Keep in mind that modern versions of Perl added some extra goodies to the -i value (from perlrun):

            If the extension doesn't contain a "*", then it is appende
+d to the
            end of the current filename as a suffix.  If the extension
+ does
            contain one or more "*" characters, then each "*" is repla
+ced with
            the current filename.  In Perl terms, you could think of t
+his as:

                ($backup = $extension) =~ s/\*/$file_name/g;

            This allows you to add a prefix to the backup file, instea
+d of (or
            in addition to) a suffix:

                $ perl -pi'orig_*' -e 's/bar/baz/' fileA    # backup t
+o 'orig_fileA'

            Or even to place backup copies of the original files into 
+another
            directory (provided the directory already exists):

                $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup 
+to 'old/fileA.orig'
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