PHP "or" Syntax

Question

I've seen this a lot: $fp = fopen($filepath, "w") or die(); But I can't seem to find any real documentation on this "or" syntax. It's obvious enough what it does, but can I use it anywhere? And must it be followed by die()? Are there any caveats to using or when you could use something like

if (file_exists($filepath))    $fp = fopen($filepath,"r"); else    myErrMessage(); 

I know it seems like a silly question, but I can't find any hard and fast rules for this. Thanks.

Answer 1

It's a logical operator and can be used in any logical expression.

http://php.net/manual/en/language.operators.logical.php

Answer 2

Let's just say that:

$result = first() || second(); 

will evaluate to:

if (first()) {     $result = true; } elseif (second()) {     $result = true; } else {     $result = false; }  

while:

$result = first() or second(); 

will evaluate to:

if ($result = first()) {     // nothing } else {     second(); } 

In other words you may consider:

$result = first() || second();  $result = (first() || second()); 

and:

$result = first() or second(); 

to be:

($result = first()) || second(); 

It is just matter of precedence.