* how to use a variable in a plain-file object?
@ 2024-05-16 15:57 Giovanni Biscuolo
2024-05-16 16:15 ` raingloom
2024-05-16 18:39 ` Tomas Volf
0 siblings, 2 replies; 5+ messages in thread
From: Giovanni Biscuolo @ 2024-05-16 15:57 UTC (permalink / raw)
To: help-guix
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Hello,
sorry for the very guile-absolute-beginner question, but I'd like to use
a declared variable in a plain-file object, so I can write something
like in this pseudo-code snippet:
--8<---------------cut here---------------start------------->8---
(define variable1 "var1-value")
(define variable2 "var2-value")
[...]
(define %my-file-object
,(plain-file "something.conf" "
# This is an example configuration file
attribute1 =" variable1 "
attribute2 =" variable2 "
"))
--8<---------------cut here---------------end--------------->8---
and obtain a "something.conf" file like this:
--8<---------------cut here---------------start------------->8---
# This is an example configuration file
attribute1 = var1-value
attribute2 = var2-value
--8<---------------cut here---------------end--------------->8---
how can I do, please?
Thanks, Gio'
--
Giovanni Biscuolo
Xelera IT Infrastructures
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: how to use a variable in a plain-file object?
2024-05-16 15:57 how to use a variable in a plain-file object? Giovanni Biscuolo
@ 2024-05-16 16:15 ` raingloom
2024-05-17 8:45 ` Giovanni Biscuolo
2024-05-16 18:39 ` Tomas Volf
1 sibling, 1 reply; 5+ messages in thread
From: raingloom @ 2024-05-16 16:15 UTC (permalink / raw)
To: Giovanni Biscuolo; +Cc: help-guix
On 2024-05-16 17:57, Giovanni Biscuolo wrote:
> Hello,
>
> sorry for the very guile-absolute-beginner question, but I'd like to use
> a declared variable in a plain-file object, so I can write something
> like in this pseudo-code snippet:
>
> --8<---------------cut here---------------start------------->8---
>
> (define variable1 "var1-value")
> (define variable2 "var2-value")
>
> [...]
>
> (define %my-file-object
> ,(plain-file "something.conf" "
> # This is an example configuration file
>
> attribute1 =" variable1 "
>
> attribute2 =" variable2 "
>
> "))
>
> --8<---------------cut here---------------end--------------->8---
>
> and obtain a "something.conf" file like this:
>
> --8<---------------cut here---------------start------------->8---
> # This is an example configuration file
>
> attribute1 = var1-value
>
> attribute2 = var2-value
>
> --8<---------------cut here---------------end--------------->8---
>
> how can I do, please?
>
> Thanks, Gio'
You probably want a G-expression.
Short untested example:
(define name "Giovanni")
(define greeting-gexp
#~(begin (with-output-to-file #$output (lambda _ (write (string-append
"Hello, " #$name "!"))))))
You should be able to use greeting-gexp in place of %my-file-object.
I highly recommend reading the relevant docs in Guix's info pages.
Online version:
https://guix.gnu.org/manual/en/html_node/G_002dExpressions.html
Related blog post:
https://guix.gnu.org/en/blog/2023/dissecting-guix-part-3-g-expressions/
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: how to use a variable in a plain-file object?
2024-05-16 15:57 how to use a variable in a plain-file object? Giovanni Biscuolo
2024-05-16 16:15 ` raingloom
@ 2024-05-16 18:39 ` Tomas Volf
2024-05-17 8:24 ` Giovanni Biscuolo
1 sibling, 1 reply; 5+ messages in thread
From: Tomas Volf @ 2024-05-16 18:39 UTC (permalink / raw)
To: Giovanni Biscuolo; +Cc: help-guix
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On 2024-05-16 17:57:55 +0200, Giovanni Biscuolo wrote:
> Hello,
>
> sorry for the very guile-absolute-beginner question, but I'd like to use
> a declared variable in a plain-file object, so I can write something
> like in this pseudo-code snippet:
>
> --8<---------------cut here---------------start------------->8---
>
> (define variable1 "var1-value")
> (define variable2 "var2-value")
>
> [...]
>
> (define %my-file-object
> ,(plain-file "something.conf" "
> # This is an example configuration file
>
> attribute1 =" variable1 "
>
> attribute2 =" variable2 "
>
> "))
>
> --8<---------------cut here---------------end--------------->8---
>
> and obtain a "something.conf" file like this:
>
> --8<---------------cut here---------------start------------->8---
> # This is an example configuration file
>
> attribute1 = var1-value
>
> attribute2 = var2-value
>
> --8<---------------cut here---------------end--------------->8---
>
> how can I do, please?
