'\" te
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.\" Copyright 1989 AT&T
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.TH DD 1M "Sep 16, 1996"
.SH NAME
dd \- convert and copy a file
.SH SYNOPSIS
.LP
.nf
\fB/usr/bin/dd\fR [\fIoperand=value\fR]...
.fi

.SH DESCRIPTION
.sp
.LP
The \fBdd\fR utility copies the specified input file to the specified output
with possible conversions. The standard input and output are used by default.
The input and output block sizes may be specified to take advantage of raw
physical I/O. Sizes are specified in bytes; a number may end with \fBk\fR,
\fBb\fR, or \fBw\fR to specify multiplication by 1024, 512, or 2, respectively.
Numbers may also be separated by \fBx\fR to indicate multiplication.
.sp
.LP
The \fBdd\fR utility reads the input one block at a time, using the specified
input block size. \fBdd\fR then processes the block of data actually returned,
which could be smaller than the requested block size. \fBdd\fR applies any
conversions that have been specified and writes the resulting data to the
output in blocks of the specified output block size.
.sp
.LP
\fBcbs\fR is used only if \fBascii\fR, \fBasciib\fR, \fBunblock\fR,
\fBebcdic\fR, \fBebcdicb\fR, \fBibm\fR, \fBibmb\fR, or \fBblock\fR conversion
is specified. In the first two cases, \fBcbs\fR characters are copied into the
conversion buffer, any specified character mapping is done, trailing blanks are
trimmed, and a \fBNEWLINE\fR is added before sending the line to output. In the
last three cases, characters up to \fBNEWLINE\fR are read into the conversion
buffer and blanks are added to make up an output record of size \fBcbs\fR.
\fBASCII\fR files are presumed to contain \fBNEWLINE\fR characters. If
\fBcbs\fR is unspecified or \fB0\fR, the \fBascii\fR, \fBasciib\fR,
\fBebcdic\fR, \fBebcdicb\fR, \fBibm\fR, and \fBibmb\fR options convert the
character set without changing the input file's block structure. The
\fBunblock\fR and \fBblock\fR options become a simple file copy.
.sp
.LP
After completion, \fBdd\fR reports the number of whole and partial input and
output blocks.
.SH OPERANDS
.sp
.LP
The following operands are supported:
.sp
.ne 2
.na
\fB\fBif=\fR\fIfile\fR\fR
.ad
.sp .6
.RS 4n
Specifies the input path. Standard input is the default.
.RE

.sp
.ne 2
.na
\fB\fBof=\fR\fIfile\fR\fR
.ad
.sp .6
.RS 4n
Specifies the output path. Standard output is the default. If the
\fBseek=\fR\fBexpr\fR conversion is not also specified, the output file will be
truncated before the copy begins, unless \fBconv=notrunc\fR is specified. If
\fBseek=\fR\fBexpr\fR is specified, but \fBconv=notrunc\fR is not, the effect
of the copy will be to preserve the blocks in the output file over which
\fBdd\fR seeks, but no other portion of the output file will be preserved. (If
the size of the seek plus the size of the input file is less than the previous
size of the output file, the output file is shortened by the copy.)
.RE

.sp
.ne 2
.na
\fB\fBibs=\fR\fIn\fR\fR
.ad
.sp .6
.RS 4n
Specifies the input block size in \fIn\fR bytes (default is \fB512\fR).
.RE

.sp
.ne 2
.na
\fB\fBobs=\fR\fIn\fR\fR
.ad
.sp .6
.RS 4n
Specifies the output block size in \fIn\fR bytes (default is \fB512\fR).
.RE

.sp
.ne 2
.na
\fB\fBbs=\fR\fIn\fR\fR
.ad
.sp .6
.RS 4n
Sets both input and output block sizes to \fIn\fR bytes, superseding \fBibs=\fR
and \fBobs=\fR. If no conversion other than \fBsync\fR,\fB noerror\fR, and
\fBnotrunc\fR is specified, each input block is copied to the output as a
single block without aggregating short blocks.
.RE

