Merge from emacs-24; up to 2012-12-06T01:39:03Z!monnier@iro.umontreal.ca

[gnu-emacs] / lisp / env.el

diff --git a/lisp/env.el b/lisp/env.el
index 9e3aed95f8a4aa8699ab2e3b791077eba43677f6..5618404cb6735e826fde1ca574f2d957cc149e28 100644 (file)
--- a/lisp/env.el
+++ b/lisp/env.el
@@ -57,31 +57,28 @@ If it is also not t, RET does not exit if it does non-null completion."
 ;; History list for VALUE argument to setenv.
 (defvar setenv-history nil)
 
+(defconst env--substitute-vars-regexp
+  "\\$\\(?:\\(?1:[[:alnum:]_]+\\)\\|{\\(?1:[^{}]+\\)}\\|\\$\\)")
 
-(defun substitute-env-vars (string)
+(defun substitute-env-vars (string &optional only-defined)
   "Substitute environment variables referred to in STRING.
 `$FOO' where FOO is an environment variable name means to substitute
 the value of that variable.  The variable name should be terminated
 with a character not a letter, digit or underscore; otherwise, enclose
 the entire variable name in braces.  For instance, in `ab$cd-x',
 `$cd' is treated as an environment variable.
+If ONLY-DEFINED is nil, references to undefined environment variables
+are replaced by the empty string; if it is non-nil, they are left unchanged.
 
 Use `$$' to insert a single dollar sign."
   (let ((start 0))
-    (while (string-match
-           (eval-when-compile
-             (rx (or (and "$" (submatch (1+ (regexp "[[:alnum:]_]"))))
-                     (and "${" (submatch (minimal-match (0+ anything))) "}")
-                     "$$")))
-           string start)
+    (while (string-match env--substitute-vars-regexp string start)
       (cond ((match-beginning 1)
             (let ((value (getenv (match-string 1 string))))
+               (if (and (null value) only-defined)
+                   (setq start (match-end 0))
               (setq string (replace-match (or value "") t t string)
-                    start (+ (match-beginning 0) (length value)))))
-           ((match-beginning 2)
-            (let ((value (getenv (match-string 2 string))))
-              (setq string (replace-match (or value "") t t string)
-                    start (+ (match-beginning 0) (length value)))))
+                       start (+ (match-beginning 0) (length value))))))
            (t
             (setq string (replace-match "$" t t string)
                   start (+ (match-beginning 0) 1)))))
@@ -185,7 +182,7 @@ VARIABLE should be a string.  Value is nil if VARIABLE is undefined in
 the environment.  Otherwise, value is a string.
 
 If optional parameter FRAME is non-nil, then it should be a
-frame.  This function will look up VARIABLE in its 'environment
+frame.  This function will look up VARIABLE in its `environment'
 parameter.
 
 Otherwise, this function searches `process-environment' for