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如何在后台等待后台作业？

tag-icon • tag-icon bash background-process jobs
如何在后台等待后台作业？

我有以下问题：

$ some_command &     # Adds a new job as a background process
$ wait && echo Foo   # Blocks until some_command is finished
$ wait && echo Foo & # Is started as a background job and is done immediately

我想做的wait &是在后台等待，直到所有其他后台作业完成了。

我有什么办法可以实现这一目标吗？

答案1

在某些时候，某些东西必须等待命令的执行。
但是，如果您可以将命令放在几个函数中，则可以安排它们执行您需要的操作：

some_command(){
    sleep 3
    echo "I am done $SECONDS"
}

other_commands(){
    # A list of all the other commands that need to be executed
    sleep 5
    echo "I have finished my tasks $SECONDS"
}

some_command &                      # First command as background job.
SECONDS=0                           # Count from here the seconds.
bg_pid=$!                           # store the background job pid.
echo "one $!"                       # Print that number.
other_commands &                    # Start other commands immediately.
wait $bg_pid && echo "Foo $SECONDS" # Waits for some_command to finish.
wait                                # Wait for all other background jobs.
echo "end of it all $SECONDS"       # all background jobs have ended.

如果睡眠时间如代码 3 和 5 所示，则 some_command 将在其余作业之前结束，并且将在执行时打印：

one 760
I am done 3
Foo 3
I have finished my tasks 5
end of it all 5

如果睡眠时间为（例如）8 和 5，则将打印以下内容：

one 766
I have finished my tasks 5
I am done 8
Foo 8
end of it all 8

注意顺序。事实上，每个部分都已尽可能结束（$SECONDS打印的价值）。

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