The FileSelect widget appears to accept the "selectmode" configuration option. Its accepted values are the same as for Tk::Listbox. Here's a sample:

use Tk::FileSelect;

my $main = Tk::MainWindow->new;
my $fsRef = $main->FileSelect(-directory => '/',
                              -selectmode => 'extended');
my @files = $fsRef->Show;
print foreach @files;
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The selectmode "extended" should allow you to select multiple files with Ctrl and Shift keys as you expect.

buckaduck