undef - remove a variable or function definition

- NAME
- SYNOPSIS
- DESCRIPTION

# NAME

undef - remove a variable or function definition

# SYNOPSIS

undef EXPR

undef

# DESCRIPTION

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.

undef - remove a variable or function definition