Do you mean you're trying to create a "copy" subroutine to use in a program? Something like:

sub copy( source, destination ) {
    open SOURCEFILE "source";
    open DESTINATIONFILE "destination";
    while (<SOURCEFILE>) {
        print DESTINATIONFILE ;
    }
    close DESTINATIONFILE;
    close SOURCEFILE;
}
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If so, then maybe the problem is in how you're opening the destination file.

open FILE "<$file";
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to read a file

open FILE ">$file";
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to write to a file, creating it if necessary

open FILE ">>$file";
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to append to a file, creating it if necessary