Question

PHP’s or is an weird keyword. Here it is in a code snippet that makes me confused:

echo 0 or 1; // prints 1

$foo = (0 or 1);
echo $foo; // prints 1

$foo = 0 or 1;
echo $foo; // prints 0 for some reason

Why does the last one print 0 and not 1?

Answer 1

This is because of different operator precedence. In the third case, the assignment is handled first. It will be interpreted like this:

($foo = 0) or 1;

The || operator has a different precedence. If you use

 $foo = 0 ||1;

It will work as you expect.

See the manual on logical operators