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PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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OD(1P) POSIX Programmer's Manual OD(1P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
od — dump files in various formats
od [-v] [-A address_base] [-j skip] [-N count] [-t type_string]...
[file...]
od [-bcdosx] [file] [[+]offset[.][b]]
The od utility shall write the contents of its input files to
standard output in a user-specified format.
The od utility shall conform to the Base Definitions volume of
POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines, 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
characters 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 number. 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
leading 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 specified.
-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
containing 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.
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, -t, or -v 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 character of the last operand is
numeric; the last operand shall be interpreted as an
offset operand on XSI-conformant systems. 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
interpreted 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.
The standard input shall be used if no file operands are
specified, and shall be used if a file operand is '-' and the
implementation treats the '-' as meaning standard input.
Otherwise, the standard input shall not be used. See the INPUT
FILES section.
The input files can be any file type.
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 POSIX.1‐2017, Section 8.2,
Internationalization Variables for the precedence of
internationalization 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
standard 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.
Default.
See the EXTENDED DESCRIPTION section.
The standard error shall be used only for diagnostic messages.
None.
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 POSIX.1‐2008.
* 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 values
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
underlying 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',
respectively.
The type specifier character a specifies that bytes shall be
interpreted as named characters from the International Reference
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 POSIX.1‐2017, 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. 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
indication that the character is continued. When either the -j
skip or -N count option is specified along with the c type
specifier, and this results in an attempt to start or finish in
the middle of a multi-byte character, the result is
implementation-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> characters.
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> characters, shall start at the first character of the
output line, and shall be followed by one or more <blank>
characters. 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>
characters.
If no -A option is specified, the input offset base is
unspecified.
The following exit values shall be returned:
0 All input files were processed successfully.
>0 An error occurred.
Default.
The following sections are informative.
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.
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 setting, 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 POSIX.1‐2017 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 character 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
approximately 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
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 problem:
* 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 version
presented here provides more normalized forms for dumping
bytes, shorts, ints, and longs in octal, signed decimal,
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 POSIX.1‐2017) 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 recognize 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 POSIX.1‐2017 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 characters 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
recognized 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 POSIX.1‐2017 or this volume of
POSIX.1‐2017. 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
POSIX.1‐2017, 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 correctly.
This volume of POSIX.1‐2017 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 unnecessarily
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 US 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 format character
when the current locale uses a superset of the
ISO/IEC 646:1991 standard as a codeset. The a type specifier
(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 seeing 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 compiler.
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.
Earlier versions of this standard allowed for implementations
with bytes other than eight bits, but this has been modified in
this version.
All option and operand interfaces marked XSI may be removed in a
future version.
c99(1p), sed(1p)
The Base Definitions volume of POSIX.1‐2017, Chapter 5, File
Format Notation, Chapter 8, Environment Variables, Section 12.2,
Utility Syntax Guidelines
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any
discrepancy between this version and the original IEEE and The
Open Group Standard, the original IEEE and The Open Group
Standard is the referee document. The original Standard can be
obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 OD(1P)
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