xxd --help
Usage:
       xxd [options] [infile [outfile]]
    or
       xxd -r [-s [-]offset] [-c cols] [-ps] [infile [outfile]]
Options:
    -a          toggle autoskip: A single '*' replaces nul-lines. Default off.
    -b          binary digit dump (incompatible with -ps,-i,-r). Default hex.
    -C          capitalize variable names in C include file style (-i).
    -c cols     format <cols> octets per line. Default 16 (-i: 12, -ps: 30).
    -E          show characters in EBCDIC. Default ASCII.
    -e          little-endian dump (incompatible with -ps,-i,-r).
    -g bytes    number of octets per group in normal output. Default 2 (-e: 4).
    -h          print this summary.
    -i          output in C include file style.
    -l len      stop after <len> octets.
    -n name     set the variable name used in C include output (-i).
    -o off      add <off> to the displayed file position.
    -ps         output in postscript plain hexdump style.
    -r          reverse operation: convert (or patch) hexdump into binary.
    -r -s off   revert with <off> added to file positions found in hexdump.
    -d          show offset in decimal instead of hex.
    -s [+][-]seek  start at <seek> bytes abs. (or +: rel.) infile offset.
    -u          use upper case hex letters.
    -v          show version: "xxd 2022-01-14 by Juergen Weigert et al.".

cat test.txt
Hello World

xxd test.txt
00000000: 4865 6c6c 6f20 576f 726c 640a            Hello World.

skip 前n字节

xxd -s 1 test.txt
00000001: 656c 6c6f 2057 6f72 6c64 0a              ello World.

xxd -s 2 test.txt
00000002: 6c6c 6f20 576f 726c 640a                 llo World.

只读取最后n字节

xxd -s -5 test.txt
00000007: 6f72 6c64 0a                             orld.

xxd -s -4 test.txt
00000008: 726c 640a                                rld.

xxd -l 6 -ps -c 3 test.txt
48656c
6c6f20

xxd -l 6  -c 3 test.txt
00000000: 4865 6c  Hel
00000003: 6c6f 20  lo

https://github.com/ckormanyos/xxd