global - Man Page

global ?varname ...?

This command has no effect unless executed in the context of a proc body. If the global command is executed in the context of a proc body, it creates local variables linked to the corresponding global variables (though these linked variables, like those created by upvar, are not included in the list returned by info locals).

If varname contains namespace qualifiers, the local variable's name is the unqualified name of the global variable, as determined by the namespace tail command.

varname is always treated as the name of a variable, not an array element.  An error is returned if the name looks like an array element, such as a(b).

This procedure sets the namespace variable ::a::x

proc reset {} {
    global a::x
    set x 0
}

This procedure accumulates the strings passed to it in a global buffer, separated by newlines.  It is useful for situations when you want to build a message piece-by-piece (as if with puts) but send that full message in a single piece (e.g. over a connection opened with socket or as part of a counted HTTP response).

proc accum {string} {
    global accumulator
    append accumulator $string \n
}

namespace(n), upvar(n), variable(n)

global, namespace, procedure, variable

info(n), set(n), upvar(n), variable(n), vwait(n).