Make 'read' handle input field splitting.

* gash/built-ins/read.scm (split-fields): New procedure.
(main): Use it to split the input into fields and assign each field to
its corresponding variable.
* tests/read.org: New file.
* Makefile.am (FULL_TESTS): Add it.

Makefile.am

@@ -142,6 +142,7 @@ FULL_TESTS =                                    \
   tests/functions.org                           \
   tests/loops.org                               \
   tests/pipes-and-booleans.org                  \
+  tests/read.org                                \
   tests/redirects.org                           \
   tests/signals.org                             \
   tests/temporary-assignments.org               \

gash/built-ins/read.scm

@@ -1,5 +1,5 @@
 ;;; Gash -- Guile As SHell
-;;; Copyright © 2018 Timothy Sample <samplet@ngyro.com>
+;;; Copyright © 2018, 2019 Timothy Sample <samplet@ngyro.com>
 ;;;
 ;;; This file is part of Gash.
 ;;;
@@ -19,7 +19,8 @@
 (define-module (gash built-ins read)
   #:use-module (gash environment)
   #:use-module (ice-9 match)
-  #:use-module (ice-9 rdelim))
+  #:use-module (ice-9 rdelim)
+  #:use-module (srfi srfi-1))
 
 ;;; Commentary:
 ;;;
@@ -27,8 +28,56 @@
 ;;;
 ;;; Code:
 
+;; The '(gash word)' module already has a 'split-fields' procedure.
+;; However, we need to be able to specify a maximum number of fields,
+;; which it cannot do.  We could extend it, but it has to deal with
+;; quotes, which we do not here.  It is simpler to write a specialized
+;; version that can deal with 'max' without quotes than it is to
+;; extend the more general version.
+(define* (split-fields str max hard-delims soft-delims
+                       #:optional (start 0) (end (string-length str)))
+  "Split @var{str} into at most @var{max} fields.  Each individual
+occurrence of a character in the set @var{hard-delims} delimits a
+field, while contiguous sequences of characters from the set
+@var{soft-delims} are treated as a single delimiter."
+  (define non-soft-delims (char-set-complement soft-delims))
+  (define all-delims (char-set-union hard-delims soft-delims))
+
+  (define* (field+next-index str i)
+    (let* ((end* (or (string-index str all-delims i end) end))
+           (start* (string-index str non-soft-delims end* end)))
+      (values (substring str i end*)
+              (if (and start*
+                       (char-set-contains? hard-delims
+                                           (string-ref str start*)))
+                  (or (string-index str non-soft-delims (1+ start*) end) end)
+                  start*))))
+
+  (cond
+   ((string-index str non-soft-delims start end)
+    => (lambda (start*)
+         (let loop ((i start*) (count 0) (acc '()))
+           (if (>= count (1- max))
+               (reverse! (cons (string-trim-right str soft-delims i end) acc))
+               (call-with-values (lambda () (field+next-index str i))
+                 (lambda (field i*)
+                   (if i*
+                       (loop i* (1+ count) (cons field acc))
+                       (reverse! (cons field acc)))))))))
+   (else '())))
+
 (define (main . args)
   (match (read-line (current-input-port))
     ((? eof-object?) 1)
-    (str (setvar! (car args) str)
-         0)))
+    (str (let* ((limit (length args))
+                (dflt (string #\space #\tab #\newline))
+                (ifs (string->char-set (getvar "IFS" dflt)))
+                (ifs/w (char-set-intersection ifs char-set:whitespace))
+                (ifs/nw (char-set-difference ifs char-set:whitespace))
+                (fields (split-fields str limit ifs/nw ifs/w)))
+           (for-each (lambda (var field)
+                       ;; XXX: Verify that VAR is a valid variable name.
+                       (setvar! var field))
+                     args
+                     (append fields (circular-list "")))
+           0))))

tests/read.org

@@ -0,0 +1,90 @@
+;;; Gash -- Guile As SHell
+;;; 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/>.
+
+* Reads a single variable
+:script:
+#+begin_src sh
+  echo foo | {
+      read x
+      echo $x
+  }
+#+end_src
+:stdout:
+#+begin_example
+  foo
+#+end_example
+
+* Reads multiple variables
+:script:
+#+begin_src sh
+  echo foo bar | {
+      read x y
+      echo $x
+      echo $y
+  }
+#+end_src
+:stdout:
+#+begin_example
+  foo
+  bar
+#+end_example
+
+* Handles more variables than fields
+:script:
+#+begin_src sh
+  echo foo bar baz | {
+      read x y
+      echo $x
+      echo $y
+  }
+#+end_src
+:stdout:
+#+begin_example
+  foo
+  bar baz
+#+end_example
+
+* Handles more fields than variables
+:script:
+#+begin_src sh
+  echo foo | {
+      read x y
+      echo $x
+      echo $y
+  }
+#+end_src
+:stdout:
+#+begin_example
+  foo
+  
+#+end_example
+
+* Trims whitespace in extra fields
+:script:
+#+begin_src sh
+  echo foo bar 'baz   ' | {
+      read x y
+      echo $x
+      echo $y
+  }
+#+end_src
+:stdout:
+#+begin_example
+  foo
+  bar baz
+#+end_example