Add the 'command' built-in.

* geesh/built-ins/command.scm: New file.
* Makefile.am: Add it.
* geesh/built-ins.scm (*built-ins*): Add 'command'.

Co-authored-by: Timothy Sample <samplet@ngyro.com>

Makefile.am

@@ -75,6 +75,7 @@ MODULES =                                       \
   geesh/built-ins/break.scm                     \
   geesh/built-ins/cd.scm                        \
   geesh/built-ins/colon.scm                     \
+  geesh/built-ins/command.scm                   \
   geesh/built-ins/continue.scm                  \
   geesh/built-ins/dot.scm                       \
   geesh/built-ins/echo.scm                      \

gash/builtins.scm

@@ -375,7 +375,6 @@ Options:
 (define %builtin-commands
   `(
     ("bg"      . ,bg-command)
-    ("command" . ,command-command)
     ("cd"      . ,cd-command)
     ("echo"    . ,echo-command)
     ("eval"    . ,eval-command)

geesh/built-ins.scm

@@ -55,7 +55,7 @@
     ("alias" . ,undefined)
     ("bg" . ,undefined)
     ("cd" . ,(@@ (geesh built-ins cd) main))
-    ("command" . ,undefined)
+    ("command" . ,(@@ (geesh built-ins command) main))
     ("false" . ,(@@ (geesh built-ins false) main))
     ("fc" . ,undefined)
     ("fg" . ,undefined)

geesh/built-ins/command.scm

@@ -0,0 +1,83 @@
+;;; Gash --- Guile As SHell
+;;; Copyright © 2018 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
+;;; Copyright © 2019 Timothy Sample <samplet@ngyro.com>
+;;;
+;;; This file is part of Gash.
+;;;
+;;; Gash 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 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; Gash 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 Gash.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (geesh built-ins command)
+  #:use-module (ice-9 getopt-long)
+  #:use-module (gash config)
+  #:use-module (geesh built-ins utils))
+
+;;; Commentary:
+;;;
+;;; The 'command' utility.
+;;;
+;;; Code:
+
+(define (PATH-search-path program)
+  (search-path (string-split (getenv "PATH") #\:) program))
+
+(define main
+  (case-lambda
+    (() #t)
+    (args
+     (let* ((option-spec
+             '((describe (single-char #\V))
+               (help)
+               (show (single-char #\v))
+               (version)))
+            (options (getopt-long (cons "command" args) option-spec
+                                  #:stop-at-first-non-option #t))
+            (help? (option-ref options 'help #f))
+            (version? (option-ref options 'version #f))
+            (files (option-ref options '() '())))
+       (cond (help? (display "Usage: command [OPTION]... [COMMAND [ARG]...]
+
+Options:
+  --help     display this help and exit
+  --version  display version information and exit
+  -v         display a description of COMMAND similar to the `type' builtin
+  -V         display a more verbose description of COMMAND
+"))
+             (version? (format #t "command (GASH) ~a\n" %version))
+             ((null? files) #t)
+             ((option-ref options 'describe #f)
+              (let ((command (car files)))
+                (cond ((built-in? command)
+                       (format #t "~a is a shell builtin\n" command)
+                       EXIT_SUCCESS)
+                      ((PATH-search-path command)
+                       =>
+                       (lambda (program)
+                         (format #t "~a is ~a\n" command program)
+                         EXIT_SUCCESS))
+                      (else EXIT_FAILURE))))
+             ((option-ref options 'show #f)
+              (let ((command (car files)))
+                (cond ((built-in? command)
+                       (format #t "~a\n" command)
+                       EXIT_SUCCESS)
+                      ((PATH-search-path command)
+                       =>
+                       (lambda (program)
+                         (format #t "~a\n" program)
+                         EXIT_SUCCESS))
+                      (else EXIT_FAILURE))))
+             (else (let* ((command (car files))
+                          (built-in? command)
+                          (args-string (string-join args)))
+                     ((@@ (geesh built-ins eval) main) args-string))))))))