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1.3. Exchanging Values Without Using Temporary Variables

1.3.1. Problem

You want to exchange the
values of two scalar variables, but don't want to use a temporary
variable.

1.3.2. Solution

Use list
assignment to reorder the variables.

($VAR1, $VAR2) = ($VAR2, $VAR1);

1.3.3. Discussion

Most programming languages require an intermediate step when swapping
two variables' values:

$temp    = $a;
$a       = $b;
$b       = $temp;

Not so in Perl. It tracks both sides of the assignment, guaranteeing
that you don't accidentally clobber any of your values. This
eliminates the temporary variable:

$a       = "alpha";
$b       = "omega";
($a, $b) = ($b, $a);        # the first shall be last -- and versa vice

You can even exchange more than two variables at once:

($alpha, $beta, $production) = qw(January March August);
# move beta       to alpha,
# move production to beta,
# move alpha      to production
($alpha, $beta, $production) = ($beta, $production, $alpha);

When this code finishes, $alpha,
$beta, and $production have the
values "March", "August", and
"January".

1.3.4. See Also

The section on "List value constructors" in
perldata(1) and on "List Values and Arrays" in
Chapter 2 of Programming Perl