Re: Why can redirection be combined in an assignment statement?

[Eli Schwartz]

On 5/10/21 2:33 PM, Andreas Kusalananda Kähäri wrote:
> On Mon, May 10, 2021 at 11:16:59AM -0500, Peng Yu wrote:
>>>         $ reverse=false; if "$reverse"; then a=$(rev); else a=$(cat); fi 
>>> <<<"hello"; echo "$a"
>>>         hello
>>>         $ reverse=true; if "$reverse"; then a=$(rev); else a=$(cat); fi 
>>> <<<"hello"; echo "$a"
>>>         olleh
>>
>> I am talking about combining just assignment and redirection, which
>> comes from these rules.
>>
>> simple_command_element: WORD
>> | ASSIGNMENT_WORD
>> | redirection
>> ;
>>
>> simple_command: simple_command_element
>> | simple_command simple_command_element
>> ;
>>
>> Your example is not about this case. Therefore, it does not serve the
>> purpose of justifying combining assignment and redirection.
> 
> Hm...  I think that
> 
>       a=$(cat) <<<"hello"
> 
> is exactly this.  You may replace <<<"hello" by <somefile if you wish.

Outside of the if/else/fi, cat waits until you enter CTRL+D, then quits
and emits nothing; $a is "".

This works though:

{ a=$(cat); } <<< "hello"

But the redirection is being read by the {} group command in order to
let the variable assignment access it.

-- 
Eli Schwartz
Arch Linux Bug Wrangler and Trusted User

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