Errexit: if a command has an exit status of anything but 0 (zero), execute the err trap (if it is set and exists).

errexit：如果某个命令产生非0(零)的退出状态并且设置了err陷阱，则执行err陷阱并退出。

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The ERR goes with the signal list within the trap command. In the following example, a non-existent file is copied, which invokes an error

ERR 在 trap 命令中提供了一个信号列表。

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