From 0301256c7ae332979e3bca3d5a5e4010ba0b22eb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20Ankarstr=C3=B6m?= <john@ankarstrom.se>
Date: Mon, 24 Sep 2018 21:40:05 +0200
Subject: First commit

---
 watch.c | 85 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)
 create mode 100644 watch.c

diff --git a/watch.c b/watch.c
new file mode 100644
index 0000000..d9e843e
--- /dev/null
+++ b/watch.c
@@ -0,0 +1,85 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/event.h>
+#include <sys/time.h>
+
+#define fail() exit(EXIT_FAILURE)
+#define fail_clean() do { status = EXIT_FAILURE; goto finally; } while (0)
+
+int main(int argc, char *argv[]) {
+	int status = EXIT_SUCCESS;
+	int fd, kq, n, i;
+	struct kevent event;
+
+	setbuf(stdout, NULL); // disable buffering even non-interactively
+
+	if (argc < 2) {
+		fprintf(stderr, "usage: %s file\n", argv[0]);
+		fail();
+	}
+
+	// 1. Open file
+	if ((fd = open(argv[1], O_RDONLY)) == -1) {
+		 perror(argv[1]);
+		 fail();
+	}
+
+	if ((kq = kqueue()) == -1) {
+		perror("kqueue");
+		fail_clean();
+	}
+
+	struct kevent change = { // event to watch for
+		.ident = fd,
+		.filter = EVFILT_VNODE,
+		.flags = EV_ADD | EV_CLEAR,
+		.fflags = NOTE_WRITE | NOTE_RENAME | NOTE_DELETE,
+		.data = 0,
+		.udata = NULL
+	};
+
+	// 2. Register event to watch for
+	if (kevent(kq, &change, 1, NULL, 0, NULL) == -1) {
+		perror("kevent");
+		fail_clean();
+	}
+	if (change.flags & EV_ERROR) {
+		fprintf(stderr, "Event error: %s", strerror(change.data));
+		fail_clean();
+	}
+
+	while (1) {
+		// 3. Wait for event
+		if ((n = kevent(kq, NULL, 0, &event, 1, NULL)) != 1) {
+			perror("kevent wait");
+			fail_clean();
+		} else if (n > 0) {
+			if (event.fflags & NOTE_WRITE) {
+				printf("%s\n", argv[1]);
+			}
+			if (event.fflags & NOTE_RENAME)
+				fprintf(stderr, "Note: file was renamed\n");
+			if (event.fflags & NOTE_DELETE) {
+				fprintf(stderr, "Error: file was deleted\n");
+				fail_clean();
+			}
+		}
+	}
+
+finally:
+	if (close(kq) == -1) {
+		perror("close");
+		fail();
+	}
+	if (close(fd) == -1) {
+		perror("close");
+		fail();
+	}
+
+	exit(status);
+}
-- 
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