Linux command to repeat a string n times

Yes this is possible. Bash has a very extensive scripting language. In this case:

for i in {1..100}; do echo 'hello'; done

More looping examples: http://www.cyberciti.biz/faq/bash-for-loop/
Full bash reference: http://www.gnu.org/software/bash/manual/bashref.html

In AWK, you could do something like this:

awk '($1 == last) || (last == "") {sum += $2}
     ($1 != last) && (last != "") {print last " " sum; sum = $2}
                                  {last = $1}
     END                          {print last " " sum}' huge_text_file.txt