implement shift.

check.sh

@@ -17,6 +17,7 @@ tests='
 01-script-backslash-twice
 01-script-$0
 01-script-$@
+01-script-shift
 
 03-echo
 03-echo-doublequotes

gash/builtins.scm

@@ -54,6 +54,7 @@
             jobs-command
             pwd-command
             set-command
+            shift-command
             ))
 
 (define (PATH-search-path program)
@@ -118,6 +119,12 @@
                                (apply set-command (map (cut string-append set <>) (cdr lst)))))
     ((h ...) (last (map set-command args)))))
 
+(define (shift-command . args)
+  (lambda _
+    (match args
+      (() (when (pair? (cdr (%command-line)))
+            (%command-line (cons (car (%command-line)) (cddr (%command-line)))))))))
+
 (define (eval-command . args)
   (lambda _
     (match args
@@ -379,6 +386,7 @@ Options:
     ("jobs"    . ,jobs-command)
     ("pwd"     . ,pwd-command)
     ("set"     . ,set-command)
+    ("shift"   . ,shift-command)
     ("test"    . ,test-command)
     ("type"    . ,type-command)
     ("["       . ,bracket-command)

gash/grammar.scm

@@ -283,5 +283,7 @@
 
     (('word 'delim) '(word ""))
 
+    (('pipeline ('command ('word "shift"))) '(shift))
+
     ((h t ...) (map transform o))
     (_ o)))

gash/script.scm

@@ -426,3 +426,6 @@
 
 (define (test . o) ;; TODO replace with implementation in scheme
   (command (cons "test" o)))
+
+(define (shift . o)
+  (apply (shift-command) o))

test/01-script-shift.sh

@@ -0,0 +1,9 @@
+echo $@
+shift
+echo $@
+shift
+echo $@
+shift
+echo $@
+shift
+echo $@

test/01-script-shift.stdout

@@ -0,0 +1,5 @@
+-s --long file0 file1
+--long file0 file1
+file0 file1
+file1
+