[PATCH 2/3] Introduce trivial new pager.c helper infrastructure

[Linus Torvalds <torvalds@osdl.org>]

This introduces the new function

	void setup_pager(void);

to set up output to be written through a pager applocation.

All in preparation for doing the simple scripts in C.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---

Ok, this should be pretty obvious, which is not to say that it shouldn't 
be improved (ie it only handles trivial definitions of PAGER). Any obvious 
improvements are left as an exercise for the reader, as not important for 
my current goal of actually having something working.


diff --git a/Makefile b/Makefile
index 3575489..0b1a998 100644
--- a/Makefile
+++ b/Makefile
@@ -205,7 +205,7 @@ LIB_OBJS = \
 	quote.o read-cache.o refs.o run-command.o \
 	server-info.o setup.o sha1_file.o sha1_name.o strbuf.o \
 	tag.o tree.o usage.o config.o environment.o ctype.o copy.o \
-	fetch-clone.o revision.o \
+	fetch-clone.o revision.o pager.o \
 	$(DIFF_OBJS)
 
 LIBS = $(LIB_FILE)
diff --git a/cache.h b/cache.h
index 58eec00..3af6b86 100644
--- a/cache.h
+++ b/cache.h
@@ -352,4 +352,7 @@ extern int copy_fd(int ifd, int ofd);
 extern int receive_unpack_pack(int fd[2], const char *me, int quiet);
 extern int receive_keep_pack(int fd[2], const char *me, int quiet);
 
+/* pager.c */
+extern void setup_pager(void);
+
 #endif /* CACHE_H */
diff --git a/pager.c b/pager.c
new file mode 100644
index 0000000..1364e15
--- /dev/null
+++ b/pager.c
@@ -0,0 +1,48 @@
+#include "cache.h"
+
+/*
+ * This is split up from the rest of git so that we might do
+ * something different on Windows, for example.
+ */
+
+static void run_pager(void)
+{
+	const char *prog = getenv("PAGER");
+	if (!prog)
+		prog = "less";
+	setenv("LESS", "-S", 0);
+	execlp(prog, prog, NULL);
+}
+
+void setup_pager(void)
+{
+	pid_t pid;
+	int fd[2];
+
+	if (!isatty(1))
+		return;
+	if (pipe(fd) < 0)
+		return;
+	pid = fork();
+	if (pid < 0) {
+		close(fd[0]);
+		close(fd[1]);
+		return;
+	}
+
+	/* return in the child */
+	if (!pid) {
+		dup2(fd[1], 1);
+		close(fd[0]);
+		close(fd[1]);
+		return;
+	}
+
+	/* The original process turns into the PAGER */
+	dup2(fd[0], 0);
+	close(fd[0]);
+	close(fd[1]);
+
+	run_pager();
+	exit(255);
+}