perlglossary.pod

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unbuffered, the system processes it one byte at a time without the use
of a holding area.  This can be rather inefficient.

=item built-in

A L</function> that is predefined in the language.  Even when hidden
by L</overriding>, you can always get at a built-in function by
L<qualifying|/qualified> its name with the C<CORE::> pseudo-package.

=item bundle

A group of related modules on L</CPAN>.  (Also, sometimes refers to a
group of command-line switches grouped into one L</switch cluster>.)

=item byte

A piece of data worth eight L<bits|/bit> in most places.

=item bytecode

A pidgin-like language spoken among 'droids when they don't wish to
reveal their orientation (see L</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.

=back

=head2 C

=over 4

=item C

A language beloved by many for its inside-out L</type> definitions,
inscrutable L</precedence> rules, and heavy L</overloading> 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.

=item C preprocessor

The typical C compiler's first pass, which processes lines beginning
with C<#> for conditional compilation and macro definition and does
various manipulations of the program text based on the current
definitions.  Also known as I<cpp>(1).

=item call by reference

An L</argument>-passing mechanism in which the L</formal arguments>
refer directly to the L</actual arguments>, and the L</subroutine> can
change the actual arguments by changing the formal arguments.  That
is, the formal argument is an L</alias> for the actual argument.  See
also L</call by value>.

=item call by value

An L</argument>-passing mechanism in which the L</formal arguments>
refer to a copy of the L</actual arguments>, and the L</subroutine>
cannot change the actual arguments by changing the formal arguments.
See also L</call by reference>.

=item callback

A L</handler> that you register with some other part of your program
in the hope that the other part of your program will L</trigger> your
handler when some event of interest transpires.

=item canonical

Reduced to a standard form to facilitate comparison.

=item capturing

The use of parentheses around a L</subpattern> in a L</regular
expression> to store the matched L</substring> as a L</backreference>.
(Captured strings are also returned as a list in L</list context>.)

=item character

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.

=item character class

A square-bracketed list of characters used in a L</regular expression>
to indicate that any character of the set may occur at a given point.
Loosely, any predefined set of characters so used.

=item character property

A predefined L</character class> matchable by the C<\p>
L</metasymbol>.  Many standard properties are defined for L</Unicode>.

=item circumfix operator

An L</operator> that surrounds its L</operand>, like the angle
operator, or parentheses, or a hug.

=item class

A user-defined L</type>, implemented in Perl via a L</package> that
provides (either directly or by inheritance) L<methods|/method> (that
is, L<subroutines|/subroutine>) to handle L<instances|/instance> of
the class (its L<objects|/object>).  See also L</inheritance>.

=item class method

A L</method> whose L</invocant> is a L</package> name, not an
L</object> reference.  A method associated with the class as a whole.

=item client

In networking, a L</process> that initiates contact with a L</server>
process in order to exchange data and perhaps receive a service.

=item cloister

A L</cluster> used to restrict the scope of a L</regular expression
modifier>.

=item closure

An L</anonymous> subroutine that, when a reference to it is generated
at run time, keeps track of the identities of externally visible
L<lexical variables|/lexical variable> even after those lexical
variables have supposedly gone out of L</scope>.  They're called
"closures" because this sort of behavior gives mathematicians a sense
of closure.

=item cluster

A parenthesized L</subpattern> used to group parts of a L</regular
expression> into a single L</atom>.

=item CODE

The word returned by the L<ref|perlfunc/ref> function when you apply
it to a reference to a subroutine.  See also L</CV>.

=item code generator

A system that writes code for you in a low-level language, such as
code to implement the backend of a compiler.  See L</program
generator>.

=item code subpattern

A L</regular expression> subpattern whose real purpose is to execute
some Perl code, for example, the C<(?{...})> and C<(??{...})>
subpatterns.

=item collating sequence

The order into which L<characters|/character> sort.  This is used by
L</string> comparison routines to decide, for example, where in this
glossary to put "collating sequence".

=item command

In L</shell> programming, the syntactic combination of a program name
and its arguments.  More loosely, anything you type to a shell (a
command interpreter) that starts it doing something.  Even more
loosely, a Perl L</statement>, which might start with a L</label> and
typically ends with a semicolon.

=item command buffering

A mechanism in Perl that lets you store up the output of each Perl
L</command> and then flush it out as a single request to the
L</operating system>.  It's enabled by setting the C<$|>
(C<$AUTOFLUSH>) variable to a true value.  It's used when you don't
want data sitting around not going where it's supposed to, which may
happen because the default on a L</file> or L</pipe> is to use
L</block buffering>.

=item command name

The name of the program currently executing, as typed on the command
line.  In C, the L</command> name is passed to the program as the
first command-line argument.  In Perl, it comes in separately as
C<$0>.

=item command-line arguments

The L<values|/value> you supply along with a program name when you
tell a L</shell> to execute a L</command>.  These values are passed to
a Perl program through C<@ARGV>.

=item comment

A remark that doesn't affect the meaning of the program.  In Perl, a
comment is introduced by a C<#> character and continues to the end of
the line.

=item compilation unit

The L</file> (or L</string>, in the case of L<eval|perlfunc/eval>)
that is currently being compiled.

