Variables (Programming Perl) - e-Reading Library

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2.4. 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 funny character.[5] 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". Thus, we have:

[5] That's another technical term in computer science. (And if it wasn't before, it is now.)

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, useful in specialized situations that we won't go into yet. They look like this:

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 funny character @, which works much like the words "these" or "those":

Construct	Meaning
`@days`	Array containing `($days[0], $days[1],... $days[n])`
`@days[3, 4, 5]`	Array slice containing `($days[3], $days[4], $days[5])`
`@days[3..5]`	Array slice containing `($days[3], $days[4], $days[5])`
`@days{'Jan','Feb'}`	Hash slice containing `($days{'Jan'},$days{'Feb'})`

Entire hashes are named by %:

Construct	Meaning
`%days`	`(Jan => 31, Feb => $leap ? 29 : 28, ...)`

Any of these constructs may also serve as an lvalue, specifying a location you could assign a value to. With arrays, hashes, and slices of arrays or hashes, the lvalue provides multiple locations to assign to, so you can assign multiple values to them all at once:

@days = 1 .. 7;


2.3. Built-in Data Types		2.5. Names