PHP

php exit

exit;

exit and echo php

//exit — Output a message and terminate the current script
<?php

$filename = '/path/to/data-file';
$file = fopen($filename, 'r')
    or exit("unable to open file ($filename)");

?>

php exit

if( !file_exists("") ) {
  exit("File not found on line 145: customers.txt. Hope you weren't buying anything ...");
} else {
  $file = fopen("customers.txt, "r");
  // rest of code here