[RFC PATCH 07/11] cmd: echo: Use getopt() with '+' prefix for option parsing

[Simon Glass]

The 'echo' command's option parser is a single strcmp against argv[1]
that decides whether to suppress the trailing newline. Convert it to
getopt() so echo follows the same shape as the other commands in this
series and exercises the '+' prefix that POSIX-style 'stop at first
non-option' callers need.

The optstring uses the '+' prefix to preserve bash echo behaviour: -n is
honoured only as the very first argument, so 'echo hello -n' still
prints 'hello -n\n' verbatim.

Two minor differences from the bash builtin remain, both of which
the user can work around with quoting or --:

* -x (an unknown short option) returns CMD_RET_USAGE rather than
  printing literally; use 'echo -- -x' to print it.
* -nfoo (joined form) parses -n and then errors on the trailing
  characters.

Add three test cases that pin down the new behaviour: trailing -n stays
literal, -- ends option parsing, and -- is consumed even after a
recognised flag. The positional loop uses getopt_pop() as an iterator.
CMD_ECHO selects GETOPT so the parser is linked in on boards that don't
already enable it.

Signed-off-by: Simon Glass <sjg at chromium.org>
---

 cmd/Kconfig          |  1 +
 cmd/echo.c           | 23 ++++++++++++++---------
 test/cmd/test_echo.c | 10 ++++++++++
 3 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/cmd/Kconfig b/cmd/Kconfig
index c71c6824a19..709696c3c41 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -1916,6 +1916,7 @@ config CMD_CAT
 config CMD_ECHO
 	bool "echo"
 	default y
+	select GETOPT
 	help
 	  Echo args to console
 
diff --git a/cmd/echo.c b/cmd/echo.c
index d1346504cfb..63422c75cc6 100644
--- a/cmd/echo.c
+++ b/cmd/echo.c
@@ -5,27 +5,32 @@
  */
 
 #include <command.h>
-#include <linux/string.h>
+#include <getopt.h>
 
 static int do_echo(struct cmd_tbl *cmdtp, int flag, int argc,
 		   char *const argv[])
 {
-	int i = 1;
+	struct getopt_state gs;
 	bool space = false;
 	bool newline = true;
+	char *arg;
+	int opt;
 
-	if (argc > 1) {
-		if (!strcmp(argv[1], "-n")) {
+	getopt_init_state(&gs, argc, argv);
+	while ((opt = getopt(&gs, "+n")) > 0) {
+		switch (opt) {
+		case 'n':
 			newline = false;
-			++i;
+			break;
+		default:
+			return CMD_RET_USAGE;
 		}
 	}
 
-	for (; i < argc; ++i) {
-		if (space) {
+	while ((arg = getopt_pop(&gs))) {
+		if (space)
 			putc(' ');
-		}
-		puts(argv[i]);
+		puts(arg);
 		space = true;
 	}
 
diff --git a/test/cmd/test_echo.c b/test/cmd/test_echo.c
index 7ed534742f7..5fc139fbe68 100644
--- a/test/cmd/test_echo.c
+++ b/test/cmd/test_echo.c
@@ -35,6 +35,16 @@ static struct test_data echo_data[] = {
 	/* Test handling of shell variables. */
 	{"setenv jQx; for jQx in 1 2 3; do echo -n \"${jQx}, \"; done; echo;",
 	 "1, 2, 3, "},
+	/* -n only suppresses the newline when it comes before any
+	 * positional argument; a trailing -n is just another argument.
+	 */
+	{"echo hello -n", "hello -n"},
+	/* "--" ends option parsing, so a following dash-prefixed token
+	 * is printed verbatim instead of being rejected.
+	 */
+	{"echo -- -x", "-x"},
+	/* "--" is consumed even when it follows a recognised flag. */
+	{"echo -n -- foo; echo done", "foodone"},
 };
 
 static int lib_test_hush_echo(struct unit_test_state *uts)
-- 
2.43.0