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 '>'), so we stick here to this behavior. Also, 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.
Signed-off-by: Francis Laniel francis.laniel@amarulasolutions.com Reviewed-by: Simon Glass sjg@chromium.org --- common/cli_hush_upstream.c | 28 +++++++++++++++++++++++++++- 1 file changed, 27 insertions(+), 1 deletion(-)
diff --git a/common/cli_hush_upstream.c b/common/cli_hush_upstream.c index f2619eb49a..d1f76d4df5 100644 --- a/common/cli_hush_upstream.c +++ b/common/cli_hush_upstream.c @@ -6128,7 +6128,33 @@ 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, using test foo < bar will show the + * following error: + * hush: can't open 'bar': No such file or directory + * Indeed, in this context, '>' and '<' are used as redirection + * operators, to use them as sorting operators, one should use: + * [[ foo < bar ]] + * Or: + * test foo < bar + * + * For the moment, we will not implement [[ ]], so we will need + * the user to escape these operators to use them as string + * comparaison operators. + * 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 '<': + printf("Redirection operator ('%c') is not supported!\nPlease escape it ('\%c') to use it as string comparaison operator.\n", (char) ch, (char) ch); + goto parse_error_exitcode1; +#endif /* __U_BOOT__ */ case '#': if (ctx.word.length == 0 && !ctx.word.has_quoted_part) { /* skip "#comment" */