dd
:dd: /dee-dee/ vt. [Unix: from IBM JCL
] Equivalent to cat
or BLT
Originally the name of a Unix copy command with special options suitable
for block-oriented devices; it was often used in heavy-handed system
maintenance, as in "Let's `dd' the root partition onto a tape, then use
the boot PROM to load it back on to a new disk". The Unix `dd(1)' was
designed with a weird, distinctly non-Unixy keyword option syntax
reminiscent of IBM System/360 JCL (which had an elaborate DD `Dataset
Definition' specification for I/O devices); though the command filled a
need, the interface design was clearly a prank. The jargon usage is now
very rare outside Unix sites and now nearly obsolete even there, as
`dd(1)' has been deprecated
for a long time (though it has no exact
replacement). The term has been displaced by BLT
or simple English
`copy'.
Jargon File Version 4.3.1, 29 JUN 2001 =
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