“fg”代表什么？

Question

ctrl-z 或 fg 没有手动输入。

“fg”在作业控制的上下文中代表什么？换句话说，输入 ctrl-z 将挂起当前作业，让我回到 shell，命令“fg”重新激活挂起的作业。“fg”代表什么？

Answer 1

前景。

与其他的bash内置插件，还有就是 help它：

$ help fg
fg: fg [job_spec]
    Move job to the foreground.

    Place the job identified by JOB_SPEC in the foreground, making it the
    current job.  If JOB_SPEC is not present, the shell's notion of the
    current job is used.

    Exit Status:
    Status of command placed in foreground, or failure if an error occurs.
$ 

此外，bgisBackGround和 ^z 位于bash手册页中的作业控制下：

   If  the operating system on which bash is running supports job control,
   bash contains facilities to use it.  Typing the suspend character (typ?
   ically ^Z, Control-Z) while a process is running causes that process to
   be stopped and returns control to bash.   Typing  the  delayed  suspend
   character  (typically  ^Y,  Control-Y) causes the process to be stopped
   when it attempts to read input from the terminal,  and  control  to  be
   returned  to bash.  The user may then manipulate the state of this job,
   using the bg command to continue it in the background, the  fg  command
   to continue it in the foreground, or the kill command to kill it.  A ^Z
   takes effect immediately, and has the additional side effect of causing
   pending output and typeahead to be discarded.