Selpg writes pages 10 to 20 to its stdout , which is redirected to " output file " ; whatever selpg writes to stderr is redirected to dev null , the null device , which means that error messages are thrown away Selpg将第10页到第20页写至标准输出,标准输出被重定向至“ output _ file ” ; selpg写至标准错误的所有内容都被重定向至/ dev / null (空设备) ,这意味着错误消息被丢弃了。