# HG changeset patch
# User Jonathan Clairembault <jonathan@clairembault.fr>
# Date 1353659093 -3600
# Node ID 8c10cf7bace0b77f4b9bbbee4ce21c48623db62a
# Parent  3417db95f24bd59b3bbf6cfe10ab8aaaeb51b38f
expand: handle backspace.

diff -r 3417db95f24b -r 8c10cf7bace0 scripts/test/expand.test
--- a/scripts/test/expand.test	Fri Nov 23 00:06:28 2012 +0100
+++ b/scripts/test/expand.test	Fri Nov 23 09:24:53 2012 +0100
@@ -11,6 +11,7 @@
 testing "expand default stdin" "expand"  "        foo     bar\n" "" "\tfoo\tbar\n"
 testing "expand single" "expand -t 2 input" "  foo bar\n" "\tfoo\tbar\n" ""
 testing "expand tablist" "expand -t 5,10,12 input" "     foo  bar foo\n" "\tfoo\tbar\tfoo\n" ""
+testing "expand backspace" "expand input" "foobarf bar\n" "foobarfoo\b\b\tbar\n" ""
 
 # advanced tests
 
diff -r 3417db95f24b -r 8c10cf7bace0 toys/posix/expand.c
--- a/toys/posix/expand.c	Fri Nov 23 00:06:28 2012 +0100
+++ b/toys/posix/expand.c	Fri Nov 23 09:24:53 2012 +0100
@@ -1,7 +1,5 @@
 /* expand.c - expands tabs to space
  *
- * FIXME: handle backspace.
- *
  * Copyright 2012 Jonathan Clairembault <jonathan at clairembault dot fr>
  *
  * See http://http://pubs.opengroup.org/onlinepubs/9699919799/nframe.html
@@ -116,7 +114,10 @@
         wrlinei += count;
       } else { /* copy input to output */
         wrbuf[wrbufi++] = rdbuf[rdbufi];
-        wrlinei += 1;
+        if (rdbuf[rdbufi] == '\b') /* go back one column on backspace */
+          wrlinei -= !!wrlinei; /* do not go below zero */
+        else
+          wrlinei += 1;
         /* flush expand buffer and reset tablist at newline */
         if (rdbuf[rdbufi] == '\n') {
           writeall(STDOUT_FILENO, wrbuf, wrbufi);