od

Display file using default settings: octal format, 8 bytes per line, byte offsets in octal, and duplicate lines replaced with *

$ od [path/to/file]

$ od [[-v|--output-duplicates]] [path/to/file]

$ od [[-t|--format]] [x] [[-A|--address-radix]] [d] [[-v|--output-duplicates]] [path/to/file]

$ od [[-t|--format]] [x1] [[-w|--width=]]4 [[-v|--output-duplicates]] [path/to/file]

$ od [[-t|--format]] [xz] [[-A|--address-radix]] [n] [[-v|--output-duplicates]] [path/to/file]

$ od [[-N|--read-bytes]] 100 [[-j|--skip-bytes]] 500 [[-v|--output-duplicates]] [path/to/file]

od [OPTION]... [FILE]...
od [-abcdfiloOsSxX]... [FILE] [[+]OFFSET[.][bB]]

-A RADIX, --address-radix=RADIX
    Address base: decimal, octal, xex, none

-j BYTES, --skip-bytes=BYTES
    Skip first BYTES input bytes

-N BYTES, --read-bytes=BYTES
    Limit output to BYTES input bytes

-S BYTES, --strings[=BYTES]
    Find printable strings of at least BYTES chars

-t TYPE, --format=TYPE
    Select output format (e.g. a, c, d, f, o, x)

-T BYTES, --width[=BYTES]
    Output width in bytes per line

-v, --output-duplicates
    Show all input data, do not use * for repeats

-w BYTES
    Input block size (GNU extension)

--traditional
    Use traditional format

-b
    Octal bytes (-t o1)

-c
    ASCII chars (-t c)

-d
    Unsigned decimal words (-t u2)

-f
    Floats (-t fF)

-i
    Signed decimal words (-t d2)

-o
    Octal words (-t o2)

-s
    Signed decimal words (-t s2)

-x
    Hex words (-t x2)

-X
    Hex words uppercase (-t xC)

od, short for 'octal dump', is a Unix/Linux command-line utility that displays file contents or standard input in various formats including octal, decimal, hexadecimal, ASCII characters, and floating-point numbers. It excels at examining binary data where text viewers fail, such as executables, images, or raw device files.

By default, od outputs data as two-byte octal words with octal byte addresses. Options allow customization: specify output radix for addresses, skip initial bytes, limit bytes read, set output width, or choose formats like hex (-x) or chars (-c). It supports both POSIX traditional options (e.g., -bcdfilosxX) and GNU long options (e.g., --format).

Typical uses include debugging binary protocols, viewing file headers (e.g., od -N 64 file for first 64 bytes), or converting data representations. Unlike hexdump, od is more portable and lightweight, adhering closely to POSIX standards. It's included in GNU coreutils and available on all major Unix-like systems.

For large files, combine with -N to avoid overwhelming output. An optional trailing offset lets you start dumping midway: od -t x1 file +16 skips first 16 bytes in hex.

For -t TYPE:
c: chars; d[N]: signed dec (N=1,2,4,8 bytes); u[N]: unsigned dec; f[N]: float; o[N]: octal; x[N], X[N]: hex (lower/upper); a: strings.

od -t x1 file: hex bytes.
od -c -N 20 /bin/ls: first 20 chars.
od -j 8 -N 16 -t d4 image.raw: 4-byte decimals starting byte 8.

Originated in Version 7 Unix (1979) by AT&T; standardized in POSIX.1-1992. GNU coreutils version enhances with long options and more formats since 1990s.

hexdump(1), xxd(1), dd(1), cat(1), head(1)