Emacs Environment – Append Values to Environment Variables from Within Emacs

emacsenvironment-variables

I am using Elisp. I would like to do the following in my init file:

; Retrieve the value of LD_LIBRARY_PATH
; Append '/path/to/some/lib/:'to it
; Save the new value of LD_LIBRARY_PATH

So far I know that I can use:

(getenv "LD_LIBRARY_PATH")

to retrieve the value, and:

(setenv "LD_LIBRARY_PATH" "foo")

to set a new value, but my knowledge of Elisp is extremely rudimentary so I don't know to proceed from this point.

Background:

This question is inspired by the fact that it is not be possible to source a shell script to manipulate this environment from within Emacs, so I would need to do this using Elisp.

Best Answer

In Elisp, string concatenation is done with concat:

(setenv "LD_LIBRARY_PATH"
  (let ((current (getenv "LD_LIBRARY_PATH"))
        (new "/path/to/some/lib"))
    (if current (concat new ":" current) new)))

Related Solutions

Emacs: Different users, different themes, same init file

Emacs has variables that describe the current hostname and username. Just like you would do in order to conditionally do something based on the hostname, you have the variable user-login-name (from the docs: "The user's name, taken from environment variables if possible.").

So, I guess something like this would apply:

(when (string-equal user-login-name "myuser")
    (load-theme 'theme1))

(when (string-equal user-login-name "commonuser")
    (load-theme 'theme2))

Shell – Sourcing a shell script from within Emacs

I don't believe this is possible, since each time you're invoking a subshell to source the script you're invoking a child process from the original process where the emacs applications was launched.

The exporting of environment variables is a one way street where only the parent can provide variables to any child processes, but no child processes can manipulate the parent's environment.

Experiment

I'm using vim but the same should apply to emacs. Sample file to source.

$ more ~/vars.bash 
export VAR=somevalue

Initial Parent environment, $VAR is unset
```
$ echo $VAR

$
```

Launch vim. Then invoke a subshell to source the above file (:sh).

# check variable
$ echo $VAR

$

# source and re-check
$ source ~/vars.bash
$ echo $VAR
somevalue

Exit subshell, return to vim. Then invoke another subshell (:sh).

$ exit

... back in vim, do another `:sh` ...

# check variable
$ echo $VAR

$