If you want to do this with a PHP script, you can use cURL to simulate an HTTP request. However, it’s easier to use a reference tool, such as abor siege, to load specific URLs.
C ab:
ab -n 1000 -c 10 http://www.example.com/login.php
From the Siege website:
Siege is a regression test and benchmark utility. It can test a single URL with user-defined users, or it can read many URLs in memory and underline them at the same time. The program reports the total number of recorded videos, transferred bytes, response time, concurrency and return status. Siege supports HTTP / 1.0 and 1.1, GET and POST directives, cookies, transaction logging and basic authentication. Its features are customizable for each user.
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