Re: [PATCH v2 01/10] t: add helper to convert object IDs to paths

From: Jeff King <peff@peff.net>
Date: Jun 18, 2019, 17:04 UTC
Message-ID: <20190618170416.GA14636@sigill.intra.peff.net>
In-Reply-To: <nycvar.QRO.7.76.6.1906181647480.44@tvgsbejvaqbjf.bet>

On Tue, Jun 18, 2019 at 06:15:46PM +0200, Johannes Schindelin wrote:

Show 8 quoted lines

> > And looking through this patch series, I see a gazillion of *new*
> > process substitutions $(test_something...) and $(basename $whatever).
> > Can't we do something about it?
> 
> I wish there was. Unix shell scripting has not evolved much in the past,
> what, 3 decades? So I don't really see a way to "pass variables by
> reference" to shell functions, short of calling `eval` (which buys
> preciously little as it _also_ has to spawn a new process [*1*]).

Really? An eval can impact the caller's state, so it _can't_ happen in a sub-process in most cases.

E.g., if I run this:

-- >8 -- #!/bin/sh

# usage: test_oid_to_path <var> <oid>
# to set the variable <var> in the caller's environment to the path of <oid>
test_oid_to_path() {
	path="${2%${2#??}}/${2#??}"
	eval "$1=\$path"
}

test_oid_to_path foo 1234abcd echo foo: $foo -- >8 --

it all happens in a single process, under both bash and dash.

-Peff