Merge branch 'jc/grep'

* jc/grep: (22 commits)
  Fix silly typo in new builtin grep
  builtin-grep: unparse more command line options.
  builtin-grep: use external grep when we can take advantage of it
  builtin-grep: -F (--fixed-strings)
  builtin-grep: -w fix
  builtin-grep: typofix
  builtin-grep: tighten argument parsing.
  builtin-grep: documentation
  Teach -f <file> option to builtin-grep.
  builtin-grep: -L (--files-without-match).
  builtin-grep: binary files -a and -I
  builtin-grep: terminate correctly at EOF
  builtin-grep: tighten path wildcard vs tree traversal.
  builtin-grep: support -w (--word-regexp).
  builtin-grep: support -c (--count).
  builtin-grep: allow more than one patterns.
  builtin-grep: allow -<n> and -[ABC]<n> notation for context lines.
  builtin-grep: printf %.*s length is int, not ptrdiff_t.
  builtin-grep: do not use setup_revisions()
  builtin-grep: support '-l' option.
  ...

5 files changed, 951 insertions, 24 deletions

diff --git a/Documentation/git-grep.txt b/Documentation/git-grep.txt
index d55456ae93..74102b7944 100644
--- a/Documentation/git-grep.txt
+++ b/Documentation/git-grep.txt
@@ -8,43 +8,82 @@ git-grep - Print lines matching a pattern
 
 SYNOPSIS
 --------
-'git-grep' [<option>...] [-e] <pattern> [--] [<path>...]
+[verse]
+'git-grep' [--cached]
+	   [-a | --text] [-I] [-i | --ignore-case] [-w | --word-regexp]
+	   [-v | --invert-match]
+	   [-E | --extended-regexp] [-G | --basic-regexp] [-F | --fixed-strings]
+	   [-n] [-l | --files-with-matches] [-L | --files-without-match]
+	   [-c | --count]
+	   [-A <post-context>] [-B <pre-context>] [-C <context>]
+	   [-f <file>] [-e <pattern>]
+	   [<tree>...]
+	   [--] [<path>...]
 
 DESCRIPTION
 -----------
-Searches list of files `git-ls-files` produces for lines
-containing a match to the given pattern.
+Look for specified patterns in the working tree files, blobs
+registered in the index file, or given tree objects.
 
 
 OPTIONS
 -------
-`--`::
-	Signals the end of options; the rest of the parameters
-	are <path> limiters.
+--cached::
+	Instead of searching in the working tree files, check
+	the blobs registerd in the index file.
+
+-a | --text::
+	Process binary files as if they were text.
+
+-i | --ignore-case::
+	Ignore case differences between the patterns and the
+	files.
+
+-w | --word-regexp::
+	Match the pattern only at word boundary (either begin at the
+	beginning of a line, or preceded by a non-word character; end at
+	the end of a line or followed by a non-word character).
+
+-v | --invert-match::
+	Select non-matching lines.
+
+-E | --extended-regexp | -G | --basic-regexp::
+	Use POSIX extended/basic regexp for patterns.  Default
+	is to use basic regexp.
 
-<option>...::
-	Either an option to pass to `grep` or `git-ls-files`.
-+
-The following are the specific `git-ls-files` options
-that may be given: `-o`, `--cached`, `--deleted`, `--others`,
-`--killed`, `--ignored`, `--modified`, `--exclude=\*`,
-`--exclude-from=\*`, and `--exclude-per-directory=\*`.
-+
-All other options will be passed to `grep`.
+-n::
+	Prefix the line number to matching lines.
 
-<pattern>::
-	The pattern to look for.  The first non option is taken
-	as the pattern; if your pattern begins with a dash, use
-	`-e <pattern>`.
+-l | --files-with-matches | -L | --files-without-match::
+	Instead of showing every matched line, show only the
+	names of files that contain (or do not contain) matches.
 
-<path>...::
-	Optional paths to limit the set of files to be searched;
-	passed to `git-ls-files`.
+-c | --count::
+	Instead of showing every matched line, show the number of
+	lines that match.
+
+-[ABC] <context>::
+	Show `context` trailing (`A` -- after), or leading (`B`
+	-- before), or both (`C` -- context) lines, and place a
+	line containing `--` between continguous groups of
+	matches.
+
+-f <file>::
+	Read patterns from <file>, one per line.
+
+`<tree>...`::
+	Search blobs in the trees for specified patterns.
+
+`--`::
+	Signals the end of options; the rest of the parameters
+	are <path> limiters.
 