I believe you can use mixed-text-file for this purpose:
/tmp/xx.scm:
(use-modules (guix gexp))
(define var1 "var1-value")
(define var2 "var2-value")
(define %my-file-object
(mixed-text-file "something.conf" "\
# This is an example configuration file
attribute1 = " var1 "
attribute2 = " var2 "
"))
%my-file-object
When I build it and inspect the result:
$ cat $(guix build -e '(load "/tmp/xx.scm")')
# This is an example configuration file
attribute1 = var1-value
attribute2 = var2-value
The mixed-text-file accepts string *and* file-like objects as arguments. That
makes it very suitable for constructing configuration files, since you can
expand paths, for example like this:
/tmp/yy.scm:
(use-modules (gnu packages base)
(guix gexp))
(define %my-file-object
(mixed-text-file "something.conf" "\
SED_PATH = " sed "/bin/sed
"))
%my-file-object
And here is the result:
$ cat $(guix build -e '(load "/tmp/yy.scm")')
SED_PATH = /gnu/store/6kkygybkxkzqy3lf6k5kzimk5mjasrvw-sed-4.8/bin/sed
Hope this is useful and have a nice day,
Tomas Volf
--
There are only two hard things in Computer Science:
cache invalidation, naming things and off-by-one errors.
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: how to use a variable in a plain-file object?
2024-05-16 18:39 ` Tomas Volf
@ 2024-05-17 8:24 ` Giovanni Biscuolo
0 siblings, 0 replies; 5+ messages in thread
From: Giovanni Biscuolo @ 2024-05-17 8:24 UTC (permalink / raw)
To: Tomas Volf; +Cc: help-guix
Hello Tomas,
Tomas Volf <~@wolfsden.cz> writes:
[...]
> I believe you can use mixed-text-file for this purpose:
Oh yes! I missed (to understand) mixed-text-file and text-file* in the
G-exp manual section [1], in particular how it can be easily used in
place of local-file and plain-file, because I missed (to understand) the
given example. Now that I see, I think I'll use that in place of
plain-file... everywhere :-O
[...]
> (use-modules (gnu packages base)
> (guix gexp))
>
> (define %my-file-object
> (mixed-text-file "something.conf" "\
> SED_PATH = " sed "/bin/sed
> "))
>
> %my-file-object
>
> And here is the result:
>
> $ cat $(guix build -e '(load "/tmp/yy.scm")')
> SED_PATH =
> /gnu/store/6kkygybkxkzqy3lf6k5kzimk5mjasrvw-sed-4.8/bin/sed
Cristal clear, also thank you for having pointed out a quick way to test
the result by building it and cat(ing) it in a shell session
This could be a nice section in the Cookbook :-)
Thank you and happy hacking!
> There are only two hard things in Computer Science:
> cache invalidation, naming things and off-by-one errors.
P.S.: I'll steal the above sentence, _verbatim_ :-)
[1] IMHO that manual section "talks" to experienced Guile programmers
and not to Guix _users_... and actually is a subsection of "Programming
interface".
--
Giovanni Biscuolo
Xelera IT Infrastructures
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: how to use a variable in a plain-file object?
2024-05-16 16:15 ` raingloom
@ 2024-05-17 8:45 ` Giovanni Biscuolo
0 siblings, 0 replies; 5+ messages in thread
From: Giovanni Biscuolo @ 2024-05-17 8:45 UTC (permalink / raw)
To: raingloom; +Cc: help-guix
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Hello raingloom
thank you for you quick reply!
raingloom@riseup.net writes:
[...]
> Short untested example:
>
> (define name "Giovanni")
> (define greeting-gexp
> #~(begin (with-output-to-file #$output (lambda _ (write (string-append
> "Hello, " #$name "!"))))))
>
> You should be able to use greeting-gexp in place of %my-file-object.
I've tested it with this code:
--8<---------------cut here---------------start------------->8---
(use-modules (guix gexp))
(define var1 "var1-value")
(define var2 "var2-value")
(define %another-file-object
#~(begin (with-output-to-file #$output (lambda _ (write (string-append "\
# This is an example configuration file
# stored in %another-file-object
attribute1 = " #$var1 "
attribute2 = " #$var2 "
"))))))
%another-file-object
--8<---------------cut here---------------end--------------->8---
And this is the result:
--8<---------------cut here---------------start------------->8---
[~/tmp]
giovanni@roquette [genv]\: cat $(guix build --no-offload -e '(load "guix-output-to-file-example.scm")')
"# This is an example configuration file\n# stored in %another-file-object\nattribute1 = var1-value\nattribute2 = var2-value\n"
--8<---------------cut here---------------end--------------->8---
The output cannot be used in place of %my-file-object, right?
AFAIU the solution is to use mixed-text-file as suggested by Tomas Volf
yesterday in this thread.
Happy hacking! Gio'
[...]
--
Giovanni Biscuolo
Xelera IT Infrastructures
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2024-05-16 15:57 how to use a variable in a plain-file object? Giovanni Biscuolo
2024-05-16 16:15 ` raingloom
2024-05-17 8:45 ` Giovanni Biscuolo
2024-05-16 18:39 ` Tomas Volf
2024-05-17 8:24 ` Giovanni Biscuolo
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