Re: i vote for $( .. <file ) be available also as non first command in subshells ( and maybe process subst ) ?

[Chet Ramey]

On 3/12/21 8:10 AM, Greg Wooledge wrote:

> OK, first things first: $(<file) is special syntax.  It is defined to
> be equivalent to $(cat file), except that it doesn't need to exec cat(1),
> so it is marginally more efficient.

Sort of, but not in the way you think. It's not an operator, nor is it
determined lexically.  In other words, it is not this:

> It's
> a new piece of syntax that consists of three characters, but you're
> allowed to put whitespace between the second and third character.

but rather a command substitution that contains a single simple command
that consists solely of a single input redirection. This requires parsing
it, which currently happens in the subshell since that's where command
substitutions are parsed.

It looks more like this pseudo-regexp:

$\([[:blank:]]*<([!<&->]|[[:blank:]]*)[![:blank:])]*.*\)

but that doesn't exactly capture it since it doesn't take into account the
fact that `file' can be quoted, and it's tricky to capture the restriction
that the character immediately following the `<' can be anything but a
character that defines a different redirection operator. I need better
regexp-fu to write the correct one.

Chet

--
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/