Accessing Elements of an Array

3.1 Accessing Elements of an Array

If you've used arrays in another language, you won't be surprised to find that Perl provides a way to subscript an array in order to refer to an element by a numeric index.

The array elements are numbered using sequential integers, beginning at zero and increasing by one for each element, like this:

$fred[0] = "yabba";

$fred[1] = "dabba";

$fred[2] = "doo";

The array name itself (in this case, "fred") is from a completely separate namespace than scalars use; you could have a scalar variable named $fred in the same program, and Perl will treat them as different things, and wouldn't be confused.^[2] (Your maintenance programmer might be confused, though, so don't capriciously make all of your variable names the same!)

^[2] The syntax is always unambiguous tricky perhaps, but unambiguous.

You can use an array element like $fred[2] in every place^[3] where you could use any other scalar variable like $fred. For example, you can get the value from an array element or change that value by the same sorts of expressions we used in the previous chapter:

^[3] Well, almost. The most notable exception is that the control variable of a foreach loop, which we'll see later in this chapter, must be a simple scalar. And there are others, like the "indirect object slot" and "indirect filehandle slot" for print and printf.

print $fred[0];

$fred[2] = "diddley";

$fred[1] .= "whatsis";

Of course, the subscript may be any expression that gives a numeric value. If it's not an integer already, it'll automatically be truncated to the next lower integer:

$number = 2.71828;

print $fred[$number - 1]; # Same as printing $fred[1]

If the subscript indicates an element that would be beyond the end of the array, the corresponding value will be undef. This is just as with ordinary scalars; if you've never stored a value into the variable, it's undef.

$blank = $fred[ 142_857 ]; # unused array element gives undef

$blanc = $mel;  # unused scalar $mel also gives undef