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Learning Perl, 5th Edition
book

Learning Perl, 5th Edition

by Randal L. Schwartz, Tom Phoenix, brian d foy
June 2008
Beginner content levelBeginner
352 pages
11h 16m
English
O'Reilly Media, Inc.
Content preview from Learning Perl, 5th Edition

Return Values

The subroutine is always invoked as part of an expression, even if the result of the expression isn’t being used. When we invoked &marine earlier, we were calculating the value of the expression containing the invocation, but then throwing away the result.

Many times, you’ll call a subroutine and actually do something with the result. This means that you’ll be paying attention to the return value of the subroutine. All Perl subroutines have a return value—there’s no distinction between those that return values and those that don’t. Not all Perl subroutines have a useful return value, however.

Since all Perl subroutines can be called in a way that needs a return value, it’d be a bit wasteful to have to declare special syntax to “return” a particular value for the majority of the cases. So Larry made it simple. As Perl is chugging along in a subroutine, it is calculating values as part of its series of actions. Whatever calculation is last performed in a subroutine is automatically also the return value.

For example, let’s define this subroutine:

sub sum_of_fred_and_barney {
  print "Hey, you called the sum_of_fred_and_barney subroutine!\n";
  $fred + $barney;  # That's the return value
}

The last expression evaluated in the body of this subroutine is the sum of $fred and $barney, so the sum of $fred and $barney will be the return value. Here’s that in action:

$fred = 3; $barney = 4; $wilma = &sum_of_fred_and_barney; # $wilma gets 7 print "\$wilma is $wilma.\n"; $betty = 3 * &sum_of_fred_and_barney; ...
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Publisher Resources

ISBN: 9780596520106Supplemental ContentErrata Page