how to control the multi_processor number

If you want to control the bash script’s multi process number.you can do like this
The really scene is to add user or delete user in your ubuntu os or ping the net in your computer.

#! /bin/bash

read -p "please input your prefix:" prefix

for i in {1..100}
do
        {
                sudo userdel $prefix$i 
                if [ $? -eq 0 ];then
                        echo "user $prefix$i is ok"
                else
                        echo "user $prefix$i failed"
                fi

        }&
done
wait
echo "all finished....."

if you type “bash multi.sh” in your terminal and hit the Enter key,you will find the number isn’t appear in sequence,but in a random order.

But unfortunately, if your computer is weird and can’t afford such heavy work.you can control the number of thread’s number.

please notice the change in the shell script below

#! /bin/bash
# ping 01
thread=5
tmp_fifofile=/tmp/$$.fifo #$$means the now process name
mkfifo $tmp_fifofile #make a named pipe file
exec 8<> $tmp_fifofile #allocate a file descriptor 8 to the file 
rm $tmp_fifofile
for i in `seq $thread`
do
        echo >&8 # to write a blank line to the file
done
ori_ip=192.168.2.
for i in {1..254}
do
        read -u 8 #to get the lock -u means get a file descriptor
        ip=$ori_ip$i
        {
                ping -c1 -W1 $ip &> /dev/null
                if [ $? -eq 0 ];then
                        echo "$ip is up"
                else
                        echo "$ip is down"
                fi
			    echo >&8  #to unlock the lock
        }&
done
wait
echo "all finished"
exec 8>&-    #to delete the file descriptor

if you execute this file you will notice that the result will return as five (which is equal to the thread you have set in the scripts)