cad5a79bd
Denys Vlasenko
2025-08-14
Subject
hush: explain "empty quoted str marker" trick
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shell/hush.c+11 -5
| @@ -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) | |