### 9.1 Global Variables

A variable that has been declared global may be accessed from within a function body without having to pass it as a formal parameter.

A variable may be declared global using a `global` declaration statement. The following statements are all global declarations.

         global a
         global a b
         global c = 2
         global d = 3 e f = 5

A global variable may only be initialized once in a `global` statement. For example, after executing the following code

         global gvar = 1
         global gvar = 2

the value of the global variable `gvar` is 1, not 2.

It is necessary declare a variable as global within a function body in order to access it. For example,

         global x
         function f ()
           x = 1;
         endfunction
         f ()

does not set the value of the global variable `x` to 1. In order to change the value of the global variable `x`, you must also declare it to be global within the function body, like this

         function f ()
           global x;
           x = 1;
         endfunction

Passing a global variable in a function parameter list will make a local copy and not modify the global value. For example, given the function

         function f (x)
           x = 0
         endfunction

and the definition of `x` as a global variable at the top level,

         global x = 13

the expression

         f (x)

will display the value of `x` from inside the function as 0, but the value of `x` at the top level remains unchanged, because the function works with a copy of its argument.

— Built-in Function: isglobal (name)

> Return 1 if name is globally visible. Otherwise, return 0. For example,

>               global x
>               isglobal ("x")
>                    => 1