unofficial mirror of guile-user@gnu.org 
 help / color / mirror / Atom feed
* Can system modify an environment variable in the current environment?
@ 2021-09-02 19:49 Mortimer Cladwell
  2021-09-02 20:06 ` Roel Janssen
  2021-09-02 20:09 ` Taylan Kammer
  0 siblings, 2 replies; 3+ messages in thread
From: Mortimer Cladwell @ 2021-09-02 19:49 UTC (permalink / raw)
  To: guile-user

Hi,

Consider my file test.scm:

(define (main args)
  (let* ((myvar (string-append "export
GUILE_LOAD_PATH=/some/random/text:$GUILE_LOAD_PATH"))
           (statement1 (system (string-append "echo " myvar " >>
$HOME/.bashrc")))
            (statement2 (system myvar)))
    (write myvar)))

At the terminal:

mbc@HP8300:~/temp$ echo $GUILE_LOAD_PATH
/home/mbc/.guix-profile/share/guile/site/3.0

mbc@HP8300:~/temp$ guile -e main -s test.scm
"export GUILE_LOAD_PATH=/some/random/text:$GUILE_LOAD_PATH"

mbc@HP8300:~/temp$ echo $GUILE_LOAD_PATH
/home/mbc/.guix-profile/share/guile/site/3.0

At the end of .bashrc I see the last line is:

export
GUILE_LOAD_PATH=/some/random/text:/home/mbc/.guix-profile/share/guile/site/3.0

If I close and reopen the terminal and:

mbc@HP8300:~$ echo $GUILE_LOAD_PATH
/some/random/text:/home/mbc/.guix-profile/share/guile/site/3.0

So statement1 works as expected, modifying .bashrc which is then effective
in modifying GUILE_LOAD_PATH on future invocations of terminal.

statement2 is an attempt to modify the current running environment, but
fails.
Note that if I paste export
GUILE_LOAD_PATH=/some/random/text:$GUILE_LOAD_PATH directly into the
terminal, that successfully modifies the variable.

Why does  (system myvar) i.e. (system "export
GUILE_LOAD_PATH=/some/random/text:$GUILE_LOAD_PATH") fail?
Thanks
Mortimer


^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: Can system modify an environment variable in the current environment?
  2021-09-02 19:49 Can system modify an environment variable in the current environment? Mortimer Cladwell
@ 2021-09-02 20:06 ` Roel Janssen
  2021-09-02 20:09 ` Taylan Kammer
  1 sibling, 0 replies; 3+ messages in thread
From: Roel Janssen @ 2021-09-02 20:06 UTC (permalink / raw)
  To: Mortimer Cladwell, guile-user

Dear Mortimer,

On Thu, 2021-09-02 at 15:49 -0400, Mortimer Cladwell wrote:
> Hi,
> 
> Consider my file test.scm:
> 
> (define (main args)
>   (let* ((myvar (string-append "export
> GUILE_LOAD_PATH=/some/random/text:$GUILE_LOAD_PATH"))
>            (statement1 (system (string-append "echo " myvar " >>
> $HOME/.bashrc")))
>             (statement2 (system myvar)))
>     (write myvar)))
> 
> At the terminal:
> 
> mbc@HP8300:~/temp$ echo $GUILE_LOAD_PATH
> /home/mbc/.guix-profile/share/guile/site/3.0
> 
> mbc@HP8300:~/temp$ guile -e main -s test.scm
> "export GUILE_LOAD_PATH=/some/random/text:$GUILE_LOAD_PATH"
> 
> mbc@HP8300:~/temp$ echo $GUILE_LOAD_PATH
> /home/mbc/.guix-profile/share/guile/site/3.0
> 
> At the end of .bashrc I see the last line is:
> 
> export
> GUILE_LOAD_PATH=/some/random/text:/home/mbc/.guix-
> profile/share/guile/site/3.0
> 
> If I close and reopen the terminal and:
> 
> mbc@HP8300:~$ echo $GUILE_LOAD_PATH
> /some/random/text:/home/mbc/.guix-profile/share/guile/site/3.0
> 
> So statement1 works as expected, modifying .bashrc which is then
> effective
> in modifying GUILE_LOAD_PATH on future invocations of terminal.
> 
> statement2 is an attempt to modify the current running environment, but
> fails.
> Note that if I paste export
> GUILE_LOAD_PATH=/some/random/text:$GUILE_LOAD_PATH directly into the
> terminal, that successfully modifies the variable.
> 
> Why does  (system myvar) i.e. (system "export
> GUILE_LOAD_PATH=/some/random/text:$GUILE_LOAD_PATH") fail?
> 

The "system" call executes in a separate environment which is exited
when the call finishes.

