PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

40 Chapter 1 PHP Crash Course
Or, equivalently on a Windows server, you can use
$out = `dir c:`;
echo ‘’.$out.’’;
Either version obtains a directory listing and stores it in $out. It can then be echoed to
the browser or dealt with in any other way.
There are other ways of executing commands on the server.We cover them in
Chapter 19,“Interacting with the File System and the Server.”
Array Operators
There are a number of array operators.The array element operators ([]) enable you to
access array elements.You can also use the => operator in some array contexts.These
operators are covered in Chapter 3.
You also have access to a number of other array operators.We cover them in detail in
Chapter 3 as well, but we included them here in Table 1.6 for completeness.
Table 1.6 PHP’s Array Operators
Operator Name Use Result
+ Union $a + $b Returns an array containing everything in $a
and $b
== Equality $a == $b Returns true if $a and $b have the same
key and pairs
=== Identity $a === $b Returns true if $a and $b have the same
key and value pairs the same order
!= Inequality $a != $b Returns true if $a and $b are not equal
Inequality $a $b Returns true if $a and $b are not equal
!== Non-identity $a !== $b Returns true if $a and $b are not identical
You will notice that the array operators in Table 1.6 all have equivalent operators that
work on scalar variables. As long as you remember that + performs addition on scalar
types and union on arrays—even if you have no interest in the set arithmetic behind that
behavior—the behaviors should make sense.You cannot usefully compare arrays to scalar
types.
The Type Operator
There is one type operator: instanceof.This operator is used in object-oriented programming,
but we mention it here for completeness. (Object-oriented programming is
covered in Chapter 6.)