Parallel bash loop over files

parallel.sh

# USAGE:
# ./parallel.sh <command> <input directory> [<threads> [<log file>]]
#
# EXAMPLE:
# ./parallel.sh longrunningcommand.java /myfiles/input/ 10 process.log
shell_command=$1
input_dir=$2
threads=$3
threads=${threads:=10}
output_log=$4
output_log=${output_log:="files_processed.log"}
rm -f ${output_log}
find ${input_dir} -name '*' -type f -print0 | while read -d $'\0' file
do
   ((i=i%threads)); ((i++==0)) && wait
   ${shell_command} ${file} &
   if [ $? -eq 0 ]; then
       echo "${file}\tOK" >> ${output_log}
   else
       echo "${file}\tFAIL" >> ${output_log}
   fi   
done

shell_command is the command that's executed over files.

A log is maintained over all the processed files.