How to stop xargs from badly merging output from multiple processes?

GNU Parallel is specifcally designed to solve this problem:

echo -n $IPs | parallel -d ' ' -j0 wget -q -O- http://{}/somepage.html | egrep --count '^string'

If your IPs are in a file it is even prettier:

cat IPs | parallel -j0 wget -q -O- http://{}/somepage.html | egrep --count '^string'

To learn more watch the intro video: http://www.youtube.com/watch?v=OpaiGYxkSuQ

This should do the trick:

echo -n $IPs | xargs --max-args=1 -I {} --delimiter ' ' --max-procs=0 \
  sh -c "wget -q -O- 'http://{}/somepage.html' | egrep --count '^string'" | \
  { NUM=0; while read i; do NUM=$(($NUM + $i)); done; echo $NUM; }

The idea here is to make separate counts and sum these at the end. Might fail if the separate counts are big enough to be mixed, but it should not be the case.