You are probably way on your way with this, but I figure I would give you two examples in one. The first you will see is the Tk::FileSelect, which brings up a browser window for the user to select a file from (I prefer this solutions, simply because history has shown my not to trust the user). However, if what you are trying to do is a little more complex than you can simply implement this by using Tk::Entry, which is an easier solution than using a Textbox.

    
    #!/usr/bin/perl -w
    use Tk;
    use Tk::FileSelect;
    use strict;

    my $mw = MainWindow->new;

    #Solution #1 the next two lines!
    my $FSref = $mw->FileSelect(-directory=>"C:/");
    my $dir = $FSref->Show;

    #solution #2 up until MainLoop
    $mw->Label(-text => 'File Name: ')->pack;
    my $filename = $mw->Entry(-width => 50, -textvariable => "$dir");
    $filename->pack;

    $mw->Button(
        -text => 'Print',
        -command => sub{do_print($filename)}
    )->pack;

    MainLoop;

    #used by solution #2, to print the output to the terminal
    sub do_print {
        my ($file) = @_;
        my $file_val = $file->get;
        print "You selected $file_val\n";
    }
[download]

What you are trying to do of "anticipating the input" cannot be done, with the value being editable on the command-line.

Very strong words, considering the shell does it all the time.

There may not be a module to do this (and I am not fully convinced of this), but it most definitely can be done. At the very worst, you would need to push the prefill onto the line, and process the backspaces / ^H yourself.

Update: See Term::ReadKey as a very possible tool to use to implement this, and Re: <STDIN> "anticipate" input? points to Term::ReadLine, which also looks like it could work (see addhistory as a possible method to do this).