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Bourne shell

The Bourne shell is a shell, or command-line interpreter, for computer operating systems. The Bourne shell was the default shell for Version 7 Unix. Many Unix-like systems continue to have /bin/sh—which will be the Bourne shell, or a symbolic link or hard link to a compatible shell—even when other shells are used by most users. Developed by Stephen Bourne at Bell Labs, it was a replacement for the Thompson shell, whose executable file had the same name—sh, it was released in 1979 in the Version 7 Unix release distributed to universities. Although it is used as an interactive command interpreter, it was intended as a scripting language and contains most of the features that are considered to produce structured programs, it gained popularity with the publication of The Unix Programming Environment by Brian Kernighan and Rob Pike—the first commercially published book that presented the shell as a programming language in a tutorial form. Work on the Bourne shell started in 1976. First appearing in Version 7 Unix, the Bourne shell superseded the Mashey shell.

Some of the primary goals of the shell were: To allow shell scripts to be used as filters. To provide programmability including control flow and variables. Control over all input/output file descriptors. Control over signal handling within scripts. No limits on string lengths. Rationalize and generalize string quoting mechanism; the environment mechanism. This allowed context to be established at startup and provided a way for shell scripts to pass context to sub scripts without having to use explicit positional parameters. Features of the Version 7 UNIX Bourne shell include: Scripts can be invoked as commands by using their filename May be used interactively or non-interactively Allows both synchronous and asynchronous execution of commands Supports input and output redirection and pipelines Provides a set of built-in commands Provides flow control constructs, quotation facilities, functions. Typeless variables Provides local and global variable scope Scripts do not require compilation before execution Does not have a goto facility, so code restructuring may be necessary Command substitution using back quotes: `command`.

Here documents using << to embed a block of input text within a script. "for ~ do ~ done" loops, in particular the use of $* to loop over arguments, as well as "for ~ in ~ do ~ done" loops for iterating over lists. "case ~ in ~ esac" selection mechanism intended to assist argument parsing. Sh provided support for environment variables using keyword parameters and exportable variables. Contains strong provisions for controlling input and output and in its expression matching facilities; the Bourne shell was the first to feature the convention of using file descriptor 2> for error messages, allowing much greater programmatic control during scripting by keeping error messages separate from data. Stephen Bourne's coding style was influenced by his experience with the ALGOL 68C compiler that he had been working on at Cambridge University. In addition to the style in which the program was written, Bourne reused portions of ALGOL 68's "if ~ ~ elif ~ ~ else ~ fi", "case ~ in ~ esac" and "for/while ~ do ~ od" clauses in the common Unix Bourne shell syntax.

Moreover, – although the v7 shell is written in C – Bourne took advantage of some macros to give the C source code an ALGOL 68 flavor. These macros inspired the IOCCC – International Obfuscated C Code Contest. Over the years, the Bourne shell was enhanced at AT&T; the various variants are thus called like the respective AT&T Unix version. As the shell was never versioned, the only way to identify it was testing its features. Features of the Bourne shell versions since 1979 include: Built-in test command – System III shell # as comment character – System III shell Colon in parameter substitutions "$" – System III shell continue with argument – System III shell cat <<-EOF for indented here documents – System III shell Functions and the return builtin – SVR2 shell Built-ins unset, type – SVR2 shell Source code de-ALGOL68-ized – SVR2 shell Modern "$@" – SVR3 shell Built-in getopts – SVR3 shell Cleaned up parameter handling allows recursively callable functions – SVR3 shell 8-bit clean – SVR3 shell Job control – SVR4 shell Multi-byte support – SVR4 shell Duplex Multi-Environment Real-Time is a hybrid time-sharing/real-time operating system developed in the 1970s at Bell Labs Indian Hill location in Naperville, Illinois uses a 1978 snapshot of Bourne Shell "VERSION sys137 DATE 1978 Oct 12 22:39:57".

The DMERT shell runs on 3B21D computers still in use in the telecommunications industry. The Korn shell written by David Korn based on the original Bourne Shell source code, was a middle road between the Bourne shell and the C shell, its syntax was chiefly drawn from the Bourne shell, while its job control features resembled those of the C shell. The functionality of the original Korn Shell was used as a basis for the POSIX shell standard. A newer version, ksh93, is used on some Linux distributions. A clone of ksh88 known as pdksh is the default shell in OpenBSD. Bill Joy, the author of the C shell, criticized the Bourne shell as being unfriendly for interactive use, a task for which Stephen Bourne himself acknowledged C shell's superiority. Bourne stated, that his shell was superior for scripting and was available on any Unix system, Tom Christiansen crit

