Regex for URL

When there is a question like this, there is usually a backstory with a business rule or rule set that the programmer is trying to implement with REGEX, and that's often a bad idea, especially when the subject matter is the REQUEST_URI.  Can you please step back from the technical details and just tell us in plain language what you want to achieve?  There may be better ways to get to the end result.  

And in any case, the rules for URLs are not really quite as simple as you may think.  If you control the creation of the URLs, that is a good step in the right direction, but with REQUEST_URI your rules must also account for (or deliberately ignore) the request variables.

This article has some ideas about how to test the REGEX, but I still think that your business-rules explanation will get you a better approach.
http://www.experts-exchange.com/Web_Development/Web_Languages-Standards/PHP/A_7830-A-Quick-Tour-of-Test-Driven-Development.html

<?php // RAY_temp_cc01.php
error_reporting(E_ALL);


// http://www.experts-exchange.com/Programming/Languages/Regular_Expressions/Q_28297813.html
// The REQUEST_URI string contains */clients/[a-zA-Z0-9].php*


// A REGULAR EXPRESSION
$rgx
= '#'           // REGEX DELIMITER
. '/clients/'   // EXPLICIT CHARACTER STRING
. '[A-Z0-9]'    // CHARACTER CLASS - LETTERS AND NUMBERS
. '{1,}'        // AT LEAST ONE CHARACTER
. '\.php'       // WITH A PHP SUFFIX
. '#'           // REGEX DELIMITER
. 'i'           // CASE-INSENSITIVE
;

// SOME TEST DATA
$uri = array
( '/clients/xyz.php?admin=1'
, '/clients/login.php?uid=ABC+OR+1+=+1'
, '/admin/clients/delete.php?id=23'
, 'clients.php'                                         // FAILS BECAUSE NO SLASH BEFORE CLIENTS
, '/clients/'                                           // FAILS BECAUSE NO .PHP
, '/clients/healthcare.gov/blunder/obamacare/fail.php'  // FAILS BECAUSE . AND SLASH NOT PERMITTED AFTER /CLIENTS/
, '/clients/images/index.php?q=gooseball'               // FAILS BECAUSE SLASH NOT PERMITTED AFTER /CLIENTS/
)
;

// TEST THE REGEX
echo '<pre>';
foreach ($uri as $str)
{
    echo PHP_EOL . $str;
    if (preg_match($rgx, $str))
    {
        echo " OK";
    }
    else
    {
        echo " FAIL";
    }
}

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