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OD(1P) POSIX Programmer's Manual OD(1P)

PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (con-
sult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on
Linux.

NAME
od - dump files in various formats

SYNOPSIS
od [-v][-A address_base][-j skip][-N count][-t type_string]...
[file...]

od [-bcdosx][file] [[+]offset[.][b]]

DESCRIPTION
The od utility shall write the contents of its input files to standard output in a user-specified format.

OPTIONS
The od utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guide-
lines, except that the order of presentation of the -t options and the -bcdosx options is significant.

The following options shall be supported:

-A address_base

Specify the input offset base. See the EXTENDED DESCRIPTION section. The application shall ensure that the
address_base option-argument is a character. The characters 'd', 'o', and 'x' specify that the offset base shall
be written in decimal, octal, or hexadecimal, respectively. The character 'n' specifies that the offset shall not
be written.

-b Interpret bytes in octal. This shall be equivalent to -t o1.

-c Interpret bytes as characters specified by the current setting of the LC_CTYPE category. Certain non-graphic char-
acters appear as C escapes: "NUL=\0", "BS=\b", "FF=\f", "NL=\n", "CR=\r", "HT=\t" ; others appear as 3-digit octal
numbers.

-d Interpret words (two-byte units) in unsigned decimal. This shall be equivalent to -t u2.

-j skip
Jump over skip bytes from the beginning of the input. The od utility shall read or seek past the first skip bytes
in the concatenated input files. If the combined input is not at least skip bytes long, the od utility shall write
a diagnostic message to standard error and exit with a non-zero exit status.

By default, the skip option-argument shall be interpreted as a decimal number. With a leading 0x or 0X, the offset shall
be interpreted as a hexadecimal number; otherwise, with a leading '0', the offset shall be interpreted as an octal num-
ber. Appending the character 'b', 'k', or 'm' to offset shall cause it to be interpreted as a multiple of 512, 1024, or
1048576 bytes, respectively. If the skip number is hexadecimal, any appended 'b' shall be considered to be the final
hexadecimal digit.

-N count
Format no more than count bytes of input. By default, count shall be interpreted as a decimal number. With a lead-
ing 0x or 0X, count shall be interpreted as a hexadecimal number; otherwise, with a leading '0', it shall be
interpreted as an octal number. If count bytes of input (after successfully skipping, if -j skip is specified) are
not available, it shall not be considered an error; the od utility shall format the input that is available.

-o Interpret words (two-byte units) in octal. This shall be equivalent to -t o2.

-s Interpret words (two-byte units) in signed decimal. This shall be equivalent to -t d2.

-t type_string

Specify one or more output types. See the EXTENDED DESCRIPTION section. The application shall ensure that the
type_string option-argument is a string specifying the types to be used when writing the input data. The string
shall consist of the type specification characters a, c, d, f, o, u, and x, specifying named character, character,
signed decimal, floating point, octal, unsigned decimal, and hexadecimal, respectively. The type specification
characters d, f, o, u, and x can be followed by an optional unsigned decimal integer that specifies the number of
bytes to be transformed by each instance of the output type. The type specification character f can be followed by
an optional F, D, or L indicating that the conversion should be applied to an item of type float, double, or long
double, respectively. The type specification characters d, o, u, and x can be followed by an optional C, S, I, or
L indicating that the conversion should be applied to an item of type char, short, int, or long, respectively.
Multiple types can be concatenated within the same type_string and multiple -t options can be specified. Output
lines shall be written for each type specified in the order in which the type specification characters are speci-
fied.

-v Write 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 byte offsets), shall be replaced with a line contain-
ing only an asterisk ( '*' ).

-x Interpret words (two-byte units) in hexadecimal. This shall be equivalent to -t x2.

Multiple types can be specified by using multiple -bcdostx options. Output lines are written for each type specified in
the order in which the types are specified.

OPERANDS
The following operands shall be supported:

file A pathname of a file to be read. If no file operands are specified, the standard input shall be used.

If there are no more than two operands, none of the -A, -j, -N, or -t options is specified, and either of the following
is true: the first character of the last operand is a plus sign ( '+' ), or there are two operands and the first charac-
ter of the last operand is numeric; the last operand shall be interpreted as an offset operand on XSI-conformant sys-
tems. Under these conditions, the results are unspecified on systems that are not XSI-conformant systems.

[+]offset[.][b]
The offset operand specifies the offset in the file where dumping is to commence. This operand is normally inter-
preted as octal bytes. If '.' is appended, the offset shall be interpreted in decimal. If 'b' is appended, the
offset shall be interpreted in units of 512 bytes.

