path: root/bin/dd/dd.1

.\"	$NetBSD: dd.1,v 1.36 2019/01/30 10:28:50 wiz Exp $
.\"
.\" Copyright (c) 1990, 1993
.\"	The Regents of the University of California.  All rights reserved.
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.\" This code is derived from software contributed to Berkeley by
.\" Keith Muller of the University of California, San Diego.
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.\"    may be used to endorse or promote products derived from this software
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.\"	@(#)dd.1	8.2 (Berkeley) 1/13/94
.\"
.Dd January 29, 2019
.Dt DD 1
.Os
.Sh NAME
.Nm dd
.Nd convert and copy a file
.Sh SYNOPSIS
.Nm
.Op operand ...
.Sh DESCRIPTION
The
.Nm
utility copies the standard input to the standard output.
Input data is read and written in 512-byte blocks.
If input reads are short, input from multiple reads are aggregated
to form the output block.
When finished,
.Nm
displays the number of complete and partial input and output blocks
and truncated input records to the standard error output.
.Pp
The following operands are available:
.Bl -tag -width of=file
.It Cm bs= Ns Ar n
Set both input and output block size, superseding the
.Cm ibs
and
.Cm obs
operands.
If no conversion values other than
.Cm noerror ,
.Cm notrunc
or
.Cm sync
are specified, then each input block is copied to the output as a
single block without any aggregation of short blocks.
.It Cm cbs= Ns Ar n
Set the conversion record size to
.Va n
bytes.
The conversion record size is required by the record oriented conversion
values.
.It Cm count= Ns Ar n
Copy only
.Va n
input blocks.
.It Cm files= Ns Ar n
Copy
.Va n
input files before terminating.
This operand is only applicable when the input device is a tape.
.It Cm ibs= Ns Ar n
Set the input block size to
.Va n
bytes instead of the default 512.
.It Cm if= Ns Ar file
Read input from
.Ar file
instead of the standard input.
.It Cm iflag= Ns Ar flags
Use comma-separated
.Ar flags
when calling
.Xr open 2
for the input file.
See the
.Sx INPUT AND OUTPUT FLAGS
section for details.
Default value is
.Va rdonly .
.It Cm iseek= Ns Ar n
Seek on the input file
.Ar n
blocks.
This is synonymous with
.Cm skip= Ns Ar n .
.It Cm msgfmt= Ns Ar fmt
Specify the message format
.Ar fmt
to be used when writing information to standard output.
Possible values are:
.Bl -tag -width xxxxx -offset indent -compact
.It quiet
turns off information summary report except for errors and
.Cm progress .
.It posix
default information summary report as specified by POSIX.
.It human
default information summary report extended with human-readable
values.
.El
.Pp
When
.Ar fmt
does not correspond to any value given above,
it contains a string that will be used as format specifier
for the information summary output.
Each conversion specification is introduced by the character
.Cm % .
The following ones are available:
.Bl -tag -width xx -offset indent -compact
.It b
total number of bytes transferred
.It B
total number of bytes transferred in
.Xr humanize_number 3
format
.It e
speed transfer
.It E
speed transfer in
.Xr humanize_number 3
format
.It i
number of partial input block(s)
.It I
number of full input block(s)
.It o
number of partial output block(s)
.It O
number of full output block(s)
.It s
time elapsed since the beginning in
.Do seconds.ms Dc
format
.It p
number of sparse output blocks
.It t
number of truncated blocks
.It w
number of odd-length swab blocks
.It P
singular/plural of
.Do block Dc
depending on number of sparse blocks
.It T
singular/plural of
.Do block Dc
depending on number of truncated blocks
.It W
singular/plural of
.Do block Dc
depending on number of swab blocks
.El
.It Cm obs= Ns Ar n
Set the output block size to
.Va n
bytes instead of the default 512.
.It Cm of= Ns Ar file
Write output to
.Ar file
instead of the standard output.
Any regular output file is truncated unless the
.Cm notrunc
conversion value is specified.
If an initial portion of the output file is skipped (see the
.Cm seek
operand)
the output file is truncated at that point.
.It Cm oflag= Ns Ar flags
Same as
.Cm iflag
but for the call to
.Xr open 2
on the output file.
The default value is
.Va creat ,
which must be explicitly added in
.Cm oflag
if this option is used in order to output to a nonexistent file.
The default or specified value is or'ed with
.Va rdwr
for a first
.Xr open 2
attempt, then on failure with
.Va wronly
on a second attempt.
In both cases,
.Va trunc
is automatically added if none of
.Cm oseek ,
.Cm seek ,
or
.Cm conv=notrunc
operands are used.
See the
.Sx INPUT AND OUTPUT FLAGS
section for details.
