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92
StringsAndPatterns
Sub-Expressions
Asub-expression is a regular expressioncontained within the main regular expres-
sion(or another sub-expression);you define one by encapsulating it inparentheses:
/a(bc.)e/
This expression will match the letter
a
,followed by the letters
b
and
c
,followed by
anycharacter and, finallytheletter
e
.As you cansee, sub-expressionsby themselves
do not have any influence onthe way a regular expressionis executed; however, you
can use them in conjunction with quantifiers to allow for complex expressions to
happenmore than once. For example:
/a(bc.)+e/
This expression will match the letter
a
,followed by the expression
bc.
repeated one
or more times,followed bythe letter
e
.
Sub-expressions can also be used as capturing patterns, which we will examine in
the nextsection.
Matching and Extracting Strings
The
preg
_
match()
functioncanbe used tomatch aregular expressionagainsta given
string. The function returns
true
if the match is successful, and can return all the
captured subpatterns in an array if an optional third parameter is passed by refer-
ence. Here’s an example:
$name = "Davey Shafik";
// Simple match
$regex = "/[a-zA-Z\s]/";
if (preg
_
match($regex, $name)) {
// Valid Name
}
// Match with subpatterns and capture
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StringsAndPatterns
93
$regex = ’/^(\w+)\s(\w+)/’;
$matches = array();
if (preg
_
match ($regex, $name, $matches)) {
var
_
dump ($matches);
}
If you run the second example, you will notice that the
$matches
array is populated,
onreturnwith thefollowing values:
array(3) {
[0]=>
string(12) "Davey Shafik"
[1]=>
string(5) "Davey"
[2]=>
string(6) "Shafik"
}
As you can see, the first element of the array contains the entire matched string,
while the second element (index 1) contains the first captured subpattern, and the
third element contains the second matched subpattern.
Performing MultipleMatches
The
preg
_
match
_
all()
function allows you to perform multiple matches on a given
string based ona single regular expression. For example:
$string = "a1bb b2cc c2dd";
$regex = "#([abc])\d#";
$matches = array();
if (preg
_
match
_
all ($regex, $string, $matches)) {
var
_
dump ($matches);
}
This scriptoutputs the following:
array(2) {
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94
StringsAndPatterns
[0]=>
array(3) {
[0]=>
string(2) "a1"
[1]=>
string(2) "b2"
[2]=>
string(2) "c2"
}
[1]=>
array(3) {
[0]=>
string(1) "a"
[1]=>
string(1) "b"
[2]=>
string(1) "c"
}
}
As you can see, all the whole-patternmatches are stored in the firstsub-array ofthe
result,whilethefirstcapturedsubpatternofevery match isstoredinthecorrespond-
ing slotofthe second sub-array.
Using PCRE to Replace Strings
Whilst
str
_
replace()
is quite flexible, it still only works on “whole” strings, that is,
whereyou knowthe exacttextto search for. Using
preg
_
replace()
,however,you can
replace text that matches a pattern we specify. It is even possible to reuse captured
subpatterns directly in the substitution string by prefixing their index with a dollar
sign. In the example below, we use this technique to replace the entire matched
patternwith a string thatis composed usingthe first captured subpattern(
$1
).
$body = "[b]Make Me Bold![/b]";
$regex = "@\[b\](.
*
?)\[/b\]@i";
$replacement = ’<b>$1</b>’;
$body = preg
_
replace($regex, $replacement, $body);
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StringsAndPatterns
95
Just like with
str
_
replace()
,we can pass arrays of search and replacement argu-
ments; however, unlike
str
_
replace()
, we can also pass in an array of subjects
on which to perform the search-and-replace operation. This can speed things up
considerably, since the regular expression (or expressions) are compiled once and
reused multiple times. Here’s anexample:
$subjects[’body’] = "[b]Make Me Bold![/b]";
$subjects[’subject’] = "[i]Make Me Italics![/i]";
$regex[] = "@\[b\](.
*
?)\[/b\]@i";
$regex[] = "@\[i\](.
*
?)\[/i\]@i";
$replacements[] = "<b>$1</b>";
$replacements[] = "<i>$1</i>";
$results = preg
_
replace($regex, $replacements, $subjects);
When you execute the code shown above, you will end up with an array that looks
like this:
array(2) {
["body"]=>
string(20) "<b>Make Me Bold!</b>"
["subject"]=>
string(23) "<i>Make Me Italic!</i>"
}
Notice how the resulting array maintains the array structure of our
$subjects
array
thatwe passed in, which,however,is not passed by reference, nor is itmodified.
Summary
This chapter covered what is most likely going to be the bulk of your work as a de-
veloper—manipulating strings, and while regular expressionsmaybe complex, they
are extremely powerful. Just remember: with great power, comes great responsibil-
ity—in this case, don’t use themif you don’thave to. Never underestimate the power
ofthestring functions and regular expressions.
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Chapter 5
Web Programming
Althoughyou willfind it used in scenarios asdiverse asqualitycontrol and point-of-
sale systems,PHP was designed primarilyas a Web-development language, and that
remains itsmost commonuse to this day.
In this chapter, we focus on the features of PHP that make it such a great choice
for developing Web applications,as well assome Web-related topicsthatyoushould
be familiar with inorder totake theexam.
Anatomy of a Web Page
Most people think of a Web page as nothing more than a collection of HTML code.
Thisisfineifyou happentobe aWebdesigner—but,asa PHP developer,yourknowl-
edge must run much deeper ifyou want to take full advantage ofwhat the Web has
to offer.
