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Perl in a Nutshell, 2nd Edition
book

Perl in a Nutshell, 2nd Edition

by Nathan Patwardhan, Ellen Siever, Stephen Spainhour
June 2002
Beginner content levelBeginner
759 pages
80h 42m
English
O'Reilly Media, Inc.
Content preview from Perl in a Nutshell, 2nd Edition

Name

defined

Synopsis

defined expr
                  

Returns a Boolean value saying whether the scalar value resulting from expr has a real value. If no argument is given, defined checks $_.

A scalar that contains no valid string, numeric, or reference value is known as the undefined value, or undef. Many operations return the undefined value under exceptional conditions, such as end-of-file, uninitialized variable, system error, and so on. This function allows you to distinguish between an undefined null string and a defined null string when you’re using operators that might return a real null string.

You can use defined to see if a subroutine exists, that is, if the subroutine definition has been successfully parsed. However, using defined on an array or a hash is not guaranteed to produce intuitive results and should be avoided.

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Publisher Resources

ISBN: 0596002416Errata Page