skip option error messages and display offset

src/input.rs

@@ -18,10 +18,21 @@ impl<'a> Read for Input<'a> {
 impl<'a> Seek for Input<'a> {
     fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
         match *self {
-            Input::File(ref mut file) => file.seek(pos),
+            Input::File(ref mut file) => {
+                let seek_res = file.seek(pos);
+                if let Err(Some(29)) = seek_res.as_ref().map_err(|err| err.raw_os_error()) {
+                    return Err(io::Error::new(
+                        io::ErrorKind::Other,
+                        "Using '--seek' is not supported when using a pipe",
+                    )
+                    .into());
+                };
+                dbg!(&seek_res);
+                seek_res
+            }
             Input::Stdin(_) => Err(io::Error::new(
                 io::ErrorKind::Other,
-                "not supported by stdin-input",
+                "Using '--seek' is not supported when reading from STDIN",
             )),
         }
     }