hush: add support for ${var/pattern/repl}, conditional on bash compat

function                                             old     new   delta
expand_vars_to_list                                 2386    2833    +447
expand_string_to_string                               69     110     +41
parse_dollar                                         681     721     +40
hush_main                                            963     945     -18
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 3/1 up/down: 528/-18)           Total: 510 bytes

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>

1 files changed, 150 insertions, 29 deletions

diff --git a/shell/hush.c b/shell/hush.c
index 4f80b7d83..9a08e90c9 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -50,7 +50,6 @@
  *
  * Bash compat TODO:
  *      redirection of stdout+stderr: &> and >&
- *      subst operator: ${var/[/]expr/expr}
  *      brace expansion: one/{two,three,four}
  *      reserved words: function select
  *      advanced test: [[ ]]
@@ -330,6 +329,17 @@
 #define _SPECIAL_VARS_STR     "_*@$!?#"
 #define SPECIAL_VARS_STR     ("_*@$!?#" + 1)
 #define NUMERIC_SPECVARS_STR ("_*@$!?#" + 3)
+#if ENABLE_HUSH_BASH_COMPAT
+/* Support / and // replace ops */
+/* Note that // is stored as \ in "encoded" string representation */
+# define VAR_ENCODED_SUBST_OPS      "\\/%#:-=+?"
+# define VAR_SUBST_OPS             ("\\/%#:-=+?" + 1)
+# define MINUS_PLUS_EQUAL_QUESTION ("\\/%#:-=+?" + 5)
+#else
+# define VAR_ENCODED_SUBST_OPS      "%#:-=+?"
+# define VAR_SUBST_OPS              "%#:-=+?"
+# define MINUS_PLUS_EQUAL_QUESTION ("%#:-=+?" + 3)
+#endif
 
 #define SPECIAL_VAR_SYMBOL   3
 
@@ -2600,6 +2610,60 @@ static arith_t expand_and_evaluate_arith(const char *arg, int *errcode_p)
 }
 #endif
 
+#if ENABLE_HUSH_BASH_COMPAT
+/* ${var/[/]pattern[/repl]} helpers */
+static char *strstr_pattern(char *val, const char *pattern, int *size)
+{
+        while (1) {
+                char *end = scan_and_match(val, pattern, SCAN_MOVE_FROM_RIGHT + SCAN_MATCH_LEFT_HALF);
+                debug_printf_varexp("val:'%s' pattern:'%s' end:'%s'\n", val, pattern, end);
+                if (end) {
+                        *size = end - val;
+                        return val;
+                }
+                if (*val == '\0')
+                        return NULL;
+                /* Optimization: if "*pat" did not match the start of "string",
+                 * we know that "tring", "ring" etc will not match too:
+                 */
+                if (pattern[0] == '*')
+                        return NULL;
+                val++;
+        }
+}
+static char *replace_pattern(char *val, const char *pattern, const char *repl, char exp_op)
+{
+        char *result = NULL;
+        unsigned res_len = 0;
+        unsigned repl_len = strlen(repl);
+
+        while (1) {
+                int size;
+                char *s = strstr_pattern(val, pattern, &size);
+                if (!s)
+                        break;
+
+                result = xrealloc(result, res_len + (s - val) + repl_len + 1);
+                memcpy(result + res_len, val, s - val);
+                res_len += s - val;
+                strcpy(result + res_len, repl);
+                res_len += repl_len;
+                debug_printf_varexp("val:'%s' s:'%s' result:'%s'\n", val, s, result);
+
+                val = s + size;
+                if (exp_op == '/')
+                        break;
+        }
+        if (val[0] && result) {
+                result = xrealloc(result, res_len + strlen(val) + 1);
+                strcpy(result + res_len, val);
+                debug_printf_varexp("val:'%s' result:'%s'\n", val, result);
+        }
+        debug_printf_varexp("result:'%s'\n", result);
+        return result;
+}
+#endif
+
 /* Expand all variable references in given string, adding words to list[]
  * at n, n+1,... positions. Return updated n (so that list[n] is next one
  * to be filled). This routine is extremely tricky: has to deal with
@@ -2750,7 +2814,7 @@ static NOINLINE int expand_vars_to_list(o_string *output, int n, char *arg, char
 
