Linux command: dd

dd

1. Role
dd command to copy files and converts the data according to the parameters and formats.

2. Format

dd [options]

3. [opitions] Specifications

• if = file name: Enter the file name, the default is standard input. That is, to specify the source file.
• of = file name: output file name defaults to the standard output. That is, specify the destination file.
• ibs = bytes: byte read into bytes, i.e., a block size of bytes specified bytes.
  obs = bytes: one byte output bytes, i.e., a block size of bytes specified bytes.
  bs = bytes: while providing read / output block size bytes bytes.
• cbs = bytes: byte conversion bytes that specify a translation buffer size.
• skip = blocks: blocks skipped blocks from beginning of the input file and then begins copying.
• seek = blocks: blocks skipped blocks from beginning of output file before starting copying.
• count = blocks: copy only blocks block, the block size is equal to the number of bytes specified ibs.
• conv = <key>, can have the following 11 kinds of keywords:
  • conversion: convert file with the specified parameters.
  • ascii: ebcdic convert to ascii
  • ebcdic: convert to ascii ebcdic
  • ibm: ascii convert to alternate ebcdic
  • block: The length of each line is converted to cbs, insufficient space partially filled with
  • unblock: that the length of each row are padded with spaces to cbs, the shortage
  • lcase: uppercase characters to lowercase characters
  • ucase: the lowercase characters converted to uppercase
  • swab: switching each pair of input byte
  • noerror: do not stop when an error occurs
  • notrunc: do not truncate the output file
  • sync: each input block to ibs bytes, less than some empty (the NUL) character filled.
• --help: Displays help information
• --version: display version information

4. Application Examples

(1) make a boot disk under Linux, use the command:

dd if=boot.img of=/dev/fd0 bs=1440k 

(2) the file testfile all converted to uppercase letters, and then turn to become testfile_1 file, using the following at the command prompt:

dd if=testfile_2 of=testfile_1 conv=ucase 

Testfile_2 of which reads:

$ cat testfile_2 #testfile_2的内容  
HELLO LINUX!  
Linux is a free unix-type opterating system.  
This is a linux testfile!  
Linux test 

After the conversion is complete, the contents testfile_1 follows:

$ dd if=testfile_2 of=testfile_1 conv=ucase #使用dd 命令，大小写转换记录了0+1 的读入  
记录了0+1 的写出  
95字节（95 B）已复制，0.000131446 秒，723 KB/s  
cmd@hdd-desktop:~$ cat testfile_1 #查看转换后的testfile_1文件内容  
HELLO LINUX!  
LINUX IS A FREE UNIX-TYPE OPTERATING SYSTEM.  
THIS IS A LINUX TESTFILE!  
LINUX TEST #testfile_2中的所有字符都变成了大写字母 

(3) by a standard input device reads the character string, and the string to uppercase, and then output to the standard output device, the command used is:

dd conv=ucase 

After entering the above command and press Enter, the input string, press the Enter key, press the key combination Ctrl + D to exit, the following results occur:

$ dd conv=ucase 
Hello Linux! #输入字符串后按回车键  
HELLO LINUX! #按组合键Ctrl+D退出，转换成大写结果  
记录了0+1 的读入  
记录了0+1 的写出  
13字节（13 B）已复制，12.1558 秒，0.0 KB/s