Programming Perl, 4th Edition

Variables

Not surprisingly, there are three variable types corresponding to the three abstract data types we mentioned earlier. Each of these is prefixed by what we call a sigil.^[40] Scalar variables are always named with an initial $, even when referring to a scalar that is part of an array or hash. It works a bit like the English word “the”. See Table 2-1.

Table 2-1. Accessing scalar values

Construct	Meaning
$days	Simple scalar value $days
$days[28]	29th element of array @days
$days{"Feb"}	“Feb” value from hash %days

Note that we can use the same name for $days, @days, and %days without Perl getting confused.

There are other, fancier scalar terms that are useful in specialized situations that we won’t go into yet. Table 2-2 shows what they look like.

Table 2-2. Syntax for scalar terms

Construct	Meaning
${days}	Same as $days but unambiguous before alphanumerics
$Dog::days	Different $days variable, in the Dog package
$#days	Last index of array @days
$days–>[28]	29th element of array pointed to by reference $days
$days[0][2]	Multidimensional array
$days{2000}{"Feb"}	Multidimensional hash
$days{2000,"Feb"}	Multidimensional hash emulation

Entire arrays (or slices of arrays and hashes) are named with the sigil @, which works much like the words “these” or “those”. Table 2-3 shows this syntax.

Table 2-3. Syntax for list terms

Construct	Meaning
@days	Array containing ($days[0], $days[1], ... $days[N])
@days[3, 4, 5]	Array slice containing ($days[3], $days[4], $days[5])
@days[3..5]	Array slice containing ...