如何重定向嵌套的linux命令输出

Question

我有点想达到这样的目的：
time (curl -s $url > /dev/null) >> out.txt
而 curl 输出将被删除，我保存时间的输出

Answer 1

试试这个：

{ time curl -s &url ;} 2>> out.txt

Answer 2

curl提供了一个指定输出的选项：

   -o, --output <file>
          Write output to <file> instead of stdout. If you are using {} or
          [] to fetch multiple documents, you can use '#'  followed  by  a
          number  in  the <file> specifier. That variable will be replaced
          with the current string for the URL being fetched. Like in:

利用它，并说：

time curl -s $url -o /dev/null >> out.txt