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diff -urpN busybox-1.17.1/findutils/grep.c busybox-1.17.1-grep/findutils/grep.c
--- busybox-1.17.1/findutils/grep.c 2010-07-06 04:25:54.000000000 +0200
+++ busybox-1.17.1-grep/findutils/grep.c 2010-08-23 02:37:08.000000000 +0200
@@ -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 -urpN busybox-1.17.1/testsuite/grep.tests busybox-1.17.1-grep/testsuite/grep.tests
--- busybox-1.17.1/testsuite/grep.tests 2010-07-06 04:25:54.000000000 +0200
+++ busybox-1.17.1-grep/testsuite/grep.tests 2010-08-23 02:37:08.000000000 +0200
@@ -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
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