Question

我是linux bash的新手，这是一个令我困惑的问题。我不明白＆＃34; hash wget＆＃34;。它的目的是什么，为什么应该进行if检查？

if [ ! -e text8 ]; then
  if **hash wget 2>/dev/null**; then
    wget http://mattmahoney.net/dc/text8.zip
  else
    curl -O http://mattmahoney.net/dc/text8.zip
  fi
  unzip text8.zip
  rm text8.zip
fi

Answer 1

如果wget可用（在PATH中），则hash wget的退出代码为0，因此语句将执行。重定向2>/dev/null只是在找不到wget时重定向错误消息。使用bash提示符中的help hash来阅读其信息。

Answer 2

在命令行中键入help hash。

XXXXX @ ubuntu：〜$ help hash hash：hash [-lr] [-p路径名] [-dt] [名称...] 记住或显示程序位置。

Determine and remember the full pathname of each command NAME.  If
no arguments are given, information about remembered commands is displayed.

Options:
  -d        forget the remembered location of each NAME
  -l        display in a format that may be reused as input
  -p pathname   use PATHNAME as the full pathname of NAME
  -r        forget all remembered locations
  -t        print the remembered location of each NAME, preceding
        each location with the corresponding NAME if multiple
        NAMEs are given
Arguments:
  NAME      Each NAME is searched for in $PATH and added to the list
        of remembered commands.

Exit Status:
Returns success unless NAME is not found or an invalid option is given.

如何理解哈希wget？

2 个答案: