Sorry if I reply to a dead question: After locking the file, open another copy of it, fstat both copies and check the inode number, like this: lockfile = “/tmp/some_name.lock”; while(1) { fd = open(lockfile, O_CREAT); flock(fd, LOCK_EX); fstat(fd, &st0); stat(lockfile, &st1); if(st0.st_ino == st1.st_ino) break; close(fd); } do_something(); unlink(lockfile); flock(fd, LOCK_UN); This prevents the … Read more
Theres nothing special about the number 200. It just happens to be the example used in the man page of the flock command; and it happens to be a large number, so it’s unlikely to conflict with the the file descriptor of any other file you open during your script. In your comment, you ask … Read more
There is a cross-platform flock command here: https://github.com/discoteq/flock I have tested it and it works well on OSX as a drop-in replacement for the util-linux flock.
Advisory locking has been used for ages and it can be used in bash scripts. I prefer simple flock (from util-linux[-ng]) over lockfile (from procmail). And always remember about a trap on exit (sigspec == EXIT or 0, trapping specific signals is superfluous) in those scripts. In 2009 I released my lockable script boilerplate (originally … Read more