* 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; 4+ 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:$GUILE_LOAD_PATH") fail?
Thanks
Mortimer
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Can system modify an environment variable in the current environment?
2021-09-02 19:49 Can system modify an environment variable in the current environment? Mortimer Cladwell
@ 2021-09-02 20:06 ` Roel Janssen
2021-09-19 6:45 ` adriano
2021-09-02 20:09 ` Taylan Kammer
1 sibling, 1 reply; 4+ messages in thread
From: Roel Janssen @ 2021-09-02 20:06 UTC (permalink / raw)
To: Mortimer Cladwell, guile-user
Dear Mortimer,
On Thu, 2021-09-02 at 15:49 -0400, Mortimer Cladwell wrote:
> Hi,
>
> Consider my file test.scm:
>
> (define (main args)
> (let* ((myvar (string-append "export
> GUILE_LOAD_PATH=/some/random/text:$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:$GUILE_LOAD_PATH") fail?
>
The "system" call executes in a separate environment which is exited
when the call finishes.
Instead you want to use the "setenv" procedure instead:
(setenv "GUILE_LOAD_PATH" (string-append "/some/random/text:" (getenv
"GUILE_LOAD_PATH")))
Or in this particular case, use the "add-to-load-path" procedure:
https://www.gnu.org/software/guile/manual/html_node/Load-Paths.html
Kind regards,
Roel Janssen
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Can system modify an environment variable in the current environment?
2021-09-02 19:49 Can system modify an environment variable in the current environment? Mortimer Cladwell
2021-09-02 20:06 ` Roel Janssen
@ 2021-09-02 20:09 ` Taylan Kammer
1 sibling, 0 replies; 4+ messages in thread
From: Taylan Kammer @ 2021-09-02 20:09 UTC (permalink / raw)
To: Mortimer Cladwell, guile-user
On 02.09.2021 21:49, Mortimer Cladwell wrote:
> Hi,
>
> Consider my file test.scm:
>
> (define (main args)
> (let* ((myvar (string-append "export
> GUILE_LOAD_PATH=/some/random/text:$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] 4+ messages in thread
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2021-09-02 19:49 Can system modify an environment variable in the current environment? Mortimer Cladwell
2021-09-02 20:06 ` Roel Janssen
2021-09-19 6:45 ` adriano
2021-09-02 20:09 ` Taylan Kammer
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