head1     head2     head3
 a         b         c
           c
 c                   a

head1 head2 head3
a b c
- c -
c - c

perl -ne '
    while (length) {
        ($word = substr($_,0,10)) =~ s/^s+|s+$//g; # trim whitespace
        $word ||= "-";
        print $word, " ";
        substr($_,0,10) = "";
    }
    print "n";
' file

sed 's/^ //g' input | tr -s "[:blank:]" "," |
awk -F, '!$1{printf "- "} $1{printf "%s ", $1}
  !$2{printf "- "} $2{printf "%s ", $2}
  !$3{print "-"} $3{print $3}'