skip option error messages and display offset

src/bin/hexyl.rs

@@ -93,10 +93,10 @@ fn run() -> Result<(), Box<dyn std::error::Error>> {
         None => Input::Stdin(stdin.lock()),
     };
 
-    let skip_arg = matches.value_of("skip");
+    let skip_arg = matches.value_of("skip").and_then(parse_hex_or_int);
 
-    if let Some(length) = skip_arg.and_then(parse_hex_or_int) {
+    if let Some(skip) = skip_arg {
-        reader.seek(SeekFrom::Start(length))?;
+        reader.seek(SeekFrom::Start(skip))?;
     }
 
     let length_arg = matches.value_of("length").or(matches.value_of("bytes"));
@@ -124,7 +124,7 @@ fn run() -> Result<(), Box<dyn std::error::Error>> {
     let display_offset = matches
         .value_of("display_offset")
         .and_then(parse_hex_or_int)
-        .unwrap_or(0);
+        .unwrap_or(skip_arg.unwrap_or(0));
 
     let stdout = io::stdout();
     let mut stdout_lock = stdout.lock();

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",
             )),
         }
     }