.It Cm oseek= Ns Ar n
Seek on the output file
.Ar n
blocks.
This is synonymous with
.Cm seek= Ns Ar n .
.It Cm seek= Ns Ar n
Seek
.Va n
blocks from the beginning of the output before copying.
On non-tape devices, an
.Xr lseek 2
operation is used.
Otherwise, existing blocks are read and the data discarded.
If the user does not have read permission for the tape, it is positioned
using the tape
.Xr ioctl 2
function calls.
If the seek operation is past the end of file, space from the current
end of file to the specified offset is filled with blocks of
.Tn NUL
bytes.
.It Cm skip= Ns Ar n
Skip
.Va n
blocks from the beginning of the input before copying.
On input which supports seeks, an
.Xr lseek 2
operation is used.
Otherwise, input data is read and discarded.
For pipes, the correct number of bytes is read.
For all other devices, the correct number of blocks is read without
distinguishing between a partial or complete block being read.
.It Cm progress= Ns Ar n
Switch on display of progress if
.Va n
is set to any non-zero value.
This will cause a
.Dq \&.
to be printed (to the standard error output) for every
.Va n
full or partial blocks written to the output file.
.Sm off
.It Cm conv= Cm value Op \&, Cm value \&...
.Sm on
Where
.Cm value
is one of the symbols from the following list.
.Bl -tag -width unblock
.It Cm ascii , oldascii
The same as the
.Cm unblock
value except that characters are translated from
.Tn EBCDIC
to
.Tn ASCII
before the
records are converted.
(These values imply
.Cm unblock
if the operand
.Cm cbs
is also specified.)
There are two conversion maps for
.Tn ASCII .
The value
.Cm ascii
specifies the recommended one which is compatible with
.At V .
The value
.Cm oldascii
specifies the one used in historic
.Tn AT&T
and pre-
.Bx 4.3 Reno
systems.
.It Cm block
Treats the input as a sequence of newline or end-of-file terminated variable
length records independent of input and output block boundaries.
Any trailing newline character is discarded.
Each input record is converted to a fixed length output record where the
length is specified by the
.Cm cbs
operand.
Input records shorter than the conversion record size are padded with spaces.
Input records longer than the conversion record size are truncated.
The number of truncated input records, if any, are reported to the standard
error output at the completion of the copy.
.It Cm ebcdic , ibm , oldebcdic , oldibm
The same as the
.Cm block
value except that characters are translated from
.Tn ASCII
to
.Tn EBCDIC
after the
records are converted.
(These values imply
.Cm block
if the operand
.Cm cbs
is also specified.)
There are four conversion maps for
.Tn EBCDIC .
The value
.Cm ebcdic
specifies the recommended one which is compatible with
.At V .
The value
.Cm ibm
is a slightly different mapping, which is compatible with the
.At V
.Cm ibm
value.
The values
.Cm oldebcdic
and
.Cm oldibm
are maps used in historic
.Tn AT&T
and pre
.Bx 4.3 Reno
systems.
.It Cm lcase
Transform uppercase characters into lowercase characters.
.It Cm noerror
Do not stop processing on an input error.
When an input error occurs, a diagnostic message followed by the current
input and output block counts will be written to the standard error output
in the same format as the standard completion message.
If the
.Cm sync
conversion is also specified, any missing input data will be replaced
with
.Tn NUL
bytes (or with spaces if a block oriented conversion value was
specified) and processed as a normal input buffer.
If the
.Cm sync
conversion is not specified, the input block is omitted from the output.
On input files which are not tapes or pipes, the file offset
will be positioned past the block in which the error occurred using
.Xr lseek 2 .
.It Cm notrunc
Do not truncate the output file.
This will preserve any blocks in the output file not explicitly written
by
.Nm .
The
.Cm notrunc
value is not supported for tapes.
.It Cm osync
Pad the final output block to the full output block size.
If the input file is not a multiple of the output block size
after conversion, this conversion forces the final output block
to be the same size as preceding blocks for use on devices that require
regularly sized blocks to be written.
This option is incompatible with use of the
.Cm bs= Ns Ar n
block size specification.
.It Cm sparse
If one or more non-final output blocks would consist solely of
.Dv NUL
bytes, try to seek the output file by the required space instead of
filling them with
.Dv NUL Ns s .
This results in a sparse file on some file systems.
.It Cm swab
Swap every pair of input bytes.
If an input buffer has an odd number of bytes, the last byte will be
ignored during swapping.
.It Cm sync
Pad every input block to the input buffer size.
Spaces are used for pad bytes if a block oriented conversion value is
specified, otherwise
.Tn NUL
bytes are used.
.It Cm ucase
Transform lowercase characters into uppercase characters.
