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+;;; -*-Emacs-Lisp-*- Functions to manipulate environment variables.
+;;; Copyright Free Software Foundation 1991
+
+;;; This file is part of GNU Emacs.
+
+;;; GNU Emacs is free software; you can redistribute it and/or modify
+;;; it under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 1, or (at your option)
+;;; any later version.
+
+;;; GNU Emacs is distributed in the hope that it will be useful,
+;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Emacs; see the file COPYING.  If not, write to
+;;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
+
+(provide 'setenv)
+
+(defun setenv (variable value)
+  "Set the value of the environment variable named VARIABLE to VALUE.
+VARIABLE and VALUE should both be strings.
+This function works by modifying process-environment."
+  (if (string-match "=" variable)
+      (error "name of environment variable contains an '=' character")
+    (let ((pattern (concat "^" (regexp-quote (concat variable "="))))
+          (scan process-environment))
+      (while scan
+        (cond
+         ((string-match pattern (car scan))
+          (setcar scan (concat variable "=" value))
+          (setq scan nil))
+         ((null (setq scan (cdr scan)))
+          (setq process-environment
+                (cons (concat variable "=" value) process-environment))))))))