lisp/env.el

   1 ;;; env.el --- functions to manipulate environment variables  -*- lexical-binding:t -*-
   2
   3 ;; Copyright (C) 1991, 1994, 2000-2018 Free Software Foundation, Inc.
   4
   5 ;; Maintainer: emacs-devel@gnu.org
   6 ;; Keywords: processes, unix
   7 ;; Package: emacs
   8
   9 ;; This file is part of GNU Emacs.
  10
  11 ;; GNU Emacs is free software: you can redistribute it and/or modify
  12 ;; it under the terms of the GNU General Public License as published by
  13 ;; the Free Software Foundation, either version 3 of the License, or
  14 ;; (at your option) any later version.
  15
  16 ;; GNU Emacs is distributed in the hope that it will be useful,
  17 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  18 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19 ;; GNU General Public License for more details.
  20
  21 ;; You should have received a copy of the GNU General Public License
  22 ;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
  23
  24 ;;; Commentary:
  25
  26 ;; UNIX processes inherit a list of name-to-string associations from their
  27 ;; parents called their `environment'; these are commonly used to control
  28 ;; program options.  This package permits you to set environment variables
  29 ;; to be passed to any sub-process run under Emacs.
  30
  31 ;; Note that the environment string `process-environment' is not
  32 ;; decoded, but the args of `setenv' and `getenv' are normally
  33 ;; multibyte text and get coding conversion.
  34
  35 ;;; Code:
  36
  37 ;; History list for environment variable names.
  38 (defvar read-envvar-name-history nil)
  39
  40 (defun read-envvar-name (prompt &optional mustmatch)
  41   "Read environment variable name, prompting with PROMPT.
  42 Optional second arg MUSTMATCH, if non-nil, means require existing envvar name.
  43 If it is also not t, RET does not exit if it does non-null completion."
  44   (completing-read prompt
  45                    (mapcar (lambda (enventry)
  46                              (let ((str (substring enventry 0
  47                                              (string-match "=" enventry))))
  48                                (if (multibyte-string-p str)
  49                                    (decode-coding-string
  50                                     str locale-coding-system t)
  51                                  str)))
  52                            (append process-environment
  53                                    ;;(frame-environment)
  54                                    ))
  55                    nil mustmatch nil 'read-envvar-name-history))
  56
  57 ;; History list for VALUE argument to setenv.
  58 (defvar setenv-history nil)
  59
  60 (defconst env--substitute-vars-regexp
  61   "\\$\\(?:\\(?1:[[:alnum:]_]+\\)\\|{\\(?1:[^{}]+\\)}\\|\\$\\)")
  62
  63 (defun substitute-env-vars (string &optional when-undefined)
  64   "Substitute environment variables referred to in STRING.
  65 `$FOO' where FOO is an environment variable name means to substitute
  66 the value of that variable.  The variable name should be terminated
  67 with a character not a letter, digit or underscore; otherwise, enclose
  68 the entire variable name in braces.  For instance, in `ab$cd-x',
  69 `$cd' is treated as an environment variable.
  70
  71 If WHEN-DEFINED is nil, references to undefined environment variables
  72 are replaced by the empty string; if it is a function, the function is called
  73 with the variable name as argument and should return the text with which
  74 to replace it or nil to leave it unchanged.
  75 If it is non-nil and not a function, references to undefined variables are
  76 left unchanged.
  77
  78 Use `$$' to insert a single dollar sign."
  79   (let ((start 0))
  80     (while (string-match env--substitute-vars-regexp string start)
  81       (cond ((match-beginning 1)
  82              (let* ((var (match-string 1 string))
  83                     (value (getenv var)))
  84                (if (and (null value)
  85                         (if (functionp when-undefined)
  86                             (null (setq value (funcall when-undefined var)))
  87                           when-undefined))
  88                    (setq start (match-end 0))
  89                  (setq string (replace-match (or value "") t t string)
  90                        start (+ (match-beginning 0) (length value))))))
  91             (t
  92              (setq string (replace-match "$" t t string)
  93                    start (+ (match-beginning 0) 1)))))
  94     string))
  95
  96 (defun substitute-env-in-file-name (filename)
  97   (substitute-env-vars filename
  98                        ;; How 'bout we lookup other tables than the env?
  99                        ;; E.g. we could accept bookmark names as well!
 100                        (if (memq system-type '(windows-nt ms-dos))
 101                            (lambda (var) (getenv (upcase var)))
 102                          t)))
 103
 104 (defun setenv-internal (env variable value keep-empty)
 105   "Set VARIABLE to VALUE in ENV, adding empty entries if KEEP-EMPTY.
