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.
If rather than formatting bugs, you encounter substantive content errors in these documents, such as mistakes in the explanations or code, please use the perlbug utility included with the Perl distribution.