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. The options are

-if f

Open file f for input.  

-of f

Open file f for output.  

-ibs n

Set input block size to n bytes (default 512).  

-obs n

Set output block size (default 512).  

-bs n

Set both input and output block size, superseding ibs and obs. 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

Set conversion buffer size.  

-skip n

Skip n input records before copying.  

-iseek n

Seek n records forward on input file before copying.  

-files n

Catenate n input files (useful only for magnetic tape or similar input device).  

-oseek n

Seek n records from beginning of output file before copying.  

-count n

Copy only n input records.  

-trunc n

By default, dd truncates the output file when it opens it; -trunc 0 opens it without truncation.  

-quiet n

By default, dd prints the number of blocks read and written once it is finished. -quiet 1 silences this summary.  

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-conv ascii    Convert EBCDIC to ASCII.


Convert ASCII to EBCDIC.  


Like ebcdic but with a slightly different character map.  


Convert variable length ASCII records to fixed length.  


Convert fixed length ASCII records to variable length.  


Map alphabetics to lower case.  


Map alphabetics to upper case.  


Swap every pair of bytes.  


Do not stop processing on an error.  


Pad every input record to ibs bytes.  

Where sizes are specified, a number of bytes is expected. A number may end with k or b to specify multiplication by 1024 or 512 respectively; a pair of numbers may be separated by x to indicate a product. Multiple conversions may be specified in the style: -conv ebcdic,ucase .

Cbs is used only if ascii, unblock, ebcdic, ibm, or block conversion is specified. In the first two cases, n characters are copied into the conversion buffer, any specified character mapping is done, trailing blanks are trimmed and 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 n. 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.






Dd reports the number of full + partial input and output blocks handled.