In 1987, the dd command is specified in the X/Open Portability Guide issue 2 of 1987. Raymond believes "the interface design was clearly a prank", due to the command's syntax resembling a JCL statement more than other Unix commands do. According to Douglas McIlroy, dd was "originally intended for converting files between the ASCII, little-endian, byte-stream world of DEC computers and the EBCDIC, big-endian, blocked world of IBM" thus, explaining the cultural context of its syntax. According to Dennis Ritchie, the name is an allusion to the DD statement found in IBM's Job Control Language (JCL), in which it is an abbreviation for "Data Definition". In 1974, the dd command appeared as part of Version 5 Unix. The dd program can also perform conversions on the data as it is copied, including byte order swapping and conversion to and from the ASCII and EBCDIC text encodings. As a result, dd can be used for tasks such as backing up the boot sector of a hard drive, and obtaining a fixed amount of random data. On Unix, device drivers for hardware (such as hard disk drives) and special device files (such as /dev/zero and /dev/random) appear in the file system just like normal files dd can also read and/or write from/to these files, provided that function is implemented in their respective driver. Unix, Unix-like, Plan 9, Inferno, WindowsÄd is a command-line utility for Unix, Plan 9, Inferno, and Unix-like operating systems and beyond, the primary purpose of which is to convert and copy files. Various open-source and commercial developersĬoreutils: git. Command-line utility for Unix and Unix-like operating systems dd Original author(s)
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