icon Top 9 categories map      RocketAware > Perl >

undef EXPR

Tips: Browse or Search all pages for efficient awareness of Perl functions, operators, and FAQs.



Home

Search Perl pages


Subjects

By activity
Professions, Sciences, Humanities, Business, ...

User Interface
Text-based, GUI, Audio, Video, Keyboards, Mouse, Images,...

Text Strings
Conversions, tests, processing, manipulation,...

Math
Integer, Floating point, Matrix, Statistics, Boolean, ...

Processing
Algorithms, Memory, Process control, Debugging, ...

Stored Data
Data storage, Integrity, Encryption, Compression, ...

Communications
Networks, protocols, Interprocess, Remote, Client Server, ...

Hard World
Timing, Calendar and Clock, Audio, Video, Printer, Controls...

File System
Management, Filtering, File & Directory access, Viewers, ...

    
undef EXPR
undef
Undefines the value of EXPR, which must be an lvalue. Use only on a scalar value, an entire array, an entire hash, or a subroutine name (using ``&''). (Using undef() will probably not do what you expect on most predefined variables or DBM list values, so don't do that.) Always returns the undefined value. You can omit the EXPR, in which case nothing is undefined, but you still get an undefined value that you could, for instance, return from a subroutine, assign to a variable or pass as a parameter. Examples:

    undef $foo;
    undef $bar{'blurfl'};             # Compare to: delete $bar{'blurfl'};
    undef @ary;
    undef %hash;
    undef &mysub;
    return (wantarray ? (undef, $errmsg) : undef) if $they_blew_it;
    select undef, undef, undef, 0.25;
    ($a, $b, undef, $c) = &foo;       # Ignore third value returned

Source: Perl builtin functions
Copyright: Larry Wall, et al.
Next: unlink LIST

Previous: umask EXPR



(Corrections, notes, and links courtesy of RocketAware.com)


[Overview Topics]

Up to: PERL




Rapid-Links: Search | About | Comments | Submit Path: RocketAware > Perl > perlfunc/undef.htm
RocketAware.com is a service of Mib Software
Copyright 2000, Forrest J. Cavalier III. All Rights Reserved.
We welcome submissions and comments