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Do you know where your variables are?


by gods
on Aug 24, 1999 at 22:42 UTC ( #271=perlfunc: print w/replies, xml ) Need Help??


See the current Perl documentation for undef.

Here is our local, out-dated (pre-5.6) version:

undef - remove a variable or function definition

undef EXPR


Undefines the value of EXPR, which must be an lvalue. Use only on a scalar value, an array (using ``@''), a hash (using ``%''), a subroutine (using ``&''), or a typeglob (using ``<*>''). (Saying undef $hash{$key} will probably not do what you expect on most predefined variables or DBM list values, so don't do that; see the delete manpage.) 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;
    undef *xyz;       # destroys $xyz, @xyz, %xyz, &xyz, etc.
    return (wantarray ? (undef, $errmsg) : undef) if $they_blew_it;
    select undef, undef, undef, 0.25;
    ($a, $b, undef, $c) = &foo;       # Ignore third value returned

Note that this is a unary operator, not a list operator.

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[Corion]: Sane Dots Supplies - your brand manufacturer for satisfying experiences!
[choroba]: preparing the trip to Vietnam + buying a new car = enough fun
[Corion]: choroba: Yeah, that's a lot of "fun" for one week...
[Corion]: I guess I should stage some product photos for Sane Dots Supplies ;)
[marto]: I had some ideas about that Corion
[marto]: I'll send a message over the weekend maybe :P
[Corion]: choroba: I avoided the "fun" of emergency shopping for a new flat iron by trying the flat iron without the timer that sat between it and the mains power. Seems as if just the timer is broken.
[Corion]: marto: Heh, would be cool!

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