From the pointofviewofthe Web server, the generationofa documentstarts with
an HTTP request, in which the client requests access to a resource using one of a
short list of methods. The client can also send a data payload (called request) along
with its request—for example, if you are posting an HTTP form, the payload could
consist of the form data, while ifyou are uploading a file, the payload would consist
of the file itself.
Once a request is received, the server decodes the data that it has received and
passes it on to the PHP interpreter (clearly, we are assuming that the request was
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98
WebProgramming
made for a PHP script—otherwise, the server can choose a different handler or, in
the case ofstatic resources,such as images,outputthemdirectly).
Upon output, the server first writes a set of response headers to the clients; these
can contain information useful to the client—such as the type of content being re-
turned,or its encoding, as well as data needed to maintain the client and the server
in a stateful exchange(we’ll explainthislater).
Forms and URLs
Most often, your script will interact with their clients using one of two HTTP meth-
ods: GETandPOST.Froma technicalperspective,themaindifferencebetweenthese
two methods is in the fact that the latter allows the client to send along a data pay-
load,while the former only allows you to send data as part of the querystring.
This, of course, doesn’t mean that you can’t submit a form using GET—only that
you will be somewhat limited in the size and type of data that you can send. For
example, you can only upload files using POST, and almost all browsers implement
limitations onthe lengthofthe querystring thatconfine theamountofdatayou can
send out with a GEToperation.
i
Contrary to popular belief, POST is not an inherently more secure to submit forms
thanGET.Weexplain thisconcept ingreater detail intheSecurity chapter.
Froman HTML perspective, the difference betweenGET and POST is limited to the
action
attribute ofthe<
form
>element:
<!--Form submitted with GET-->
<form action="index.php" method="GET">
List: <input type="text" name="list" /><br />
Order by:
<select name="orderby">
<option value="name">Name</option>
<option value="city">City</option>
<option value="zip">ZIP Code</option>
</select><br />
Sort order:
WebProgramming
99
<select name="direction">
<option value="asc">Ascending</option>
<option value="desc">Descending</option>
</select>
</form>
<!--Form submitted with POST-->
<form action="index.php" method="POST">
<input type="hidden" name="login" value="1" />
<input type="text" name="user" />
<input type="password" name="pass’ />
</form>
GET and URLs
Whena form is submitted using the GET method, its values are encoded directly in
the query string portion of the URL. For example, if you submit the form above by
entering
user
in the
List
box and choosing to sort by
Name
in
Ascending
order, the
browser willcallup our
index.php
scriptwith the following URL:
http://example.org/index.php?list=user&orderby=name&direction=asc
As you can see, the data has been encoded and appended to the and of the URL for
our script. In order to access the data, we must nowuse the
$
_
GET
superglobal array.
Each argument is accessible through anarraykey ofthe same name:
echo $
_
GET[’list’];
You cancreate arrays by using array notation...
http://example.org/index.php?list=user&order[by]=column&order[dir]=asc
..and thenaccess themusing the following syntax:
echo $
_
GET[’order’][’by’];
echo $
_
GET[’order’][’direction’];
100
WebProgramming
Note that, clearly, there is nothing that stops you from creating URLs that already
contain query data—there is no special trick to it, other than the data must be en-
coded using a particular mechanism that, in PHP, is provided by the
urlencode()
function:
$data = "Max & Ruby";
echo "http://www.phparch.com/index.php?name=" . urlencode ($data);
The PHP interpreter will automatically decode all incoming data for us, so there is
noneed to execute
urldecode()
on anything extracted from
$
_
GET
.
Using POST
Whensendingtheformweintroducedabovewiththe
method
attributesetto
post
,the
data is accessible using the
$
_
POST
superglobal array. Just like
$
_
GET
,
$
_
POST
contains
onearrayelementnamed after each inputname.
if ($
_
POST[’login’]) {
if ($
_
POST[’user’] == "admin" &&
$
_
POST[’pass’] == "secretpassword") {
// Handle login
}
}
In this example, we first check that the submit button was clicked, thenwe validate
that theuser input is correct.
Also, similarly toGET input,we canagainuse arraynotation:
<form method="post">
<p>
Please choose all languages you currently know or would like
to learn in the next 12 months.
</p>
<p>
<label>
<input type="checkbox" name="languages[]" value="PHP" />
PHP
</label>
<label>
WebProgramming
101
<input type="checkbox" name="languages[]" value="Perl" />
Perl
</label>
<label>
<input type="checkbox" name="languages[]" value="Ruby" />
Ruby
</label>
<br />
<input type="submit" value="Send" name="poll" />
</p>
</form>
The formabove hasthree checkboxes, allnamed
languages[]
;these willallbe added
individually to an array called
languages
in the
$
_
POST
superglobal array—just like
when you use an empty key (e.g.
$array[] = “foo”
)to append a new element to an
existing array inPHP. Onceinside your script,you willbe able toaccess these values
as follows:
foreach ($
_
POST[’languages’] as $language) {
switch ($language) {
case ’PHP’ :
echo "PHP? Awesome! <br />";
break;
case ’Perl’ :
echo "Perl? Ew. Just Ew. <br />";
break;
case ’Ruby’ :
echo "Ruby? Can you say... ’bandwagon?’ <br />";
break;
default:
echo "Unknown language!";
}
}
WhenYou Don’tKnow How Data IsSent
If you need to write a script that is supposed to work just as well with both GETand
POST requests, you can use the
$
_
REQUEST
superglobal array; the latter is filled in
using data from different sources in an order specified by a setting in your
php.ini
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