 
 Author
 ------
-Written by Linus Torvalds <torvalds@osdl.org>
+Originally written by Linus Torvalds <torvalds@osdl.org>, later
+revamped by Junio C Hamano.
+
 
 Documentation
 --------------
diff --git a/Makefile b/Makefile
index f4b6ef8751..93779b06f1 100644
--- a/Makefile
+++ b/Makefile
@@ -216,7 +216,8 @@ LIB_OBJS = \
 	$(DIFF_OBJS)
 
 BUILTIN_OBJS = \
-	builtin-log.o builtin-help.o builtin-count.o builtin-diff.o builtin-push.o
+	builtin-log.o builtin-help.o builtin-count.o builtin-diff.o builtin-push.o \
+	builtin-grep.o
 
 GITLIBS = $(LIB_FILE) $(XDIFF_LIB)
 LIBS = $(GITLIBS) -lz
diff --git a/builtin-grep.c b/builtin-grep.c
new file mode 100644
index 0000000000..66111de514
--- /dev/null
+++ b/builtin-grep.c
@@ -0,0 +1,885 @@
+/*
+ * Builtin "git grep"
+ *
+ * Copyright (c) 2006 Junio C Hamano
+ */
+#include "cache.h"
+#include "blob.h"
+#include "tree.h"
+#include "commit.h"
+#include "tag.h"
+#include "tree-walk.h"
+#include "builtin.h"
+#include <regex.h>
+#include <fnmatch.h>
+#include <sys/wait.h>
+
+/*
+ * git grep pathspecs are somewhat different from diff-tree pathspecs;
+ * pathname wildcards are allowed.
+ */
+static int pathspec_matches(const char **paths, const char *name)
+{
+	int namelen, i;
+	if (!paths || !*paths)
+		return 1;
+	namelen = strlen(name);
+	for (i = 0; paths[i]; i++) {
+		const char *match = paths[i];
+		int matchlen = strlen(match);
+		const char *cp, *meta;
+
+		if ((matchlen <= namelen) &&
+		    !strncmp(name, match, matchlen) &&
+		    (match[matchlen-1] == '/' ||
+		     name[matchlen] == '\0' || name[matchlen] == '/'))
+			return 1;
+		if (!fnmatch(match, name, 0))
+			return 1;
+		if (name[namelen-1] != '/')
+			continue;
+
+		/* We are being asked if the directory ("name") is worth
+		 * descending into.
+		 *
+		 * Find the longest leading directory name that does
+		 * not have metacharacter in the pathspec; the name
+		 * we are looking at must overlap with that directory.
+		 */
+		for (cp = match, meta = NULL; cp - match < matchlen; cp++) {
+			char ch = *cp;
+			if (ch == '*' || ch == '[' || ch == '?') {
+				meta = cp;
+				break;
+			}
+		}
+		if (!meta)
+			meta = cp; /* fully literal */
+
+		if (namelen <= meta - match) {
+			/* Looking at "Documentation/" and
+			 * the pattern says "Documentation/howto/", or
+			 * "Documentation/diff*.txt".  The name we
+			 * have should match prefix.
+			 */
+			if (!memcmp(match, name, namelen))
+				return 1;
+			continue;
+		}
+
+		if (meta - match < namelen) {
+			/* Looking at "Documentation/howto/" and
+			 * the pattern says "Documentation/h*";
+			 * match up to "Do.../h"; this avoids descending
+			 * into "Documentation/technical/".
+			 */
+			if (!memcmp(match, name, meta - match))
+				return 1;
+			continue;
+		}
+	}
+	return 0;
+}
+
+struct grep_pat {
+	struct grep_pat *next;
+	const char *origin;
+	int no;
+	const char *pattern;
+	regex_t regexp;
+};
+
+struct grep_opt {
+	struct grep_pat *pattern_list;
+	struct grep_pat **pattern_tail;
+	regex_t regexp;
+	unsigned linenum:1;
+	unsigned invert:1;
+	unsigned name_only:1;
+	unsigned unmatch_name_only:1;
+	unsigned count:1;
+	unsigned word_regexp:1;
+	unsigned fixed:1;
