Section 3.1.  Accessing Elements of an Array

Table of Contents

3.1. Accessing Elements of an Array

If you've used arrays in another language, you won't be surprised to find Perl provides a way to subscript an array 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 (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. Perl treats them as different things and doesn't get confused.[*] (Your maintenance programmer might be confused though, so don't capriciously make all of your variable names the same.)

[*] The syntax is always unambiguous; tricky perhaps, but unambiguous.

You can use an array element like $fred[2] in every place[Section 3.1.  Accessing Elements of an Array] 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:

[Section 3.1.  Accessing Elements of an Array] Well, almost. The most notable exception is that the control variable of a foreach loop, which you'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, 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 the same as 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

    Table of Contents
    © 2000- NIV