在后台运行进程，直到在bash脚本中停止

Question

我有一个bash脚本，该脚本执行一系列命令来修改文件系统上的文件。我想在运行这些命令的同时运行后台进程，以便在另一个实例已经运行时无法调用我的bash脚本。

几乎类似以下内容：

#!/bin/bash
if pgrep mystery_background_cmd; then
    echo 'The file is being modified right now. Exiting.'
fi
<script commands here>
bg_pid="$( mystery_background_cmd & echo "${!}" )"
<do other commands here>
kill "${bg_pid}"

因此，实际上：

$ ./script.sh &
Modifying files...
$ ./script.sh &
The file is being modified right now. Exiting.

或者更好的是，像这样：

$ ./script.sh &
Modifying files... # 1st instance
$ ./script.sh & 
The file is being modified right now. Seconds until re-check: {5..1} # 2nd instance
The file is being modified right now. Seconds until re-check: {5..1} # 2nd instance
Finished modifying! # 1st instance
Modifying files... # 2nd instance

我正在使用bash 3.2.57（1）-release和macOS High Sierra 10.13.6。