gloss.htm

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<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
Stands for "Data Base Management" routines, a set of routines that
emulate an <em class="emphasis">associative array</em> using disk files.
The routines use a dynamic hashing scheme to locate any entry with
only two disk accesses.  DBM files allow a Perl program to keep a
persistent <em class="emphasis">hash</em> across multiple invocations.  You
can <tt class="literal">tie</tt> your hash variables to various DBM
implementations--see <em class="emphasis">AnyDBM_File</em>(3) and
the entry on <tt class="literal">DB_File</tt> in <a href="ch32_01.htm">Chapter 32, "Standard Modules"</a>.
</p>
</dd>
</dl>

<dl>
<dt>declaration</dt>
<dd>
<p>
<a name="INDEX-"></a>
An <em class="emphasis">assertion</em> that states something exists and
perhaps describes what it's like, without giving any commitment as
to how or where you'll use it.  A declaration is like the part of
your recipe that says, "two cups flour, one large egg, four or
five tadpoles..."  See <em class="emphasis">statement</em>
for its opposite.  Note that some declarations also function as
statements.  Subroutine declarations also act as definitions if
a body is supplied.
</p>
</dd>
</dl>

<dl>
<dt>decrement</dt>
<dd>
<p>
<a name="INDEX-"></a>
To subtract a value from a variable, as in "decrement <tt class="literal">$x</tt>"
(meaning to remove 1 from its value) or "decrement <tt class="literal">$x</tt> by 3".
</p>
</dd>
</dl>

<dl>
<dt>default</dt>
<dd>
<p>
<a name="INDEX-"></a>
A <em class="emphasis">value</em> chosen for you if you don't supply a
value of your own.
</p>
</dd>
</dl>

<dl>
<dt>defined</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
Having a meaning.  Perl thinks that some of the things people try to
do are devoid of meaning, in particular, making use of variables that
have never been given a <em class="emphasis">value</em> and performing
certain operations on data that isn't there.  For example, if you try
to read data past the end of a file, Perl will hand you back an
undefined value.  See also <em class="emphasis">false</em>, and the
<tt class="literal">defined</tt> operator in <a href="ch29_01.htm">Chapter 29, "Functions"</a>.
</p>
</dd>
</dl>

<dl>
<dt>delimiter</dt>
<dd>
<p>
<a name="INDEX-"></a>
A <em class="emphasis">character</em> or <em class="emphasis">string</em> that
sets bounds to an arbitrarily-sized textual object, not to be confused
with a <em class="emphasis">separator</em> or
<em class="emphasis">terminator</em>.  "To delimit" really just means "to
surround" or "to enclose" (like these parentheses are doing).
</p>
</dd>
</dl>

<dl>
<dt>dereference</dt>
<dd>
<p>
<a name="INDEX-"></a>
A fancy computer science term meaning "to follow a
<em class="emphasis">reference</em> to what it
points to".  The "de" part of it refers to the fact that you're
taking away one level of <em class="emphasis">indirection</em>.
</p>
</dd>
</dl>

<dl>
<dt>derived class</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
A <em class="emphasis">class</em> that defines some of its
<em class="emphasis">methods</em> in terms of a more generic
class, called a <em class="emphasis">base class</em>.  Note that classes
aren't classified
exclusively into base classes or derived classes: a class can function
as both a derived class and a base class simultaneously, which is kind
of classy.
</p>
</dd>
</dl>

<dl>
<dt>descriptor</dt>
<dd>
<p>
See <em class="emphasis">file descriptor</em>.
<a name="INDEX-"></a>
</p>
</dd>
</dl>

<dl>
<dt>destroy</dt>
<dd>
<p>
<a name="INDEX-"></a>
To deallocate the memory of a <em class="emphasis">referent</em>
(first triggering its <tt class="literal">DESTROY</tt>
method, if it has one).
</p>
</dd>
</dl>

<dl>
<dt>destructor</dt>
<dd>
<p>
<a name="INDEX-"></a>
A special <em class="emphasis">method</em> that is called when an
<em class="emphasis">object</em> is thinking about
<em class="emphasis">destroying</em> itself.  A Perl program's
<tt class="literal">DESTROY</tt> method doesn't do the actual destruction;
Perl just <em class="emphasis">triggers</em> the method in case the
<em class="emphasis">class</em> wants to do any associated cleanup.
</p>
</dd>
</dl>

