This is my first patch so go easy if it doesn't apply or something. This is from a discussion on clpm. I didn't write any of it, Abigail and nobull did, so whatever is right in here give them credit, whatever is blatantly wrong, flame me mercilessly. --- pod/perlfaq5.pod.old Sat Apr 28 11:03:44 2001 +++ pod/perlfaq5.pod Sun Apr 29 01:28:01 2001 @@ -723,6 +723,35 @@ If the count doesn't impress your friends, then the code might. :-) +=head2 All I want to do is append a small amount of text to the end of a +file. Do I *still* have to use locking? + +If you are on a system that correctly implements flock() and you use the +example appending code from "perldoc -f flock" everything will be OK +even if the OS you are on doesn't implement append mode correctly (if +such a system exists.) So if you are happy to restrict yourself to OSs +that implement flock() (and that's not really much of a restriction) +then that is what you should do. + +If you know you are only going to use a system that does correctly +implement appending (i.e. not Win32) then you can omit the seek() from +the above code. + +If you know you are only writing code to run on an OS and filesystem that +does implement append mode correctly (a local filesystem on a modern +Unix for example), and you keep the file in block-buffered mode and you +write less than one buffer-full of output between each manual flushing +of the buffer then each bufferload is almost garanteed to be written to +the end of the file in one chunk without getting intermingled with +anyone else's output. You can also use the syswrite() function which is +simply a wrapper around your systems write(2) system call. + +There is still a small theoretical chance that a signal will interrupt +the system level write() operation before completion. There is also a +possibility that some STDIO implementations may call multiple system +level write()s even if the buffer was empty to start. There may be some +systems where this probability is reduced to zero. + =head2 How do I randomly update a binary file? If you're just trying to patch a binary, in many cases something as --- pod/perlfaq.pod.old Sat Apr 28 17:45:02 2001 +++ pod/perlfaq.pod Sat Apr 28 17:48:54 2001 @@ -692,6 +692,11 @@ =item * +All I want to do is append a small amount of text to the end of a +file. Do I *still* have to use locking? + +=item * + How do I randomly update a binary file? =item * -- Gwyn Judd (b.judd@xtra.co.nz) Wives are young men's mistresses, companions for middle age, and old men's nurses. -Francis BaconThread Next