#!shebang
use strict;
use warnings;

# do ...;           # (whatever sets up the call)

call executable     # (using system, exec, backticks or ....);

# First time check for file written by executable
if (exists $thefile) {    # the file_in_line_13) {
    readit();
} else {
    sleep (some amount of time);
    goto (in some form or another) 18;
}


sub readit {
    open '<', EXEOUT, $thefile ; 
    $latest = <EXEOUT>;
    close EXEOUT;
    print "$latest \n"; # (to user);
    recheck();
}

sub recheck {
    my $timesIdential = 1;
    sleep (time);
    open '<', EXEOUT, $thefile ; 
    $newlatest = <EXEOUT>;
    if ( $newlatest ne $latest ) { 
        clearscreen (OS dependant);
        readit();
    } else {
        $timesIdentical++;
        if ($timesIdentical = n) { 
        # for some "n" sufficient to convince you 
        # that the executable is done
        clearscreen;
        print "Done\n\n" . $newlatest . "\n";
        exit();
        }
    }   
}