+#define GREP_BINARY_DEFAULT	0
+#define GREP_BINARY_NOMATCH	1
+#define GREP_BINARY_TEXT	2
+	unsigned binary:2;
+	int regflags;
+	unsigned pre_context;
+	unsigned post_context;
+};
+
+static void add_pattern(struct grep_opt *opt, const char *pat,
+			const char *origin, int no)
+{
+	struct grep_pat *p = xcalloc(1, sizeof(*p));
+	p->pattern = pat;
+	p->origin = origin;
+	p->no = no;
+	*opt->pattern_tail = p;
+	opt->pattern_tail = &p->next;
+	p->next = NULL;
+}
+
+static void compile_patterns(struct grep_opt *opt)
+{
+	struct grep_pat *p;
+	for (p = opt->pattern_list; p; p = p->next) {
+		int err = regcomp(&p->regexp, p->pattern, opt->regflags);
+		if (err) {
+			char errbuf[1024];
+			char where[1024];
+			if (p->no)
+				sprintf(where, "In '%s' at %d, ",
+					p->origin, p->no);
+			else if (p->origin)
+				sprintf(where, "%s, ", p->origin);
+			else
+				where[0] = 0;
+			regerror(err, &p->regexp, errbuf, 1024);
+			regfree(&p->regexp);
+			die("%s'%s': %s", where, p->pattern, errbuf);
+		}
+	}
+}
+
+static char *end_of_line(char *cp, unsigned long *left)
+{
+	unsigned long l = *left;
+	while (l && *cp != '\n') {
+		l--;
+		cp++;
+	}
+	*left = l;
+	return cp;
+}
+
+static int word_char(char ch)
+{
+	return isalnum(ch) || ch == '_';
+}
+
+static void show_line(struct grep_opt *opt, const char *bol, const char *eol,
+		      const char *name, unsigned lno, char sign)
+{
+	printf("%s%c", name, sign);
+	if (opt->linenum)
+		printf("%d%c", lno, sign);
+	printf("%.*s\n", (int)(eol-bol), bol);
+}
+
+/*
+ * NEEDSWORK: share code with diff.c
+ */
+#define FIRST_FEW_BYTES 8000
+static int buffer_is_binary(const char *ptr, unsigned long size)
+{
+	if (FIRST_FEW_BYTES < size)
+		size = FIRST_FEW_BYTES;
+	if (memchr(ptr, 0, size))
+		return 1;
+	return 0;
+}
+
+static int fixmatch(const char *pattern, char *line, regmatch_t *match)
+{
+	char *hit = strstr(line, pattern);
+	if (!hit) {
+		match->rm_so = match->rm_eo = -1;
+		return REG_NOMATCH;
+	}
+	else {
+		match->rm_so = hit - line;
+		match->rm_eo = match->rm_so + strlen(pattern);
+		return 0;
+	}
+}
+
+static int grep_buffer(struct grep_opt *opt, const char *name,
+		       char *buf, unsigned long size)
+{
+	char *bol = buf;
+	unsigned long left = size;
+	unsigned lno = 1;
+	struct pre_context_line {
+		char *bol;
+		char *eol;
+	} *prev = NULL, *pcl;
+	unsigned last_hit = 0;
+	unsigned last_shown = 0;
+	int binary_match_only = 0;
+	const char *hunk_mark = "";
+	unsigned count = 0;
+
+	if (buffer_is_binary(buf, size)) {
+		switch (opt->binary) {
+		case GREP_BINARY_DEFAULT:
+			binary_match_only = 1;
+			break;
+		case GREP_BINARY_NOMATCH:
+			return 0; /* Assume unmatch */
+			break;
+		default:
+			break;
+		}
+	}
+
+	if (opt->pre_context)
+		prev = xcalloc(opt->pre_context, sizeof(*prev));
+	if (opt->pre_context || opt->post_context)
+		hunk_mark = "--\n";
+
+	while (left) {
+		regmatch_t pmatch[10];
+		char *eol, ch;
+		int hit = 0;
+		struct grep_pat *p;
+
+		eol = end_of_line(bol, &left);
+		ch = *eol;
+		*eol = 0;
+
+		for (p = opt->pattern_list; p; p = p->next) {
+			if (!opt->fixed) {
+				regex_t *exp = &p->regexp;
+				hit = !regexec(exp, bol, ARRAY_SIZE(pmatch),
