Linux Unix 命令行上的 2> 是什么意思？
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What does the 2> mean on the Unix command-line?
提问by Smith
scriptlist=`ls $directory_/fallback_* 2> /dev/null`
What exactly is the purpose of the 2>part of the command?
I omitted it and ran the command, it just works fine.
2>命令部分的目的究竟是什么？我省略了它并运行了命令，它工作正常。
And, if the output of ls is getting stored in /dev/null file, what exactly the variable scriptlistwill contain.
When I executed the code, the output was in the variable and nothing was there in file null. If we remove 2, then output is in file instead of variable.
Any idea what exactly this line of code doing?
并且，如果 ls 的输出存储在 /dev/null 文件中，那么该变量scriptlist将包含什么内容。当我执行代码时，输出在变量中，而在 file 中没有任何内容null。如果我们删除2，则输出在文件中而不是变量中。知道这行代码到底在做什么吗？
回答by devnull
any idea what exactly the '2' is doing over here
知道这里的“2”到底在做什么
Here 2is a file descriptor referring to STDERR.
这2是一个文件描述符，引用STDERR.
2> /dev/nullimplies that STDERRbe redirected to the null device /dev/null.
2> /dev/null意味着STDERR被重定向到空设备/dev/null。
The complete line you've mentioned stores the output, i.e. STDOUT(ignoring the STDERR), returned by ls $directory_/fallback_*into the variable scriptlist.
您提到的完整行存储输出，即STDOUT（忽略STDERR），返回ls $directory_/fallback_*到变量scriptlist。
回答by Yu Hao
File descriptor 2represents standard error. (other special file descriptors include 0for standard input and 1for standard output).
文件描述符2代表标准错误。（其他特殊文件描述符包括0标准输入和1标准输出）。
2> /dev/nullmeans to redirect standard error to /dev/null. /dev/nullis a special device that discards everything that is written to it.
2> /dev/null意味着将标准错误重定向到/dev/null. /dev/null是一种特殊的设备，它会丢弃写入其中的所有内容。
Putting all together, this line of code stores the standard output of command ls $directory_/fallback_* 2> /dev/nullinto the variable scriptlist, and the standard error is discarded.
综上所述，这行代码将 command 的标准输出存储ls $directory_/fallback_* 2> /dev/null到变量 中scriptlist，并丢弃标准错误。
回答by Suvarna Pattayil
scriptlist=`ls $directory_/fallback_* 2> /dev/null`
As you have enclosed the whole line ls $directory_/fallback_* 2> /dev/nullin backticks,
the output of the lscommand is stored in scriptlistvariable.
由于您ls $directory_/fallback_* 2> /dev/null用反引号将整行括起来，因此ls命令的输出存储在scriptlist变量中。
Also, the 2>is for redirectingthe output of stderrto /dev/null(nowhere).
