Shell script for scheduling jobs

Suppose you want to schedule many runs of myscript.py for different parameters, but never more than 8 at a time (e.g. because your machine has only 8 processor cores), then you can do:

 for param in `cat params.txt`; do  
   # wait if more than 7 jobs are running together  
   njobs=`ps aux | grep myscript | wc -l`  
   if [ $njobs -gt 8 ]; then          # 7 jobs + 1 grep  
     while [ $njobs -gt 8 ]; do  
       sleep 10  
     done  
   fi  
   python myscript.py param &     # schedule background job here  
 done