+					       pmatch, 0);
+			}
+			else {
+				hit = !fixmatch(p->pattern, bol, pmatch);
+			}
+
+			if (hit && opt->word_regexp) {
+				/* Match beginning must be either
+				 * beginning of the line, or at word
+				 * boundary (i.e. the last char must
+				 * not be alnum or underscore).
+				 */
+				if ((pmatch[0].rm_so < 0) ||
+				    (eol - bol) <= pmatch[0].rm_so ||
+				    (pmatch[0].rm_eo < 0) ||
+				    (eol - bol) < pmatch[0].rm_eo)
+					die("regexp returned nonsense");
+				if (pmatch[0].rm_so != 0 &&
+				    word_char(bol[pmatch[0].rm_so-1]))
+					hit = 0;
+				if (pmatch[0].rm_eo != (eol-bol) &&
+				    word_char(bol[pmatch[0].rm_eo]))
+					hit = 0;
+			}
+			if (hit)
+				break;
+		}
+		/* "grep -v -e foo -e bla" should list lines
+		 * that do not have either, so inversion should
+		 * be done outside.
+		 */
+		if (opt->invert)
+			hit = !hit;
+		if (opt->unmatch_name_only) {
+			if (hit)
+				return 0;
+			goto next_line;
+		}
+		if (hit) {
+			count++;
+			if (binary_match_only) {
+				printf("Binary file %s matches\n", name);
+				return 1;
+			}
+			if (opt->name_only) {
+				printf("%s\n", name);
+				return 1;
+			}
+			/* Hit at this line.  If we haven't shown the
+			 * pre-context lines, we would need to show them.
+			 * When asked to do "count", this still show
+			 * the context which is nonsense, but the user
+			 * deserves to get that ;-).
+			 */
+			if (opt->pre_context) {
+				unsigned from;
+				if (opt->pre_context < lno)
+					from = lno - opt->pre_context;
+				else
+					from = 1;
+				if (from <= last_shown)
+					from = last_shown + 1;
+				if (last_shown && from != last_shown + 1)
+					printf(hunk_mark);
+				while (from < lno) {
+					pcl = &prev[lno-from-1];
+					show_line(opt, pcl->bol, pcl->eol,
+						  name, from, '-');
+					from++;
+				}
+				last_shown = lno-1;
+			}
+			if (last_shown && lno != last_shown + 1)
+				printf(hunk_mark);
+			if (!opt->count)
+				show_line(opt, bol, eol, name, lno, ':');
+			last_shown = last_hit = lno;
+		}
+		else if (last_hit &&
+			 lno <= last_hit + opt->post_context) {
+			/* If the last hit is within the post context,
+			 * we need to show this line.
+			 */
+			if (last_shown && lno != last_shown + 1)
+				printf(hunk_mark);
+			show_line(opt, bol, eol, name, lno, '-');
+			last_shown = lno;
+		}
+		if (opt->pre_context) {
+			memmove(prev+1, prev,
+				(opt->pre_context-1) * sizeof(*prev));
+			prev->bol = bol;
+			prev->eol = eol;
+		}
+
+	next_line:
+		*eol = ch;
+		bol = eol + 1;
+		if (!left)
+			break;
+		left--;
+		lno++;
+	}
+
+	if (opt->unmatch_name_only) {
+		/* We did not see any hit, so we want to show this */
+		printf("%s\n", name);
+		return 1;
+	}
+
+	/* NEEDSWORK:
+	 * The real "grep -c foo *.c" gives many "bar.c:0" lines,
+	 * which feels mostly useless but sometimes useful.  Maybe
+	 * make it another option?  For now suppress them.
+	 */
+	if (opt->count && count)
+		printf("%s:%u\n", name, count);
+	return !!last_hit;
+}
+
+static int grep_sha1(struct grep_opt *opt, const unsigned char *sha1, const char *name)
+{
+	unsigned long size;
+	char *data;
+	char type[20];
+	int hit;
+	data = read_sha1_file(sha1, type, &size);