.sp
.ne 2
.na
\fB\fBcbs=\fR\fIn\fR\fR
.ad
.sp .6
.RS 4n
Specifies the conversion block size for \fBblock\fR and \fBunblock\fR in bytes
by \fIn\fR (default is \fB0\fR). If \fBcbs=\fR is omitted or given a value of
\fB0\fR, using \fBblock\fR or \fBunblock\fR produces unspecified results.
.sp
This option is used only if \fBASCII\fR or \fBEBCDIC\fR conversion is
specified. For the \fBascii\fR and \fBasciib\fR operands, the input is handled
as described for the \fBunblock\fR operand except that characters are converted
to \fBASCII\fR before the trailing \fBSPACE\fR characters are deleted. For the
\fBebcdic\fR, \fBebcdicb\fR, \fBibm\fR, and \fBibmb\fR operands, the input is
handled as described for the \fBblock\fR operand except that the characters are
converted to \fBEBCDIC\fR or IBM \fBEBCDIC\fR after the trailing \fBSPACE\fR
characters are added.
.RE

.sp
.ne 2
.na
\fB\fBfiles=\fR\fIn\fR\fR
.ad
.sp .6
.RS 4n
Copies and concatenates \fIn\fR input files before terminating (makes sense
only where input is a magnetic tape or similar device).
.RE

.sp
.ne 2
.na
\fB\fBskip=\fR\fIn\fR\fR
.ad
.sp .6
.RS 4n
Skips \fIn\fR input blocks (using the specified input block size) before
starting to copy. On seekable files, the implementation reads the blocks or
seeks past them. On non-seekable files, the blocks are read and the data is
discarded.
.RE

.sp
.ne 2
.na
\fB\fBiseek=\fR\fIn\fR\fR
.ad
.sp .6
.RS 4n
Seeks \fIn\fR blocks from beginning of input file before copying (appropriate
for disk files, where \fBskip\fR can be incredibly slow).
.RE

.sp
.ne 2
.na
\fB\fBoseek=\fR\fIn\fR\fR
.ad
.sp .6
.RS 4n
Seeks \fIn\fR blocks from beginning of output file before copying.
.RE

.sp
.ne 2
.na
\fB\fBseek=\fR\fIn\fR\fR
.ad
.sp .6
.RS 4n
Skips \fIn\fR blocks (using the specified output block size) from beginning of
output file before copying. On non-seekable files, existing blocks are read and
space from the current end-of-file to the specified offset, if any, is filled
with null bytes. On seekable files, the implementation seeks to the specified
offset or reads the blocks as described for non-seekable files.
.RE

.sp
.ne 2
.na
\fB\fBcount=\fR\fIn\fR\fR
.ad
.sp .6
.RS 4n
Copies only \fIn\fR input blocks.
.RE

.sp
.ne 2
.na
\fB\fBconv=\fR\fIvalue\fR[\fB,\fR\fIvalue\fR.\|.\|.\|]\fR
.ad
.sp .6
.RS 4n
Where \fIvalue\fRs are comma-separated symbols from the following list:
.sp
.ne 2
.na
\fB\fBascii\fR\fR
.ad
.RS 11n
Converts \fBEBCDIC\fR to \fBASCII\fR.
.RE

.sp
.ne 2
.na
\fB\fBasciib\fR\fR
.ad
.RS 11n
Converts \fBEBCDIC\fR to \fBASCII\fR using \fBBSD\fR-compatible character
translations.
.RE

.sp
.ne 2
.na
\fB\fBebcdic\fR\fR
.ad
.RS 11n
Converts \fBASCII\fR to \fBEBCDIC\fR. If converting fixed-length \fBASCII\fR
records without NEWLINEs, sets up a pipeline with \fBdd conv=unblock\fR
beforehand.
.RE

.sp
.ne 2
.na
\fB\fBebcdicb\fR\fR
.ad
.RS 11n
Converts \fBASCII\fR to \fBEBCDIC\fR using \fBBSD\fR-compatible character
translations. If converting fixed-length \fBASCII\fR records without
\fBNEWLINE\fRs, sets up a pipeline with \fBdd conv=unblock\fR beforehand.
.RE

.sp
.ne 2
.na
\fB\fBibm\fR\fR
.ad
.RS 11n
Slightly different map of \fBASCII\fR to \fBEBCDIC\fR. If converting
fixed-length \fBASCII\fR records without \fBNEWLINE\fRs, sets up a pipeline
with \fBdd conv=unblock\fR beforehand.
.RE

.sp
.ne 2
.na
\fB\fBibmb\fR\fR
.ad
.RS 11n
Slightly different map of \fBASCII\fR to \fBEBCDIC\fR using
\fBBSD\fR-compatible character translations. If converting fixed-length
\fBASCII\fR records without \fBNEWLINE\fRs, sets up a pipeline with \fBdd
conv=unblock\fR beforehand.
.RE

