Looking for basic information on building crawlers and bots in php

Hey everyone I was interested in building some crawlers and bots in php. Im not sure where to start does anyone have any good resources or any suggestions on how to approach a project like this for the first time?

 

Learn cURL, regular expression and rest you need logic to create a bot. There is no science or definition to create a crawler / bot.

 

try first with this code, play a little with it:

<?php
  $original_file = file_get_contents("http://www.domain.com");
  $stripped_file = strip_tags($original_file, "<a>");
  preg_match_all("/<a(?:[^>]*)href=\"([^\"]*)\"(?:[^>]*)>(?:[^<]*)<\/a>/is", $stripped_file, $matches);

  //DEBUGGING

  //$matches[0] now contains the complete A tags; ex: <a href="link">text</a>
  //$matches[1] now contains only the HREFs in the A tags; ex: link

  header("Content-type: text/plain"); //Set the content type to plain text so the print below is easy to read!
  print_r($matches); //View the array to see if it worked
?>

Code (markup):

 

Thanks for the help.

what about how to target multiple websites and link hop rather than simply know the domain or url you want to query