+	if (!data) {
+		error("'%s': unable to read %s", name, sha1_to_hex(sha1));
+		return 0;
+	}
+	hit = grep_buffer(opt, name, data, size);
+	free(data);
+	return hit;
+}
+
+static int grep_file(struct grep_opt *opt, const char *filename)
+{
+	struct stat st;
+	int i;
+	char *data;
+	if (lstat(filename, &st) < 0) {
+	err_ret:
+		if (errno != ENOENT)
+			error("'%s': %s", filename, strerror(errno));
+		return 0;
+	}
+	if (!st.st_size)
+		return 0; /* empty file -- no grep hit */
+	if (!S_ISREG(st.st_mode))
+		return 0;
+	i = open(filename, O_RDONLY);
+	if (i < 0)
+		goto err_ret;
+	data = xmalloc(st.st_size + 1);
+	if (st.st_size != xread(i, data, st.st_size)) {
+		error("'%s': short read %s", filename, strerror(errno));
+		close(i);
+		free(data);
+		return 0;
+	}
+	close(i);
+	i = grep_buffer(opt, filename, data, st.st_size);
+	free(data);
+	return i;
+}
+
+static int exec_grep(int argc, const char **argv)
+{
+	pid_t pid;
+	int status;
+
+	argv[argc] = NULL;
+	pid = fork();
+	if (pid < 0)
+		return pid;
+	if (!pid) {
+		execvp("grep", (char **) argv);
+		exit(255);
+	}
+	while (waitpid(pid, &status, 0) < 0) {
+		if (errno == EINTR)
+			continue;
+		return -1;
+	}
+	if (WIFEXITED(status)) {
+		if (!WEXITSTATUS(status))
+			return 1;
+		return 0;
+	}
+	return -1;
+}
+
+#define MAXARGS 1000
+#define ARGBUF 4096
+#define push_arg(a) do { \
+	if (nr < MAXARGS) argv[nr++] = (a); \
+	else die("maximum number of args exceeded"); \
+	} while (0)
+
+static int external_grep(struct grep_opt *opt, const char **paths, int cached)
+{
+	int i, nr, argc, hit, len;
+	const char *argv[MAXARGS+1];
+	char randarg[ARGBUF];
+	char *argptr = randarg;
+	struct grep_pat *p;
+
+	len = nr = 0;
+	push_arg("grep");
+	push_arg("-H");
+	if (opt->fixed)
+		push_arg("-F");
+	if (opt->linenum)
+		push_arg("-n");
+	if (opt->regflags & REG_EXTENDED)
+		push_arg("-E");
+	if (opt->word_regexp)
+		push_arg("-w");
+	if (opt->name_only)
+		push_arg("-l");
+	if (opt->unmatch_name_only)
+		push_arg("-L");
+	if (opt->count)
+		push_arg("-c");
+	if (opt->post_context || opt->pre_context) {
+		if (opt->post_context != opt->pre_context) {
+			if (opt->pre_context) {
+				push_arg("-B");
+				len += snprintf(argptr, sizeof(randarg)-len,
+						"%u", opt->pre_context);
+				if (sizeof(randarg) <= len)
+					die("maximum length of args exceeded");
+				push_arg(argptr);
+				argptr += len;
+			}
+			if (opt->post_context) {
+				push_arg("-A");
+				len += snprintf(argptr, sizeof(randarg)-len,
+						"%u", opt->post_context);
+				if (sizeof(randarg) <= len)
+					die("maximum length of args exceeded");
+				push_arg(argptr);
+				argptr += len;
+			}
+		}
+		else {
+			push_arg("-C");
+			len += snprintf(argptr, sizeof(randarg)-len,
+					"%u", opt->post_context);
+			if (sizeof(randarg) <= len)
+				die("maximum length of args exceeded");
+			push_arg(argptr);
+			argptr += len;
+		}
+	}
+	for (p = opt->pattern_list; p; p = p->next) {
+		push_arg("-e");
+		push_arg(p->pattern);
+	}
+	push_arg("--");
+
+	hit = 0;
+	argc = nr;
+	for (i = 0; i < active_nr; i++) {
+		struct cache_entry *ce = active_cache[i];
+		if (ce_stage(ce) || !S_ISREG(ntohl(ce->ce_mode)))
