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Perl Language Reference Manual
by Larry Wall and others
Paperback (6"x9"), 724 pages
ISBN 9781906966027
RRP £29.95 ($39.95)

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29.2 B

backreference
A substring captured by a subpattern within unadorned parentheses in a regex. Backslashed decimal numbers (\1, \2, etc.) later in the same pattern refer back to the corresponding subpattern in the current match. Outside the pattern, the numbered variables ($1, $2, etc.) continue to refer to these same values, as long as the pattern was the last successful match of the current dynamic scope.
backtracking
The practice of saying, "If I had to do it all over, I'd do it differently," and then actually going back and doing it all over differently. Mathematically speaking, it's returning from an unsuccessful recursion on a tree of possibilities. Perl backtracks when it attempts to match patterns with a regular expression, and its earlier attempts don't pan out. See 11.5.
backward compatibility
Means you can still run your old program because we didn't break any of the features or bugs it was relying on.
bareword
A word sufficiently ambiguous to be deemed illegal under use strict 'subs' ("strict subs" (strict) in the Perl Library Reference Manual (Volume 1)). In the absence of that stricture, a bareword is treated as if quotes were around it.
base class
A generic object type; that is, a class from which other, more specific classes are derived genetically by inheritance. Also called a "superclass" by people who respect their ancestors.
big-endian
From Swift: someone who eats eggs big end first. Also used of computers that store the most significant byte of a word at a lower byte address than the least significant byte. Often considered superior to little-endian machines. See also little-endian.
binary
Having to do with numbers represented in base 2. That means there's basically two numbers, 0 and 1. Also used to describe a "non-text file", presumably because such a file makes full use of all the binary bits in its bytes. With the advent of Unicode, this distinction, already suspect, loses even more of its meaning.
binary operator
An operator that takes two operands.
bind
To assign a specific network address to a socket.
bit
An integer in the range from 0 to 1, inclusive. The smallest possible unit of information storage. An eighth of a byte or of a dollar. (The term "Pieces of Eight" comes from being able to split the old Spanish dollar into 8 bits, each of which still counted for money. That's why a 25-cent piece today is still "two bits".)
bit shift
The movement of bits left or right in a computer word, which has the effect of multiplying or dividing by a power of 2.
bit string
A sequence of bits that is actually being thought of as a sequence of bits, for once.
bless
In corporate life, to grant official approval to a thing, as in, "The VP of Engineering has blessed our WebCruncher project." Similarly in Perl, to grant official approval to a referent so that it can function as an object, such as a WebCruncher object. See .
block
What a process does when it has to wait for something: "My process blocked waiting for the disk." As an unrelated noun, it refers to a large chunk of data, of a size that the operating system likes to deal with (normally a power of two such as 512 or 8192). Typically refers to a chunk of data that's coming from or going to a disk file.
BLOCK
A syntactic construct consisting of a sequence of Perl statements that is delimited by braces. The if and while statements are defined in terms of BLOCKs, for instance. Sometimes we also say "block" to mean a lexical scope; that is, a sequence of statements that act like a BLOCK, such as within an eval ( ) or a file, even though the statements aren't delimited by braces.
block buffering
A method of making input and output efficient by passing one block at a time. By default, Perl does block buffering to disk files. See buffer and command buffering.
Boolean
A value that is either true or false.
Boolean context
A special kind of scalar context used in conditionals to decide whether the scalar value returned by an expression is true or false. Does not evaluate as either a string or a number. See context.
breakpoint
A spot in your program where you've told the debugger to stop execution so you can poke around and see whether anything is wrong yet.
broadcast
To send a datagram to multiple destinations simultaneously.
BSD
A psychoactive drug, popular in the 80s, probably developed at U. C. Berkeley or thereabouts. Similar in many ways to the prescription-only medication called "System V", but infinitely more useful. (Or, at least, more fun.) The full chemical name is "Berkeley Standard Distribution".
bucket
A location in a hash table containing (potentially) multiple entries whose keys "hash" to the same hash value according to its hash function. (As internal policy, you don't have to worry about it, unless you're into internals, or policy.)
buffer
A temporary holding location for data. Block buffering means that the data is passed on to its destination whenever the buffer is full. Line buffering means that it's passed on whenever a complete line is received. Command buffering means that it's passed every time you do a print ( ) command (or equivalent). If your output is unbuffered, the system processes it one byte at a time without the use of a holding area. This can be rather inefficient.
built-in
A function that is predefined in the language. Even when hidden by overriding, you can always get at a built-in function by qualifying its name with the CORE:: pseudo-package.
bundle
A group of related modules on CPAN. (Also, sometimes refers to a group of command-line switches grouped into one switch cluster.)
byte
A piece of data worth eight bits in most places.
bytecode
A pidgin-like language spoken among 'droids when they don't wish to reveal their orientation (see endian). Named after some similar languages spoken (for similar reasons) between compilers and interpreters in the late 20th century. These languages are characterized by representing everything as a non-architecture-dependent sequence of bytes.
ISBN 9781906966027Perl Language Reference ManualSee the print edition