dd.1

UNIX v6源代码 这几乎是最经典的unix版本 unix操作系统设计和莱昂氏unix源代码分析都是用的该版

.th DD I 5/15/74
.sh NAME
dd \*- convert and copy a file
.sh SYNOPSIS
.bd dd
[option=value] ...
.sh DESCRIPTION
.it 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.
.s3
.ft I
.lp +15 15
option	values
.ft R
.lp +15 15
if=	input file name; standard input is default
.lp +15 15
of=	output file name; standard output is default
.lp +15 15
ibs=	input block size (default 512)
.lp +15 15
obs=	output block size (default 512)
.lp +15 15
bs=	set both input and output block size,
superseding
.it ibs
and
.it obs;
also, if no conversion is specified,
it is particularly efficient since no copy need be done
.lp +15 15
cbs=\fIn\fR	conversion buffer size
.lp +15 15
skip=\fIn\fR	skip \fIn\fR input records before starting copy
.lp +15 15
count=\fIn\fR	copy only \fIn\fR input records
.lp +15 15
conv=ascii	convert EBCDIC to ASCII
.lp +15 10
ebcdic	convert ASCII to EBCDIC
.lp +15 10
lcase	map alphabetics to lower case
.lp +15 10
ucase	map alphabetics to upper case
.lp +15 10
swab	swap every pair of bytes
.lp +15 10
noerror	do not stop processing on an error
.lp +15 10
sync	pad every input record to \fIibs\fR
.lp +15 10
.li
... , ...	several comma-separated conversions
.i0
.s3
.fi
Where sizes are specified,
a number of bytes is expected.
A number may end with
.bd "k, b"
or
.bd w
to specify multiplication by
1024, 512, or 2 respectively.
Also a pair of numbers may be separated by
.bd x
to indicate a product.
.s3
.it Cbs
is used only if
.it ascii
or
.it ebcdic
conversion is specified.
In the former case
.it 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
.it cbs.
.s3
After completion,
.it dd
reports the number of whole and partial input and output
blocks.
.s3
For example, to read an EBCDIC tape blocked ten 80-byte
EBCDIC card images per record into the ASCII file
.it x:
.s3
dd  if=/dev/rmt0  of=x  ibs=800  cbs=80  conv=ascii,lcase
.s3
Note the use of raw magtape.
.it Dd
is especially suited to I/O on the raw
physical devices because it allows reading
and writing in arbitrary record sizes.
.sh "SEE ALSO"
cp (I)
.sh BUGS
The ASCII/EBCDIC conversion tables are
taken
from the 256 character standard in
the CACM Nov, 1968.
It is not clear how this relates to real life.
.s3
Newlines are inserted only on conversion to ASCII;
padding is done only on conversion to EBCDIC.
There should be separate options.