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Perl Cookbook
book

Perl Cookbook

by Tom Christiansen, Nathan Torkington
August 1998
Intermediate to advanced content levelIntermediate to advanced
800 pages
39h 20m
English
O'Reilly Media, Inc.
Content preview from Perl Cookbook

Exchanging Values Without Using Temporary Variables

Problem

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

Solution

Use list assignment to reorder the variables.

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

Discussion

Most programming languages force you to use 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 lets you eliminate 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“.

See Also

The section on “List value constructors” in perldata(1) and Chapter 2 of Programming Perl

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Publisher Resources

ISBN: 1565922433Supplemental ContentCatalog PageErrata