Question

A simple and seemingly reliable way to do locking under bash is:

exec 9>>lockfile
flock 9

However, bash notoriously propagates such a fd lock to all forked stuff including executed programs etc.

Is there any way to tell bash not to duplicate the fd? It’s great that the lock is attached to a fd which gets removed when the program terminates, no matter how it gets terminated.

I know I can do stuff like:

run_some_prog 9>&-

But that is quite tedious.

Is there any better solution?

Answer 1

You can use the -o command line option to flock(1) (long option --close, which might be better for writing in scripts for the self-documenting nature) to specify that the file descriptor should be closed before executing commands via flock(1):

   -o, --close
          Close the file descriptor on which the lock is held
          before executing command.  This is useful if command
          spawns a child process which should not be holding
          the lock.