Chris McNab

Not to be confused with Chris McNab, Welsh author and military expert. Christopher Ross McNab is an author, computer hacker, founder of AlphaSOC. McNab is best known for his Network Security Assessment books, which detail practical penetration testing tactics that can be adopted to evaluate the security of networks in-line with CESG CHECK, PCI DSS, NIST SP 800-115 standards. During 2012 and 2013, McNab undertook incident response work on behalf of organizations in California and Nevada targeted by Alexsey Belan. In 2011, McNab worked with the Attorney General of Guatemala under a United States Agency for International Development project to secure the computer networks that underpin the legal system within the country. McNab, Chris. Network Security Assessment. O’Reilly Media. ISBN 978-1-4919-1095-5. McNab, Chris. Network Security Assessment. O’Reilly Media. ISBN 978-0-5965-1030-5. McNab, Chris. Network Security Assessment. O’Reilly Media. ISBN 978-0-5960-0611-2

Back (horse)

The back describes the area of horse anatomy where the saddle goes, in popular usage extends to include the loin or lumbar region behind the thoracic vertebrae, crucial to a horse's weight-carrying ability. These two sections of the vertebral column beginning at the withers, the start of the thoracic vertebrae, extend to the last lumbar vertebra; because horses are ridden by humans, the strength and structure of the horse's back is critical to the animal's usefulness. The thoracic vertebrae are the true "back" vertebral structures of the skeleton, providing the underlying support of the saddle, the lumbar vertebrae of the loin provide the coupling that joins the back to the hindquarters. Integral to the back structure is the rib cage, which provides support to the horse and rider. A complex design of bone, muscle and ligaments all work together to allow a horse to support the weight of a rider; the structure of the back varies from horse to horse and varies a great deal by breed and condition of the animal.

A horse has an average total of 18 thoracic vertebrae, with five located in the withers. Each thoracic vertebra is associated with a rib. A horse has, on average, six lumbar vertebrae; some breeds, such as the Arabian, will sometimes, but not always, have five lumbar vertebrae and 17 thoracic vertebrae. There appears to be little correlation between back length and number of vertebrae, as many horses with short backs do have the typical number of vertebrae; the length of each vertebra in the lumbar region seems to have the greater influence on the strength of the horse's back. The horse has no collarbone. Hence the entire torso is attached to the shoulders by powerful muscles and ligaments; the spine of a horse's back is supported by muscles, three ligaments, abdominal muscles. The Spinalis Dorsi originates on the fourth cervical vertebra and inserts beneath the thoracic section of the Trapezius; the Longissimus dorsi originates from the last four cervical vertebrae, courses along the spine, inserting into the ilium and sacrum.

This muscle contracts the spine and raises and supports the head and neck, is the main muscle used for rearing, kicking and turning. It is the longest and strongest muscle in the body, is the muscle the rider sits on; the Intercostal muscles begin at the spaces between the ribs and aid in breathing. The external and internal abdominal obliques are attached to the ribs and pelvic bones, support the internal organs; the Supraspinous ligament ends at the croup. It supports the head and neck, its traction force aids in supporting the weaker thoracic and lumbar areas, it attaches to the spines of the cervical vertebrae. In the wither and neck area, it is called the nuchal ligament. Horses' back shape can vary from horse to horse; the upper curvature of a horse's withers and loin is called the "topline." The line of the belly from elbow to flank is the "under line" or "bottom line." In terms of the back, both are important. The underline is where the abdominal muscles are, like in humans, can provide tremendous support to the back when well-conditioned.

The topline will vary with some relationship between the two. When being ridden, a horse's back may either be stiff or relaxed as it moves, depending on the tension and strength of ligaments, muscles or tendons; the length of the back may affect smoothness of gait, ability to collect and move with agility, limits how much weight the horse can carry, can impact if a horse might be capable of being laterally gaited. The height of the withers varies and affects freedom of shoulder movement, length of stride, is a major area of concern in proper saddle fitting. A horse's back and ribcage in cross section is described as "deep" or "narrow", depending on the width of the ribs and the depth of the heartgirth, it can be a "pear" shape, an "apple" or inverted "U" shape, may be wide or narrow, short or long, or combinations of these characteristics. Wider but shorter ribs and loins will be stronger than long and narrow ribs and loins. If the ribs "fall off" of the back the back will be narrow, whereas if the ribs are well sprung, the back will be wide.

The average horse can carry up to 25% of its body weight, but body build and back structure, may allow it to carry somewhat more or less. Physical condition plays a role. A horse, in good physical condition, with well-developed abdominal and back muscles, will be able to carry more weight for a longer time than one, not in shape. There are two primary flaws in back conformation, a "too-straight" or "roach" back and its opposite, a too low or "swayback". Horses may have "well-sprung" ribs or be too narrow, called "slab-sided." A horse may have high bony withers, not a flaw, though they can make a saddle hard to fit. Too low withers, called "mutton withers," can make it difficult to keep a saddle on without rolling or slipping, may be correlated to a shorter stride. A roach back is characterized by a back that has insufficient curvature; such animals will have difficulty with flexion and are rough-gaited. Conformational defects such as straight shoulders are correlated with a roach back; when the span of the back dips excessively in the center, a condition known as lordosis, it is called swaybacked.

It is a common back condi