Hex dump
In computing, a hex dump is a textual hexadecimal view (on screen or paper) of (often, but not necessarily binary) computer data, from memory or from a computer file or storage device. Looking at a hex dump of data is usually done in the context of either debugging, reverse engineering or digital forensics.[1] Interactive editors that provide a similar view but also manipulating the data in question are called hex editors.
In a hex dump, each byte (8 bits) is represented as a two-digit hexadecimal number. Hex dumps are commonly organized into rows of 8 or 16 bytes, sometimes separated by whitespaces. Some hex dumps have the hexadecimal memory address at the beginning.
Some common names for this program function are hexdump, hd, od, xxd and simply dump or even D.
Samples
A sample text file:
0123456789ABCDEF /* ********************************************** */ Table with TABs (09) 1 2 3 3.14 6.28 9.42
as displayed by Unix hexdump:
0000000 30 31 32 33 34 35 36 37 38 39 41 42 43 44 45 46 0000010 0a 2f 2a 20 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 0000020 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 0000040 2a 2a 20 2a 2f 0a 09 54 61 62 6c 65 20 77 69 74 0000050 68 20 54 41 42 73 20 28 30 39 29 0a 09 31 09 09 0000060 32 09 09 33 0a 09 33 2e 31 34 09 36 2e 32 38 09 0000070 39 2e 34 32 0a 0000075
The leftmost column is the hexadecimal displacement (or address) for the values of the following columns. Each row displays 16 bytes, with the exception of the row containing a single *. The * is used to indicate multiple occurrences of the same display were omitted. The last line displays the number of bytes taken from the input.
An additional column shows the corresponding ASCII character translation with hexdump -C or hd:
00000000 30 31 32 33 34 35 36 37 38 39 41 42 43 44 45 46 |0123456789ABCDEF| 00000010 0a 2f 2a 20 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a |./* ************| 00000020 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a |****************| 00000040 2a 2a 20 2a 2f 0a 09 54 61 62 6c 65 20 77 69 74 |** */..Table wit| 00000050 68 20 54 41 42 73 20 28 30 39 29 0a 09 31 09 09 |h TABs (09)..1..| 00000060 32 09 09 33 0a 09 33 2e 31 34 09 36 2e 32 38 09 |2..3..3.14.6.28.| 00000070 39 2e 34 32 0a |9.42.| 00000075
This is helpful when trying to locate TAB characters in a file which is expected to use multiple spaces.
The -v option causes hexdump to display all data verbosely:
00000000 30 31 32 33 34 35 36 37 38 39 41 42 43 44 45 46 |0123456789ABCDEF| 00000010 0a 2f 2a 20 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a |./* ************| 00000020 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a |****************| 00000030 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a |****************| 00000040 2a 2a 20 2a 2f 0a 09 54 61 62 6c 65 20 77 69 74 |** */..Table wit| 00000050 68 20 54 41 42 73 20 28 30 39 29 0a 09 31 09 09 |h TABs (09)..1..| 00000060 32 09 09 33 0a 09 33 2e 31 34 09 36 2e 32 38 09 |2..3..3.14.6.28.| 00000070 39 2e 34 32 0a |9.42.| 00000075
od
POSIX[2] command can be used to display a hex dump with the -t x option.
# od -tx1 tableOfTabs.txt 0000000 30 31 32 33 34 35 36 37 38 39 41 42 43 44 45 46 0000020 0a 2f 2a 20 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 0000040 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 0000100 2a 2a 20 2a 2f 0a 09 54 61 62 6c 65 20 77 69 74 0000120 68 20 54 41 42 73 20 28 30 39 29 0a 09 31 09 09 0000140 32 09 09 33 0a 09 33 2e 31 34 09 36 2e 32 38 09 0000160 39 2e 34 32 0a 0000165
Character evaluations can be added with the -c option:
0000000 0 1 2 3 4 5 6 7 8 9 A B C D E F
30 31 32 33 34 35 36 37 38 39 41 42 43 44 45 46
0000020 \n / * * * * * * * * * * * * *
0a 2f 2a 20 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a
0000040 * * * * * * * * * * * * * * * *
2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a
0000100 * * * / \n \t T a b l e w i t
2a 2a 20 2a 2f 0a 09 54 61 62 6c 65 20 77 69 74
0000120 h T A B s ( 0 9 ) \n \t 1 \t \t
68 20 54 41 42 73 20 28 30 39 29 0a 09 31 09 09
0000140 2 \t \t 3 \n \t 3 . 1 4 \t 6 . 2 8 \t
32 09 09 33 0a 09 33 2e 31 34 09 36 2e 32 38 09
0000160 9 . 4 2 \n
39 2e 34 32 0a
0000165
In this output the TAB characters are displayed as \t and NEWLINE characters as \n.
