od [man page] - dump files in octal and other formats


od [OPTION]... [FILE]...
od [-abcdfilosx]... [FILE] [[+]OFFSET[.][b]]
od --traditional [OPTION]... [FILE] [[+]OFFSET[.][b] 

Frequently used options

t, --format=TYPE
      select output format or formats
-a    same as -t a,  select named characters
-c    same as -t c,  select ASCII characters or
      backslash escapes
-x    same as -t x2, select hexadecimal 2-byte 
-l    same as -t dL, select decimal longs


Suppose that we have a file which contains:

$ echo -e "one\ntwo\nthree\nfour\nfive\n\nsix" > file 

od - create sample file
by default all output from od command comes as octal:

$ od file 

od - octal output
Fist column is a octal offset of a file and the following output is a file content in octal representation.With -c option we can instruct od command to represent values in a file as ASCII.

$ od -a file 

od - ASCII output :[[Image:od02.gif]] To get understanding of what a offset is, we can use wc command to get total number of bytes in the file and that convert it with bc to octal number.

$ wc -c file
$ echo "obase=8; ibase=10; 29;" | bc

od - bc to octal number