Throttle background processes

Example to throttle the number of unzips running when a large number of files need to be unzipped

#!/bin/sh
cd /data/somefolder/rzips
TARD=/data/somefolder/anotherfolder
LOGF=/data/somefolder/unziplog
COUNTER=0
for z in *.zip; do
  LOGFILE=$LOGF/${z}.log
  CNTUNZIP=`ps -ef|grep -c unzip`
  while [ $CNTUNZIP -gt 51 ]; do
    sleep 1
    CNTUNZIP=`ps -ef|grep -c unzip`
  done
  let COUNTER=COUNTER+1
  echo "#: $COUNTER - Unzipping $z"
  nohup unzip $z -x LOG* -d $TARD > $LOGFILE 2>&1 &
done