I'm taking a wild shot-in-the-dark here, but according to 'perldoc -f open':

       open FILEHANDLE,EXPR
       open FILEHANDLE,MODE,EXPR
       open FILEHANDLE,MODE,EXPR,LIST
       open FILEHANDLE,MODE,REFERENCE
       open FILEHANDLE

       <snip>

       In the 2-arguments (and 1-argument) form opening
       ’-’ opens STDIN and opening ’>-’ opens STDOUT.
[download]

So, I'm wondering if changing your

    my $file = 'STDIN';
        to
    my $file = '-';
[download]

would work???

HTH.