-.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,
-.I unblock,
-.I ebcdic,
-.I ibm,
-or
-.I block
-conversion is specified.
-In the first two cases,
-.I cbs
-characters are placed into the conversion buffer, any specified
-character mapping is done,
-trailing blanks trimmed and new-line added
-before sending the line to the output.
-In the latter three cases, characters are read into the
-conversion buffer, 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
-.I x:
-.IP
-.nf
-dd if=/dev/rmt0 of=x ibs=800 cbs=80 conv=ascii,lcase
-.fi
-.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.
-.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.
-.br
-One must specify ``conv=noerror,sync'' when copying
-raw disks with bad sectors to insure
-.I dd
-stays synchronized.
+.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 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 seek= Ns Ar n
+Seek
+.Va n
+blocks from the beginning of the output before copying.
+On non-tape devices, a
+.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, a
+.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 Xo
+.Cm conv=
+.Ns Cm value Ns Op \&, Cm value \&...
+.Xc
+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 ECBDIC
+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 System V.
+The value
+.Cm oldascii
+specifies the one used in historic
+.Tn AT&T
+and pre-4.3BSD-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-4.3BSD-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 dd .
+The
+.Cm notrunc
+value is not supported for tapes.
+.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.
+If the number ends with a ``b'', ``k'', ``m'' or ``w'', the number
+is multiplied by 512, 1024 (1K), 1048576 (1M) or the number of bytes
+in an integer, respectively.
+Two or more numbers may be separated by an ``x'' to indicate a product.
+.Pp
+When finished,
+.Nm dd
+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 dd
+receives a
+.Dv SIGINFO
+(see the ``status'' argument for
+.Xr stty 1 )
+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.
+If
+.Nm dd
+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 dd
+will exit.
+.Pp
+The
+.Nm dd
+utility exits 0 on success and >0 if an error occurred.
+.Sh SEE ALSO
+.Xr cp 1 ,
+.Xr mt 1 ,
+.Xr tr 1
+.Sh STANDARDS
+The
+.Nm dd
+utility is expected to be a superset of the
+.St -p1003.2
+standard.
+The
+.Cm files
+operand and the
+.Cm ascii ,
+.Cm ebcdic ,
+.Cm ibm ,
+.Cm oldascii ,
+.Cm oldebcdic
+and
+.Cm oldibm
+values are extensions to the
+.Tn POSIX
+standard.
projects / unix-history / blobdiff