(defvar read-envvar-name-history nil)
(defun read-envvar-name (prompt &optional mustmatch)
"Read environment variable name, prompting with PROMPT.
Optional second arg MUSTMATCH, if non-nil, means require existing envvar name.
If it is also not t, RET does not exit if it does non-null completion."
(completing-read prompt
(mapcar (function
(lambda (enventry)
(list (substring enventry 0
(string-match "=" enventry)))))
process-environment)
nil mustmatch nil 'read-envvar-name-history))
(defvar setenv-history nil)
(defun setenv (variable &optional value unset)
"Set the value of the environment variable named VARIABLE to VALUE.
VARIABLE should be a string. VALUE is optional; if not provided or is
`nil', the environment variable VARIABLE will be removed.
Interactively, a prefix argument means to unset the variable.
Interactively, the current value (if any) of the variable
appears at the front of the history list when you type in the new value.
This function works by modifying `process-environment'."
(interactive
(if current-prefix-arg
(list (read-envvar-name "Clear environment variable: " 'exact) nil t)
(let* ((var (read-envvar-name "Set environment variable: " nil))
(value (getenv var)))
(when value
(push value setenv-history))
(list var (read-from-minibuffer (format "Set %s to value: " var)
nil nil nil 'setenv-history
value)))))
(if unset (setq value nil))
(if (string-match "=" variable)
(error "Environment variable name `%s' contains `='" variable)
(let ((pattern (concat "\\`" (regexp-quote (concat variable "="))))
(case-fold-search nil)
(scan process-environment)
found)
(if (string-equal "TZ" variable)
(set-time-zone-rule value))
(while scan
(cond ((string-match pattern (car scan))
(setq found t)
(if (eq nil value)
(setq process-environment (delq (car scan) process-environment))
(setcar scan (concat variable "=" value)))
(setq scan nil)))
(setq scan (cdr scan)))
(or found
(if value
(setq process-environment
(cons (concat variable "=" value)
process-environment)))))))
(defun getenv (variable)
"Get the value of environment variable VARIABLE.
VARIABLE should be a string. Value is nil if VARIABLE is undefined in
the environment. Otherwise, value is a string.
This function consults the variable `process-environment'
for its value."
(interactive (list (read-envvar-name "Get environment variable: " t)))
(let ((value (getenv-internal variable)))
(when (interactive-p)
(message "%s" (if value value "Not set")))
value))
(provide 'env)