STDIN
The standard input shall be used only if no file operands are specified. See the INPUT FILES section.

INPUT FILES
The input files can be any file type.

ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of od:

LANG Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions
volume of IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables for the precedence of international-
ization variables used to determine the values of locale categories.)

LC_ALL If set to a non-empty string value, override the values of all the other internationalization variables.

LC_CTYPE
Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-
byte as opposed to multi-byte characters in arguments and input files).

LC_MESSAGES
Determine the locale that should be used to affect the format and contents of diagnostic messages written to stan-
dard error.

LC_NUMERIC

Determine the locale for selecting the radix character used when writing floating-point formatted output.

NLSPATH
Determine the location of message catalogs for the processing of LC_MESSAGES .

ASYNCHRONOUS EVENTS
Default.

STDOUT
See the EXTENDED DESCRIPTION section.

STDERR
The standard error shall be used only for diagnostic messages.

OUTPUT FILES
None.

EXTENDED DESCRIPTION
The od utility shall copy sequentially each input file to standard output, transforming the input data according to the
output types specified by the -t option or the -bcdosx options. If no output type is specified, the default output
shall be as if -t oS had been specified.

The number of bytes transformed by the output type specifier c may be variable depending on the LC_CTYPE category.

The default number of bytes transformed by output type specifiers d, f, o, u, and x corresponds to the various C-language
types as follows. If the c99 compiler is present on the system, these specifiers shall correspond to the sizes used by
default in that compiler. Otherwise, these sizes may vary among systems that conform to IEEE Std 1003.1-2001.

* For the type specifier characters d, o, u, and x, the default number of bytes shall correspond to the size of the
underlying implementation's basic integer type. For these specifier characters, the implementation shall support val-
ues of the optional number of bytes to be converted corresponding to the number of bytes in the C-language types char,
short, int, and long. These numbers can also be specified by an application as the characters 'C', 'S', 'I', and 'L',
respectively. The implementation shall also support the values 1, 2, 4, and 8, even if it provides no C-Language
types of those sizes. The implementation shall support the decimal value corresponding to the C-language type long
long. The byte order used when interpreting numeric values is implementation-defined, but shall correspond to the
order in which a constant of the corresponding type is stored in memory on the system.

* For the type specifier character f, the default number of bytes shall correspond to the number of bytes in the under-
lying implementation's basic double precision floating-point data type. The implementation shall support values of the
optional number of bytes to be converted corresponding to the number of bytes in the C-language types float, double,
and long double. These numbers can also be specified by an application as the characters 'F', 'D', and 'L', respec-
tively.

The type specifier character a specifies that bytes shall be interpreted as named characters from the International Ref-
erence Version (IRV) of the ISO/IEC 646:1991 standard. Only the least significant seven bits of each byte shall be used
for this type specification. Bytes with the values listed in the following table shall be written using the corresponding
names for those characters.

Table: Named Characters in od

Value Name Value Name Value Name Value Name
\000 nul \001 soh \002 stx \003 etx
\004 eot \005 enq \006 ack \007 bel
\010 bs \011 ht \012 lf or nl \013 vt
\014 ff \015 cr \016 so \017 si
\020 dle \021 dc1 \022 dc2 \023 dc3
\024 dc4 \025 nak \026 syn \027 etb
\030 can \031 em \032 sub \033 esc
\034 fs \035 gs \036 rs \037 us
\040 sp \177 del

Note: The "\012" value may be written either as lf or nl.

The type specifier character c specifies that bytes shall be interpreted as characters specified by the current setting
of the LC_CTYPE locale category. Characters listed in the table in the Base Definitions volume of IEEE Std 1003.1-2001,
Chapter 5, File Format Notation ( '\\' , '\a', '\b', '\f', '\n', '\r', '\t', '\v' ) shall be written as the corresponding
escape sequences, except that backslash shall be written as a single backslash and a NUL shall be written as '\0' . Other
non-printable characters shall be written as one three-digit octal number for each byte in the character. If the size of
a byte on the system is greater than nine bits, the format used for non-printable characters is implementation-defined.
Printable multi-byte characters shall be written in the area corresponding to the first byte of the character; the two-
character sequence "**" shall be written in the area corresponding to each remaining byte in the character, as an indica-
tion that the character is continued. When either the -j skip or -N count option is specified along with the c type spec-
ifier, and this results in an attempt to start or finish in the middle of a multi-byte character, the result is implemen-
tation-defined.

