How to use PHP to query the contents of a JSON array stored in a flat file and return the result?

Experts,

I have a flat file (users.php) with a JSON array stored within.

The JSON array takes the following format:

[{"name":"Sam Smith","profltitle":", MBA","location":"San Francisco","displayspecialty":"Accounting","headshotphoto":"2235396_photoweb.jpg","homepageurl":"http:\/\/example.com"},{"name":"Paula Jones","profltitle":", MA","location":"San Jose","displayspecialty":"Human Resources","headshotphoto":"2235555_photoweb.jpg","homepageurl":"http:\/\/example.com"}]

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Users are allowed to specify a search term via a textbox:

<input name="searchfor" id="searchfor" type="text" />

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Using the search term provided by the user I need to query the JSON array and pull results that match the given search term. The matching values need to be returned in a JSON format.

This is the programming logic as I see it now:

<?php
//DEFINE SEARCH TERM AS PROVIDED BY USER
$term = addslashes($_POST['searchfor']);
//DEFINE JSON ARRAY
$json_array = fopen('users.php');
//USING SEARCH TERM QUERY ARRAY
...
//PROVIDE THE RESULTS IN JSON FORMAT
...
?>

Any assistance would be helpful.