Question

I’ve read that one of the differences between include and require is that
while include only includes the included file if the include statement is
encountered, require includes the file into the file hosting the require
statement even when the require code is not reached by the execution flow.

How can this have any implications. After all, if I have a file which says:

<?php
  echo __LINE__;
?>

the output will always be 3, instead of printing the line inside at the
position inside the file which includes such include file.

Answer 1

Let’s say you are running a mission critical application and will lose $1 per second. And some libraries are only used in certain case and are not affecting your business flow. You should probably use include_once for these optional libraries. Because if the file is not there require will stop your application from running with a fatal error.