Instead you want to use the "setenv" procedure instead:
(setenv "GUILE_LOAD_PATH" (string-append "/some/random/text:" (getenv
"GUILE_LOAD_PATH")))

Or in this particular case, use the "add-to-load-path" procedure:
https://www.gnu.org/software/guile/manual/html_node/Load-Paths.html



Kind regards,
Roel Janssen




^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: Can system modify an environment variable in the current environment?
  2021-09-02 19:49 Can system modify an environment variable in the current environment? Mortimer Cladwell
  2021-09-02 20:06 ` Roel Janssen
@ 2021-09-02 20:09 ` Taylan Kammer
  1 sibling, 0 replies; 3+ messages in thread
From: Taylan Kammer @ 2021-09-02 20:09 UTC (permalink / raw)
  To: Mortimer Cladwell, guile-user

On 02.09.2021 21:49, Mortimer Cladwell wrote:
> Hi,
> 
> Consider my file test.scm:
> 
> (define (main args)
>   (let* ((myvar (string-append "export
> GUILE_LOAD_PATH=/some/random/text:$GUILE_LOAD_PATH"))
>            (statement1 (system (string-append "echo " myvar " >>
> $HOME/.bashrc")))
>             (statement2 (system myvar)))
>     (write myvar)))
> 
> At the terminal:
> 
> mbc@HP8300:~/temp$ echo $GUILE_LOAD_PATH
> /home/mbc/.guix-profile/share/guile/site/3.0
> 
> mbc@HP8300:~/temp$ guile -e main -s test.scm
> "export GUILE_LOAD_PATH=/some/random/text:$GUILE_LOAD_PATH"
> 
> mbc@HP8300:~/temp$ echo $GUILE_LOAD_PATH
> /home/mbc/.guix-profile/share/guile/site/3.0
> 
> At the end of .bashrc I see the last line is:
> 
> export
> GUILE_LOAD_PATH=/some/random/text:/home/mbc/.guix-profile/share/guile/site/3.0
> 
> If I close and reopen the terminal and:
> 
> mbc@HP8300:~$ echo $GUILE_LOAD_PATH
> /some/random/text:/home/mbc/.guix-profile/share/guile/site/3.0
> 
> So statement1 works as expected, modifying .bashrc which is then effective
> in modifying GUILE_LOAD_PATH on future invocations of terminal.
> 
> statement2 is an attempt to modify the current running environment, but
> fails.
> Note that if I paste export
> GUILE_LOAD_PATH=/some/random/text:$GUILE_LOAD_PATH directly into the
> terminal, that successfully modifies the variable.
> 
> Why does  (system myvar) i.e. (system "export
> GUILE_LOAD_PATH=/some/random/text:$GUILE_LOAD_PATH") fail?
> Thanks
> Mortimer
> 

Hi Mortimer,

The "system" procedure starts a child-process in the operating system.
In the Unix process model, the changes to the environment made by a child
process do not affect the parent.

Note that anything for which you use "system" above can be done directly
within Guile by using the appropriate procedures, instead of starting a
child process using the system shell.

You might want to look for I/O related procedures to figure out how you
can append text to an existing file.  This might help:

https://www.gnu.org/software/guile/manual/html_node/File-Ports.html

Setting an environment variable is simple, just use 'setenv':

https://www.gnu.org/software/guile/manual/html_node/Runtime-Environment.html

Hope that helps. :-)

-- 
Taylan



^ permalink raw reply	[flat|nested] 3+ messages in thread

end of thread, other threads:[~2021-09-02 20:09 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-09-02 19:49 Can system modify an environment variable in the current environment? Mortimer Cladwell
2021-09-02 20:06 ` Roel Janssen
2021-09-02 20:09 ` Taylan Kammer

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).