dd.1

unix v7是最后一个广泛发布的研究型UNIX版本

.TH DD 1 
.SH NAME
dd \- convert and copy a file
.SH SYNOPSIS
.B dd
[option=value] ...
.SH DESCRIPTION
.I Dd
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 size may be
specified to take advantage of raw physical I/O.
.PP
.br
.ns
.TP 15
.I option
.I values
.br
.ns
.TP 
if=
input file name; standard input is default
.br
.ns
.TP 
of=
output file name; standard output is default
.br
.ns
.TP 
.RI ibs= n
input block size
.I n
bytes (default 512)
.br
.ns
.TP 
.RI obs= n
output block size (default 512)
.br
.ns
.TP 
.RI bs= n
set both input and output block size,
superseding
.I ibs
and
.I obs;
also, if no conversion is specified,
it is particularly efficient since no copy need be done
.br
.ns
.TP 
.RI cbs= n
conversion buffer size
.br
.ns
.TP 
.RI skip= n
skip
.IR n ""
input records before starting copy
.br
.ns
.TP
.RI files= n
copy
.I n
files from (tape) input
.br
.ns
.TP 
.RI seek= n
seek
.I n
records from beginning of output file before copying
.br
.ns
.TP 
count=\fIn\fR
copy only
.IR n ""
input records
.br
.ns
.TP 
conv=ascii
.ds h \h'\w'conv='u'
convert EBCDIC to ASCII
.br
.ns
.IP \*hebcdic
convert ASCII to EBCDIC
.br
.ns
.IP \*hibm
slightly different map of ASCII to EBCDIC
.br
.ns
.IP \*hlcase
map alphabetics to lower case
.br
.ns
.IP \*hucase
map alphabetics to upper case
.br
.ns
.IP \*hswab
swap every pair of bytes
.br
.ns
.IP \*hnoerror
do not stop processing on an error
.br
.ns
.IP \*hsync
pad every input record to
.I  ibs
.br
.ns
.IP "\*h... , ..."
several comma-separated conversions
.PP
.fi
Where sizes are specified,
a number of bytes is expected.
A number may end with
.B "k, b"
or
.B w
to specify multiplication by
1024, 512, or 2 respectively;
a pair of numbers may be separated by
.B x
to indicate a product.
.PP
.I Cbs
is used only if
.I ascii
or
.I ebcdic
conversion is specified.
In the former case
.I cbs
characters are placed into the conversion buffer, converted to
ASCII, and trailing blanks trimmed and new-line added
before sending the line to the output.
In the latter case ASCII characters are read into the
conversion buffer, converted to EBCDIC, and blanks added
to make up an
output record of size
.IR cbs .
.PP
After completion,
.I dd
reports the number of whole and partial input and output
blocks.
.PP
For example, to read an EBCDIC tape blocked ten 80-byte
EBCDIC card images per record into the ASCII file
.IR x :
.IP ""
dd if=/dev/rmt0 of=x ibs=800 cbs=80 conv=ascii,lcase
.PP
Note the use of raw magtape.
.I Dd
is especially suited to I/O on the raw
physical devices because it allows reading
and writing in arbitrary record sizes.
.PP
To skip over a file before copying from magnetic tape do
.IP""
(dd of=/dev/null; dd of=x) </dev/rmt0
.SH "SEE ALSO"
cp(1), tr(1)
.SH DIAGNOSTICS
f+p records in(out): numbers of full and partial records read(written)
.SH BUGS
The ASCII/EBCDIC conversion tables are
taken
from the 256 character standard in
the CACM Nov, 1968.
The `ibm' conversion, while less blessed as a standard,
corresponds better to certain IBM print train conventions.
There is no universal solution.
.PP
Newlines are inserted only on conversion to ASCII;
padding is done only on conversion to EBCDIC.
These should be separate options.