2 files changed, 50 insertions, 24 deletions

diff --git a/editors/sed.c b/editors/sed.c
index a2df93165..87fc755eb 100644
--- a/editors/sed.c
+++ b/editors/sed.c
@@ -673,7 +673,7 @@ static void do_subst_w_backrefs(char *line, char *replace)
 
         /* go through the replacement string */
         for (i = 0; replace[i]; i++) {
-                /* if we find a backreference (\1, \2, etc.) print the backref'ed * text */
+                /* if we find a backreference (\1, \2, etc.) print the backref'ed text */
                 if (replace[i] == '\\') {
                         unsigned backref = replace[++i] - '0';
                         if (backref <= 9) {
@@ -707,8 +707,10 @@ static void do_subst_w_backrefs(char *line, char *replace)
 static int do_subst_command(sed_cmd_t *sed_cmd, char **line_p)
 {
         char *line = *line_p;
-        int altered = 0;
         unsigned match_count = 0;
+        bool altered = 0;
+        bool prev_match_empty = 1;
+        bool tried_at_eol = 0;
         regex_t *current_regex;
 
         current_regex = sed_cmd->sub_match;
@@ -737,46 +739,64 @@ static int do_subst_command(sed_cmd_t *sed_cmd, char **line_p)
         do {
                 int i;
 
-                /* Work around bug in glibc regexec, demonstrated by:
-                 * echo " a.b" | busybox sed 's [^ .]* x g'
-                 * The match_count check is so not to break
-                 * echo "hi" | busybox sed 's/^/!/g'
-                 */
-                if (!G.regmatch[0].rm_so && !G.regmatch[0].rm_eo && match_count) {
-                        pipe_putc(*line++);
-                        goto next;
-                }
-
                 match_count++;
 
                 /* If we aren't interested in this match, output old line to
-                   end of match and continue */
+                 * end of match and continue */
                 if (sed_cmd->which_match
                  && (sed_cmd->which_match != match_count)
                 ) {
                         for (i = 0; i < G.regmatch[0].rm_eo; i++)
                                 pipe_putc(*line++);
+                        /* Null match? Print one more char */
+                        if (G.regmatch[0].rm_so == i && *line)
+                                pipe_putc(*line++);
                         goto next;
                 }
 
-                /* print everything before the match */
+                /* Print everything before the match */
                 for (i = 0; i < G.regmatch[0].rm_so; i++)
                         pipe_putc(line[i]);
 
-                /* then print the substitution string */
-                do_subst_w_backrefs(line, sed_cmd->string);
+                /* Then print the substitution string,
+                 * unless we just matched empty string after non-empty one.
+                 * Example: string "cccd", pattern "c*", repl "R":
+                 * result is "RdR", not "RRdR": first match "ccc",
+                 * second is "" before "d", third is "" after "d".
+                 * Second match is NOT replaced!
+                 */
+                if (prev_match_empty || i != 0) {
+                        dbg("inserting replacement at %d in '%s'", i, line);
+                        do_subst_w_backrefs(line, sed_cmd->string);
+                } else {
+                        dbg("NOT inserting replacement at %d in '%s'", i, line);
+                }
+
+                /* If matched string is empty (f.e. "c*" pattern),
+                 * copy verbatim one char after it before attempting more matches
+                 */
+                prev_match_empty = (G.regmatch[0].rm_eo == i);
+                if (prev_match_empty && line[i]) {
+                        pipe_putc(line[i]);
+                        G.regmatch[0].rm_eo++;
+                }
 
-                /* advance past the match */
+                /* Advance past the match */
+                dbg("line += %d", G.regmatch[0].rm_eo);
                 line += G.regmatch[0].rm_eo;
-                /* flag that something has changed */
-                altered++;
+                /* Flag that something has changed */
+                altered = 1;
 
                 /* if we're not doing this globally, get out now */
                 if (sed_cmd->which_match != 0)
                         break;
  next:
-                if (*line == '\0')
-                        break;
+                /* Exit if we are at EOL and already tried matching at it */
+                if (*line == '\0') {
+                        if (tried_at_eol)
+                                break;
+                        tried_at_eol = 1;
+                }
 
 //maybe (G.regmatch[0].rm_eo ? REG_NOTBOL : 0) instead of unconditional REG_NOTBOL?
         } while (regexec(current_regex, line, 10, G.regmatch, REG_NOTBOL) != REG_NOMATCH);
@@ -1127,7 +1147,7 @@ static void process_files(void)
                 case 's':
                         if (!do_subst_command(sed_cmd, &pattern_space))
                                 break;
-                        dbg("do_subst_command succeeeded:'%s'", pattern_space);
+                        dbg("do_subst_command succeeded:'%s'", pattern_space);
                         substituted |= 1;
 
                         /* handle p option */
diff --git a/testsuite/sed.tests b/testsuite/sed.tests
index 9fa8e190c..375beb518 100755
--- a/testsuite/sed.tests
+++ b/testsuite/sed.tests
@@ -52,10 +52,8 @@ testing "sed with empty match" "sed 's/z*//g'" "string\n" "" "string\n"
 testing "sed s//p" "sed -e s/foo/bar/p -e s/bar/baz/p" "bar\nbaz\nbaz\n" \
         "" "foo\n"
 testing "sed -n s//p" "sed -ne s/abc/def/p" "def\n" "" "abc\n"
-test x"$SKIP_KNOWN_BUGS" = x"" && {
 testing "sed s//g (exhaustive)" "sed -e 's/[[:space:]]*/,/g'" ",1,2,3,4,5,\n" \
         "" "12345\n"
-}
 testing "sed s arbitrary delimiter" "sed -e 's woo boing '" "boing\n" "" "woo\n"
 testing "sed s chains" "sed -e s/foo/bar/ -e s/bar/baz/" "baz\n" "" "foo\n"
 testing "sed s chains2" "sed -e s/foo/bar/ -e s/baz/nee/" "bar\n" "" "foo\n"
@@ -296,6 +294,14 @@ testing "sed -i finishes ranges correctly" \
         "sed '1,2d' -i input; echo \$?; cat input" \
         "0\n3\n4\n" "1\n2\n3\n4\n" ""
 
+testing "sed zero chars match/replace advances correctly 1" \
+        "sed 's/l*/@/g'" \
+        "@h@e@o@\n" "" "helllo\n"
+
+testing "sed zero chars match/replace advances correctly 2" \
+        "sed 's [^ .]* x g'" \
+        "x x.x\n" "" " a.b\n"
+
 # testing "description" "commands" "result" "infile" "stdin"
 
 exit $FAILCOUNT