                         var = arg;
                         *p = '\0';
-                        exp_saveptr = arg[1] ? strchr("%#:-=+?", arg[1]) : NULL;
+                        exp_saveptr = arg[1] ? strchr(VAR_ENCODED_SUBST_OPS, arg[1]) : NULL;
                         first_char = arg[0] = first_ch & 0x7f;
                         exp_op = 0;
 
@@ -2767,7 +2831,7 @@ static NOINLINE int expand_vars_to_list(o_string *output, int n, char *arg, char
                                         exp_saveptr = var + 1;
                                 } else {
                                         /* ${?}, ${var}, ${var:0}, ${var[:]%0} etc */
-                                        exp_saveptr = var+1 + strcspn(var+1, "%#:-=+?");
+                                        exp_saveptr = var+1 + strcspn(var+1, VAR_ENCODED_SUBST_OPS);
                                 }
                                 exp_op = exp_save = *exp_saveptr;
                                 if (exp_op) {
@@ -2775,7 +2839,7 @@ static NOINLINE int expand_vars_to_list(o_string *output, int n, char *arg, char
                                         if (exp_op == ':') {
                                                 exp_op = *exp_word++;
                                                 if (ENABLE_HUSH_BASH_COMPAT
-                                                 && (exp_op == '\0' || !strchr("%#:-=+?"+3, exp_op))
+                                                 && (exp_op == '\0' || !strchr(MINUS_PLUS_EQUAL_QUESTION, exp_op))
                                                 ) {
                                                         /* oops... it's ${var:N[:M]}, not ${var:?xxx} or some such */
                                                         exp_op = ':';
@@ -2799,7 +2863,7 @@ static NOINLINE int expand_vars_to_list(o_string *output, int n, char *arg, char
                                         val = utoa(G.root_pid);
                                         break;
                                 case '!': /* bg pid */
-                                        val = G.last_bg_pid ? utoa(G.last_bg_pid) : (char*)"";
+                                        val = G.last_bg_pid ? utoa(G.last_bg_pid) : "";
                                         break;
                                 case '?': /* exitcode */
                                         val = utoa(G.last_exitcode);
@@ -2843,13 +2907,47 @@ static NOINLINE int expand_vars_to_list(o_string *output, int n, char *arg, char
                                                 //              exp_op, to_be_freed, exp_word, loc);
                                                 free(exp_exp_word);
                                                 if (loc) { /* match was found */
-                                                        if (scan_flags & SCAN_MATCH_LEFT_HALF) /* # or ## */
+                                                        if (scan_flags & SCAN_MATCH_LEFT_HALF) /* #[#] */
                                                                 val = loc;
-                                                        else /* % or %% */
+                                                        else /* %[%] */
                                                                 *loc = '\0';
                                                 }
                                         }
-                                } else if (exp_op == ':') {
+                                }
+#if ENABLE_HUSH_BASH_COMPAT
+                                else if (exp_op == '/' || exp_op == '\\') {
+                                        /* Empty variable always gives nothing: */
+                                        // "v=''; echo ${v/*/w}" prints ""
+                                        if (val && val[0]) {
+                                                /* It's ${var/[/]pattern[/repl]} thing */
+                                                char *pattern, *repl, *t;
+                                                pattern = expand_pseudo_dquoted(exp_word);
+                                                if (!pattern)
+                                                        pattern = xstrdup(exp_word);
+                                                debug_printf_varexp("pattern:'%s'->'%s'\n", exp_word, pattern);
+                                                *p++ = SPECIAL_VAR_SYMBOL;
+                                                exp_word = p;
+                                                p = strchr(p, SPECIAL_VAR_SYMBOL);
+                                                *p = '\0';
+                                                repl = expand_pseudo_dquoted(exp_word);
+                                                debug_printf_varexp("repl:'%s'->'%s'\n", exp_word, repl);
+                                                /* HACK ALERT. We depend here on the fact that
+                                                 * G.global_argv and results of utoa and get_local_var_value
+                                                 * are actually in writable memory:
+                                                 * replace_pattern momentarily stores NULs there. */
+                                                t = (char*)val;
+                                                to_be_freed = replace_pattern(t,
+                                                                pattern,
+                                                                (repl ? repl : exp_word),
+                                                                exp_op);
+                                                if (to_be_freed) /* at least one replace happened */
+                                                        val = to_be_freed;
+                                                free(pattern);
+                                                free(repl);
+                                        }
+                                }
+#endif
+                                else if (exp_op == ':') {
 #if ENABLE_HUSH_BASH_COMPAT && ENABLE_SH_MATH_SUPPORT
         /* It's ${var:N[:M]} bashism.
          * Note that in encoded form it has TWO parts:
@@ -3084,6 +3182,16 @@ static char *expand_string_to_string(const char *str)
 {
         char *argv[2], **list;
 