+			continue;
+		if (!pathspec_matches(paths, ce->name))
+			continue;
+		argv[argc++] = ce->name;
+		if (argc < MAXARGS)
+			continue;
+		hit += exec_grep(argc, argv);
+		argc = nr;
+	}
+	if (argc > nr)
+		hit += exec_grep(argc, argv);
+	return 0;
+}
+
+static int grep_cache(struct grep_opt *opt, const char **paths, int cached)
+{
+	int hit = 0;
+	int nr;
+	read_cache();
+
+#ifdef __unix__
+	/*
+	 * Use the external "grep" command for the case where
+	 * we grep through the checked-out files. It tends to
+	 * be a lot more optimized
+	 */
+	if (!cached) {
+		hit = external_grep(opt, paths, cached);
+		if (hit >= 0)
+			return hit;
+	}
+#endif
+
+	for (nr = 0; nr < active_nr; nr++) {
+		struct cache_entry *ce = active_cache[nr];
+		if (ce_stage(ce) || !S_ISREG(ntohl(ce->ce_mode)))
+			continue;
+		if (!pathspec_matches(paths, ce->name))
+			continue;
+		if (cached)
+			hit |= grep_sha1(opt, ce->sha1, ce->name);
+		else
+			hit |= grep_file(opt, ce->name);
+	}
+	return hit;
+}
+
+static int grep_tree(struct grep_opt *opt, const char **paths,
+		     struct tree_desc *tree,
+		     const char *tree_name, const char *base)
+{
+	unsigned mode;
+	int len;
+	int hit = 0;
+	const char *path;
+	const unsigned char *sha1;
+	char *down;
+	char *path_buf = xmalloc(PATH_MAX + strlen(tree_name) + 100);
+
+	if (tree_name[0]) {
+		int offset = sprintf(path_buf, "%s:", tree_name);
+		down = path_buf + offset;
+		strcat(down, base);
+	}
+	else {
+		down = path_buf;
+		strcpy(down, base);
+	}
+	len = strlen(path_buf);
+
+	while (tree->size) {
+		int pathlen;
+		sha1 = tree_entry_extract(tree, &path, &mode);
+		pathlen = strlen(path);
+		strcpy(path_buf + len, path);
+
+		if (S_ISDIR(mode))
+			/* Match "abc/" against pathspec to
+			 * decide if we want to descend into "abc"
+			 * directory.
+			 */
+			strcpy(path_buf + len + pathlen, "/");
+
+		if (!pathspec_matches(paths, down))
+			;
+		else if (S_ISREG(mode))
+			hit |= grep_sha1(opt, sha1, path_buf);
+		else if (S_ISDIR(mode)) {
+			char type[20];
+			struct tree_desc sub;
+			void *data;
+			data = read_sha1_file(sha1, type, &sub.size);
+			if (!data)
+				die("unable to read tree (%s)",
+				    sha1_to_hex(sha1));
+			sub.buf = data;
+			hit |= grep_tree(opt, paths, &sub, tree_name, down);
+			free(data);
+		}
+		update_tree_entry(tree);
+	}
+	return hit;
+}
+
+static int grep_object(struct grep_opt *opt, const char **paths,
+		       struct object *obj, const char *name)
+{
+	if (!strcmp(obj->type, blob_type))
+		return grep_sha1(opt, obj->sha1, name);
+	if (!strcmp(obj->type, commit_type) ||
+	    !strcmp(obj->type, tree_type)) {
+		struct tree_desc tree;
+		void *data;
+		int hit;
+		data = read_object_with_reference(obj->sha1, tree_type,
+						  &tree.size, NULL);
+		if (!data)
+			die("unable to read tree (%s)", sha1_to_hex(obj->sha1));
+		tree.buf = data;
+		hit = grep_tree(opt, paths, &tree, name, "");
+		free(data);
+		return hit;
+	}
+	die("unable to grep from object of type %s", obj->type);
+}
+
+static const char builtin_grep_usage[] =
+"git-grep <option>* <rev>* [-e] <pattern> [<path>...]";
+
+int cmd_grep(int argc, const char **argv, char **envp)
+{
+	int hit = 0;
+	int cached = 0;