<dl>
<dt>device</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
A whiz-bang hardware gizmo (like a disk or tape drive or a modem or a
joystick or a mouse) attached to your computer, that the
<em class="emphasis">operating system</em> tries to make look like a
<em class="emphasis">file</em> (or a bunch of files).  Under Unix, these
fake files tend to live in the <em class="emphasis">/dev</em> directory.
</p>
</dd>
</dl>

<dl>
<dt>directive</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
A <em class="emphasis">pod</em> directive.  See
<a href="ch26_01.htm">Chapter 26, "Plain Old Documentation"</a>.
</p>
</dd>
</dl>

<dl>
<dt>directory</dt>
<dd>
<p>
A special file that contains other files.  Some <em class="emphasis">operating systems</em> call
these "folders", "drawers", or "catalogs".
</p>
</dd>
</dl>

<dl>
<dt>directory handle</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
A name that represents a particular instance of opening a directory
to read it, until you close it.  See the <tt class="literal">opendir</tt> function.
</p>
</dd>
</dl>

<dl>
<dt>dispatch</dt>
<dd>
<p>
To send something to its correct destination.  Often used
metaphorically to indicate a transfer of programmatic control to a
destination selected algorithmically, often by lookup in a table of
function <em class="emphasis">references</em> or, in the case of object <em class="emphasis">methods</em>, by traversing
the inheritance tree looking for the most specific definition for
the method.
</p>
</dd>
</dl>

<dl>
<dt>distribution</dt>
<dd>
<p>
A standard, bundled release of a system of software.  The default usage
implies source code is included.  If that is not the case, it will
be called a "binary-only" distribution.
</p>
</dd>
</dl>

<dl>
<dt>dweomer</dt>
<dd>
<p>
<a name="INDEX-"></a>
An enchantment, illusion, phantasm, or jugglery.  Said when Perl's
magical <em class="emphasis">dwimmer</em> effects don't do what you expect,
but rather seem to be the product of arcane dweomercraft, sorcery, or
wonder working.  [From Old English]
</p>
</dd>
</dl>

<dl>
<dt>dwimmer</dt>
<dd>
<p>
<a name="INDEX-"></a>
DWIM is an acronym for "Do What I Mean", the principle that something
should just do what you want it to do without an undue amount of fuss.
A bit of code that does "dwimming" is a "dwimmer".  Dwimming can
require a great deal of behind-the-scenes magic, which (if it doesn't
stay properly behind the scenes) is called a <em class="emphasis">dweomer</em>
instead.
</p>
</dd>
</dl>

<dl>
<dt>dynamic scoping</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
Dynamic scoping works over a dynamic scope, making variables visible
throughout the rest of the <em class="emphasis">block</em> in which they
are first used and in any <em class="emphasis">subroutines</em> that are
called by the rest of the block.  Dynamically scoped variables can
have their values temporarily changed (and implicitly restored later)
by a <tt class="literal">local</tt> operator.  (Compare <em class="emphasis">lexical
scoping</em>.)  Used more loosely to mean how a subroutine that
is in the middle of calling another subroutine "contains" that
subroutine at <em class="emphasis">run time</em>.
</p>
</dd>
</dl>

<dl>
<dt>eclectic</dt>
<dd>
<p>
Derived from many sources.  Some would say <em class="emphasis">too</em> many.
</p>
</dd>
</dl>

<dl>
<dt>element</dt>
<dd>
<p>
<a name="INDEX-"></a>
A basic building block.  When you're talking about an <em class="emphasis">array</em>, it's one
of the items that make up the array.
</p>
</dd>
</dl>

<dl>
<dt>embedding</dt>
<dd>
<p>
<a name="INDEX-"></a>
When something is contained in something else, particularly when that
might be considered surprising: "I've embedded a complete Perl
interpreter in my editor!"
</p>
</dd>
</dl>

<dl>
<dt>empty subclass test</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
The notion that an empty <em class="emphasis">derived class</em> should behave exactly like its
<em class="emphasis">base class</em>.
</p>
</dd>
</dl>

