#!/usr/bin/env perl
use warnings;
use strict;

$| = 1;                         # enable auto-flush

my $count = $ARGV[0] // 10;     # init count to 10 if no args

countdown($count);              # do the thing

sub countdown {
    my ($ct) = @_;              # force list context with ($ct)
    $ct = abs($ct);             # sanitize input w absolute value
    while ($ct--) {             # run loop while $ct is truthy
        print "\r\033[K$ct";    # clear whole line each iteration
        nap(.1);                # sub-second sleep timer hack ~100ms
    }
    print "...done!";           
}

# some perl magic
sub nap {
    my ($naptime) = @_;
    select(undef,undef,undef,$naptime);
}