How do I get the list of all environment variables available in a Lisp process?

Question

I want to enumerate the list of all environment variables available in my Lisp process. I want the same list that is returned by the C variable environ.

Neither SBCL nor Clozure CL seem to provide it out of the box. Can I do it using CFFI?

Answer 1

Interfacing with the OS and common lisp is still quite dependent on your lisp distribution. So more or less is not easy to find a good library that works in all CL distributions.

I recommend you to work with UIOP, which comes with ASDF 3 and above and it is the best library for working with the OS inside common lisp nowadays. However it doesn't have a function to list the environment variables, furthermother if we take a look at how it works with environment varables we can see that for every lisp distribution we have a different version of accessing the variables only for example:

(defun getenv (x)
    "Query the environment, as in C getenv.
Beware: may return empty string if a variable is present but empty;
use getenvp to return NIL in such a case."
    (declare (ignorable x))
    #+(or abcl clasp clisp ecl xcl) (ext:getenv x)
    #+allegro (sys:getenv x)
    #+clozure (ccl:getenv x)
    #+cmucl (unix:unix-getenv x)
    #+scl (cdr (assoc x ext:*environment-list* :test #'string=))
    #+cormanlisp
    (let* ((buffer (ct:malloc 1))
           (cname (ct:lisp-string-to-c-string x))
           (needed-size (win:getenvironmentvariable cname buffer 0))
           (buffer1 (ct:malloc (1+ needed-size))))
      (prog1 (if (zerop (win:getenvironmentvariable cname buffer1 needed-size))
                 nil
                 (ct:c-string-to-lisp-string buffer1))
        (ct:free buffer)
        (ct:free buffer1)))
    #+gcl (system:getenv x)
    #+genera nil
    #+lispworks (lispworks:environment-variable x)
    #+mcl (ccl:with-cstrs ((name x))
            (let ((value (_getenv name)))
              (unless (ccl:%null-ptr-p value)
                (ccl:%get-cstring value))))
    #+mkcl (#.(or (find-symbol* 'getenv :si nil) (find-symbol* 'getenv :mk-ext nil)) x)
    #+sbcl (sb-ext:posix-getenv x)
    #-(or abcl allegro clasp clisp clozure cmucl cormanlisp ecl gcl genera lispworks mcl mkcl sbcl scl xcl)
    (not-implemented-error 'getenv))

  (defsetf getenv (x) (val)
    "Set an environment variable."
      (declare (ignorable x val))
    #+allegro `(setf (sys:getenv ,x) ,val)
    #+clisp `(system::setenv ,x ,val)
    #+clozure `(ccl:setenv ,x ,val)
    #+cmucl `(unix:unix-setenv ,x ,val 1)
    #+ecl `(ext:setenv ,x ,val)
    #+lispworks `(hcl:setenv ,x ,val)
    #+mkcl `(mkcl:setenv ,x ,val)
    #+sbcl `(progn (require :sb-posix) (symbol-call :sb-posix :setenv ,x ,val 1))
    #-(or allegro clisp clozure cmucl ecl lispworks mkcl sbcl)
'(not-implemented-error '(setf getenv))

so for getting one variable:

CL-USER> (uiop:getenv "GEM_PATH")
"/Users/toni/.rvm/gems/ruby-2.1.6@afs-dev:/Users/toni/.rvm/gems/ruby-2.1.6@global"

as pointed in a comment if you are usign SBCL you can get this with it:

SB-EXT:POSIX-ENVIRON

example in c:

extern char **environ;
//...