+	int seen_dashdash = 0;
+	struct grep_opt opt;
+	struct object_list *list, **tail, *object_list = NULL;
+	const char *prefix = setup_git_directory();
+	const char **paths = NULL;
+	int i;
+
+	memset(&opt, 0, sizeof(opt));
+	opt.pattern_tail = &opt.pattern_list;
+	opt.regflags = REG_NEWLINE;
+
+	/*
+	 * If there is no -- then the paths must exist in the working
+	 * tree.  If there is no explicit pattern specified with -e or
+	 * -f, we take the first unrecognized non option to be the
+	 * pattern, but then what follows it must be zero or more
+	 * valid refs up to the -- (if exists), and then existing
+	 * paths.  If there is an explicit pattern, then the first
+	 * unrecocnized non option is the beginning of the refs list
+	 * that continues up to the -- (if exists), and then paths.
+	 */
+
+	tail = &object_list;
+	while (1 < argc) {
+		const char *arg = argv[1];
+		argc--; argv++;
+		if (!strcmp("--cached", arg)) {
+			cached = 1;
+			continue;
+		}
+		if (!strcmp("-a", arg) ||
+		    !strcmp("--text", arg)) {
+			opt.binary = GREP_BINARY_TEXT;
+			continue;
+		}
+		if (!strcmp("-i", arg) ||
+		    !strcmp("--ignore-case", arg)) {
+			opt.regflags |= REG_ICASE;
+			continue;
+		}
+		if (!strcmp("-I", arg)) {
+			opt.binary = GREP_BINARY_NOMATCH;
+			continue;
+		}
+		if (!strcmp("-v", arg) ||
+		    !strcmp("--invert-match", arg)) {
+			opt.invert = 1;
+			continue;
+		}
+		if (!strcmp("-E", arg) ||
+		    !strcmp("--extended-regexp", arg)) {
+			opt.regflags |= REG_EXTENDED;
+			continue;
+		}
+		if (!strcmp("-F", arg) ||
+		    !strcmp("--fixed-strings", arg)) {
+			opt.fixed = 1;
+			continue;
+		}
+		if (!strcmp("-G", arg) ||
+		    !strcmp("--basic-regexp", arg)) {
+			opt.regflags &= ~REG_EXTENDED;
+			continue;
+		}
+		if (!strcmp("-n", arg)) {
+			opt.linenum = 1;
+			continue;
+		}
+		if (!strcmp("-H", arg)) {
+			/* We always show the pathname, so this
+			 * is a noop.
+			 */
+			continue;
+		}
+		if (!strcmp("-l", arg) ||
+		    !strcmp("--files-with-matches", arg)) {
+			opt.name_only = 1;
+			continue;
+		}
+		if (!strcmp("-L", arg) ||
+		    !strcmp("--files-without-match", arg)) {
+			opt.unmatch_name_only = 1;
+			continue;
+		}
+		if (!strcmp("-c", arg) ||
+		    !strcmp("--count", arg)) {
+			opt.count = 1;
+			continue;
+		}
+		if (!strcmp("-w", arg) ||
+		    !strcmp("--word-regexp", arg)) {
+			opt.word_regexp = 1;
+			continue;
+		}
+		if (!strncmp("-A", arg, 2) ||
+		    !strncmp("-B", arg, 2) ||
+		    !strncmp("-C", arg, 2) ||
+		    (arg[0] == '-' && '1' <= arg[1] && arg[1] <= '9')) {
+			unsigned num;
+			const char *scan;
+			switch (arg[1]) {
+			case 'A': case 'B': case 'C':
+				if (!arg[2]) {
+					if (argc <= 1)
+						usage(builtin_grep_usage);
+					scan = *++argv;
+					argc--;
+				}
+				else
+					scan = arg + 2;
+				break;
+			default:
+				scan = arg + 1;
+				break;
+			}
+			if (sscanf(scan, "%u", &num) != 1)
+				usage(builtin_grep_usage);
+			switch (arg[1]) {
+			case 'A':
+				opt.post_context = num;
+				break;
+			default:
+			case 'C':
+				opt.post_context = num;
+			case 'B':
+				opt.pre_context = num;
+				break;
+			}
+			continue;
+		}
+		if (!strcmp("-f", arg)) {