The input data shall be manipulated in blocks, where a block is defined as a multiple of the least common multiple of the
number of bytes transformed by the specified output types. If the least common multiple is greater than 16, the results
are unspecified. Each input block shall be written as transformed by each output type, one per written line, in the
order that the output types were specified. If the input block size is larger than the number of bytes transformed by the
output type, the output type shall sequentially transform the parts of the input block, and the output from each of the
transformations shall be separated by one or more <blank>s.

If, as a result of the specification of the -N option or end-of-file being reached on the last input file, input data
only partially satisfies an output type, the input shall be extended sufficiently with null bytes to write the last byte
of the input.

Unless -A n is specified, the first output line produced for each input block shall be preceded by the input offset,
cumulative across input files, of the next byte to be written. The format of the input offset is unspecified; however, it
shall not contain any <blank>s, shall start at the first character of the output line, and shall be followed by one or
more <blank>s. In addition, the offset of the byte following the last byte written shall be written after all the input
data has been processed, but shall not be followed by any <blank>s.

If no -A option is specified, the input offset base is unspecified.

EXIT STATUS
The following exit values shall be returned:

0 All input files were processed successfully.

>0 An error occurred.

CONSEQUENCES OF ERRORS
Default.

The following sections are informative.

APPLICATION USAGE
XSI-conformant applications are warned not to use filenames starting with '+' or a first operand starting with a numeric
character so that the old functionality can be maintained by implementations, unless they specify one of the -A, -j, or
-N options. To guarantee that one of these filenames is always interpreted as a filename, an application could always
specify the address base format with the -A option.

EXAMPLES
If a file containing 128 bytes with decimal values zero to 127, in increasing order, is supplied as standard input to the
command:

od -A d -t a

on an implementation using an input block size of 16 bytes, the standard output, independent of the current locale set-
ting, would be similar to:

0000000 nul soh stx etx eot enq ack bel bs ht nl vt ff cr so si
0000016 dle dc1 dc2 dc3 dc4 nak syn etb can em sub esc fs gs rs us
0000032 sp ! " # $ % & ' ( ) * + , - . /
0000048 0 1 2 3 4 5 6 7 8 9 : ; < = > ?
0000064 @ A B C D E F G H I J K L M N O
0000080 P Q R S T U V W X Y Z [ \ ] ^ _
0000096 ` a b c d e f g h i j k l m n o
0000112 p q r s t u v w x y z { | } ~ del
0000128

Note that this volume of IEEE Std 1003.1-2001 allows nl or lf to be used as the name for the ISO/IEC 646:1991 standard
IRV character with decimal value 10. The IRV names this character lf (line feed), but traditional implementations have
referred to this character as newline ( nl) and the POSIX locale character set symbolic name for the corresponding char-
acter is a <newline>.

The command:

od -A o -t o2x2x -N 18

on a system with 32-bit words and an implementation using an input block size of 16 bytes could write 18 bytes in approx-
imately the following format:

0000000 032056 031440 041123 042040 052516 044530 020043 031464
342e 3320 4253 4420 554e 4958 2023 3334
342e3320 42534420 554e4958 20233334
0000020 032472
353a
353a0000
0000022

The command:

od -A d -t f -t o4 -t x4 -N 24 -j 0x15

on a system with 64-bit doubles (for example, IEEE Std 754-1985 double precision floating-point format) would skip 21
bytes of input data and then write 24 bytes in approximately the following format:

0000000 1.00000000000000e+00 1.57350000000000e+01
07774000000 00000000000 10013674121 35341217270
3ff00000 00000000 402f3851 eb851eb8
0000016 1.40668230000000e+02
10030312542 04370303230
40619562 23e18698
0000024

RATIONALE
The od utility went through several names in early proposals, including hd, xd, and most recently hexdump. There were
several objections to all of these based on the following reasons:

* The hd and xd names conflicted with historical utilities that behaved differently.

* The hexdump description was much more complex than needed for a simple dump utility.

* The od utility has been available on all historical implementations and there was no need to create a new name for a
utility so similar to the historical od utility.

The original reasons for not standardizing historical od were also fairly widespread. Those reasons are given below along
with rationale explaining why the standard developers believe that this version does not suffer from the indicated prob-
lem:

* The BSD and System V versions of od have diverged, and the intersection of features provided by both does not meet the
needs of the user community. In fact, the System V version only provides a mechanism for dumping octal bytes and
shorts, signed and unsigned decimal shorts, hexadecimal shorts, and ASCII characters. BSD added the ability to dump
floats, doubles, named ASCII characters, and octal, signed decimal, unsigned decimal, and hexadecimal longs. The ver-
sion presented here provides more normalized forms for dumping bytes, shorts, ints, and longs in octal, signed deci-
mal, unsigned decimal, and hexadecimal; float, double, and long double; and named ASCII as well as current locale
characters.