int i = 0;
while(environ[i]) {
  printf("%s\n", environ[i++]); // prints in form of "variable=value"
}

| GEM_HOME=/Users/toni/.rvm/gems/ruby-2.1.6@afs-dev                                                                                                                                                                                       |
| SHELL=/bin/bash                                                                                                                                                                                                                         |
| TERM=dumb                                                                                                                                                                                                                               |
| TMPDIR=/var/folders/zs/t9wnzpqj2bdgjjgjwb8pqxc80000gn/T/                                                                                                                                                                                |
| Apple_PubSub_Socket_Render=/private/tmp/com.apple.launchd.e0K30SfWTc/Render                                                                                                                                                             |
| USER=toni                                                                                                                                                                                                                               |
| SSH_AUTH_SOCK=/private/tmp/com.apple.launchd.KvlUaU8PD5/Listeners                                                                                                                                                                       |
| __CF_USER_TEXT_ENCODING=0x1F5:0x0:0x8                                                                                                                                                                                                   |
| PATH=/Users/toni/.rvm/gems/ruby-2.1.6@afs-dev/bin:/Users/toni/.rvm/gems/ruby-2.1.6@global/bin:/Users/toni/.rvm/rubies/ruby-2.1.6/bin/:/usr/texbin:/Library/TeX/texbin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Users/toni/.rvm/bin |
| PWD=/Users/toni/learn/lisp/cl-l/stackoverflow/scripts                                                                                                                                                                                   |
| LANG=es_ES.UTF-8                                                                                                                                                                                                                        |
| XPC_FLAGS=0x0                                                                                                                                                                                                                           |
| XPC_SERVICE_NAME=org.gnu.Emacs.13016                                                                                                                                                                                                    |
| SHLVL=1                                                                                                                                                                                                                                 |
| HOME=/Users/toni                                                                                                                                                                                                                        |
| BUNDLE_PATH=/Users/toni/.rvm/gems/ruby-2.1.6@afs-dev                                                                                                                                                                                    |
| LOGNAME=toni                                                                                                                                                                                                                            |
| GEM_PATH=/Users/toni/.rvm/gems/ruby-2.1.6@afs-dev:/Users/toni/.rvm/gems/ruby-2.1.6@global                                                                                                                                               |
| DISPLAY=/private/tmp/com.apple.launchd.ljkiChb2wE/org.macosforge.xquartz:0                                                                                                                                                              |
| _=/tmp/babel-6131RLH/C-bin-6131T_s                                                                                                                                                                                                      |

example in SBCL

(sb-ext:posix-environ)


("TERM=dumb" "TERMCAP=" "COLUMNS=139" "INSIDE_EMACS=25.2.1,comint"
 "BUNDLE_PATH=/Users/toni/.rvm/gems/ruby-2.1.6@afs-dev"
 "GEM_PATH=/Users/toni/.rvm/gems/ruby-2.1.6@afs-dev:/Users/toni/.rvm/gems/ruby-2.1.6@global"
 "GEM_HOME=/Users/toni/.rvm/gems/ruby-2.1.6@afs-dev" "LANG=es_ES.UTF-8"
 "XPC_FLAGS=0x0" "USER=toni" "XPC_SERVICE_NAME=org.gnu.Emacs.13016"
 "DISPLAY=/private/tmp/com.apple.launchd.ljkiChb2wE/org.macosforge.xquartz:0"
 "LOGNAME=toni"
 "PATH=/Users/toni/.rvm/gems/ruby-2.1.6@afs-dev/bin:/Users/toni/.rvm/gems/ruby-2.1.6@global/bin:/Users/toni/.rvm/rubies/ruby-2.1.6/bin/:/usr/texbin:/Library/TeX/texbin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Users/toni/.rvm/bin"
 "SSH_AUTH_SOCK=/private/tmp/com.apple.launchd.KvlUaU8PD5/Listeners"
 "Apple_PubSub_Socket_Render=/private/tmp/com.apple.launchd.e0K30SfWTc/Render"
 "SHELL=/bin/bash" "HOME=/Users/toni" "__CF_USER_TEXT_ENCODING=0x1F5:0x0:0x8"
 "TMPDIR=/var/folders/zs/t9wnzpqj2bdgjjgjwb8pqxc80000gn/T/"
 "SBCL_HOME=/Users/toni/.roswell/impls/x86-64/darwin/sbcl/1.3.16/lib/sbcl"
 "ROS_OPTS=((\"program\"\"(:eval\\\"(ros:quicklisp)\\\")\")(\"lispdir\"\"/usr/local/Cellar/roswell/17.4.8.76/etc/roswell/\")(\"verbose\"\"0\")(\"homedir\"\"/Users/toni/.roswell/\")(\"wargv0\"\"/usr/local/bin/ros\")(\"argv0\"\"/usr/local/bin/ros\")(\"quicklisp\"\"/Users/toni/.roswell/lisp/quicklisp/\")(\"impl\"\"sbcl/1.3.16\")(\"dynamic-space-size\"\"3gb\")(\"sbcl.version\"\"1.3.16\")(\"allegro.version\"\"100express\")(\"ccl-bin.version\"\"1.11\")(\"ecl.version\"\"16.1.3\")(\"slime.version\"\"2017.02.27\")(\"sbcl-bin.version\"\"1.2.11\")(\"default.lisp\"\"sbcl\"))")

