ash: catch EOF in read builtin

The read builtin didn't detect EOF so it wasn't possible to cleanly
terminate a loop like:

   while read -r; do echo $REPLY; done

Consider how Linux handles EOF (represented as ^D, though this isn't
echoed):

   $ awk '{print}' | xxd
   abc^D123
   ^D
   00000000: 6162 6331 3233 0a                        abc123.

Contrast with busybox-w32 on Windows (where the ^Z is echoed):

   $ awk '{print}' | xxd
   abc^Z123
   ^Z
   00000000: 6162 631a 3132 330a                      abc.123.

In both cases EOF is only detected at the start of a line.  On Linux
EOF within a line is dropped; on Windows it's output as a literal ctrl-Z.

Implement similar behaviour for the read builtin.

1 files changed, 2 insertions, 2 deletions

diff --git a/shell/shell_common.c b/shell/shell_common.c
index af05625a4..320cd88fd 100644
--- a/shell/shell_common.c
+++ b/shell/shell_common.c
@@ -235,8 +235,8 @@ shell_builtin_read(struct builtin_read_params *params)
                         int64_t key;
 
                         key = read_key(fd, NULL, timeout);
-                        if (key == 0x03 || key == -1) {
-                                /* ^C or timeout */
+                        if (key == 0x03 || key == -1 || (key == 0x1a && bufpos == 0)) {
+                                /* ^C, timeout or ^Z at start of buffer */
                                 retval = (const char *)(uintptr_t)1;
                                 goto ret;
                         }