4bf085424
Denys Vlasenko
2018-08-11
Subject
hush: add a comment on how globbing (should) work
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shell/hush.c+35 -0
| @@ -3151,6 +3151,41 @@ static int o_get_last_ptr(o_string *o, int n) | |
| return ((int)(uintptr_t)list[n-1]) + string_start; | |
| } | |
| + | /* |
| + | * Globbing routines. |
| + | * |
| + | * Most words in commands need to be globbed, even ones which are |
| + | * (single or double) quoted. This stems from the possiblity of |
| + | * constructs like "abc"* and 'abc'* - these should be globbed. |
| + | * Having a different code path for fully-quoted strings ("abc", |
| + | * 'abc') would only help performance-wise, but we still need |
| + | * code for partially-quoted strings. |
| + | * |
| + | * Unfortunately, if we want to match bash and ash behavior in all cases, |
| + | * the logic can't be see as "shell-syntax argument is first transformed |
| + | * to a string, then globbed, and if globbing does not match anything, |
| + | * it is used verbatim". Here are two examples where it fails: |
| + | * |
| + | * echo 'b\*'? |
| + | * |
| + | * The globbing can't be avoided (because of '?' at the end). |
| + | * The glob pattern is: b\\\*? - IOW, both \ and * are literals |
| + | * and are glob-escaped. If this does not match, bash/ash print b\*? |
| + | * - IOW: they "unbackslash" the pattern. |
| + | * Now, look at this: |
| + | * |
| + | * v='\\\*'; echo b$v? |
| + | * |
| + | * The glob pattern is the same here: b\\\*? - an unquoted $var expansion |
| + | * should be used as glob pattern with no changes. However, if glob |
| + | * does not match, bash/ash print b\\\*? - NOT THE SAME as 1st example! |
| + | * |
| + | * ash implements this by having an encoded representation of the word |
| + | * to glob, which IS NOT THE SAME as the glob pattern - it has more data. |
| + | * Glob pattern is derived from it. If glob fails, the decision what result |
| + | * should be is made using that encoded representation. Not glob pattern. |
| + | */ |
| + | |
| #if ENABLE_HUSH_BRACE_EXPANSION | |
| /* There in a GNU extension, GLOB_BRACE, but it is not usable: | |
| * first, it processes even {a} (no commas), second, | |