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 conversion 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, conversion results cannot be assured as characters in supplementary code sets are also subject to conversion

ebcdic convert ASCII to EBCDIC, conversion results cannot be assured as characters in supplementary code sets are also subject to conversion

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, multibyte characters are not converted

ucase map alphabetics to upper case, multibyte characters are not converted

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. 

INTERNATIONAL FUNCTIONS

dd can process characters from supplementary code sets. 

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)

  —  Essential Utilities