- 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 delete.) 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
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Note that this is a unary operator, not a list operator.
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