Perl Pocket Reference, 4th Edition

Chapter 9. Context

Perl expressions are always evaluated in a context that determines the outcome of the evaluation.

Boolean	A special form of scalar context in which it only matters if the result is true or false. Anything that is undefined or evaluates to an empty string, the number zero, or the string "0" is considered false; everything else is true (including strings like "00").
List	A list value is expected. Acceptable values are literal lists, arrays, and hashes. Slices of arrays, hashes, and lists are also acceptable. A scalar value will be interpreted as a one-argument list.
Scalar	A single scalar value is expected.
Void	No value is expected. If a value is provided, it is discarded.

The following functions relate to context:

scalar expr

Forces scalar context for the expression.

wantarray

Returns true in list context, false in scalar context, and undef in void context.