man hexdump可以发现关于-e format_string的解释，除了支持printf的convertion specifier外，还额外支持以下转换符号：

 _a[dox]     Display the input offset, cumulative across input files, of the next byte to be displayed.  The appended char-
             acters d, o, and x specify the display base as decimal, octal or hexadecimal respectively.

 _A[dox]     Identical to the _a conversion string except that it is only performed once, when all of the input data has
             been processed.

 _c          Output characters in the default character set.  Nonprinting characters are displayed in three character,
             zero-padded octal, except for those representable by standard escape notation (see above), which are displayed
             as two character strings.

 _p          Output characters in the default character set.  Nonprinting characters are displayed as a single “.”.

 _u          Output US ASCII characters, with the exception that control characters are displayed using the following,
             lower-case, names.  Characters greater than 0xff, hexadecimal, are displayed as hexadecimal strings.

而printf的format格式是

[flag][field width][precision][length modifier][convertion specifier]

把"%06_ax " 16/1 "%02X " "\n"对号入座

%06_ax是flag为0，field width为6的_ax转换符。

%02X是flag为0，field width为2的X转换符。

16/1分别是hexdump的format unit的iteration count和byte count。

A format string contains any number of format units, separated by whitespace. A format unit contains up to three items: an iteration count, a byte count, and a format.