On Sun, Nov 17, 2024, at 1:16 PM, Mike Peters wrote:
> On 2024-11-16 22:56, Lawrence Velázquez wrote:
>> Be aware that <(<file) is undocumented and was removed [1] after
>> Emanuele brought it up [2]; it will not work in future releases.
>
> I don't know what documentation it was missing from, but this usage is
> consistent and logically valid with the manual... Process substitution
> 'takes the form of <(list) or >(list)'. The grammar defines 'list' to
> be 'a sequence of one or more pipes', a 'pipeline' to be 'a sequence of
> one or more commands'. Command substitution takes the form $(command)
> or `command`, and since `<file` is valid as specified by the cat
> shortcut, <file must be a valid simple command. SIMPLE COMMAND
> EXPANSION explicit allows redirections*: "If no command name results,
> redirections are performed, but do not affect the current shell
> environment." Thus the manual's grammar technically does document the
> validity of <(<file).
I wasn't clear. <(<file) remains valid syntactically, but it no
longer behaves like <(cat file).
> I hope it's removal is documented in the manual.
The removed behavior was not documented to begin with.
>> There might be an argument for it if the documentation read:
>>
>> The command substitution $(cat <file) can be replaced by
>> the equivalent but faster $(<file).
>>
>> But it doesn't.
>>
>
> I disagree. The REDIRECTION section of the manual uses the word 'word'
> when it might refer to either a file descriptor or a file, so I think
> "there might be an argument" if the declaration involved incorporating
> 'word' in place of 'file'.
That wouldn't really make a difference. The important changes would
be adding a redirection to the first substitution and removing the
space from the second. A simple "file"/"word" swap wouldn't justify
the confusion...
The command substitution $(cat word) can be replaced by the
equivalent but faster $(< word).
...since $(cat &3) and $(< &3) are still nonsense.
(Also, in the manual "&n" is never a valid substitution for "word".)
--
vq
