MPE/iX Shell and Utilities Reference Manual, Vol 1
dd(1) MPE/iX Shell and Utilities dd(1)
NAME
dd — copy and convert input blocks
SYNOPSIS
dd [bs=s][cbs=s][conv=conversion][count=n][ibs=s][if=file]
[imsg=string][iseek=n][obs=s][of=file][omsg=string][seek=n]
[skip=n]
DESCRIPTION
Note: The
MPE/iX implementation of this utility does not function exactly as this man page
describes. For details, see the MPE/iX NOTES section at the end of this man page.
dd reads and writes data by blocks. It is frequently used for devices such as tapes which have
discrete block sizes, or for fast multi-sector reads from disks. dd performs conversions to
accommodate computers that require de-blocking, conversion to/from
EBCDIC, and fixed
length records.
dd processes the input data as follows:
1. dd reads an input block.
2. If this input block is smaller than the specified input block size, dd pads it to the
specified size with null bytes. When you also specify a block or unblock conver-
sion, dd uses spaces instead of null bytes.
3. If you specified bs=size and requested no conversion other than sync or noerror,
dd writes the padded (if necessary) input block to the output as a single block and
omits the remaining steps.
4. If you specified the swab conversion, dd swaps each pair of input bytes. If there is
an odd number of input bytes, dd does not attempt to swap the last byte.
5. dd performs all remaining conversions on the input data independently of the input
block boundaries. A fixed-length input or output record may span these boundaries.
6. dd gathers the converted data into output blocks of the specified size. When dd
reaches the end of the input, it writes the remaining output as a block (without pad-
ding if conv=sync is not specified). As a result, the final output block may be
shorter than the output block size.
bs=size
sets both input and output block sizes to size bytes. You can suffix this decimal num-
ber with w, b, k,or xnumber, to multiply it by 2, 512, 1024, or number respec-
tively. You can also specify size as two decimal numbers (with or without suffixes)
separated by x to indicate the product of the two values. Processing is faster when
1-168 Commands and Utilities