Daftar Isi

• undef EXPR

• undef

  Undefines the value of EXPR, which must be an lvalue. Use only on ascalar 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 orDBM list values, so don't do that; see delete. Always returns theundefined value. You can omit the EXPR, in which case nothing isundefined, but you still get an undefined value that you could, forinstance, return from a subroutine, assign to a variable, or pass as aparameter. 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.