#!/bin/bash# self-exec.shechoecho "This line appears ONCE in the script, yet it keeps echoing."echo "The PID of this instance of the script is still $$."#     上邊這行展示了并沒有fork出子shell.echo "==================== Hit Ctl-C to exit ===================="sleep 1exec $0   #  產生了本腳本的另一個實例,          #+ 但是這個新產生的實例卻代替了原來的實例.echo "This line will never echo!"  # 為什么不是這樣?exit 0