Shell Programming and Scripting

oldIFS=$IFS
IFS="
"
write_snack()
{
  if a=$(grep -Fwil "$word" $snack); then
    if ! $wordfound; then
      printf "%s\n" "$word is found in: "
      wordfound=true
    fi
    printf "%s\n" "$a"
  fi
  i=0
  snack=""
}
 
snacksize=25          # Nr of files to feed to grep at a time
i=0 snack="" 
filelist=$(find /path/to/files -type f)
while read word
do
  wordfound=false
  for f in $filelist
  do
    if [ $((i+=1)) -lt $snacksize ]; then
      snack=${snack}${IFS}${f}
    else
      write_snack
    fi
  done
  if [ $i -gt 0 ]; then
    write_snack
  fi
  printf "\n"
done < input.txt > output.txt