shell [orig. Multics
n.
techspeak, widely propagated via Unix] 1. [techspeak] The
command interpreter used to pass commands to an operating system;
so called because it is the part of the operating system that
interfaces with the outside world. 2. More generally, any
interface program that mediates access to a special resource or
server for convenience, efficiency,
or security reasons; for this meaning, the usage is usually `a
shell around' whatever. This sort of program is also called a
`wrapper'. 3. A skeleton program, created by hand or by another
program (like, say, a parser generator), which provides the
necessary incantations to set
up some task and the control flow to drive it (the term driver is sometimes used synonymously).
The user is meant to fill in whatever code is needed to get real
work done. This usage is common in the AI and Microsoft Windows
worlds, and confuses Unix hackers.
Historical note: Apparently, the original Multics shell (sense
1) was so called because it was a shell (sense 3); it ran user
programs not by starting up separate processes, but by
dynamically linking the programs into its own code, calling them
as subroutines, and then dynamically de-linking them on return.
The VMS command interpreter still does something very like
this.
Node:shell out, Next:shift left (or
right) logical, Previous:shell, Up:= S
=
shell out vi.
[Unix] To spawn an interactive
subshell from within a program (e.g., a mailer or editor). "Bang
foo runs foo in a subshell, while bang alone shells out."
Node:shift left
(or right) logical, Next:shim,
Previous:shell out,
Up:= S =
shift left (or right) logical
[from any of various machines' instruction sets] 1. vi. To
move oneself to the left (right). To move out of the way. 2.
imper. "Get out of that (my) seat! You can shift to that empty
one to the left (right)." Often used without the `logical', or as
`left shift' instead of `shift left'. Sometimes heard as LSH
/lish/, from the PDP-10 instruction
set. See Programmer's
Cheer.
Node:shim, Next:shitogram, Previous:shift left (or right)
logical, Up:= S =
shim n.
A small piece of data inserted in order to achieve a desired
memory alignment or other addressing property. For example, the
PDP-11 Unix linker, in split I&D (instructions and data)
mode, inserts a two-byte shim at location 0 in data space so that
no data object will have an address of 0 (and be confused with
the C null pointer). See also loose
bytes.