[9fans] tip'o'day -- hack

[9fans] tip'o'day -- hack

[Tim Newsham]

This one's from Mike Haertel as described in:

   http://tinyurl.com/arnnd

Thanks for Andrey for pointing this out.  You can establish a two
way pipe to a command in /srv:

   $ cmd <[0=1] | echo 0 > /srv/name

and then access /srv/name to communicate with the command.  As
an example:

   $ mail <[0=1] | echo 0 > /srv/mailcons
   $ con -l /srv/mailcons
   ... connected to mail until ^\ quit ...
   $ con -l /srv/mailcons
   ... connected again ...

will let you detach and re-attach to the pipe to a long-lived
mail command.

Tim Newsham
http://www.lava.net/~newsham/

Re: [9fans] tip'o'day -- hack

[David Leimbach]

that's just cool

On 4/21/05, Tim Newsham <newsham@lava.net> wrote:
> This one's from Mike Haertel as described in:
> 
>    http://tinyurl.com/arnnd
> 
> Thanks for Andrey for pointing this out.  You can establish a two
> way pipe to a command in /srv:
> 
>    $ cmd <[0=1] | echo 0 > /srv/name
> 
> and then access /srv/name to communicate with the command.  As
> an example:
> 
>    $ mail <[0=1] | echo 0 > /srv/mailcons
>    $ con -l /srv/mailcons
>    ... connected to mail until ^\ quit ...
>    $ con -l /srv/mailcons
>    ... connected again ...
> 
> will let you detach and re-attach to the pipe to a long-lived
> mail command.
> 
> Tim Newsham
> http://www.lava.net/~newsham/
>

Re: [9fans] tip'o'day -- hack

[rog]

that reminds me of a similar little thing:

if you want to pipe into or from a remote command, you can do
something like:

% echo hello |[3=1] cpu -c 'wc < /mnt/term/fd/3 > /mnt/term/fd/1' | tr '0-9' X
      X       X       X
% 

(note that you can't use /mnt/term/fd/0 for stdin because that's
exportfs's input - the network connection itself)

[aside: actually, i'm not sure why cpu needs to open /mnt/term/dev/cons; if it
always did something like the above, then cpu would be even more
seamless than it is

as it is, if you don't have a local /dev/cons (e.g.  running when from
a cron job) you have to manufacture one.
]

Re: [9fans] tip'o'day -- hack

[Russ Cox]

you're supposed to use rx for this.

echo hello | rx wc | tr '0-9'

cpu is for interactive sessions, hence the /dev/cons.

if someone wants to update rx to use ssl like cpu does,
please go ahead.

russ

Re: [9fans] tip'o'day -- hack

[rog]

> you're supposed to use rx for this.
> 
> echo hello | rx wc | tr '0-9'
> 
> cpu is for interactive sessions, hence the /dev/cons.

it's true that rx does this (and without the 9p overhead too), but you
don't get /mnt/term with rx, and that's sometimes crucial.