Syntax for specifying a command in git config

> Certain git config parameters (notably sendemail.smtpServer) expect an
> absolute path in order to use a command. If the value begins with a / git
> interprets it as a command; otherwise, it's interpreted it as a server
> hostname.
> 
> Using an absolute path is not very portable, however. If I want to have a
> common shared config file across multiple machines, each of which uses a
> command for smtpServer (e.g. msmtp) but installed at different locations, I
> have to modify the config file on each machine to update the absolute path.
> 
> Obviously this is not a *huge* deal, but it is a minor annoyance. I'm
> wondering if it would be possible to add a new syntax to config options like
> this. For example,
> 
>     [sendemail]
>             smtpServer = !msmtp
> 
> The leading ! character says "the following value is a command that should
> be looked up in PATH". This is congruent with alias definitions, where the
> leading ! means to run the following value as a command directly instead of
> as a git subcommand.
> 
> This also is unambiguous since server hostnames will never begin with a !
> character.

>> Obviously this is not a *huge* deal, but it is a minor annoyance. I'm
>> wondering if it would be possible to add a new syntax to config options like
>> this. For example,
>> 
>>     [sendemail]
>>             smtpServer = !msmtp
>> 
>> The leading ! character says "the following value is a command that should
>> be looked up in PATH". This is congruent with alias definitions, where the
>> leading ! means to run the following value as a command directly instead of
>> as a git subcommand.
>> 
>> This also is unambiguous since server hostnames will never begin with a !
>> character.
>
> IMHO this is a good path forward. There's a thread from a few months ago
> which talks about this idea:
>
>   https://lore.kernel.org/git/YCvotU6KVruFuf9%2F@coredump.intra.peff.net/
>
> There's some back and forth, and I'm not sure if I convinced Junio in
> the end. But certainly a patch would be a good way to restart the
> conversation. :)

> > IMHO this is a good path forward. There's a thread from a few months ago
> > which talks about this idea:
> >
> >   https://lore.kernel.org/git/YCvotU6KVruFuf9%2F@coredump.intra.peff.net/
> >
> > There's some back and forth, and I'm not sure if I convinced Junio in
> > the end. But certainly a patch would be a good way to restart the
> > conversation. :)
> 
> The argument is not just about configuration but applies equally to
> its command line argument "--smtp-server=<what>", right?  I think it
> makes sense in both of these places.  I further wonder if we should
> allow not just a single token, but supplying an initial few arguments,
> too, e.g.
> 
> 	git send-email --smtp-server="/usr/bin/env msmtp"
> 	git send-email --smtp-server="!my-msa --emulate-sendmail"

>> 	git send-email --smtp-server="/usr/bin/env msmtp"
>> 	git send-email --smtp-server="!my-msa --emulate-sendmail"
>
> Yes, the patch under discussion does apply to both the command-line
> option and the config option (and I agree it should).
>
> I didn't think about arguments, but you're right that may be a useful
> feature. And if done via the shell, as brian suggested elsewhere, would
> be more consistent with other parts of Git using "!" syntax.

> It does make things a little weird in that:
>
>   git send-email --smtp-server='/path/to/my-sendmail foo'
>
> and
>
>   git send-email --smtp-server '!my-sendmail foo'
>
> behave differently (the first does not work; it looks for an executable
> with a space in the name).