if ( -e $file ) {
    open FH, $file      or die "Failed: $! trying open existing $file\n";
    # read it
    open FH, '>', $file or die "Failed: $! trying to re-open $file\n";    
}
else {
    open FH, '>'.$file  or die "Failed: $! trying to create new $file\n";
    # do stuff
}