#!/bin/bash

dir=/home/me
mkdir $dir/tmp
>$dir/pid

cat $dir/file2 | while read field
do
  nohup grep $field $dir/file1 > $dir/tmp/${field}_out &   #Do grep for each field in background
  echo $! >>$dir/pid
done

#Now check if all the background process is completed
while true
do
  is_running=0 
  cat $dir/pid | while read pid
   do
    is_running=$(ps -ef  | grep $pid | grep -vc grep )
    [ $is_running -ne 0 ] && break
  done
  [ $is_running -eq 0 ] && break
  sleep 30
done

[ -f $dir/output ] && mv $dir/output $dir/output.old
>$dir/output 

for file in $dir/tmp/*_out
do
  cat $file >> $dir/output     #Make the output file from all the result
done

rm -rf $dir/tmp
rm $dir/pid