How to use the Linux dd command

Dd can read data from the standard input or file, convert data according to the specified format, and then output to the file, device, or standard output.

Parameter description:

• If = File name: Enter the file name. The default value is standard input. Specifies the source file.
• Of = File name: name of the output file. The default value is standard output. Specifies the target file.
• Ibs = bytes: read bytes at a time, that is, specify a block size as bytes.
  Obs = bytes: outputs bytes at a time, that is, specify a block size as bytes.
  Bs = bytes: set the size of the read/output block to bytes at the same time.
• Cbs = bytes: bytes are converted at a time, that is, the size of the conversion buffer.
• Skip = blocks: the blocks are skipped from the beginning of the input file and then copied.
• Seek = blocks: the blocks are skipped from the beginning of the output file and then copied.
• Count = blocks: copy only blocks. The block size is equal to the number of bytes specified by ibs.
• Conv = <keyword>. There are 11 types of keywords:
  • Conversion: convert the file with the specified parameter.
  • Ascii: convert ebcdic to ascii
  • Ebcdic: convert ascii to ebcdic
  • Ibm: convert ascii to alternate ebcdic
  • Block: converts each row to the length of cbs. Spaces are used to fill the remaining parts.
  • Unblock: the length of each row is cbs, and the remaining part is filled with spaces.
  • Lcase: converts uppercase to lowercase.
  • Ucase: converts lowercase to uppercase.
  • Swab: swap each pair of input bytes
  • Noerror: do not stop when an error occurs
  • Notrunc: the output file is not truncated.
  • Sync: fill each input block into ibs bytes, and fill the remaining part with null (NUL) characters.
• -- Help: displays help information.
• -- Version: displays version information.

Instance

To create a boot disk in Linux, run the following command:

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

Convert all English letters in the testfile file into uppercase letters and convert them to the testfile_1 file. Run the following command at the command prompt:

Dd if = testfile_2 of = testfile_1 conv = ucase

The content of testfile_2 is:

$ Cat testfile_2 # content of testfile_2

Hello linux!

Linux is a free unix-type opterating system.

This is a linux testfile!

Linux test

After the conversion is complete, the content of testfile_1 is as follows:

$ Dd if = testfile_2 of = testfile_1 conv = ucase # Using the dd command, the case-sensitivity conversion records the read from 0 + 1.

Records the write records of 0 + 1

95 bytes (95 B) replicated, 0.000131446 seconds, 723 KB/s

Cmd @ hdd-desktop :~ $ Cat testfile_1 # view the converted content of testfile_1

Hello linux!

Linux is a free UNIX-TYPE opterating system.

This is a linux testfile!

All characters in linux test # testfile_2 are converted into uppercase letters.

The standard input device reads the string, converts it to uppercase, and then outputs it to the standard output device. The command used is:

Dd conv = ucase

Enter the preceding command, press enter, enter the string, press enter, and press Ctrl + D to exit. The following result is displayed:

$ Dd conv = ucase

Hello Linux! # Enter a string and press enter

Hello linux! # Press the combination key Ctrl + D to exit and convert to the big write result

Read records of 0 + 1

Records the write records of 0 + 1

13 bytes (13 B) copied, 12.1558 seconds, 0.0 KB/s