dd.1

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 1 代码 · 共 207 行

.\" SCCSID: @(#)dd.1	4.1	12/9/88
.TH dd 1 
.SH Name
dd \- copy and convert data
.SH Syntax
.B dd
[\|\fIoption = value...\fR\|]  
.SH Description
.NXB "dd command"
.NXR "file" "converting"
The 
.PN dd
command copies an input file
to an output with
any requested conversions.  The
.PN dd
command is especially suited to I/O on the raw physical
devices because it allows reading and writing in arbitrary
record sizes.
.PP 
After completion,
.PN dd
reports the number of whole and partial input and
output blocks.
.PP
This utility supports EOT handling which allows the use of
multiple media.  The utility prompts for the next volume when it
encounters the end of the current volume.
.SH Options
.NXB "dd command" "options"
Where sizes (\fIn\fR) are given for an option, 
the number may end
with \fBk\fR for kilobytes (1024 bytes), \fBb\fR for
blocks (512 bytes), or \fBw\fR for words (2 bytes).
Also, two numbers may be separated by the character x to
indicate a product.
.IP \fBif=\fIname\fR 20
Input file name.  The standard input is the default.
.IP \fBof=\fIname\fR 20
Output file name.  The standard output is the default.
.IP \fBibs=\fIn\fR 20
Input block size,
.I n
bytes. The default is 512 bytes.
Some devices do not support greater than 65,535 bytes.
.IP \fBobs=\fIn\fR 20
Output block size,
.I n
bytes.  The default is 512 bytes.
Some devices do not support greater than 65,535 bytes.
.IP \fBbs=\fIn\fR 20
Set both input and output block size to \fIn\fR bytes,
superseding
.B ibs
and
.BR obs .
Also, if \fBbs\fR is specified,
the copy is more efficient, since no blocking conversion is
necessary.
.IP \fBcbs=\fIn\fR 20
Conversion buffer size, \fIn\fR bytes.  Use only if
.BR ascii ,
.BR unblock ,
.BR ebcdic ,
.BR ibm ,
or
.B block
conversion is specified.  For
.B ascii
and
.BR unblock , 
\fIn\fR characters are placed into the conversion
buffer, any specified character mapping is done, trailing blanks are trimmed
and new line added before sending the line to the output.  For
.BR ebcdic ,
.BR ibm ,
or
.BR block ,
characters are read into the conversion buffer, and blanks added to make
an output record of size \fIn\fR bytes.
.IP \fBskip=\fIn\fR 20
Skip
.I n 
input records before starting to copy.
.IP \fBfiles=\fIn\fR 20
Copy
.I n
input files before terminating.  This option is useful only
when the input is a magnetic tape or similar device.
.IP \fBseek=\fIn\fR 20
Seek
.I n
records from beginning of output file before copying.
.IP \fBrbuf=\fIn\fR 20
Use
.I n
buffers for reading from those raw devices that support
n-buffered I/O.  (See Section 4 to check whether a
specific device supports n-buffered I/O.)  All 
.I n 
reads are started and each read must complete before the
data can be used.  This allows an n-buffered read-ahead
on supported raw devices.
.IP "" 20
A default of eight read buffers are used if the read
device supports n-buffered I/O and the write device
does not.
.IP "" 20
The \fBrbuf\fR option cannot
be used with the \fBwbuf\fR option.
.IP \fBwbuf=\fIn\fR 20
Use
.I n
buffers for writing from those raw devices that support
n-buffered I/O.  (See Section 4 to check whether a
specific device supports n-buffered I/O.)
Each write is started but not known
to be complete until all 
.I n
buffers have been used.  (This allows an n-buffered
write-behind on supported raw devices).  
.IP "" 20
A default of eight write buffers are used if the write
device supports n-buffered I/O.
.IP "" 20
The \fBwbuf\fR
option cannot be used with the \fBrbuf\fR option.
.IP \fBcount=\fIn\fR 20
Copy only
.I n 
input records.
.IP \fBconv=ascii\fR 20
Convert EBCDIC to ASCII.
.IP \fBconv=ebcdic\fR 20
Convert ASCII to EBCDIC.
.IP \fBconv=ibm\fR 20
Slightly different map of ASCII to EBCDIC (see RESTRICTIONS).  
.IP \fBconv=block\fR 20 
Convert variable length records to fixed length.  
.IP \fBconv=unblock\fR 20
Convert fixed length records to variable length.
.IP \fBconv=lcase\fR 20
Map alphabetics to lower case.
.IP \fBconv=ucase\fR 20
Map alphabetics to upper case.
.IP \fBconv=swab\fR 20
Swap every pair of bytes.
.IP \fBconv=noerror\fR 20
Do not stop processing on an error.
.IP \fBconv=sync\fR 20
Pad every input record to
.IR ibs .
.IP \fBconv=nomulti\fR 20
Disable multiple tape volumes.
.IP \fBconv=sparse\fR 20
Create a sparse output file.
.IP "\fBconv=... , ...\fR" 20
Include several arguments for the \fBconv\fR option, separated
by commas (see example below).
.NXE "dd command" "options"
.SH Examples
.NXR "dd command" "example"
The following example shows how to read
an EBCDIC tape blocked ten 80-byte
EBCDIC card images per record into the ASCII file
.I x:
.EX
dd if=/dev/rmt0h of=x ibs=800 cbs=80 conv=ascii,lcase
.EE
.PP
Note the use of raw magtape.
As noted in the DESCRIPTION, the
.PN dd
command is especially suited to I/O on the raw
physical devices because it allows reading
and writing in arbitrary record sizes.
.SH Restrictions
.NXR "dd command" "restricted"
The ASCII/EBCDIC conversion tables are
taken
from the 256-character standard in
the 
.I
Communications of the ACM, 
.R
November, 1968.
.PP
The \fBibm\fR conversion
corresponds to certain IBM print train conventions.
.PP
One must specify ``conv=noerror,sync'' when copying
raw disks with bad sectors to ensure that
.I dd
stays synchronized.
.br
On SCSI tape devices when reading a multi-volume tape set the command
will exit normally upon hitting EOT on any volume rather than
automatically unloading the volume and prompting for the next volume
as is normal. The user should load the next volume and issue the command
anew.
.SH Diagnostics
.NXR "dd command" "diagnostics"
f+p records in(out): numbers of full and partial records read(written)
.SH See Also
cp(1), tr(1), nbuf(4)
.NXE "dd command"