Introduce trivial new pager.c helper infrastructure

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

1 files changed, 48 insertions, 0 deletions

diff --git a/pager.c b/pager.c
new file mode 100644
index 0000000000..1364e15d23
--- /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);
+}