Re: What code make both `cat < /tmp/1.txt` and `< /tmp/1.txt cat` valid?

[Koichi Murase]

 simple_command_element: WORD
        |       ASSIGNMENT_WORD
        |       redirection

2021年5月11日(火) 0:32 Peng Yu <pengyu.ut@gmail.com>:
> I am trying to understand how bash is implemented
> $ < /tmp/1.txt cat
>
> [...]
>
> I see `redirection_list` is just a list of redirection.
>
> redirection_list: redirection
>         |       redirection_list redirection
>
> But then it should be following `shell_command`. How come
> redirection_list can be anywhere in a command including the beginning?
>
> command:
> ...
>         |       shell_command redirection_list

"cat" is not "shell_command" but "simple_command". "shell_command" is
some compound commands like for, while, select, etc., and indeed we
cannot write « < file while read line; do something; done » but can
write « while read line; do something; done < file ».

« < /tmp/1.txt cat » is fits the following rules:

command:        simple_command

simple_command: simple_command_element
        |       simple_command simple_command_element

simple_command_element: WORD
        |       ASSIGNMENT_WORD
        |       redirection