[git commit master 1/1] grep: fix -o match with empty string (suggested by Colin Watson <cjwatson at ubuntu.com>)

[Denys Vlasenko]

commit: http://git.busybox.net/busybox/commit/?id=3d8b96d58d74d775e34de8d19a03db5380eb8f2c
branch: http://git.busybox.net/busybox/commit/?id=refs/heads/master

function                                             old     new   delta
grep_file                                           1216    1251     +35

Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
 findutils/grep.c     |   10 +++++++---
 testsuite/grep.tests |    4 ++++
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/findutils/grep.c b/findutils/grep.c
index 688ea6a..024f276 100644
--- a/findutils/grep.c
+++ b/findutils/grep.c
@@ -461,15 +461,19 @@ static int grep_file(FILE *file)
 						if (found)
 							print_line(gl->pattern, strlen(gl->pattern), linenum, ':');
 					} else while (1) {
+						unsigned start = gl->matched_range.rm_so;
 						unsigned end = gl->matched_range.rm_eo;
+						unsigned len = end - start;
 						char old = line[end];
 						line[end] = '\0';
-						print_line(line + gl->matched_range.rm_so,
-								end - gl->matched_range.rm_so,
-								linenum, ':');
+						/* Empty match is not printed: try "echo test | grep -o ''" */
+						if (len != 0)
+							print_line(line + start, len, linenum, ':');
 						if (old == '\0')
 							break;
 						line[end] = old;
+						if (len == 0)
+							end++;
 #if !ENABLE_EXTRA_COMPAT
 						if (regexec(&gl->compiled_regex, line + end,
 								1, &gl->matched_range, REG_NOTBOL) != 0)
diff --git a/testsuite/grep.tests b/testsuite/grep.tests
index 520a184..ffce033 100755
--- a/testsuite/grep.tests
+++ b/testsuite/grep.tests
@@ -98,5 +98,9 @@ testing "grep -o does not loop forever" \
 	'grep -o "[^/]*$"' \
 	"test\n" \
 	"" "/var/test\n"
+testing "grep -o does not loop forever on zero-length match" \
+	'grep -o "" | head -n1' \
+	"" \
+	"" "test\n"
 
 exit $FAILCOUNT
-- 
1.7.1