1DD(1) General Commands Manual DD(1)
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6 dd - convert and copy a file
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9 dd [option=value] ...
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12 Dd copies the specified input file to the specified output with possi‐
13 ble conversions. The standard input and output are used by default.
14 The input and output block size may be specified to take advantage of
15 raw physical I/O.
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17 option values
18 if= input file name; standard input is default
19 of= output file name; standard output is default
20 ibs=n input block size n bytes (default 512)
21 obs=n output block size (default 512)
22 bs=n set both input and output block size, superseding ibs
23 and obs; also, if no conversion is specified, it is par‐
24 ticularly efficient since no copy need be done
25 cbs=n conversion buffer size
26 skip=n skip n input records before starting copy
27 files=n copy n input files before terminating (makes sense only
28 where input is a magtape or similar device).
29 seek=n seek n records from beginning of output file before
30 copying
31 count=n copy only n input records
32 conv=ascii convert EBCDIC to ASCII
33 ebcdic convert ASCII to EBCDIC
34 ibm slightly different map of ASCII to EBCDIC
35 block convert variable length records to fixed length
36 unblock convert fixed length records to variable length
37 lcase map alphabetics to lower case
38 ucase map alphabetics to upper case
39 swab swap every pair of bytes
40 noerror do not stop processing on an error
41 sync pad every input record to ibs
42 ... , ... several comma-separated conversions
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44 Where sizes are specified, a number of bytes is expected. A number may
45 end with k, b or w to specify multiplication by 1024, 512, or 2 respec‐
46 tively; a pair of numbers may be separated by x to indicate a product.
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48 Cbs is used only if ascii, unblock, ebcdic, ibm, or block conversion is
49 specified. In the first two cases, cbs characters are placed into the
50 conversion buffer, any specified character mapping is done, trailing
51 blanks trimmed and new-line added before sending the line to the out‐
52 put. In the latter three cases, characters are read into the conver‐
53 sion buffer, and blanks added to make up an output record of size cbs.
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55 After completion, dd reports the number of whole and partial input and
56 output blocks.
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58 For example, to read an EBCDIC tape blocked ten 80-byte EBCDIC card
59 images per record into the ASCII file x:
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61 dd if=/dev/rmt0 of=x ibs=800 cbs=80 conv=ascii,lcase
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63 Note the use of raw magtape. Dd is especially suited to I/O on the raw
64 physical devices because it allows reading and writing in arbitrary
65 record sizes.
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68 cp(1), tr(1)
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71 f+p records in(out): numbers of full and partial records read(written)
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74 The ASCII/EBCDIC conversion tables are taken from the 256 character
75 standard in the CACM Nov, 1968. The `ibm' conversion, while less
76 blessed as a standard, corresponds better to certain IBM print train
77 conventions. There is no universal solution.
78 One must specify ``conv=noerror,sync'' when copying raw disks with bad
79 sectors to insure dd stays synchronized.
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81 Certain combinations of arguments to conv= are permitted. However, the
82 block or unblock option cannot be combined with ascii, ebcdic or ibm.
83 Invalid combinations silently ignore all but the last mutually-exclu‐
84 sive keyword.
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884th Berkeley Distribution April 29, 1985 DD(1)