Skip to Main Content
Perl Pocket Reference, 5th Edition
book

Perl Pocket Reference, 5th Edition

by Johan Vromans
July 2011
Intermediate to advanced content levelIntermediate to advanced
104 pages
2h 14m
English
O'Reilly Media, Inc.
Content preview from Perl Pocket Reference, 5th Edition

Subroutines

Subroutines need a declaration, i.e., a specification of how they should be called, and a definition, i.e., a specification of what they should do when called.

sub name [ ( proto ) ] [ attributes ] ;

Declares name as a subroutine, optionally specifying the prototype and attributes. Declaring a subroutine is optional, but allows the subroutine to be called just like Perl’s built-in operators.

sub [ name ] [ ( proto ) ] [ attributes ] block

Defines subroutine name, with optional prototype and attributes. If the subroutine has been declared with a prototype or attributes, the definition should have the same prototype and attributes. When name is omitted, the subroutine is anonymous and the definition returns a reference to the code.

When a subroutine is called, the statements in block are executed. Parameters are passed as a flat list of scalars as array @_. The elements of @_ are aliases for the scalar parameters. The call returns the value of the last expression evaluated. wantarray (page 11) can be used to determine the context in which the subroutine was called.

Subroutines that have an empty prototype and do nothing but return a fixed value are inlined, e.g., sub PI() { 3.1415 }. See also the subsection Prototypes.

attributes are introduced with a : (colon). Perl supports the following attributes:

lvalue

The subroutine returns a scalar variable that can be assigned to.

method

The subroutine is a method.

There are several ways to call a subroutine.

name ( [ parameters ] )

The most ...

Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Start your free trial

You might also like

Perl Testing: A Developer's Notebook

Perl Testing: A Developer's Notebook

Ian Langworth, Chromatic
Perl Hacks

Perl Hacks

Chromatic, Damian Conway, Curtis Ovid Poe, Curtis (Ovid) Poe

Publisher Resources

ISBN: 9781449311186Errata Page