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.
The iteration count is an optional positive integer, which
defaults to one. Each format is applied iteration count times.
The byte count is an optional positive integer. If specified it
defines the number of bytes to be interpreted by each iteration
of the format.
If an iteration count and/or a byte count is specified, a single
slash must be placed after the iteration count and/or before the
byte count to disambiguate them. Any whitespace before or after
the slash is ignored.
The format is required and must be surrounded by double quote ("
") marks. It is interpreted as a fprintf-style format string (see
fprintf(3), with the following exceptions:
1.
An asterisk (*) may not be used as a field width or
precision.
2.
A byte count or field precision is required for each s
conversion character (unlike the fprintf3 default which
prints the entire string if the precision is unspecified).
3.
The conversion characters h, l, n, p, and q are not
supported.
4.
The single character escape sequences described in the C
standard are supported:
┌──────────────────┬────┐
│ │ │
│NULL │ \0 │
├──────────────────┼────┤
│ │ │
│<alert character> │ \a │
├──────────────────┼────┤
│ │ │
│<backspace> │ \b │
├──────────────────┼────┤
│ │ │
│<form-feed> │ \f │
├──────────────────┼────┤
│ │ │
│<newline> │ \n │
├──────────────────┼────┤
│ │ │
│<carriage return> │ \r │
├──────────────────┼────┤
│ │ │
│<tab> │ \t │
├──────────────────┼────┤
│ │ │
│<vertical tab> │ \v │
└──────────────────┴────┘
Conversion strings
The hexdump utility also supports the following additional
conversion strings.
_a[dox]
Display the input offset, cumulative across input
files, of the next byte to be displayed. The appended
characters 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.
Non-printing 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.
Non-printing 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.
┌────────┬─────────┬─────────┬─────────┬─────────┬─────────┐
│ │ │ │ │ │ │
│000 nul │ 001 soh │ 002 stx │ 003 etx │ 004 eot │ 005 enq │
├────────┼─────────┼─────────┼─────────┼─────────┼─────────┤
│ │ │ │ │ │ │
│006 ack │ 007 bel │ 008 bs │ 009 ht │ 00A lf │ 00B vt │
├────────┼─────────┼─────────┼─────────┼─────────┼─────────┤
│ │ │ │ │ │ │
│00C ff │ 00D cr │ 00E so │ 00F si │ 010 dle │ 011 dc1 │
├────────┼─────────┼─────────┼─────────┼─────────┼─────────┤
│ │ │ │ │ │ │
│012 dc2 │ 013 dc3 │ 014 dc4 │ 015 nak │ 016 syn │ 017 etb │
├────────┼─────────┼─────────┼─────────┼─────────┼─────────┤
│ │ │ │ │ │ │
│018 can │ 019 em │ 01A sub │ 01B esc │ 01C fs │ 01D gs │
├────────┼─────────┼─────────┼─────────┼─────────┼─────────┤
│ │ │ │ │ │ │
│01E rs │ 01F us │ 0FF del │ │ │ │
└────────┴─────────┴─────────┴─────────┴─────────┴─────────┘
Colors
When put at the end of a format specifier, hexdump
highlights the respective string with the color
specified. Conditions, if present, are evaluated
prior to highlighting.
_L[color_unit_1,color_unit_2,...,color_unit_n]
The full syntax of a color unit is as follows:
[!]COLOR[:VALUE][@OFFSET_START[-END]]
!
Negate the condition. Please note that it only
makes sense to negate a unit if both a
value/string and an offset are specified. In that
case the respective output string will be
highlighted if and only if the value/string does
not match the one at the offset.
COLOR
One of the 8 basic shell colors.
VALUE
A value to be matched specified in hexadecimal,
or octal base, or as a string. Please note that
the usual C escape sequences are not interpreted
by hexdump inside the color_units.
OFFSET
An offset or an offset range at which to check
for a match. Please note that lone OFFSET_START
uses the same value as END offset.
Counters
The default and supported byte counts for the
conversion characters are as follows:
%_c, %_p, %_u, %c
One byte counts only.
%d, %i, %o, %u, %X, %x
Four byte default, one, two and four byte counts
supported.
%E, %e, %f, %G, %g
Eight byte default, four byte counts supported.
The amount of data interpreted by each format string
is the sum of the data required by each format unit,
which is the iteration count times the byte count, or
the iteration count times the number of bytes
required by the format if the byte count is not
specified.
The input is manipulated in blocks, where a block is
defined as the largest amount of data specified by
any format string. Format strings interpreting less
than an input block's worth of data, whose last
format unit both interprets some number of bytes and
does not have a specified iteration count, have the
iteration count incremented until the entire input
block has been processed or there is not enough data
remaining in the block to satisfy the format string.
If, either as a result of user specification or
hexdump modifying the iteration count as described
above, an iteration count is greater than one, no
trailing whitespace characters are output during the
last iteration.
It is an error to specify a byte count as well as
multiple conversion characters or strings unless all
but one of the conversion characters or strings is _a
or _A.
If, as a result of the specification of the -n option
or end-of-file being reached, input data only
partially satisfies a format string, the input block
is zero-padded sufficiently to display all available
data (i.e., any format units overlapping the end of
data will display some number of the zero bytes).
Further output by such format strings is replaced by
an equivalent number of spaces. An equivalent number
of spaces is defined as the number of spaces output
by an s conversion character with the same field
width and precision as the original conversion
character or conversion string but with any '+', ' ',
'#' conversion flag characters removed, and
referencing a NULL string.
If no format strings are specified, the default
display is very similar to the -x output format (the
-x option causes more space to be used between format
units than in the default output).
