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命令后的这些符号“$@”>/dev/null 2>&1”是什么意思？

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命令后的这些符号“$@”>/dev/null 2>&1”是什么意思？

我最近在这里找到了解决我的问题的方法，但我不能完全理解这个命令中的所有内容的含义：

xdg-open "$@">/dev/null 2>&1

答案1

“$@”

"$@"相当于"$1" "$2" ...（命令的位置参数，当参数中有特殊字符（例如空格）时适用）。

从man bash：

   Special Parameters
       The shell treats several parameters specially.  These parameters may  only
       be referenced; assignment to them is not allowed.
       *      Expands  to the positional parameters, starting from one.  When the
              expansion is not within double quotes,  each  positional  parameter
              expands  to  a  separate  word.  In contexts where it is performed,
              those words are subject to  further  word  splitting  and  pathname
              expansion.   When  the  expansion  occurs  within double quotes, it
              expands to a single word with the value of each parameter separated
              by  the first character of the IFS special variable.  That is, "$*"
              is equivalent to "$1c$2c...", where c is the first character of the
              value  of  the  IFS  variable.  If IFS is unset, the parameters are
              separated by spaces.  If IFS is null,  the  parameters  are  joined
              without intervening separators.
       @      Expands  to the positional parameters, starting from one.  When the
              expansion occurs within double quotes, each parameter expands to  a
              separate  word.   That  is, "$@" is equivalent to "$1" "$2" ...  If
              the double-quoted expansion occurs within a word, the expansion  of
              the first parameter is joined with the beginning part of the origi‐
              nal word, and the expansion of the last parameter  is  joined  with
              the  last  part of the original word.  When there are no positional
              parameters, "$@" and $@ expand to nothing (i.e., they are removed).

>

将标准输出重定向到文件

/dev/null

这个特殊文件意味着输出将被重定向到“无任何地方”，换句话说，不会写入任何地方。

请参阅man null此处了解更多详情。

2>

将错误输出重定向到文件

2>&1

将错误输出重定向到标准输出

从man bash：

   Note that the order of redirections is significant.  For example, the com‐
   mand

          ls > dirlist 2>&1

   directs both standard output and standard error to the file dirlist, while
   the command

          ls 2>&1 > dirlist

   directs only the standard output to file  dirlist,  because  the  standard
   error  was  duplicated from the standard output before the standard output
   was redirected to dirlist.

答案2

  • "$@"：脚本或函数调用的所有参数。
  • >: 表示重定向stdout（与 相同1>）。
  • >/dev/null: 表示重定向stdout到/dev/null，也就是丢弃输出。
  • 2>&1将 errout( 2>) 重定向到 stdout( &1)。

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