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dd is a command-line utility for Unix and Unix-like operating systems whose primary purpose is to convert and copy files.〔(【引用サイトリンク】 title=dd man page )〕 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; can also read and/or write from/to these files, provided that function is implemented in their respective driver. As a result, can be used for tasks such as backing up the boot sector of a hard drive, and obtaining a fixed amount of random data. The 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. The name may be an allusion to the DD statement found in IBM's Job Control Language (JCL),〔(【引用サイトリンク】 title=dd )〕 where the initials stand for "Data Description."〔See this old discussion (【引用サイトリンク】 title=The Unix "dd" command )〕 The command's syntax resembles the JCL statement more than it does other Unix commands, so the syntax may have been a joke.〔 Another explanation for the command's name is that "cc" (for "convert and copy", as in the command's description) was already taken by the C compiler. Originally intended to convert between ASCII and EBCDIC, first appeared in Version 5 Unix. The command is specified by IEEE Std 1003.1-2008, which is part of the Single UNIX Specification. == Usage == The command line syntax of differs from many other Unix programs, in that it uses the syntax for its command line options, rather than the more-standard or formats. By default, reads from stdin and writes to stdout, but these can be changed by using the (input file) and (output file) options. Usage varies across different operating systems. Also, certain features of will depend on the computer system capabilities, such as 's ability to implement an option for direct memory access. Sending a SIGINFO signal (or a USR1 signal on Linux) to a running process makes it print I/O statistics to standard error once and then continue copying (note that signals may terminate the process on OS X). can read standard input from the keyboard. When end-of-file (EOF) is reached, will exit. Signals and EOF are determined by the software. For example, Unix tools ported to Windows vary as to the EOF: Cygwin uses (the usual Unix EOF) and MKS Toolkit uses Following the Unix philosophy of developing small yet capable software, does one thing and contains no logic other than that required to implement the low-level decisions based on user-specified command-line options. Often, the options are changed for each run of in a multi-step process to empirically produce desired results. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Dd (Unix)」の詳細全文を読む スポンサード リンク
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