Dd (Unix) - Usage

Usage

The command line syntax of dd differs from many other Unix programs, in that it uses the syntax option=value for its command line options, rather than the more-standard -option value and --option=value formats. By default, dd reads from STDIN and writes to STDOUT, but these can be changed by using the if (input file) and of (output file) options.

Usage varies across different operating systems. Also, certain features of dd will depend on the computer system capabilities, such as dd's ability to implement an option for direct memory access. Sending a SIGINFO signal (or a USR1 signal on Linux) to a running dd process makes it print I/O statistics to standard error and then continue copying (note that signals may terminate the process on OS X). dd can read standard input from the keyboard. When end-of-file (EOF) is reached, dd 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 (the usual Windows EOF).

In compliance with the Unix philosophy, dd does one thing well. Unlike a sophisticated and highly abstracted utility, dd has no algorithm other than in the low-level decisions of the user concerning how to vary the run options. Often the options are changed for each run of dd in a multi-step process to solve a computer problem.

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