Make guix commands pipeable

Make guix commands pipeable

[pkill9]

I would like to be able to pipe files into guix commands.

Specifically the `guix system build` command, so I can build a system
configuration on a remote Guix system over SSH, i.e. `cat config.scm |
ssh <remote-system> guix system build -`, or perhaps using the
`--expression` flag which would make more sense, e.g. `cat config.scm |
ssh <remote-system> guix system build -e -`.

While you can currently just copy over a file and then use that, it
would be a little cleaner and more stateless to use a pipe.

What do other people think?

Re: Make guix commands pipeable

[david larsson]

On 2021-03-20 13:13, pkill9 wrote:
> I would like to be able to pipe files into guix commands.
> 
> Specifically the `guix system build` command, so I can build a system
> configuration on a remote Guix system over SSH, i.e. `cat config.scm |
> ssh <remote-system> guix system build -`, or perhaps using the
> `--expression` flag which would make more sense, e.g. `cat config.scm |
> ssh <remote-system> guix system build -e -`.
> 
> While you can currently just copy over a file and then use that, it
> would be a little cleaner and more stateless to use a pipe.
> 
> What do other people think?

I like pipes and this would be nice to have. Though an easy way to wrap 
things in bash and make them pipable at the same time is to use the -t 
check like this:

f(){ [[ ! -t 0 ]] && mapfile -t Args ; if [[ -n "${Args[@]}" ]]; then 
printf 'some_command %s ' "${Args[@]}" ; else printf 'some_command %s ' 
"$@"; fi ; }
printf '%s\n' a b c | f
f a b c

So you could define f as: f(){ [[ ! -t 0 ]] && mapfile -t -d '' Args ; 
if [[ -n "${Args[@]}" ]]; then ssh <remote-system> guix system build -e 
"${Args[@]//$'\n'/}" ; else ssh <remote-system> guix system build -e 
"$@"; fi ; }

and then I think you should be able to cat config.scm | f

Notice -d '' above which means use null as delimiter which will most 
often put everything in index 0 of the list. Also notice the parameter 
expansion which removes all newlines from the content.

I do agree though that it would be nicer to just have '-' as a guix 
input arg causing any guix command to read from stdin.

I hope it helps!

Best regards,
David

Re: Make guix commands pipeable

[Léo Le Bouter]

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> I do agree though that it would be nicer to just have '-' as a guix 
> input arg causing any guix command to read from stdin.

Doesnt /dev/stdin work?

The only reason it could not is that somehow the file descriptor needs
to be seekable.

Léo

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Re: Make guix commands pipeable

[pkill9]

> Doesnt /dev/stdin work?
> 
> The only reason it could not is that somehow the file descriptor needs
> to be seekable.
> 
> Léo

This doesn't work for me, with `cat <file> | guix build -f /dev/stdin`
i get "guix build: error: failed to load '/dev/stdin': No such file or
directory"

Re: Make guix commands pipeable

[pkill9]

> Doesnt /dev/stdin work?
> 
> The only reason it could not is that somehow the file descriptor needs
> to be seekable.
> 
> Léo

This doesn't work for me, with `cat <file> | guix build -f /dev/stdin`
i get "guix build: error: failed to load '/dev/stdin': No such file or
directory"

Re: Make guix commands pipeable

[zimoun]

Hi,

On Sat, 20 Mar 2021 at 12:13, pkill9 <pkill9@runbox.com> wrote:
> I would like to be able to pipe files into guix commands.

Well, this work:

  guix search hello | recsel -C -P name | xargs guix build

> Specifically the `guix system build` command, so I can build a system
> configuration on a remote Guix system over SSH, i.e. `cat config.scm |
> ssh <remote-system> guix system build -`, or perhaps using the
> `--expression` flag which would make more sense, e.g. `cat config.scm |
> ssh <remote-system> guix system build -e -`.

Does “cat config.scm | ssh <remote> xargs -0 guix system -e” work?

Indeed, maybe some commands are expecting a real file and cannot read
from stdin.


Cheers,
simon