+        /* This is generally an optimization, but it also
+         * handles "", which otherwise trips over !list[0] check below.
+         * (is this ever happens that we actually get str="" here?)
+         */
+        if (!strchr(str, SPECIAL_VAR_SYMBOL) && !strchr(str, '\\')) {
+                //TODO: Can use on strings with \ too, just unbackslash() them?
+                debug_printf_expand("string_to_string(fast)='%s'\n", str);
+                return xstrdup(str);
+        }
+
         argv[0] = (char*)str;
         argv[1] = NULL;
         list = expand_variables(argv, EXPVAR_FLAG_ESCAPE_VARS | EXPVAR_FLAG_SINGLEWORD);
@@ -3271,7 +3379,7 @@ static void re_execute_shell(char ***to_free, const char *s,
         *pp++ = (char *) G.argv0_for_re_execing;
         *pp++ = param_buf;
         for (cur = G.top_var; cur; cur = cur->next) {
-                if (cur->varstr == hush_version_str)
+                if (strcmp(cur->varstr, hush_version_str) == 0)
                         continue;
                 if (cur->flg_read_only) {
                         *pp++ = (char *) "-R";
@@ -6170,8 +6278,8 @@ static void add_till_backquote(o_string *dest, struct in_str *input)
  *
  * Also adapted to eat ${var%...} and $((...)) constructs, since ... part
  * can contain arbitrary constructs, just like $(cmd).
- * In bash compat mode, it needs to also be able to stop on '}' or ':'
- * for ${var:N[:M]} parsing.
+ * In bash compat mode, it needs to also be able to stop on ':' or '/'
+ * for ${var:N[:M]} and ${var/P[/R]} parsing.
  */
 #define DOUBLE_CLOSE_CHAR_FLAG 0x80
 static int add_till_closing_bracket(o_string *dest, struct in_str *input, unsigned end_ch)
@@ -6323,19 +6431,30 @@ static int parse_dollar(o_string *as_string,
                                 /* handle parameter expansions
                                  * http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02_06_02
                                  */
-                                if (!strchr("%#:-=+?", ch)) /* ${var<bad_char>... */
+                                if (!strchr(VAR_SUBST_OPS, ch)) /* ${var<bad_char>... */
                                         goto bad_dollar_syntax;
-                                o_addchr(dest, ch);
 
