Length is optional

src/main.rs

@@ -1,5 +1,6 @@
 use std::fs::File;
 use std::io;
+use std::usize::MAX;
 
 mod colormap;
 
@@ -35,7 +36,12 @@ fn main() {
     };
 
     if !args.revert {
-        hexdump(reader, args.length.unwrap());
+        let length = if args.length.is_some() {
+            args.length.unwrap()
+        } else {
+            MAX
+        };
+        hexdump(reader, length);
     } else {
         let writer: Box<dyn io::Write> = Box::new(io::stdout());
         bindump(reader, writer);