cli: hush_modern: Enable using < and > as string compare operators

In Busybox hush, '<' and '>' are used as redirection operators.
For example, cat foo > bar will write content of file foo inside file bar.
In U-Boot, we do not have file system, so we can hardly redirect command output
inside a file.

But, in actual U-Boot hush, these operators ('<' and '>') are used as string
compare operators.
For example, test aaa < bbb returns 0 as aaa is before bbb in the dictionary.
Busybox hush also permits this, but operators need to be escaped ('\<' and
'\>').
Indeed, if escaping is needed it permits the developer to think about its code,
as in a lot of case, we want to compare integers (using '-lt' or '-gt') rather
than strings.

As testing in U-Boot is handled by the test command, we will stick with the
original behaviour and not adapt to Busybox one.

Nonetheless, if one day we decide to implement test with '[[ ]]', we will then
stick to upstream Busybox behavior.

Signed-off-by: Francis Laniel <francis.laniel@amarulasolutions.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

common/cli_hush_upstream.c

@@ -6159,7 +6159,28 @@ static struct pipe *parse_stream(char **pstring,
 			if (parse_redirect(&ctx, redir_fd, redir_style, input))
 				goto parse_error_exitcode1;
 			continue; /* get next char */
-#endif /* !__U_BOOT__ */
+#else /* __U_BOOT__ */
+			/*
+			 * In U-Boot, '<' and '>' can be used in test command to test if
+			 * a string is, alphabetically, before or after another.
+			 * In 2021 Busybox hush, we will keep the same behavior and so not treat
+			 * them as redirection operator.
+			 *
+			 * Indeed, in U-Boot, tests are handled by the test command and not by the
+			 * shell code.
+			 * So, better to give this character as input to test command.
+			 *
+			 * NOTE In my opinion, when you use '<' or '>' I am almost sure
+			 * you wanted to use "-gt" or "-lt" in place, so thinking to
+			 * escape these will make you should check your code (sh syntax
+			 * at this level is, for me, error prone).
+			 */
+			case '>':
+				fallthrough;
+			case '<':
+				o_addQchr(&ctx.word, ch);
+				continue;
+#endif /* __U_BOOT__ */
 		case '#':
 			if (ctx.word.length == 0 && !ctx.word.has_quoted_part) {
 				/* skip "#comment" */