* It would not be possible to come up with a compatible superset of the BSD and System V flags that met the requirements
of the standard developers. The historical default od output is the specified default output of this utility. None of
the option letters chosen for this version of od conflict with any of the options to historical versions of od.

* On systems with different sizes for short, int, and long, there was no way to ask for dumps of ints, even in the BSD
version. Because of the way options are named, the name space could not be extended to solve these problems. This is
why the -t option was added (with type specifiers more closely matched to the printf() formats used in the rest of
this volume of IEEE Std 1003.1-2001) and the optional field sizes were added to the d, f, o, u, and x type specifiers.
It is also one of the reasons why the historical practice was not mandated as a required obsolescent form of od.
(Although the old versions of od are not listed as an obsolescent form, implementations are urged to continue to rec-
ognize the older forms for several more years.) The a, c, f, o, and x types match the meaning of the corresponding
format characters in the historical implementations of od except for the default sizes of the fields converted. The d
format is signed in this volume of IEEE Std 1003.1-2001 to match the printf() notation. (Historical versions of od
used d as a synonym for u in this version. The System V implementation uses s for signed decimal; BSD uses i for
signed decimal and s for null-terminated strings.) Other than d and u, all of the type specifiers match format charac-
ters in the historical BSD version of od.

The sizes of the C-language types char, short, int, long, float, double, and long double are used even though it is rec-
ognized that there may be zero or more than one compiler for the C language on an implementation and that they may use
different sizes for some of these types. (For example, one compiler might use 2 bytes shorts, 2 bytes ints, and 4 bytes
longs, while another compiler (or an option to the same compiler) uses 2 bytes shorts, 4 bytes ints, and 4 bytes longs.)
Nonetheless, there has to be a basic size known by the implementation for these types, corresponding to the values
reported by invocations of the getconf utility when called with system_var operands {UCHAR_MAX}, {USHORT_MAX},
{UINT_MAX}, and {ULONG_MAX} for the types char, short, int, and long, respectively. There are similar constants required
by the ISO C standard, but not required by the System Interfaces volume of IEEE Std 1003.1-2001 or this volume of
IEEE Std 1003.1-2001. They are {FLT_MANT_DIG}, {DBL_MANT_DIG}, and {LDBL_MANT_DIG} for the types float, double, and long
double, respectively. If the optional c99 utility is provided by the implementation and used as specified by this volume
of IEEE Std 1003.1-2001, these are the sizes that would be provided. If an option is used that specifies different sizes
for these types, there is no guarantee that the od utility is able to interpret binary data output by such a program cor-
rectly.

This volume of IEEE Std 1003.1-2001 requires that the numeric values of these lengths be recognized by the od utility and
that symbolic forms also be recognized. Thus, a conforming application can always look at an array of unsigned long data
elements using od -t uL.

* The method of specifying the format for the address field based on specifying a starting offset in a file unnecessar-
ily tied the two together. The -A option now specifies the address base and the -S option specifies a starting offset.

* It would be difficult to break the dependence on U.S. ASCII to achieve an internationalized utility. It does not seem
to be any harder for od to dump characters in the current locale than it is for the ed or sed l commands. The c type
specifier does this without difficulty and is completely compatible with the historical implementations of the c for-
mat character when the current locale uses a superset of the ISO/IEC 646:1991 standard as a codeset. The a type speci-
fier (from the BSD a format character) was left as a portable means to dump ASCII (or more correctly ISO/IEC 646:1991
standard (IRV)) so that headers produced by pax could be deciphered even on systems that do not use the
ISO/IEC 646:1991 standard as a subset of their base codeset.

The use of "**" as an indication of continuation of a multi-byte character in c specifier output was chosen based on see-
ing an implementation that uses this method. The continuation bytes have to be marked in a way that is not ambiguous with
another single-byte or multi-byte character.

An early proposal used -S and -n, respectively, for the -j and -N options eventually selected. These were changed to
avoid conflicts with historical implementations.

The original standard specified -t o2 as the default when no output type was given. This was changed to -t oS (the length
of a short) to accommodate a supercomputer implementation that historically used 64 bits as its default (and that defined
shorts as 64 bits). This change should not affect conforming applications. The requirement to support lengths of 1, 2,
and 4 was added at the same time to address an historical implementation that had no two-byte data types in its C com-
piler.

The use of a basic integer data type is intended to allow the implementation to choose a word size commonly used by
applications on that architecture.

FUTURE DIRECTIONS
All option and operand interfaces marked as extensions may be withdrawn in a future version.