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perlfunc:undef

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

undef

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

undef



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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[vrk]: Hope he gets better soon.
[Discipulus]: hdb sorry i profit; is known that a prime number is never a figurate one nor the sumattion of two adjacent figurates of the same order? like 3th triangular+3th tetrahedric
[Discipulus]: if known where i can read about the matter?
[choroba]: he's not really sick, we just got nobody to look after him today
[Discipulus]: create an account for him; we are funny baby sitters ;=) come here child, want to listen the typeglob tale?
[vrk]: choroba Oh, that's good.
[vrk]: Discipulus I don't know much about prime numbers, but wouldn't that kind of an answer be in a graduate-level number theory book?
[Discipulus]: my 8 yo daughter has two weeks of sleep disturbs.. we are gonna be crazy..

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