code>$i</code> to the value of <?=$i?>. </p>
<? $i += 2; ?>
<p> Now I added 2 to it, so it has become <?=$i?>. </p>
</body>
</html>Here's the source code, again.
What would be the basic Perl CGI script that does the same thing?
Perhaps something like this:
#!/usr/bin/perl print "Content-type: text/html\n\n<html><body bgcolor=white>"; $i = 3; print "<p>I have set <code>\$i</code> to the value of $i.</p>"; $i += 2; print "<p> Now I added 2 to it, so it has become $i. </p> "; print "</body></html>";
Here's this script in action.
Here's the CGI.pm version of it.
#!/usr/bin/perl
use CGI;
$query = new CGI;
print $query->header;
print $query->start_html(-bgcolor=>'white');
$i = 3;
print qq{
<p> I have set <code>\$i</code> to the value of $i. </p>
};
$i += 2;
print qq{
<p> Now I have added 2 to it, so it has become $i.</p>
};
print $query->end_html;Hashtables are used in Perl, and they are also used in PHP.
Here's some code in Perl,
%prices = ("Tires" => 100,
"Oil" => 10,
"Spark Plugs" => 4);
$prices{"Tires"} -= 90;
foreach $key (keys %prices) {
print $key, " --> ", $price{$key}, "<p>";
} Here's the code:
<html><body bgcolor=white>
<? $prices = array("Tires" => 100,
"Oil" => 10,
"Spark Plugs" => 4);
$prices["Tires"] -= 10;
while ($element = each ($prices)) {
echo $element["key"] . " --> " .
$element["value"] . "<br>";
}
?>
</body></html>
Here's the source
code for that. (Note we reset the array).
Now a word about sessions.
HTTP is connectionless, and keeping state with CGI requires
Here's a typical script.
Here's the source code.
Here's the source code again:
<? session_start();
if (session_is_registered("acc")) {
if ($fun == "add") $acc += $arg;
else if ($fun == "sub") $acc -= $arg;
} else {
$acc = 0;
session_register("acc");
}
?>
<html>
<head>
<title>Sessions Examples</title>
</head>
<body bgcolor=white>
<form method="POST" action="<? echo $SCRIPT_NAME; ?>">
The current value of the accumulator is: <? echo $acc ?> <p>
<table cellpadding=2>
<tr>
<td> Amount: </td>
<td> <input type="text" name="arg" size=4> </td>
<td> Function: </td>
<td> <select name="fun">
<option value="non"> Click Me!
<option value="add"> Deposit
<option value="sub"> Withdraw
</select>
</td>
</tr>
</table>
<p> Enter the amount, select a function, then press
<input type="submit" value="Proceed"> <p>
</form>
</body>
</html>/tmp if I work with this calculator a bit (which
is what the example wants to bring forth):
My accumulator was 122 at the time I printed the file.burrowww.cs.indiana.edu% ls -ld /tmp/sess_05e56a5ed8be5e3a0ef771d9fb582df9 -rw------- 1 dgerman faculty 10 Oct 17 14:44 /tmp/sess_05e56a5ed8be5e3a0ef771d9fb582df9 burrowww.cs.indiana.edu% cat /tmp/sess_05e56a5ed8be5e3a0ef771d9fb582df9 acc|i:122;burrowww.cs.indiana.edu% burrowww.cs.indiana.edu%
The name of the file contains the random session ID (in blue).
The contents of the file contains the server-side state (environment).
That is in red.
Note that for every browser that calls, a session ID is created.
The session ID is sent to the browser, and kept in a cookie, there.
(Other ways of storing the session ID on the browser are possible, too).
A file with the ownership of the server will then be created on the server.
Where will it be created?
Your config file (php.ini) determines
that, and here's the line in it.
To summarize:ifx.nullformat = 0 [Session] ; Handler used to store/retrieve data. session.save_handler = files ; Argument passed to save_handler. In the case of files, this is the path ; where data files are stored. session.save_path = /tmp ; Whether to use cookies. session.use_cookies = 1 ; Name of the session (used as cookie name). session.name = PHPSESSID ; Initialize session on request startup. session.auto_start = 0
session_start()
checks to see if an ID is submitted by the browser with the request, and if that ID is already available on the server.
a new one will be generated, and will be sent to the browser. This is the beginning of a new session. The browser has to keep it and submit it with every new request.
then we know
who we are talking to, so we refer to the corresponding
file in the session.save_path directory.
session_register(varName)
is used to associate variable names with values. These are stored under the appropriate session ID file on the server side (see my example above). They are retrieved from that file during subsequent calls in the same session (that is, for the same session ID).
session_is_registered(varName)
is used to check if a variable is registered already or not (that is, if it's stored on the server side in the file for this session ID).
session_unregister(varName)
is used to delete a variable from the file on the server associated with the session in which this instruction is run.
session_destroy()
deletes the session, that is, the file.
Experiments done Monday-Tuesday with
We need to further investigate that, later.
We will cover cookies when we look at Javascript.
At that time we will look at cookies from three points of view:
What do you need to turn in in the next lab?