The \fBascii\fR (or \fBasciib\fR), \fBebcdic\fR (or \fBebcdicb\fR), and
\fBibm\fR (or \fBibmb\fR) values are mutually exclusive.
.sp
.ne 2
.na
\fB\fBblock\fR\fR
.ad
.RS 11n
Treats the input as a sequence of \fBNEWLINE\fR-terminated or
\fBEOF\fR-terminated variable-length records independent of the input block
boundaries. Each record is converted to a record with a fixed length specified
by the conversion block size. Any \fBNEWLINE\fR character is removed from the
input line. \fBSPACE\fR characters are appended to lines that are shorter than
their conversion block size to fill the block. Lines that are longer than the
conversion block size are truncated to the largest number of characters that
will fit into that size. The number of truncated lines is reported.
.RE

.sp
.ne 2
.na
\fB\fBunblock\fR\fR
.ad
.RS 11n
Converts fixed-length records to variable length. Reads a number of bytes equal
to the conversion block size (or the number of bytes remaining in the input, if
less than the conversion block size), delete all trailing \fBSPACE\fR
characters, and append a \fBNEWLINE\fR character.
.RE

The  \fBblock\fR and \fBunblock\fR values are mutually exclusive.
.sp
.ne 2
.na
\fB\fBlcase\fR\fR
.ad
.RS 9n
Maps upper-case characters specified by the \fBLC_CTYPE\fR keyword
\fBtolower\fR to the corresponding lower-case character. Characters for which
no mapping is specified are not modified by this conversion.
.RE

.sp
.ne 2
.na
\fB\fBucase\fR\fR
.ad
.RS 9n
Maps lower-case characters specified by the \fBLC_CTYPE\fR keyword
\fBtoupper\fR to the corresponding upper-case character. Characters for which
no mapping is specified are not modified by this conversion.
.RE

The \fBlcase\fR and \fBucase\fR symbols are mutually exclusive.
.sp
.ne 2
.na
\fB\fBswab\fR\fR
.ad
.RS 11n
Swaps every pair of input bytes. If the current input record is an odd number
of bytes, the last byte in the input record is ignored.
.RE

.sp
.ne 2
.na
\fB\fBnoerror\fR\fR
.ad
.RS 11n
Does not stop processing on an input error. When an input error occurs, a
diagnostic message is written on standard error, followed by the current input
and output block counts in the same format as used at completion. If the
\fBsync\fR conversion is specified, the missing input is replaced with null
bytes and processed normally. Otherwise, the input block will be omitted from
the output.
.RE

.sp
.ne 2
.na
\fB\fBnotrunc\fR\fR
.ad
.RS 11n
Does not truncate the output file. Preserves blocks in the output file not
explicitly written by this invocation of \fBdd\fR. (See also the preceding
\fBof=\fR\fIfile\fR operand.)
.RE

.sp
.ne 2
.na
\fB\fBsync\fR\fR
.ad
.RS 11n
Pads every input block to the size of the \fBibs=\fR buffer, appending null
bytes. (If either \fBblock\fR or \fBunblock\fR is also specified, appends
\fBSPACE\fR characters, rather than null bytes.)
.RE

.RE

.sp
.LP
If operands other than \fBconv=\fR are specified more than once, the last
specified \fBoperand=\fR\fIvalue\fR is used.
.sp
.LP
For the \fBbs=\fR, \fBcbs=\fR, \fBibs=\fR, and \fBobs=\fR operands, the
application must supply an expression specifying a size in bytes. The
expression, \fBexpr\fR, can be:
.RS +4
.TP
1.
a positive decimal number
.RE
.RS +4
.TP
2.
a positive decimal number followed by \fBk\fR, specifying multiplication by
1024
.RE
.RS +4
.TP
3.
a positive decimal number followed by \fBM\fR, specifying multiplication by
1024*1024
.RE
.RS +4
.TP
4.
a positive decimal number followed by \fBG\fR, specifying multiplication by
1024*1024*1024
.RE
.RS +4
.TP
5.
a positive decimal number followed by \fBT\fR, specifying multiplication by
1024*1024*1024*1024
.RE
.RS +4
.TP
6.
a positive decimal number followed by \fBP\fR, specifying multiplication by
1024*1024*1024*1024*1024
.RE
.RS +4
.TP
7.
a positive decimal number followed by \fBE\fR, specifying multiplication by
1024*1024*1024*1024*1024*1024
.RE
.RS +4
.TP
8.
a positive decimal number followed by \fBZ\fR, specifying multiplication by
1024*1024*1024*1024*1024*1024*1024
.RE
.RS +4
.TP
9.
a positive decimal number followed by \fBb\fR, specifying multiplication by
512
.RE
.RS +4
.TP
10.
two or more positive decimal numbers (with or without \fBk\fR or \fBb\fR)
separated by \fBx\fR, specifying the product of the indicated values.
.RE
.sp
.LP
All of the operands will be processed before any input is read.
.SH USAGE
.sp
.LP
See \fBlargefile\fR(5) for the description of the behavior of \fBdd\fR when
encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).
.SH EXAMPLES
.LP
\fBExample 1 \fRCopying from one tape drive to another
.sp
.LP
The following example copies from tape drive \fB0\fR to tape drive \fB1\fR,
using a common historical device naming convention.

