gloss.htm

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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 <em class="emphasis">regular
expression</em>, and its earlier attempts don't pan out.
See "The Little Engine That /Could(n't)?/" in
<a href="ch05_01.htm">Chapter 5, "Pattern Matching"</a>.
</p>
</dd>
</dl>


<dl>
<a name="INDEX-"></a>
<dt>backward compatibility</dt>
<dd>
<p>
Means you can still run your old program because we didn't break
any of the features or bugs it was relying on.
</p>
</dd>
</dl>

<a name="INDEX-"></a>

<dl>
<a name="INDEX-"></a>
<dt>bareword</dt>
<dd>
<p>
A word sufficiently ambiguous to be deemed illegal under <tt class="literal">use
strict 'subs'</tt>.  In the absence of that stricture, a bareword
is treated as if quotes were around it.
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<dt>base class</dt>
<dd>
<p>
A generic <em class="emphasis">object</em> type; that is, a
<em class="emphasis">class</em> from which other, more specific classes are
derived genetically by <em class="emphasis">inheritance</em>.  Also called
a "superclass" by people who respect their ancestors.
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<dt>big-endian</dt>
<dd>
<p>
From Swift: someone who eats eggs big end first.  Also used of
computers that store the most significant <em class="emphasis">byte</em> of
a word at a lower byte address than the least significant byte.  Often
considered superior to little-endian machines.  See also
<em class="emphasis">little-endian</em>.
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<dt>binary</dt>
<dd>
<p>
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 <em class="emphasis">Unicode</em>,
this distinction, already suspect, loses even more of its meaning.
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<dt>binary operator</dt>
<dd>
<p>
An <em class="emphasis">operator</em> that takes two <em class="emphasis">operands</em>.
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<dt>bind</dt>
<dd>
<p>
To assign a specific <em class="emphasis">network address</em> to a
<em class="emphasis">socket</em>.
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<dt>bit</dt>
<dd>
<p>
An integer in the range from 0 to 1, inclusive.  The smallest possible
unit of information storage.  An eighth of a
<em class="emphasis">byte</em> 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".)
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<dt>bit shift</dt>
<dd>
<p>
The movement of bits left or right in a computer word, which has the
effect of multiplying or dividing by a power of 2.
</p>
</dd>
</dl>

<dl>
<dt>bit string</dt>
<dd>
<p>
A sequence of <em class="emphasis">bits</em> that is actually being
thought of as a sequence of bits, for once.
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<dt>bless</dt>
<dd>
<p>
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 <em class="emphasis">referent</em> so
that it can function as an <em class="emphasis">object</em>, such as a
WebCruncher object.  See the <tt class="literal">bless</tt> function in
<a href="ch29_01.htm">Chapter 29, "Functions"</a>.
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<a name="INDEX-"></a>
<dt>block</dt>
<dd>
<p>
What a <em class="emphasis">process</em> 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 <em class="emphasis">operating
system</em> 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.
</p>
</dd>
</dl>

<dl>
<dt>BLOCK</dt>
<dd>
<p>
A syntactic construct consisting of a sequence of Perl
<em class="emphasis">statements</em> that is delimited by braces.  The
<tt class="literal">if</tt> and <tt class="literal">while</tt> statements are
defined in terms of <em class="replaceable">BLOCK</em>s, for
instance.  Sometimes we also say "block" to mean a lexical scope; that
is, a sequence of statements that act like a
<em class="replaceable">BLOCK</em>, such as within an <tt class="literal">eval</tt>
or a file, even though the statements aren't delimited by braces.
</p>
</dd>
</dl>

<a name="INDEX-"></a>
<dl>
<dt>block buffering</dt>
<dd>
<p>
A method of making input and output efficient by passing one
<em class="emphasis">block</em> at a time.  By default, Perl does block
buffering to disk files.  See <em class="emphasis">buffer</em> and
<em class="emphasis">command buffering</em>.
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<dt>Boolean</dt>
<dd>
<p>
A value that is either <em class="emphasis">true</em> or <em class="emphasis">false</em>.
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<dt>Boolean context</dt>
<dd>
<p>
A special kind of <em class="emphasis">scalar context</em> used in
conditionals to decide whether the <em class="emphasis">scalar value</em>
returned by an expression is <em class="emphasis">true</em> or
<em class="emphasis">false</em>.  Does not evaluate as either a string or a
number.  See <em class="emphasis">context</em>.
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<dt>breakpoint</dt>
<dd>
<p>
A spot in your program where you've told the debugger to stop
<em class="emphasis">execution</em> so you can poke around and see whether
anything is wrong yet.
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<dt>broadcast</dt>
<dd>
<p>
To send a <em class="emphasis">datagram</em> to multiple destinations
simultaneously.
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<dt>BSD</dt>
<dd>
<p>
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".
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a><a name="INDEX-"></a>
<dt>bucket</dt>
<dd>
<p>
A location in a <em class="emphasis">hash table</em> 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.)
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<dt>buffer</dt>
<dd>
<p>
A temporary holding location for data.  <em class="emphasis">Block
buffering</em> means that the data is passed on to its
destination whenever the buffer is full.  <em class="emphasis">Line
buffering</em> means that it's passed on whenever a complete
line is received.  <em class="emphasis">Command buffering</em> means that
it's passed every time you do a <tt class="literal">print</tt> 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.
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<dt>built-in</dt>
<dd>
<p>
A <em class="emphasis">function</em> that is predefined in the language.
Even when hidden by <em class="emphasis">overriding</em>, you can always
get at a built-in function by <em class="emphasis">qualifying</em> its name
with the <tt class="literal">CORE::</tt> pseudo-package.
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<dt>bundle</dt>
<dd>
<p>
A group of related modules on <em class="emphasis">CPAN</em>.  (Also,
sometimes refers to a group of command-line switches grouped into
one <em class="emphasis">switch cluster</em>.)
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<dt>byte</dt>
<dd>
<p>
A piece of data worth eight <em class="emphasis">bits</em> in most places.
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<dt>bytecode</dt>
<dd>
<p>
A pidgin-like language spoken among 'droids when they don't wish to
reveal their orientation (see <em class="emphasis">endian</em>).  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.
</p>
</dd>
</dl>

