use strict;
use warnings;
use Win32::GUI();

my $startdir = 'C:\Users';

my $output_file = Win32::GUI::GetSaveFileName(
    -title  => "Save as...",
    -directory => $startdir,
    -file   => "output.txt",
    -filter => [
        "Text documents (*.txt)" , "*.txt", 
        "All files" , "*.*",
        ],
);

if($output_file){
    print("Using $output_file as output.");
}
else{
    print("No output file chosen.");
}