                                 /* Eat everything until closing '}' (or ':') */
                                 end_ch = '}';
                                 if (ENABLE_HUSH_BASH_COMPAT
                                  && ch == ':'
-                                 && !strchr("%#:-=+?"+3, i_peek(input))
+                                 && !strchr(MINUS_PLUS_EQUAL_QUESTION, i_peek(input))
                                 ) {
                                         /* It's ${var:N[:M]} thing */
                                         end_ch = '}' * 0x100 + ':';
                                 }
+                                if (ENABLE_HUSH_BASH_COMPAT
+                                 && ch == '/'
+                                ) {
+                                        /* It's ${var/[/]pattern[/repl]} thing */
+                                        if (i_peek(input) == '/') { /* ${var//pattern[/repl]}? */
+                                                i_getch(input);
+                                                nommu_addchr(as_string, '/');
+                                                ch = '\\';
+                                        }
+                                        end_ch = '}' * 0x100 + '/';
+                                }
+                                o_addchr(dest, ch);
  again:
                                 if (!BB_MMU)
                                         pos = dest->length;
@@ -6352,14 +6471,18 @@ static int parse_dollar(o_string *as_string,
                                 if (ENABLE_HUSH_BASH_COMPAT && (end_ch & 0xff00)) {
                                         /* close the first block: */
                                         o_addchr(dest, SPECIAL_VAR_SYMBOL);
-                                        /* while parsing N from ${var:N[:M]}... */
+                                        /* while parsing N from ${var:N[:M]}
+                                         * or pattern from ${var/[/]pattern[/repl]} */
                                         if ((end_ch & 0xff) == last_ch) {
-                                                /* ...got ':' - parse the rest */
+                                                /* got ':' or '/'- parse the rest */
                                                 end_ch = '}';
                                                 goto again;
                                         }
-                                        /* ...got '}', not ':' - it's ${var:N}! emulate :999999999 */
-                                        o_addstr(dest, "999999999");
+                                        /* got '}' */
+                                        if (end_ch == '}' * 0x100 + ':') {
+                                                /* it's ${var:N} - emulate :999999999 */
+                                                o_addstr(dest, "999999999");
+                                        } /* else: it's ${var/[/]pattern} */
                                 }
                                 break;
                         }
@@ -7186,13 +7309,6 @@ static int set_mode(const char cstate, const char mode)
 int hush_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int hush_main(int argc, char **argv)
 {
-        static const struct variable const_shell_ver = {
-                .next = NULL,
-                .varstr = (char*)hush_version_str,
-                .max_len = 1, /* 0 can provoke free(name) */
-                .flg_export = 1,
-                .flg_read_only = 1,
-        };
         int opt;
         unsigned builtin_argc;
         char **e;
@@ -7205,10 +7321,18 @@ int hush_main(int argc, char **argv)
         G.argv0_for_re_execing = argv[0];
 #endif
         /* Deal with HUSH_VERSION */
-        G.shell_ver = const_shell_ver; /* copying struct here */
+        G.shell_ver.flg_export = 1;
+        G.shell_ver.flg_read_only = 1;
+        /* Code which handles ${var/P/R} needs writable values for all variables,
+         * therefore we xstrdup: */
+        G.shell_ver.varstr = xstrdup(hush_version_str),
         G.top_var = &G.shell_ver;
         debug_printf_env("unsetenv '%s'\n", "HUSH_VERSION");
         unsetenv("HUSH_VERSION"); /* in case it exists in initial env */
+        /* reinstate HUSH_VERSION in environment */
+        debug_printf_env("putenv '%s'\n", G.shell_ver.varstr);
+        putenv(G.shell_ver.varstr);
+
         /* Initialize our shell local variables with the values
          * currently living in the environment */
         cur_var = G.top_var;
@@ -7224,9 +7348,6 @@ int hush_main(int argc, char **argv)
                 }
                 e++;
         }
-        /* reinstate HUSH_VERSION */
-        debug_printf_env("putenv '%s'\n", hush_version_str);
-        putenv((char *)hush_version_str);
 
         /* Export PWD */
         set_pwd_var(/*exp:*/ 1);