xref: /freebsd/bin/dd/dd.1 (revision 380a989b3223d455375b4fae70fd0b9bdd43bafb)
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4.\" This code is derived from software contributed to Berkeley by
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35.\"     @(#)dd.1	8.2 (Berkeley) 1/13/94
36.\"	$Id: dd.1,v 1.7 1998/05/06 06:51:35 charnier Exp $
37.\"
38.Dd January 13, 1994
39.Dt DD 1
40.Os
41.Sh NAME
42.Nm dd
43.Nd convert and copy a file
44.Sh SYNOPSIS
45.Nm dd
46.Op operands ...
47.Sh DESCRIPTION
48The
49.Nm
50utility copies the standard input to the standard output.
51Input data is read and written in 512-byte blocks.
52If input reads are short, input from multiple reads are aggregated
53to form the output block.
54When finished,
55.Nm
56displays the number of complete and partial input and output blocks
57and truncated input records to the standard error output.
58.Pp
59The following operands are available:
60.Bl -tag -width of=file
61.It Cm bs= Ns Ar n
62Set both input and output block size to
63.Va n
64bytes, superseding the
65.Cm ibs
66and
67.Cm obs
68operands.
69If no conversion values other than
70.Cm noerror ,
71.Cm notrunc
72or
73.Cm sync
74are specified, then each input block is copied to the output as a
75single block without any aggregation of short blocks.
76.It Cm cbs= Ns Ar n
77Set the conversion record size to
78.Va n
79bytes.
80The conversion record size is required by the record oriented conversion
81values.
82.It Cm count= Ns Ar n
83Copy only
84.Va n
85input blocks.
86.It Cm files= Ns Ar n
87Copy
88.Va n
89input files before terminating.
90This operand is only applicable when the input device is a tape.
91.It Cm ibs= Ns Ar n
92Set the input block size to
93.Va n
94bytes instead of the default 512.
95.It Cm if= Ns Ar file
96Read input from
97.Ar file
98instead of the standard input.
99.It Cm obs= Ns Ar n
100Set the output block size to
101.Va n
102bytes instead of the default 512.
103.It Cm of= Ns Ar file
104Write output to
105.Ar file
106instead of the standard output.
107Any regular output file is truncated unless the
108.Cm notrunc
109conversion value is specified.
110If an initial portion of the output file is skipped (see the
111.Cm seek
112operand),
113the output file is truncated at that point.
114.It Cm seek= Ns Ar n
115Seek
116.Va n
117blocks from the beginning of the output before copying.
118On non-tape devices, an
119.Xr lseek 2
120operation is used.
121Otherwise, existing blocks are read and the data discarded.
122If the user does not have read permission for the tape, it is positioned
123using the tape
124.Xr ioctl 2
125function calls.
126If the seek operation is past the end of file, space from the current
127end of file to the specified offset is filled with blocks of
128.Tn NUL
129bytes.
130.It Cm skip= Ns Ar n
131Skip
132.Va n
133blocks from the beginning of the input before copying.
134On input which supports seeks, an
135.Xr lseek 2
136operation is used.
137Otherwise, input data is read and discarded.
138For pipes, the correct number of bytes is read.
139For all other devices, the correct number of blocks is read without
140distinguishing between a partial or complete block being read.
141.It Xo
142.Cm conv=
143.Ns Cm value Ns Op \&, Cm value \&...
144.Xc
145Where
146.Cm value
147is one of the symbols from the following list.
148.Bl -tag -width unblock
149.It Cm ascii , oldascii
150The same as the
151.Cm unblock
152value except that characters are translated from
153.Tn EBCDIC
154to
155.Tn ASCII
156before the
157records are converted.
158(These values imply
159.Cm unblock
160if the operand
161.Cm cbs
162is also specified.)
163There are two conversion maps for
164.Tn ASCII .
165The value
166.Cm ascii
167specifies the recommended one which is compatible with System V.
168The value
169.Cm oldascii
170specifies the one used in historic
171.Tn AT&T
172and pre-4.3BSD-reno systems.
173.It Cm block
174Treats the input as a sequence of newline or end-of-file terminated variable
175length records independent of input and output block boundaries.
176Any trailing newline character is discarded.
177Each input record is converted to a fixed length output record where the
178length is specified by the
179.Cm cbs
180operand.
181Input records shorter than the conversion record size are padded with spaces.
182Input records longer than the conversion record size are truncated.
183The number of truncated input records, if any, are reported to the standard
184error output at the completion of the copy.
185.It Cm ebcdic , ibm , oldebcdic , oldibm
186The same as the
187.Cm block
188value except that characters are translated from
189.Tn ASCII
190to
191.Tn EBCDIC
192after the
193records are converted.
194(These values imply
195.Cm block
196if the operand
197.Cm cbs
198is also specified.)
