Just because I haven't done Tk for a while. Probably needs some tweaking for directories and paths.

#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11130955
use warnings;
use Tk;
use Path::Tiny;

my $code;
my $file;
my $execute;

my $mw = MainWindow->new;
my $button = $mw->Button(-text => 'Execute', -command => \&execute,
  -state => 'disabled',
  )->pack(-side => 'bottom');
my $frame = $mw->Frame->pack(-fill => 'both', -expand => 1);
$frame->Label(-text => 'Perl Script', -fg => 'blue',
  )->grid(-row => 1, -column => 1, -sticky => 'ew');
$frame->Label(-text => 'Data File', -fg => 'blue',
  )->grid(-row => 1, -column => 2, -sticky => 'ew');
my $codelist = $frame->Scrolled(Listbox => -scrollbars => 'osoe',
  -exportselection => 0,
  )->grid(-row => 2, -column => 1, -sticky => 'nsew');
my $filelist = $frame->Scrolled(Listbox => -scrollbars => 'osoe',
  -exportselection => 0,
  )->grid(-row => 2, -column => 2, -sticky => 'nsew');
$frame->gridRowconfigure( 2, -weight => 1 );
$frame->gridColumnconfigure( $_, -weight => 1 ) for 1, 2;
$codelist->bind('<ButtonRelease-1>' =>
  sub {$code = $codelist->get($codelist->curselection); ready() } );
$filelist->bind('<ButtonRelease-1>' =>
  sub {$file = $filelist->get($filelist->curselection); ready() } );

sub execute
  {
  $execute++;
  $mw->destroy;
  }

sub ready { $code && $file and $button->configure(-state => 'normal') 
+}

$codelist->insert(end => sort grep -x, path('.')->children(qr/\.pl$/) 
+);
$filelist->insert(end => sort +path('.')->children(qr/\.d$/) );

MainLoop;

$execute or exit;
$code or die "no code selected";
$file or die "no file selected";
print "exec $code $file\n";
#exec 'perl', $code, $file; ### FIXME testing - uncomment to actually 
+run
die "exec failed $!";
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