Teach rev-list an option to read revs from the standard input.

When --stdin option is given, in addition to the <rev>s listed
on the command line, the command can read one rev parameter per
line from the standard input.  The list of revs ends at the
first empty line or EOF.

Note that you still have to give all the flags from the command
line; only rev arguments (including A..B, A...B, and A^@ notations)
can be give from the standard input.

Signed-off-by: Junio C Hamano <junkio@cox.net>

Documentation/git-rev-list.txt

@@ -17,6 +17,7 @@ SYNOPSIS
 	     [ \--remove-empty ]
 	     [ \--not ]
 	     [ \--all ]
+	     [ \--stdin ]
 	     [ \--topo-order ]
 	     [ \--parents ]
 	     [ [\--objects | \--objects-edge] [ \--unpacked ] ]
@@ -171,6 +172,11 @@ limiting may be applied.
 	Pretend as if all the refs in `$GIT_DIR/refs/` are listed on the
 	command line as '<commit>'.
 
+--stdin::
+
+	In addition to the '<commit>' listed on the command
+	line, read them from the standard input.
+
 --merge::
 
 	After a failed merge, show refs that touch files having a

builtin-rev-list.c

@@ -23,6 +23,7 @@ static const char rev_list_usage[] =
 "    --no-merges\n"
 "    --remove-empty\n"
 "    --all\n"
+"    --stdin\n"
 "  ordering output:\n"
 "    --topo-order\n"
 "    --date-order\n"
@@ -304,10 +305,28 @@ static void mark_edges_uninteresting(struct commit_list *list)
 	}
 }
 
+static void read_revisions_from_stdin(struct rev_info *revs)
+{
+	char line[1000];
+
+	while (fgets(line, sizeof(line), stdin) != NULL) {
+		int len = strlen(line);
+		if (line[len - 1] == '\n')
+			line[--len] = 0;
+		if (!len)
+			break;
+		if (line[0] == '-')
+			die("options not supported in --stdin mode");
+		if (handle_revision_arg(line, revs, 0, 1))
+			die("bad revision '%s'", line);
+	}
+}
+
 int cmd_rev_list(int argc, const char **argv, const char *prefix)
 {
 	struct commit_list *list;
 	int i;
+	int read_from_stdin = 0;
 
 	init_revisions(&revs, prefix);
 	revs.abbrev = 0;
@@ -329,6 +348,12 @@ int cmd_rev_list(int argc, const char **argv, const char *prefix)
 			bisect_list = 1;
 			continue;
 		}
+		if (!strcmp(arg, "--stdin")) {
+			if (read_from_stdin++)
+				die("--stdin given twice?");
+			read_revisions_from_stdin(&revs);
+			continue;
+		}
 		usage(rev_list_usage);
 
 	}