[RFC] Explicity-remote commands in Eshell

[Jim Porter]

One of the nice features of Eshell is that since it's aware of Tramp, 
connecting to a different machine (or changing users on a machine) is 
just a matter of cd'ing into a remote directory:

  cd /ssh:user@somewhere:~/some/dir

In addition, Eshell routes data in pipelines through buffers. In 
principle, this means it should be easy to build cross-host pipelines in 
Eshell, where the output of a command on host A is piped into the input 
of a command on host B. However, it's not easy to spell this in Eshell; 
the best I can come up with is to use a subshell like this:

  {cd /ssh:user@somewhere: && remote-command} | local-command

Instead, I think we could make this easier:

  /ssh:user@somewhere:remote-command | local-command

What do people think of the above syntax? It's a little bit different 
from the usual Tramp syntax, since the local part shouldn't be expanded 
using 'expand-file-name'; it's an executable somewhere on the remote 
$PATH. I can't think of any problems with supporting this syntax in 
Eshell[1], but I'm interested to hear others' thoughts.

Attached is a patch demonstrating this. The only non-Eshell change I had 
to make was to enhance 'file-remote-p' so that I can tell Tramp not to 
call 'expand-file-name'.

As a footnote: you might wonder how to execute a program on your local 
host when the current Eshell directory is remote. In my patch, I chose 
to do this via quoted file names:

  /:local-command

[1] Tramp shouldn't need to know about this syntax in other places. It 
can just be something Eshell understands.

0001-Add-support-for-explicitly-remote-commands-in-Eshell.patch
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