=item compile phase

Any time before Perl starts running your main program.  See also
L</run phase>.  Compile phase is mostly spent in L</compile time>, but
may also be spent in L</run time> when C<BEGIN> blocks,
L<use|perlfunc/use> declarations, or constant subexpressions are being
evaluated.  The startup and import code of any L<use|perlfunc/use>
declaration is also run during compile phase.

=item compile time

The time when Perl is trying to make sense of your code, as opposed to
when it thinks it knows what your code means and is merely trying to
do what it thinks your code says to do, which is L</run time>.

=item compiler

Strictly speaking, a program that munches up another program and spits
out yet another file containing the program in a "more executable"
form, typically containing native machine instructions.  The I<perl>
program is not a compiler by this definition, but it does contain a
kind of compiler that takes a program and turns it into a more
executable form (L<syntax trees|/syntax tree>) within the I<perl>
process itself, which the L</interpreter> then interprets.  There are,
however, extension L<modules|/module> to get Perl to act more like a
"real" compiler.  See L<O>.

=item composer

A "constructor" for a L</referent> that isn't really an L</object>,
like an anonymous array or a hash (or a sonata, for that matter).  For
example, a pair of braces acts as a composer for a hash, and a pair of
brackets acts as a composer for an array.  See L<perlref/Making
References>.

=item concatenation

The process of gluing one cat's nose to another cat's tail.  Also, a
similar operation on two L<strings|/string>.

=item conditional

Something "iffy".  See L</Boolean context>.

=item connection

In telephony, the temporary electrical circuit between the caller's
and the callee's phone.  In networking, the same kind of temporary
circuit between a L</client> and a L</server>.

=item construct

As a noun, a piece of syntax made up of smaller pieces.  As a
transitive verb, to create an L</object> using a L</constructor>.

=item constructor

Any L</class method>, instance L</method>, or L</subroutine>
that composes, initializes, blesses, and returns an L</object>.
Sometimes we use the term loosely to mean a L</composer>.

=item context

The surroundings, or environment.  The context given by the
surrounding code determines what kind of data a particular
L</expression> is expected to return.  The three primary contexts are
L</list context>, L</scalar context>, and L</void context>.  Scalar
context is sometimes subdivided into L</Boolean context>, L</numeric
context>, L</string context>, and L</void context>.  There's also a
"don't care" scalar context (which is dealt with in Programming Perl,
Third Edition, Chapter 2, "Bits and Pieces" if you care).

=item continuation

The treatment of more than one physical L</line> as a single logical
line.  L</Makefile> lines are continued by putting a backslash before
the L</newline>.  Mail headers as defined by RFC 822 are continued by
putting a space or tab I<after> the newline.  In general, lines in
Perl do not need any form of continuation mark, because L</whitespace>
(including newlines) is gleefully ignored.  Usually.

=item core dump

The corpse of a L</process>, in the form of a file left in the
L</working directory> of the process, usually as a result of certain
kinds of fatal error.

=item CPAN

The Comprehensive Perl Archive Network.  (See L<perlfaq2/What modules and extensions are available for Perl?  What is CPAN?  What does CPANE<sol>srcE<sol>... mean?>).

=item cracker

Someone who breaks security on computer systems.  A cracker may be a
true L</hacker> or only a L</script kiddie>.

=item current package

The L</package> in which the current statement is compiled.  Scan
backwards in the text of your program through the current L<lexical
scope|/lexical scoping> or any enclosing lexical scopes till you find
a package declaration.  That's your current package name.

=item current working directory

See L</working directory>.

=item currently selected output channel

The last L</filehandle> that was designated with
L<select|perlfunc/select>(C<FILEHANDLE>); L</STDOUT>, if no filehandle
has been selected.

=item CV

An internal "code value" typedef, holding a L</subroutine>.  The L</CV>
type is a subclass of L</SV>.

=back

=head2 D

=over 4

=item dangling statement

A bare, single L</statement>, without any braces, hanging off an C<if>
or C<while> conditional.  C allows them.  Perl doesn't.

=item data structure

How your various pieces of data relate to each other and what shape
they make when you put them all together, as in a rectangular table or
a triangular-shaped tree.

=item data type

A set of possible values, together with all the operations that know
how to deal with those values.  For example, a numeric data type has a
certain set of numbers that you can work with and various mathematical
operations that you can do on the numbers but would make little sense
on, say, a string such as C<"Kilroy">.  Strings have their own
operations, such as L</concatenation>.  Compound types made of a
number of smaller pieces generally have operations to compose and
decompose them, and perhaps to rearrange them.  L<Objects|/object>
that model things in the real world often have operations that
correspond to real activities.  For instance, if you model an
elevator, your elevator object might have an C<open_door()>
L</method>.

=item datagram

A packet of data, such as a L</UDP> message, that (from the viewpoint
of the programs involved) can be sent independently over the network.
(In fact, all packets are sent independently at the L</IP> level, but
L</stream> protocols such as L</TCP> hide this from your program.)

=item DBM

Stands for "Data Base Management" routines, a set of routines that
emulate an L</associative array> 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
L</hash> across multiple invocations.  You can L<tie|perlfunc/tie>
your hash variables to various DBM implementations--see L<AnyDBM_File>
and L<DB_File>.

=item declaration

An L</assertion> 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
L</statement> for its opposite.  Note that some declarations also
function as statements.  Subroutine declarations also act as
definitions if a body is supplied.

=item decrement