my $str  = "mom went to the food market today and got me some milk";
my $maxl = 18;
my $show;
foreach (split(/\s+/, $str)) {
    if (length("$show $_")+3 >= $maxl) { $show .= '...' and last }
    else                               { $show .= " $_"          }
}
print substr($show, 1),"\n";