my $filename = take_user_input();

$filename =~ s/\W//g; # allows only alphanumerics and the  underscore

$filename = $filename . ".txt"; # forces them to only open .txt files

if (-T $filename) # checks to see if the file is a text file
{
  open IN, "<", $filename or die &cant_open_file;
  print join "", <IN>;
  close IN;
}

else
{
  &cant_open_file;
}