sub myGlobalInit
... do things ... and ...
$globalInitialDir = a value;
$globalSelectedDir = a value;
$globalMyWindow = Tk::MainWindow->new;
end sub

sub myGlobalaskforFile
...
if defined ($globalInitialDir)
# user not specified any preference - use our default
localInitDir = globalInitialDir 
filename = globalMyWindow -> getOpenFile (-initialdir => $localInitDir )
else
if defined ($globalSelectedDir)
# use what the user has selected before as our 'base'
localInitDir = globalSelectedDir
filename = globalMyWindow -> getOpenFile (-initialdir => $localInitDir )

return filename
end sub

In project modules ...
myGlobalInit();
# set up a default for globalInitialDir that differs from the default set up in the above call
$globalInitialDir = some value that I specify
file = myGlobalaskForFile ()
...