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?