一个while循环

[root@web03 server]# cat 66.sh 
#!/bin/bash

flag=true
a=0
b=0
while $flag

do

    echo "${a}"
    ((a++))
    
    while $flag
    do
        echo "$b"
        ((b++))
        
        if [ ${b} -gt 4 ]
        then
            flag=false
            echo "${flag}  99999"
        fi
    done


    sleep 3
done