+			FILE *patterns;
+			int lno = 0;
+			char buf[1024];
+			if (argc <= 1)
+				usage(builtin_grep_usage);
+			patterns = fopen(argv[1], "r");
+			if (!patterns)
+				die("'%s': %s", argv[1], strerror(errno));
+			while (fgets(buf, sizeof(buf), patterns)) {
+				int len = strlen(buf);
+				if (buf[len-1] == '\n')
+					buf[len-1] = 0;
+				/* ignore empty line like grep does */
+				if (!buf[0])
+					continue;
+				add_pattern(&opt, strdup(buf), argv[1], ++lno);
+			}
+			fclose(patterns);
+			argv++;
+			argc--;
+			continue;
+		}
+		if (!strcmp("-e", arg)) {
+			if (1 < argc) {
+				add_pattern(&opt, argv[1], "-e option", 0);
+				argv++;
+				argc--;
+				continue;
+			}
+			usage(builtin_grep_usage);
+		}
+		if (!strcmp("--", arg))
+			break;
+		if (*arg == '-')
+			usage(builtin_grep_usage);
+
+		/* First unrecognized non-option token */
+		if (!opt.pattern_list) {
+			add_pattern(&opt, arg, "command line", 0);
+			break;
+		}
+		else {
+			/* We are looking at the first path or rev;
+			 * it is found at argv[1] after leaving the
+			 * loop.
+			 */
+			argc++; argv--;
+			break;
+		}
+	}
+
+	if (!opt.pattern_list)
+		die("no pattern given.");
+	if ((opt.regflags != REG_NEWLINE) && opt.fixed)
+		die("cannot mix --fixed-strings and regexp");
+	if (!opt.fixed)
+		compile_patterns(&opt);
+
+	/* Check revs and then paths */
+	for (i = 1; i < argc; i++) {
+		const char *arg = argv[i];
+		unsigned char sha1[20];
+		/* Is it a rev? */
+		if (!get_sha1(arg, sha1)) {
+			struct object *object = parse_object(sha1);
+			struct object_list *elem;
+			if (!object)
+				die("bad object %s", arg);
+			elem = object_list_insert(object, tail);
+			elem->name = arg;
+			tail = &elem->next;
+			continue;
+		}
+		if (!strcmp(arg, "--")) {
+			i++;
+			seen_dashdash = 1;
+		}
+		break;
+	}
+
+	/* The rest are paths */
+	if (!seen_dashdash) {
+		int j;
+		for (j = i; j < argc; j++)
+			verify_filename(prefix, argv[j]);
+	}
+
+	if (i < argc)
+		paths = get_pathspec(prefix, argv + i);
+	else if (prefix) {
+		paths = xcalloc(2, sizeof(const char *));
+		paths[0] = prefix;
+		paths[1] = NULL;
+	}
+
+	if (!object_list)
+		return !grep_cache(&opt, paths, cached);
+
+	if (cached)
+		die("both --cached and trees are given.");
+
+	for (list = object_list; list; list = list->next) {
+		struct object *real_obj;
+		real_obj = deref_tag(list->item, NULL, 0);
+		if (grep_object(&opt, paths, real_obj, list->name))
+			hit = 1;
+	}
+	return !hit;
+}
diff --git a/builtin.h b/builtin.h
index bb63f0729a..7744f7d2f6 100644
--- a/builtin.h
+++ b/builtin.h
@@ -23,5 +23,6 @@ extern int cmd_diff(int argc, const char **argv, char **envp);
 extern int cmd_count_objects(int argc, const char **argv, char **envp);
 
 extern int cmd_push(int argc, const char **argv, char **envp);
+extern int cmd_grep(int argc, const char **argv, char **envp);
 
 #endif
diff --git a/git.c b/git.c
index 49ba5189d9..a94d9ee5a7 100644
--- a/git.c
+++ b/git.c
@@ -49,6 +49,7 @@ static void handle_internal_command(int argc, const char **argv, char **envp)
 		{ "push", cmd_push },
 		{ "count-objects", cmd_count_objects },
 		{ "diff", cmd_diff },
+		{ "grep", cmd_grep },
 	};
 	int i;