Add support for a "length" flag

[m-braha]

Hi! Often when I am looking at hex from binary files, I only want to see the first N bytes.

For example, with hexyl:

> hexyl -n 5 synth0.vgm
┌────────┬─────────────────────────┬─────────────────────────┬────────┬────────┐
│00000000│ 56 67 6d 20 8f          ┊                         │Vgm ×   ┊        │
└────────┴─────────────────────────┴─────────────────────────┴────────┴────────┘

A --length/-n <N> flag would be awesome. I haven't looked at your code yet but I can try adding this support in a PR if you want.

Thanks for the cool tool!

[Arnau478]

I have mixed opinions on this. I like the "one program one thing" design from UNIX-like systems. For instance, on Linux, it's as simple as piping head with hevi.

$ hevi test_file
00000000 | 4865 6c6c 6f0a                          | Hello.           |
File size: 6 bytes
$ head test_file -c 2 | hevi -
00000000 | 4865                                    | He               |
File size: 2 bytes

I think this approach is a much neater one. That way, we can focus on hex dumps (doing one thing and doing it well).

That being said, I am aware it's not as simple on Windows. I hate the idea of sacrificing design decisions to suit an OS that's designed around bad principles, but honestly this doesn't "pollute" hevi much.

I'm afraid it could lead a series of additions I'm strongly against. That's the only reason I want to really think about this.