"&!“在csh中

Question

a.csh是打印某些消息的c脚本。下面这行是做什么的？

source a.csh > &! b.log

执行后，b.log文件包含a.csh的输出。但是"&!“的作用是什么呢？

Answer 1

>name将标准输出重定向到name；>&将标准输出和标准错误重定向到name，>!覆盖noclobber设置以防止意外覆盖现有文件。

它们可以组合为>&!name，以将标准输出和标准错误重定向到name，从而覆盖noclobber设置。

在您的示例中，>和&!之间的空格使其看起来像是两个不同的运算符，但实际上它只是>&!。

另请参阅man csh (搜索>&)：

   > name
   >! name
   >& name
   >&! name
           The file name is used as standard output.  If the file does not
           exist  then it is created; if the file exists, it is truncated,
           its previous contents being lost.

           If the shell variable noclobber is set, then the file must  not
           exist  or  be  a  character  special  file (e.g., a terminal or
           `/dev/null') or an error results.  This helps prevent  acciden‐
           tal  destruction  of  files.  In this case the `!' forms can be
           used to suppress this check.  If notempty is given  in  noclob‐
           ber,  `>'  is  allowed  on  empty  files;  if  ask  is  set, an
           interacive confirmation is presented, rather than an error.

           The forms involving `&' route the diagnostic  output  into  the
           specified  file  as  well  as  the  standard  output.   name is
           expanded in the same way as `<' input filenames are.

(“诊断输出”是标准错误的csh语言)。