<dl>
<a name="INDEX-"></a>
<dt>C</dt>
<dd>
<p>
A language beloved by many for its inside-out
<em class="emphasis">type</em> definitions, inscrutable
<em class="emphasis">precedence</em> rules, and heavy
<em class="emphasis">overloading</em> of the function-call mechanism.
(Well, actually, people first switched to C because they found
lowercase identifiers easier to read than upper.)  Perl is written in
C, so it's not surprising that Perl borrowed a few ideas from it.
</p>
</dd>
</dl>

<dl>
<dt>C preprocessor</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
The typical C compiler's first pass, which processes lines beginning
with <tt class="literal">#</tt> for conditional compilation and macro definition
and does various manipulations of the program text based on the current
definitions.  Also known as <em class="emphasis">cpp</em>(1).
</p>
</dd>
</dl>

<dl>
<dt>call by reference</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
An <em class="emphasis">argument</em>-passing mechanism in which
the <em class="emphasis">formal arguments</em> refer directly to the
<em class="emphasis">actual arguments</em>, and the
<em class="emphasis">subroutine</em> can change the actual arguments by
changing the formal arguments.  That is, the formal argument is an
<em class="emphasis">alias</em> for the actual argument.  See also
<em class="emphasis">call by value</em>.
</p>
</dd>
</dl>

<dl>
<dt>call by value</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
An <em class="emphasis">argument</em>-passing mechanism in which
the <em class="emphasis">formal arguments</em> refer to a copy of the
<em class="emphasis">actual arguments</em>, and the
<em class="emphasis">subroutine</em> cannot change the actual arguments by
changing the formal arguments.  See also <em class="emphasis">call by
reference</em>.
</p>
</dd>
</dl>

<dl>
<dt>callback</dt>
<dd>
<p>
<a name="INDEX-"></a>
A <em class="emphasis">handler</em> that you register with some other part
of your program in the hope that the other part of your program will
<em class="emphasis">trigger</em> your handler when some event of interest
transpires.
</p>
</dd>
</dl>

<dl>
<dt>canonical</dt>
<dd>
<p>
<a name="INDEX-"></a>
Reduced to a standard form to facilitate comparison.
</p>
</dd>
</dl>

<dl>
<dt>capturing</dt>
<dd>
<p>
<a name="INDEX-"></a>
The use of parentheses around a <em class="emphasis">subpattern</em> in a
<em class="emphasis">regular expression</em> to store the matched
<em class="emphasis">substring</em> as a
<em class="emphasis">backreference</em>.  (Captured strings are also
returned as a list in <em class="emphasis">list context</em>.)
</p>
</dd>
</dl>

<dl>
<dt>character</dt>
<dd>
<p>
<a name="INDEX-"></a>
A small integer representative of a unit of orthography.  Historically,
characters were usually stored as fixed-width integers (typically in a
byte, or maybe two, depending on the character set), but with the advent
of UTF-8, characters are often stored in a variable number of bytes
depending on the size of the integer that represents the character.  Perl
manages this transparently for you, for the most part.
</p>
</dd>
</dl>

<dl>
<dt>character class</dt>
<dd>
<p>
<a name="INDEX-"></a>
A square-bracketed list of characters used in a <em class="emphasis">regular
expression</em> to indicate that any character of the set may
occur at a given point.  Loosely, any predefined set of characters so
used.
</p>
</dd>
</dl>

<dl>
<dt>character property</dt>
<dd>
<p>
<a name="INDEX-"></a>
A predefined <em class="emphasis">character class</em> matchable by the
<tt class="literal">\p</tt><em class="emphasis">metasymbol</em>.  Many standard
properties are defined for <em class="emphasis">Unicode</em>.
</p>
</dd>
</dl>

<dl>
<dt>circumfix operator</dt>
<dd>
<p>
<a name="INDEX-"></a>
An <em class="emphasis">operator</em> that surrounds its
<em class="emphasis">operand</em>, like the angle operator, or parentheses,
or a hug.
</p>
</dd>
</dl>

<dl>
<dt>class</dt>
<dd>
<p>
<a name="INDEX-"></a>
A user-defined <em class="emphasis">type</em>, implemented in Perl via a
<em class="emphasis">package</em> that provides (either directly or by