So for other implementations you mut investigate how to,

Finally exist a good library called OSICAT that:

OSICAT is a lightweight operating system interface for Common Lisp on Unix-platforms. It is not a POSIX-style API, but rather a simple lispy accompaniment to the standard ANSI facilities.

so in your case you must use:

(osicat:environment)

(("TERM" . "dumb") ("TERMCAP" . "") ("COLUMNS" . "139") ("INSIDE_EMACS" . "25.2.1,comint") ("BUNDLE_PATH" . "/Users/toni/.rvm/gems/ruby-2.1.6@afs-dev") ("GEM_PATH" . "/Users/toni/.rvm/gems/ruby-2.1.6@afs-dev:/Users/toni/.rvm/gems/ruby-2.1.6@global") ("GEM_HOME" . "/Users/toni/.rvm/gems/ruby-2.1.6@afs-dev") ("LANG" . "es_ES.UTF-8") ("XPC_FLAGS" . "0x0") ("USER" . "toni") ("XPC_SERVICE_NAME" . "org.gnu.Emacs.13016") ("DISPLAY" . "/private/tmp/com.apple.launchd.ljkiChb2wE/org.macosforge.xquartz:0") ("LOGNAME" . "toni") ("PATH" . "/Users/toni/.rvm/gems/ruby-2.1.6@afs-dev/bin:/Users/toni/.rvm/gems/ruby-2.1.6@global/bin:/Users/toni/.rvm/rubies/ruby-2.1.6/bin/:/usr/texbin:/Library/TeX/texbin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Users/toni/.rvm/bin") ("SSH_AUTH_SOCK" . "/private/tmp/com.apple.launchd.KvlUaU8PD5/Listeners") ("Apple_PubSub_Socket_Render" . "/private/tmp/com.apple.launchd.e0K30SfWTc/Render") ("SHELL" . "/bin/bash") ("HOME" . "/Users/toni") ("__CF_USER_TEXT_ENCODING" . "0x1F5:0x0:0x8") ("TMPDIR" . "/var/folders/zs/t9wnzpqj2bdgjjgjwb8pqxc80000gn/T/") ("ROS_OPTS" . "((\"program\"\"(:eval\\\"(ros:quicklisp)\\\")\")(\"lispdir\"\"/usr/local/Cellar/roswell/17.4.8.76/etc/roswell/\")(\"verbose\"\"0\")(\"homedir\"\"/Users/toni/.roswell/\")(\"wargv0\"\"/usr/local/bin/ros\")(\"argv0\"\"/usr/local/bin/ros\")(\"quicklisp\"\"/Users/toni/.roswell/lisp/quicklisp/\")(\"impl\"\"ccl-bin/1.11\")(\"dynamic-space-size\"\"3gb\")(\"sbcl.version\"\"1.3.16\")(\"allegro.version\"\"100express\")(\"ccl-bin.version\"\"1.11\")(\"ecl.version\"\"16.1.3\")(\"slime.version\"\"2017.02.27\")(\"sbcl-bin.version\"\"1.2.11\")(\"default.lisp\"\"ccl-bin\"))"))

SO I hope that this should work