The Perl 5 module IO::InSitu provides the open_rw( ) subroutine:
It takes the names of two files: one to be opened for reading, the
other for writing. It returns a list of two filehandles, opened to
those two files. However, if the two filenames refer to the same
file, open_rw( ) first makes a temporary copy of the file, which
it opens for input. It then opens the original file for output. In
such cases, when the input filehandle is eventually closed, IO::InSitu
arranges for the temporary file to be automatically deleted.