3.4.3 The Context--List vs. Scalar

It may have occurred to you by now that in certain places we can use a list, and in other places we can use a scalar. Perl knows this as well, and decides which is permitted by something called a context.

The context can be either list context or scalar context. Many operations do different things depending on what the current context is.

For example, it is actually valid to use an array variable, such as @array, in a scalar context. When you do this, the array variable evaluates to the number of elements in the array. Consider this example:

use strict;
my @things = qw/a few of my favorite/;
my $count  = @things;                   # $count is 5
my @moreThings = @things;               # @moreThings is same as @things

Note that Perl knows not to try and stuff @things into a scalar, which does not make any sense. It evaluates @things in a scalar context and given the number of elements in the array.

You must always be aware of the context of your operations. Assuming the wrong context can cause a plethora of problems for the new Perl programmer.