hush: explain "empty quoted str marker" trick

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 11 insertions, 5 deletions

diff --git a/shell/hush.c b/shell/hush.c
index d65da3b98..002140b1a 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -5656,15 +5656,20 @@ static struct pipe *parse_stream(char **pstring,
                 nommu_addchr(&ctx.as_string, ch);
                 if (ch == '\'') {
                         ctx.word.has_quoted_part = 1;
-                        next = i_getch(input);
-                        if (next == '\'' && !ctx.pending_redirect/*why?*/) {
+                        ch = i_getch(input);
+                        if (ch == '\'' && !ctx.pending_redirect/*why?*/) {
  insert_empty_quoted_str_marker:
-                                nommu_addchr(&ctx.as_string, next);
+                                nommu_addchr(&ctx.as_string, ch);
+//Just inserting nothing doesn't work: consider
+// CMD $EMPTYVAR
+// CMD ''
+//At execution time both will expand argv[1] to empty string
+//and thus the argument will "vanish".
+//But for second CMD, it should not vanish!
                                 o_addchr(&ctx.word, SPECIAL_VAR_SYMBOL);
                                 o_addchr(&ctx.word, SPECIAL_VAR_SYMBOL);
                                 continue; /* get next char */
                         }
-                        ch = next;
                         while (1) {
                                 if (ch == EOF) {
                                         syntax_error_unterm_ch('\'');
@@ -5789,6 +5794,7 @@ static struct pipe *parse_stream(char **pstring,
                                 if ((ctx.is_assignment == MAYBE_ASSIGNMENT
                                     || ctx.is_assignment == WORD_IS_KEYWORD)
                                  && ch == '='
+                                // && !ctx.word.has_quoted_part // unnecessary, "empty quoted str marker" trick handles this too
                                  && endofname(ctx.word.data)[0] == '='
                                 ) {
                                         ctx.is_assignment = DEFINITELY_ASSIGNMENT;
@@ -5983,7 +5989,7 @@ static struct pipe *parse_stream(char **pstring,
                 case '"':
                         ctx.word.has_quoted_part = 1;
                         if (next == '"' && !ctx.pending_redirect) {
-                                i_getch(input); /* eat second " */
+                                ch = i_getch(input); /* eat second " */
                                 goto insert_empty_quoted_str_marker;
                         }
                         if (ctx.is_assignment == NOT_ASSIGNMENT)