DUMP, DDT and DEBUG
In the CP/M 8-bit operating system used on early personal computers, the standard DUMP program would list a file 16 bytes per line with the hex offset at the start of the line and the ASCII equivalent of each byte at the end.[3](pp((1-41)), 5-40–5-46) Bytes outside the standard range of printable ASCII characters (20 to 7E) would be displayed as a single period for visual alignment. This same format was used to display memory when invoking the D command in the standard CP/M debugger DDT.[3](p4-5) Later incarnations of the format (e.g. in the DOS debugger DEBUG) changed the space between the 8th and 9th byte to a dash, without changing the overall width.
This notation has been retained in operating systems that were directly or indirectly derived from CP/M, including DR-DOS, MS-DOS/PC DOS, OS/2 and Windows. On Linux systems, the command hexcat produces this classic output format, too. The main reason for the design of this format is that it fits the maximum amount of data on a standard 80-character-wide screen or printer, while still being very easy to read and skim visually.
1234:0000: 57 69 6B 69 70 65 64 69 61 2C 20 74 68 65 20 66 Wikipedia, the f 1234:0010: 72 65 65 20 65 6E 63 79 63 6C 6F 70 65 64 69 61 ree encyclopedia 1234:0020: 20 74 68 61 74 20 61 6E 79 6F 6E 65 20 63 61 6E that anyone can 1234:0030: 20 65 64 69 74 00 00 00 00 00 00 00 00 00 00 00 edit...........
Here the leftmost column represents the address at which the bytes represented by the following columns are located. CP/M and various DOS systems ran in real mode on the x86 CPUs, where addresses are composed of two parts (base and offset).
In the above examples the final 00s are non-existent bytes beyond the end of the file. Some dump tools display other characters so that it is clear they are beyond the end of the file, typically using spaces or asterisks, e.g.:
1234:0000: 57 69 6B 69 70 65 64 69 61 2C 20 74 68 65 20 66 Wikipedia, the f 1234:0010: 72 65 65 20 65 6E 63 79 63 6C 6F 70 65 64 69 61 ree encyclopedia 1234:0020: 20 74 68 61 74 20 61 6E 79 6F 6E 65 20 63 61 6E that anyone can 1234:0030: 20 65 64 69 74 edit
or
1234:0000: 57 69 6B 69 70 65 64 69 61 2C 20 74 68 65 20 66 Wikipedia, the f 1234:0010: 72 65 65 20 65 6E 63 79 63 6C 6F 70 65 64 69 61 ree encyclopedia 1234:0020: 20 74 68 61 74 20 61 6E 79 6F 6E 65 20 63 61 6E that anyone can 1234:0030: 20 65 64 69 74 ** ** ** ** ** ** ** ** ** ** ** edit
See also
References
- ↑ "02: hexdump". COMPSCI 365/590F. Digital Forensics. Spring 2017. https://people.cs.umass.edu/~liberato/courses/2017-spring-compsci365/assignments/02-hexdump/.
- ↑ "POSIX". https://www.unix.com/man-page/posix/1p/od/.
- ↑ 3.0 3.1 CP/M Operating System Manual (3 ed.). Pacific Grove, California, USA: Digital Research. September 1983. pp. ((1-41)), ((4-5)), 5-40-5-46. http://www.cpm.z80.de/manuals/cpm22-m.pdf. Retrieved 2023-10-29.
External links
- How to Use the Hexdump Unix Utility Extensive examples.
- hdr Hexdump with colored ranges to ease visualization. Options to skip data, displaying bitfields, complex range definition, ... follow the link to 'hdr_examples.pod'.
- Hex cheatsheet for looking up byte-nibbles and nibble-bits.
de:Dump#Hexdump
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