<dl>
<dt>en passant</dt>
<dd>
<p>
<a name="INDEX-"></a>
When you change a <em class="emphasis">value</em> as it is being 
copied.  [From French, "in passing",
as in the exotic pawn-capturing maneuver in chess.]
</p>
</dd>
</dl>

<dl>
<dt>encapsulation</dt>
<dd>
<p>
<a name="INDEX-"></a>
The veil of abstraction separating the <em class="emphasis">interface</em>
from the <em class="emphasis">implementation</em> (whether enforced or
not), which mandates that all access to an
<em class="emphasis">object</em>'s state be through
<em class="emphasis">methods</em> alone.
</p>
</dd>
</dl>

<dl>
<dt>endian</dt>
<dd>
<p>
See <em class="emphasis">little-endian</em> and <em class="emphasis">big-endian</em>.
</p>
</dd>
</dl>

<dl>
<dt>environment</dt>
<dd>
<p>
<a name="INDEX-"></a>
The collective set of <em class="emphasis">environment variables</em> your <em class="emphasis">process</em> inherits
from its parent.  Accessed via <tt class="literal">%ENV</tt>.
</p>
</dd>
</dl>

<dl>
<dt>environment variable</dt>
<dd>
<p>
<a name="INDEX-"></a>
A mechanism by which some high-level agent such as a user can pass
its preferences down to its future offspring (child <em class="emphasis">processes</em>,
grandchild processes, great-grandchild processes, and so on).  Each
environment variable is a
<em class="emphasis">key</em>/<em class="emphasis">value</em> pair, like one entry
in a <em class="emphasis">hash</em>.
</p>
</dd>
</dl>

<dl>
<dt>EOF</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a><a name="INDEX-"></a>
End of File.  Sometimes used metaphorically as the terminating
string of a <em class="emphasis">here document</em>.
</p>
</dd>
</dl>

<dl>
<dt>errno</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a><a name="INDEX-"></a>
The error number returned by a <em class="emphasis">syscall</em> when it fails.  Perl
refers to the error by the name <tt class="literal">$!</tt> (or <tt class="literal">$OS_ERROR</tt> if you
use the English module).
</p>
</dd>
</dl>

<dl>
<dt>error</dt>
<dd>
<p>
See <em class="emphasis">exception</em> or <em class="emphasis">fatal error</em>.
</p>
</dd>
</dl>

<dl>
<dt>escape sequence</dt>
<dd>
<p>
See <em class="emphasis">metasymbol</em>.
</p>
</dd>
</dl>

<dl>
<dt>exception</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
A fancy term for an error.  See <em class="emphasis">fatal error</em>.
</p>
</dd>
</dl>

<dl>
<dt>exception handling</dt>
<dd>
<p>
The way a program responds to an error.
The exception handling mechanism in Perl is the <tt class="literal">eval</tt> operator.
</p>
</dd>
</dl>

<dl>
<dt>exec</dt>
<dd>
<p>
<a name="INDEX-"></a>
To throw away the current <em class="emphasis">process</em>'s program
and replace it with another without exiting the process or relinquishing
any resources held (apart from the old memory image).
</p>
</dd>
</dl>

<dl>
<dt>executable file</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
A <em class="emphasis">file</em> that is specially marked to tell the <em class="emphasis">operating system</em>
that it's okay to run this file as a program.  Usually shortened to
"executable".
</p>
</dd>
</dl>

<dl>
<dt>execute</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
To run a <em class="emphasis">program</em> or
<em class="emphasis">subroutine</em>.  (Has nothing to do with the
<tt class="literal">kill</tt> built-in, unless you're trying to run
a <em class="emphasis">signal handler</em>.)
</p>
</dd>
</dl>

<dl>
<dt>execute bit</dt>
<dd>
<p>
<a name="INDEX-"></a><a name="INDEX-"></a>
The special mark that tells the operating system it can run this
program.  There are actually three execute bits under Unix, and which
bit gets used depends on whether you own the file singularly,
collectively, or not at all.
</p>
</dd>
</dl>

<dl>
<dt>exit status</dt>
<dd>
<p>
See <em class="emphasis">status</em>.
</p>
</dd>
</dl>

<dl>