.It Cm unblock
Treats the input as a sequence of fixed length records independent of input
and output block boundaries.
The length of the input records is specified by the
.Cm cbs
operand.
Any trailing space characters are discarded and a newline character is
appended.
.El
.El
.Pp
Where sizes are specified, a decimal number of bytes is expected.
Two or more numbers may be separated by an
.Dq x
to indicate a product.
Each number may have one of the following optional suffixes:
.Bl -tag -width 3n -offset indent -compact
.It b
Block; multiply by 512
.It k
Kibi; multiply by 1024 (1 KiB)
.It m
Mebi; multiply by 1048576 (1 MiB)
.It g
Gibi; multiply by 1073741824 (1 GiB)
.It t
Tebi; multiply by 1099511627776 (1 TiB)
.It w
Word; multiply by the number of bytes in an integer
.El
.Pp
When finished,
.Nm
displays the number of complete and partial input and output blocks,
truncated input records and odd-length byte-swapping blocks to the
standard error output.
A partial input block is one where less than the input block size
was read.
A partial output block is one where less than the output block size
was written.
Partial output blocks to tape devices are considered fatal errors.
Otherwise, the rest of the block will be written.
Partial output blocks to character devices will produce a warning message.
A truncated input block is one where a variable length record oriented
conversion value was specified and the input line was too long to
fit in the conversion record or was not newline terminated.
.Pp
Normally, data resulting from input or conversion or both are aggregated
into output blocks of the specified size.
After the end of input is reached, any remaining output is written as
a block.
This means that the final output block may be shorter than the output
block size.
.Pp
If
.Nm
receives a
.Dv SIGINFO
signal
(see the
.Ic status
argument for
.Xr stty 1 ) ,
the current input and output block counts will
be written to the standard error output
in the same format as the standard completion message.
If
.Nm
receives a
.Dv SIGINT
signal, the current input and output block counts will
be written to the standard error output
in the same format as the standard completion message and
.Nm
will exit.
.Sh INPUT AND OUTPUT FLAGS
There are flags valid for input only, for output only, or for either.
.Pp
The flags that apply to both input and output are:
.Bl -tag -width directory
.It Cm alt_io
Use Alternative I/O.
.It Cm async
Use
.Dv SIGIO
signaling for I/O.
.It Cm cloexec
Set the close-on-exec flag.
.It Cm direct
Directly access the data, skipping any caches.
.It Cm directory
Not available for
.Nm .
.It Cm exlock
Atomically obtain an exclusive lock.
.It Cm noctty
Do not consider the file as a potential controlling tty.
.It Cm nofollow
Do not follow symbolic links.
.It Cm nonblock
Do not block on open or I/O requests.
.It Cm nosigpipe
Return
.Er EPIPE
instead of raising
.Dv SIGPIPE .
.It Cm shlock
Atomically obtain a shared lock.
.It Cm sync
All I/O will be performed with full synchronization.
.El
.Pp
The flags that apply to only input are:
.Bl -tag -width directory
.It Cm rdonly
Set the read-only flag.
.It Cm rdwr
Set the read and write flags.
.It Cm rsync
Enable read synchronization, if the
.Cm sync
option is also set.
.El
.Pp
The flags that apply to only output are:
.Bl -tag -width directory
.It Cm append
Append to the output by default.
.It Cm creat
Create the output file.
.It Cm dsync
Wait for all data to be synchronously written.
.It Cm excl
Ensure that output is to a new file.
.It Cm trunc
Truncate the output file before writing.
.It Cm wronly
Set the write-only flag.
.El
See
.Xr open 2
and
.Xr ioctl 2
for more details.
.Sh EXIT STATUS
.Ex -std dd
.Sh EXAMPLES
To print summary information in human-readable form:
.Pp
.Dl dd if=/dev/zero of=/dev/null count=1 msgfmt=human
.Pp
To customize the information summary output and print it through
.Xr unvis 3 :
.Bd -literal -offset indent
dd if=/dev/zero of=/dev/null count=1 \e
     msgfmt='speed:%E, in %s seconds\en' 2>&1 | unvis
.Ed
.Sh SEE ALSO
.Xr cp 1 ,
.Xr mt 1 ,
.Xr tr 1
.Sh STANDARDS
The
.Nm
utility is expected to be a superset of the
.St -p1003.2
standard.
The
.Cm files
and
.Cm msgfmt
operands and the
.Cm ascii ,
.Cm ebcdic ,
.Cm ibm ,
.Cm oldascii ,
.Cm oldebcdic
and
.Cm oldibm
values are extensions to the
.Tn POSIX
standard.
.Sh HISTORY
A
.Nm
utility appeared in
.At v5 .