Add support for $$

* geesh/environment.scm (*root-pid*): New variable.
(get-root-pid): New public function.
* geesh/word.scm (parameter-ref): Handle '$'.

geesh/environment.scm

@@ -23,6 +23,7 @@
   #:use-module (srfi srfi-26)
   #:export (get-status
             set-status!
+            get-root-pid
             getvar
             setvar!
             unsetvar!
@@ -60,7 +61,7 @@
 ;;; Code:
 
 
-;;; Status.
+;;; Status and PID.
 
 (define *status* 0)
 
@@ -72,6 +73,11 @@
   "Set the current status."
   (set! *status* n))
 
+(define *root-pid* (getpid))
+
+(define (get-root-pid)
+  *root-pid*)
+
 
 ;;; Variables.
 

geesh/word.scm

@@ -230,6 +230,7 @@ the environment.  If @var{name} is unset, return @code{#f}."
     ("0" (car (program-arguments)))
     ("#" (number->string (length (cdr (program-arguments)))))
     ("?" (number->string (get-status)))
+    ("$" (number->string (get-root-pid)))
     (x (let ((n (string->number x)))
          (if (and n (integer? n) (> n 0)
                   (<= n (length (cdr (program-arguments)))))