NAME

dd - convert and copy a file

SYNOPSIS

dd [option=value] ...

DESCRIPTION

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 sizes may be specified to take advantage of raw physical I/O.

option          values
if=file         input file name; standard input is default
of=file         output file name; standard output is default
ibs=n           input block size n bytes (default 512)
obs=n           output block size n bytes (default 512)
bs=n            set  both  input  and  output  block   size,
                superseding ibs and obs; also, if no conver-
                sion is specified, preserve the input  block
                size  instead  of  packing short blocks into
                the  output  buffer  (this  is  particularly
                efficient  since  no  in-core  copy  need be
                done)
cbs=n           conversion  buffer  size   (logical   record
                length)
files=n         copy and concatenate n  input  files  before
                terminating (makes sense only where input is
                a magnetic tape or similar device)
skip=n          skip n input  blocks  before  starting  copy
                (appropriate  for magnetic tape, where iseek
                is undefined)
iseek=n         seek n blocks from beginning of  input  file
                before  copying (appropriate for disk files,
                where skip can be incredibly slow)
oseek=n         seek n blocks from beginning of output  file
                before copying
seek=n          identical to oseek,  retained  for  backward
                compatibility
count=n         copy only n input blocks
conv=ascii      convert EBCDIC to ASCII
     ebcdic     convert ASCII to EBCDIC
     ibm        slightly different map of ASCII to EBCDIC
     block      convert new-line terminated ASCII records to
                fixed length
     unblock    convert fixed length ASCII records  to  new-
                line terminated records
     lcase      map alphabetics to lower case
     ucase      map alphabetics to upper case
     swab       swap every pair of bytes
     noerror    do not stop processing on an error (limit of
                5 consecutive errors)

     sync       pad every input block to ibs
     several comma-separated conversions

Where sizes are specified, a number of bytes is expected. A number may end with k, b, or w to specify multiplication by 1024, 512, or 2, respectively; a pair of numbers may be separated by x to indicate multiplication.

cbs is used only if ascii, unblock, ebcdic, ibm, or block conversion is specified. In the first two cases, cbs characters are copied into the conversion buffer, any specified character mapping is done, trailing blanks are trimmed and a new-line is added before sending the line to the output. In the latter three cases, characters are read into the conversion buffer and blanks are added to make up an output record of size cbs. If cbs is unspecified or zero, the ascii, ebcdic, and ibm options convert the character set without changing the block structure of the input file; the unblock and block options become a simple file copy.

After completion, dd reports the number of whole and partial input and output blocks.

EXAMPLE

This command will read an EBCDIC tape blocked ten 80-byte EBCDIC card images per tape block into the ASCII file x: dd if=/dev/rmt/0h of=x ibs=800 obs=8k cbs=80 conv=ascii,lcase

Note the use of raw magnetic tape. dd is especially suited to I/O on the raw physical devices because it allows reading and writing in arbitrary block sizes.

SEE ALSO

cp(1)

NOTES

Do not use dd to copy files between filesystems having different block sizes.

Using a blocked device to copy a file will result in extra nulls being added to the file to pad the final block to the block boundary.

DIAGNOSTICS

f+p records in(out) numbers of full and partial blocks read(written)