.sp
.in +2
.nf
example% \fBdd if=/dev/rmt/0h  of=/dev/rmt/1h\fR
.fi
.in -2
.sp

.LP
\fBExample 2 \fRStripping the first 10 bytes from standard input
.sp
.LP
The following example strips the first 10 bytes from standard input:

.sp
.in +2
.nf
example% \fBdd ibs=10  skip=1\fR
.fi
.in -2
.sp

.LP
\fBExample 3 \fRReading a tape into an ASCII file
.sp
.LP
This example reads an \fBEBCDIC\fR tape blocked ten 80-byte \fBEBCDIC\fR card
images per block into the \fBASCII\fR file \fBx\fR:

.sp
.in +2
.nf
example% \fBdd if=/dev/tape of=x ibs=800 cbs=80 conv=ascii,lcase\fR
.fi
.in -2
.sp

.LP
\fBExample 4 \fRUsing conv=sync to write to tape
.sp
.LP
The following example uses \fBconv=sync\fR when writing to a tape:

.sp
.in +2
.nf
example% \fBtar cvf - . | compress | dd obs=1024k of=/dev/rmt/0 conv=sync\fR
.fi
.in -2
.sp

.SH ENVIRONMENT VARIABLES
.sp
.LP
See \fBenviron\fR(5) for descriptions of the following environment variables
that affect the execution of \fBdd\fR: \fBLANG\fR, \fBLC_ALL\fR,
\fBLC_CTYPE\fR, \fBLC_MESSAGES\fR, and \fBNLSPATH\fR.
.SH EXIT STATUS
.sp
.LP
The following exit values are returned:
.sp
.ne 2
.na
\fB\fB0\fR\fR
.ad
.RS 6n
The input file was copied successfully.
.RE

.sp
.ne 2
.na
\fB\fB>0\fR\fR
.ad
.RS 6n
An error occurred.
.RE

.sp
.LP
If an input error is detected and the \fBnoerror\fR conversion has not been
specified, any partial output block will be written to the output file, a
diagnostic message will be written, and the copy operation will be
discontinued. If some other error is detected, a diagnostic message will be
written and the copy operation will be discontinued.
.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
.TE

.SH SEE ALSO
.sp
.LP
\fBcp\fR(1), \fBsed\fR(1), \fBtr\fR(1), \fBattributes\fR(5), \fBenviron\fR(5),
\fBlargefile\fR(5), \fBstandards\fR(5)
.SH DIAGNOSTICS
.sp
.ne 2
.na
\fB\fBf+p records in(out)\fR\fR
.ad
.RS 23n
numbers of full and partial blocks read(written)
.RE

.SH NOTES
.sp
.LP
Do not use \fBdd\fR to copy files between file systems having different block
sizes.
.sp
.LP
Using a  blocked device to copy a file will result in extra nulls being added
to the file to pad the final block to the block boundary.
.sp
.LP
When  \fBdd\fR reads from a pipe, using the  \fBibs=X\fR and  \fBobs=Y\fR
operands, the output will always be blocked in chunks of size Y. When
\fBbs=Z\fR is used, the output blocks will be whatever was available to be read
from the pipe at the time.
.sp
.LP
When using \fBdd\fR to copy files to a tape device, the file size must be a
multiple of the device sector size (for example, 512 Kbyte).  To  copy files of
arbitrary size to a tape device, use  \fBtar\fR(1) or  \fBcpio\fR(1).
.sp
.LP
For \fBSIGINT\fR, \fBdd\fR writes status information to standard error before
exiting. It takes the standard action for all other signals.