Linux and UNIX Man Pages

Linux & Unix Commands - Search Man Pages

BSD 2.11 - man page for dd (bsd section 1)

DD(1)							      General Commands Manual							     DD(1)

dd - convert and copy a file
dd [option=value] ...
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 size may be specified to take advantage of raw physical I/O. option values if= input file name; standard input is default of= output file name; standard output is default ibs=n input block size n bytes (default 512) obs=n output block size (default 512) bs=n set both input and output block size, superseding ibs and obs; also, if no conversion is specified, it is particularly effi- cient since no copy need be done cbs=n conversion buffer size skip=n skip n input records before starting copy files=n copy n input files before terminating (makes sense only where input is a magtape or similar device). seek=n seek n records from beginning of output file before copying count=n copy only n input records conv=ascii convert EBCDIC to ASCII ebcdic convert ASCII to EBCDIC ibm slightly different map of ASCII to EBCDIC block convert variable length records to fixed length unblock convert fixed length records to variable length 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 sync pad every input record 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 a product. Cbs is used only if ascii, unblock, ebcdic, ibm, or block conversion is specified. In the first two cases, 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 cbs. After completion, dd reports the number of whole and partial input and output blocks. For example, to read an EBCDIC tape blocked ten 80-byte EBCDIC card images per record into the ASCII file x: dd if=/dev/rmt0 of=x ibs=800 cbs=80 conv=ascii,lcase Note the use of raw magtape. Dd is especially suited to I/O on the raw physical devices because it allows reading and writing in arbitrary record sizes.
cp(1), tr(1)
f+p records in(out): numbers of full and partial records read(written)
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. One must specify ``conv=noerror,sync'' when copying raw disks with bad sectors to insure dd stays synchronized. Certain combinations of arguments to conv= are permitted. However, the block or unblock option cannot be combined with ascii, ebcdic or ibm. Invalid combinations silently ignore all but the last mutually-exclusive keyword. 4th Berkeley Distribution April 29, 1985 DD(1)