simple introduction for pipe line

1. multiple commands execute in order

        command1 ; command2         no logic   ->  execute commands in order

        command1 && command2    logic and ->  execute command1, if correct then execute command2, if error then dont execute command2

        command1 || command2       logic or    ->   execute command1, if error then execute command2, if correct then dont execute command2

                eg.   command && echo yes|| echo no

2. pipe line operator

        command1 | command2     the output correct rusult of command1 as the operation object of command2

                eg.  ll -a /etc | more

                eg.  netstat -an | grep "ESTABLISHED" | wc -l