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特殊变量 命令 意义 $# 传递到脚本的参数列表
$? 前个命令执行情况,0成功,其它值失败 $$ 脚本运行的当前进程号 $! 运行脚本最后一个命令 $* 显示脚本全部参数
by dradhzn
1 - denotes stdout ( standard output )
2 - denotes stderr ( standard error ) /dev/null . apparently is null , nothing , empty , zero etc , etc . 2>/dev/null - redirect stderr to nothing , it turns stderr off. >/dev/null 2>&1 also can write as 1>/dev/null 2>&1 - stdout redirect to /dev/null (no stdout) ,and redirect stderr to stdout (stderr gone as well) . end up it turns both stderr and stdout off a little practice may help to undstand above . #ls /usr /nothing #ls /usr /nothing 2>/dev/null #ls /usr /nothing >/dev/null 2>&1
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