199There are four conversion maps for
200.Tn EBCDIC .
201The value
202.Cm ebcdic
203specifies the recommended one which is compatible with
204.At V .
205The value
206.Cm ibm
207is a slightly different mapping, which is compatible with the
208.At V
209.Cm ibm
210value.
211The values
212.Cm oldebcdic
213and
214.Cm oldibm
215are maps used in historic
216.Tn AT&T
217and pre-4.3BSD-reno systems.
218.It Cm lcase
219Transform uppercase characters into lowercase characters.
220.It Cm noerror
221Do not stop processing on an input error.
222When an input error occurs, a diagnostic message followed by the current
223input and output block counts will be written to the standard error output
224in the same format as the standard completion message.
225If the
226.Cm sync
227conversion is also specified, any missing input data will be replaced
228with
229.Tn NUL
230bytes (or with spaces if a block oriented conversion value was
231specified) and processed as a normal input buffer.
232If the
233.Cm sync
234conversion is not specified, the input block is omitted from the output.
235On input files which are not tapes or pipes, the file offset
236will be positioned past the block in which the error occurred using
237.Xr lseek 2 .
238.It Cm notrunc
239Do not truncate the output file.
240This will preserve any blocks in the output file not explicitly written
241by
242.Nm Ns .
243The
244.Cm notrunc
245value is not supported for tapes.
246.It Cm osync
247Pad the final output block to the full output block size.
248If the input file is not a multiple of the output block size
249after conversion, this conversion forces the final output block
250to be the same size as preceding blocks for use on devices that require
251regularly sized blocks to be written.
252This option is incompatible with use of the
253.Cm bs= Ns Ar n
254block size specification.
255.It Cm sparse
256If one or more output blocks would consist solely of
257.Tn NUL
258bytes, try to seek the output file by the required space instead of
259filling them with
260.Tn NULs ,
261resulting in a sparse file.
262.It Cm swab
263Swap every pair of input bytes.
264If an input buffer has an odd number of bytes, the last byte will be
265ignored during swapping.
266.It Cm sync
267Pad every input block to the input buffer size.
268Spaces are used for pad bytes if a block oriented conversion value is
269specified, otherwise
270.Tn NUL
271bytes are used.
272.It Cm ucase
273Transform lowercase characters into uppercase characters.
274.It Cm unblock
275Treats the input as a sequence of fixed length records independent of input
276and output block boundaries.
277The length of the input records is specified by the
278.Cm cbs
279operand.
280Any trailing space characters are discarded and a newline character is
281appended.
282.El
283.El
284.Pp
285Where sizes are specified, a decimal number of bytes is expected.
286If the number ends with a ``b'', ``k'', ``m'' or ``w'', the number
287is multiplied by 512, 1024 (1K), 1048576 (1M) or the number of bytes
288in an integer, respectively.
289Two or more numbers may be separated by an ``x'' to indicate a product.
290.Pp
291When finished,
292.Nm
293displays the number of complete and partial input and output blocks,
294truncated input records and odd-length byte-swapping blocks to the
295standard error output.
296A partial input block is one where less than the input block size
297was read.
298A partial output block is one where less than the output block size
299was written.
300Partial output blocks to tape devices are considered fatal errors.
301Otherwise, the rest of the block will be written.
302Partial output blocks to character devices will produce a warning message.
303A truncated input block is one where a variable length record oriented
304conversion value was specified and the input line was too long to
305fit in the conversion record or was not newline terminated.
306.Pp
307Normally, data resulting from input or conversion or both are aggregated
308into output blocks of the specified size.
309After the end of input is reached, any remaining output is written as
310a block.
311This means that the final output block may be shorter than the output
312block size.
313.Pp
314If
315.Nm
316receives a
317.Dv SIGINFO
318(see the ``status'' argument for
319.Xr stty 1 )
320signal, the current input and output block counts will
321be written to the standard error output
322in the same format as the standard completion message.
323If
324.Nm
325receives a
326.Dv SIGINT
327signal, the current input and output block counts will
328be written to the standard error output
329in the same format as the standard completion message and
330.Nm
331will exit.
332.Pp
333The
334.Nm
335utility exits 0 on success or >0 if an error occurred.
336.Sh SEE ALSO
337.Xr cp 1 ,
338.Xr mt 1 ,
339.Xr tr 1
340.Sh STANDARDS
341The
342.Nm
343utility is expected to be a superset of the
344.St -p1003.2
345standard.
346The
347.Cm files
348operand and the
349.Cm ascii ,
350.Cm ebcdic ,
351.Cm ibm ,
352.Cm oldascii ,
353.Cm oldebcdic
354and
355.Cm oldibm
356values are extensions to the
357.Tn POSIX
358standard.
359