Tue 13 December 2005
In tips.
Ian Wienand
More from the "things you'd learn if you read the manual" department, although the manual as currently written is a little esoteric on this feature of hexdump.
$ hexdump -e ' [iterations]/[byte_count] "[format string]" '
As you might guess, this means apply format string to groups of byte_count bytes, iterations times. Format string is likeprintf.
You can of course chain multiple formats together, or put them in a file. So say you needed to clag some binary data into a C array, a-la firmware for loading into a driver. You could use
$ hexdump -v -e '6/4 "0x%08x, "' -e '"\n"' ./dump
to get something that fits in 80 columns and is almost ready to go.
Manual on How to Use the Hexdump Unix Utility
Every time I go to use hexdump I find myself stumbling over it's bizarre argument format and ineffectual manual. Because I look at binary files often I decided to work up this page more for myself than anyone else.
Here is a sample usage of hexdump:
cat file | hexdump -v -e '"\\\x" 1/1 "%02x" " "'
And here is some sample output from it:
\x97\x6d\xea\xd1\x21\x02\x12\x80\x01\x9d...
Argument Description
The -v argument is needed to not print duplicate chars as a *. The -e argument has 5 parts separated by whitespace. I'm not sure how multiple format entries interact.
- An optional starting string (in quotes) which is printed before each conversion. In the first example below we are printing x before each hex character ("x").
- An interation count which defaults to 1 if not supplied but has to be supplied if you want a byte count. This tells how many times to do the conversion before we print the end string. So if you were decoding 4 things, each of 1 byte, you'd say 4/1.
- A byte count which is separated from the interation count by a /. I don't think there is a way to specify a byte count without an interation count. This specifies how many bytes are in each item that is being decoded.
- A sprintf format. The manual is somewhat useful here. Some standard ones apply and there are _ extensions. In the first example below this is "%02X" which prints each byte as a 2 character, 0 prefixed capital hex number.
- An optional ending string (in quotes) which is printed after the conversion. A space in the first example below (" ").
Format Examples
Print an "x" to start, take 1 item / 1 byte, print it as a 2 digit 0 prefixed hex value ("%02X"), and end with a space.
echo "hello there" | hexdump -v -e '"x" 1/1 "%02X" " "'
Outputs something like:
x68 x65 x6C x6C x6F x20 x74 x68 x65 x72 x65 x0A
Print an "[" to start, take 2 items / each 1 byte, print them as a 3 digit 0 prefixed octal value followed by a space ("%03o "), and end with "]\n".
echo "hello there" | hexdump -v -e '"[" 2/1 "%03o " "]\n"'
Outputs something like:
[150 145]
[154 154]
[157 040]
[164 150]
[145 162]
[145 012]
NOTE: the trailing space in "%03o " format will not be printed at the end of each interation.
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