Shell Programming and Scripting

lock  --name="xyz" &
lockpid=$!
# wait until we have the lock
block --name "xyz"
# OK, we have the lock, keep the lock until we are done
mkdir "/cygdrive/f/abc"
cp def /cygdrive/f/abc/"
# All done: raise the mutex so the child process running lock will now release the semaphore and exit
unlock --name="xyz"
# I don't know if we really need the unlock command, we could just kill the lock and hope it releases the semaphore
kill $lockpid

$ man 2 flock


FLOCK(2)                   Linux Programmer's Manual                  FLOCK(2)



NAME
       flock - apply or remove an advisory lock on an open file

SYNOPSIS
       #include <sys/file.h>

       int flock(int fd, int operation);

DESCRIPTION
       Apply or remove an advisory lock on the open file specified by fd.  The
       argument operation is one of the following:

           LOCK_SH  Place a shared lock.  More than one  process  may  hold  a
                    shared lock for a given file at a given time.

           LOCK_EX  Place  an  exclusive  lock.   Only one process may hold an
                    exclusive lock for a given file at a given time.

           LOCK_UN  Remove an existing lock held by this process.

       A call to flock() may block if an incompatible lock  is  held  by
       another  process.  To make a nonblocking request, include LOCK_NB
       (by ORing) with any of the above operations.

...

$ perldoc -f flock

       flock FILEHANDLE,OPERATION
               Calls flock(2), or an emulation of it, on FILEHANDLE.  Returns
               true for success, false on failure.  Produces a fatal error if
               used on a machine that doesn't implement flock(2), fcntl(2)
               locking, or lockf(3).  "flock" is Perl's portable file locking
               interface, although it locks only entire files, not records.

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