For your specific question, there is no difference between the two. If you don't put any of the input or output type characters in the filename, then it defaults to read only. perldoc -f open should explain that in detail.

As for one open() affecting another one, perl's open() is always subject to the the host OS's file system semantics. If the host's open causes problems, then perl's open will too.

For years a standard trick in the *ix world is to have one process write to a file and another use "tail -f" to watch that file as it gets updated. This has worked well for decades, and the biggest issue being that when they are on two different machines, the commit from the client to the file server is usually at 8k boundaries (I think that is a NFSism), so it doesn't flow smoothly. But it does work.

Since you are using the term folder instead of directory I assume that you are using some MS operating system. I avoid them as much as possible, so I don't know how this will work there. Good luck with that.

- doug