... dedicated to understanding hexidecimal!

 

Linux Command Line Hex Editor

January 16, 2009

Ever had a need for a quick and dirty command line hex editor on your Linux box?


I know I have and whenever I get into a pinch I turn to hexdump. Hexdump is an easy to use no frills hex editor that is present by default on most Linux distributions. Usually I find myself using the hexdump -c <filename> option. But I've included the whole man page below for your viewing pleasure. Enjoy!


HEXDUMP(1) BSD General Commands Manual HEXDUMP(1)

NAME

hexdump - ascii, decimal, hexadecimal, octal dump

SYNOPSIS

[-bcCdovx] [-e format_string] [-f format_file] [-n length] [-s skip] file ...

DESCRIPTION

The hexdump utility is a filter which displays the specified files, or the standard input, if no files are specified, in a user specified format.

The options are as follows:

-b One-byte octal display. Display the input offset in hexadecimal, followed by sixteen space-separated, three column, zero-filled, bytes of input data, in octal, per line.

-c One-byte character display. Display the input offset in hexadecimal, followed by sixteen space-separated, three column, space-filled, characters of input data per line.

-C Canonical hex+ASCII display. Display the input offset in hexadecimal, followed by sixteen space-separated, two column, hexadecimal bytes, followed by the same sixteen bytes in %_p format enclosed in ââ|ââ characters.

-d Two-byte decimal display. Display the input offset in hex- adecimal, followed by eight space-separated, five column, zero-filled, two-byte units of input data, in unsigned decimal, per line.

-e format_string. Specify a format string to be used for displaying data.

-f format_file. Specify a file that contains one or more newline separated format strings. Empty lines and lines whose first non-blank character is a hash mark (#) are ignored.

-n length Interpret only length bytes of input.

-o Two-byte octal display. Display the input offset in hexadecimal, followed by eight space-separated, six column, zerofilled, two byte quantities of input data, in octal, per line.

-s offset Skip offset bytes from the beginning of the input. By default, offset is interpreted as a decimal number. With a leading 0x or 0X, offset is interpreted as a hexadecimal number, otherwise, with a leading 0, offset is interpreted as an octal number. Appending the character b, k, or m to offset causes it to be interpreted as a multiple of 512, 1024, or 1048576, respectively.

-v The -v option causes hexdump to display all input data. Without the -v option, any number of groups of output lines, which would be identical to the immediately preceding group of output lines (except for the input offsets), are replaced with a line comprised of a single asterisk.

-x Two-byte hexadecimal display. Display the input offset in hexadecimal, followed by eight, space separated, four column, zero-filled, two-byte quantities of input data, in hexadecimal, per line.

For each input file, hexdump sequentially copies the input to standard output, transforming the data according to the format strings specified by the -e and -f options, in the order that they were specified.

Formats

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:

- An asterisk (*) may not be used as a field width or precision.

- A byte count or field precision is required for each ââsââ conversion character (unlike the fprintf(3) default which prints the entire string if the precision is unspecified).

- The conversion characters ââhââ, ââlââ, âânââ, ââpââ and ââqââ are not supported.

- The single character escape sequences described in the C stan- dard are supported:

NUL \0

<alert character> \a

<backspace> \b

<form-feed> \f

<newline> \n

<carriage return> \r

<tab> \t

<vertical tab> \v

Hexdump 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. 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 â.â

_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

The default and supported byte counts for the conversion characters are as follows:

%_c, %_p, %_u, %c One byte counts only.

%u, %X, %xâ Four byte default, one, two and four byte counts supported.

%G, %gâ %f, 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 ââblocksââ, 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 num- ber 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 â+â â#â ing a NULL string.

If no format strings are specified, the default display is equivalent to specifying the -x option.

hexdump exits 0 on success and >0 if an error occurred.

EXAMPLES

Display the input in perusal format:

"%06.6_ao " 12/1 "%3_u "

"\t\t" "%_p "

"\n"

Implement the -x option:

"%07.7_Ax\n"

"%07.7_ax " 8/2 "%04x " "\n"

STANDARDS

The hexdump utility is expected to be IEEE Std 1003.

BSD April 18, 1994 BSD     

 

What the future has in store

You can expect this site to change fairly regularly (probably a least once per week). I will be using it mostly as a way to centrally house my ideas and as a way to test new and/or exciting projects that I happen to be working on. If you'd like to see something on this site or have any sort of feedback please feel free to contact me.