 106 Changes ENV by side-effect, and returns its new value."
 107   (let ((pattern (concat "\\`" (regexp-quote variable) "\\(=\\|\\'\\)"))
 108         (case-fold-search nil)
 109         (scan env)
 110         prev found)
 111     ;; Handle deletions from the beginning of the list specially.
 112     (if (and (null value)
 113              (not keep-empty)
 114              env
 115              (stringp (car env))
 116              (string-match pattern (car env)))
 117         (cdr env)
 118       ;; Try to find existing entry for VARIABLE in ENV.
 119       (while (and scan (stringp (car scan)))
 120         (when (string-match pattern (car scan))
 121           (if value
 122               (setcar scan (concat variable "=" value))
 123             (if keep-empty
 124                 (setcar scan variable)
 125               (setcdr prev (cdr scan))))
 126           (setq found t
 127                 scan nil))
 128         (setq prev scan
 129               scan (cdr scan)))
 130       (if (and (not found) (or value keep-empty))
 131           (cons (if value
 132                     (concat variable "=" value)
 133                   variable)
 134                 env)
 135         env))))
 136
 137 ;; Fixme: Should the environment be recoded if LC_CTYPE &c is set?
 138
 139 (defun setenv (variable &optional value substitute-env-vars)
 140   "Set the value of the environment variable named VARIABLE to VALUE.
 141 VARIABLE should be a string.  VALUE is optional; if not provided or
 142 nil, the environment variable VARIABLE will be removed.
 143
 144 Interactively, a prefix argument means to unset the variable, and
 145 otherwise the current value (if any) of the variable appears at
 146 the front of the history list when you type in the new value.
 147 This function always replaces environment variables in the new
 148 value when called interactively.
 149
 150 SUBSTITUTE-ENV-VARS, if non-nil, means to substitute environment
 151 variables in VALUE with `substitute-env-vars', which see.
 152 This is normally used only for interactive calls.
 153
 154 The return value is the new value of VARIABLE, or nil if
 155 it was removed from the environment.
 156
 157 This function works by modifying `process-environment'.
 158
 159 As a special case, setting variable `TZ' calls `set-time-zone-rule' as
 160 a side-effect."
 161   (interactive
 162    (if current-prefix-arg
 163        (list (read-envvar-name "Clear environment variable: " 'exact) nil)
 164      (let* ((var (read-envvar-name "Set environment variable: " nil))
 165             (value (getenv var)))
 166        (when value
 167          (add-to-history 'setenv-history value))
 168        ;; Here finally we specify the args to give call setenv with.
 169        (list var
 170              (read-from-minibuffer (format "Set %s to value: " var)
 171                                    nil nil nil 'setenv-history
 172                                    value)
 173              t))))
 174   (if (and (multibyte-string-p variable) locale-coding-system)
 175       (let ((codings (find-coding-systems-string (concat variable value))))
 176         (unless (or (eq 'undecided (car codings))
 177                     (memq (coding-system-base locale-coding-system) codings))
 178           (error "Can't encode `%s=%s' with `locale-coding-system'"
 179                  variable (or value "")))))
 180   (and value
 181        substitute-env-vars
 182        (setq value (substitute-env-vars value)))
 183   (if (multibyte-string-p variable)
 184       (setq variable (encode-coding-string variable locale-coding-system)))
 185   (if (and value (multibyte-string-p value))
 186       (setq value (encode-coding-string value locale-coding-system)))
 187   (if (string-match "=" variable)
 188       (error "Environment variable name `%s' contains `='" variable))
 189   (if (string-equal "TZ" variable)
 190       (set-time-zone-rule value))
 191   (setq process-environment (setenv-internal process-environment
 192                                              variable value t))
 193   value)
 194
 195 (defun getenv (variable &optional frame)
 196   "Get the value of environment variable VARIABLE.
 197 VARIABLE should be a string.  Value is nil if VARIABLE is undefined in
 198 the environment.  Otherwise, value is a string.
 199
 200 If optional parameter FRAME is non-nil, then it should be a
 201 frame.  This function will look up VARIABLE in its `environment'
 202 parameter.
 203
 204 Otherwise, this function searches `process-environment' for
 205 VARIABLE.  If it is not found there, then it continues the search
 206 in the environment list of the selected frame."
 207   (interactive (list (read-envvar-name "Get environment variable: " t)))
 208   (let ((value (getenv-internal (if (multibyte-string-p variable)
 209                                     (encode-coding-string
 210                                      variable locale-coding-system)
 211                                   variable)
 212                                 (and frame
 213                                      (assq 'environment
 214                                            (frame-parameters frame))))))
 215     (if (and enable-multibyte-characters value)
 216         (setq value (decode-coding-string value locale-coding-system)))
 217     (when (called-interactively-p 'interactive)
 218       (message "%s" (if value value "Not set")))
 219     value))
 220
 221 (provide 'env)
 222
 223 ;;; env.el ends here