For example this link can be used:
http://demo:demo@demo.pimatic.org/api/variables/variable-set.temperature (buth will output all values)

This script for example will pick the one value needed (Temperature: 14)

<?php
$curl = curl_init();
   curl_setopt ($curl, CURLOPT_URL, "http://demo:demo@demo.pimatic.org/api/variables/variable-set.temperature");
  curl_setopt ($curl, CURLOPT_RETURNTRANSFER, 1);

$result = curl_exec ($curl);// curl to a variable
  curl_close ($curl);

$result = json_decode($result, true);// decode to associative array
$result = $result['variable']['value'];//pick desired value

print "Temperature: ".$result; 
?>