I've had a general need several times to filter file I/O against existing opened file handles. The approach I've generally used is to create tie packages and tie the file handle. One issue with that is how to give the tie package the real file handle to use.

As a simple example, suppose I want to create a tie that upper cases everything either written to or read from a file handle. In order to read or write the data once it's converted, I need to pass the tie package the file handle being tied. However, if I use that file handle as is, it's tied by the time I use it internally, which causes me to recursively call back into the tie package. Not good. I can dup the file handle internally in the package, but to do that I need to know if it's opened for read or write. That leaves me with having to dup it before I tie it, then passing the dup'ed file handle as an argument.

Am I missing some better way to handle this?

In reply to The best way to filter file I/O by steves

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