bash中有什么区别beetwen $ echo Hello world>文件和$ echo Hello>文件世界？

Question

$ echo Hello world > file
$ echo Hello > file world
$ echo > file Hello world
$ > file echo Hello world

他们都做同样的事情,但我不知道为什么.

Answer 1

来自man bash:

   Simple Commands
       A  simple  command  is a sequence of optional variable assignments fol-
       lowed by blank-separated words and redirections, and  terminated  by  a
       control operator.  The first word specifies the command to be executed,
       and is passed as argument zero.  The  remaining  words  are  passed  as
       arguments to the invoked command.

也就是说,它没有指定"单词和重定向"的顺序.稍后在REDIRECTIONS部分:

REDIRECTION
       [...]
       The [...] redirection  opera-
       tors may precede or appear anywhere within a simple command or may fol-
       low a command.  Redirections are processed in the  order  they  appear,
       from left to right.
       [...]

所以它们可以出现在任

正如你自己也观察到的那样,它们在结果方面没有区别.但是在可读性方面存在差异.

这是最直观的编写方式:

echo Hello world > file

真的很容易理解.在>看起来像一个箭头,不是吗.

其他不是那么直观,不太可读.我建议坚持第一种写作风格.