perlglossary.pod

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=head1 NAME

perlglossary - Perl Glossary

=head1 DESCRIPTION

A glossary of terms (technical and otherwise) used in the Perl documentation.
Other useful sources include the Free On-Line Dictionary of Computing
L<http://foldoc.doc.ic.ac.uk/foldoc/index.html>, the Jargon File
L<http://catb.org/~esr/jargon/>, and Wikipedia L<http://www.wikipedia.org/>.

=head2 A

=over 4

=item accessor methods

A L</method> used to indirectly inspect or update an L</object>'s
state (its L<instance variables|/instance variable>).

=item actual arguments

The L<scalar values|/scalar value> that you supply to a L</function>
or L</subroutine> when you call it.  For instance, when you call
C<power("puff")>, the string C<"puff"> is the actual argument.  See
also L</argument> and L</formal arguments>.

=item address operator

Some languages work directly with the memory addresses of values, but
this can be like playing with fire.  Perl provides a set of asbestos
gloves for handling all memory management.  The closest to an address
operator in Perl is the backslash operator, but it gives you a L</hard
reference>, which is much safer than a memory address.

=item algorithm

A well-defined sequence of steps, clearly enough explained that even a
computer could do them.

=item alias

A nickname for something, which behaves in all ways as though you'd
used the original name instead of the nickname.  Temporary aliases are
implicitly created in the loop variable for C<foreach> loops, in the
C<$_> variable for L<map|perlfunc/map> or L<grep|perlfunc/grep>
operators, in C<$a> and C<$b> during L<sort|perlfunc/sort>'s
comparison function, and in each element of C<@_> for the L</actual
arguments> of a subroutine call.  Permanent aliases are explicitly
created in L<packages|/package> by L<importing|/import> symbols or by
assignment to L<typeglobs|/typeglob>.  Lexically scoped aliases for
package variables are explicitly created by the L<our|perlfunc/our>
declaration.

=item alternatives

A list of possible choices from which you may select only one, as in
"Would you like door A, B, or C?"  Alternatives in regular expressions
are separated with a single vertical bar: C<|>.  Alternatives in
normal Perl expressions are separated with a double vertical bar:
C<||>.  Logical alternatives in L</Boolean> expressions are separated
with either C<||> or C<or>.

=item anonymous

Used to describe a L</referent> that is not directly accessible
through a named L</variable>.  Such a referent must be indirectly
accessible through at least one L</hard reference>.  When the last
hard reference goes away, the anonymous referent is destroyed without
pity.

=item architecture

The kind of computer you're working on, where one "kind" of computer
means all those computers sharing a compatible machine language.
Since Perl programs are (typically) simple text files, not executable
images, a Perl program is much less sensitive to the architecture it's
running on than programs in other languages, such as C, that are
compiled into machine code.  See also L</platform> and L</operating
system>.

=item argument

A piece of data supplied to a L<program|/executable file>,
L</subroutine>, L</function>, or L</method> to tell it what it's
supposed to do.  Also called a "parameter".

=item ARGV

The name of the array containing the L</argument> L</vector> from the
command line.  If you use the empty C<< E<lt>E<gt> >> operator, L</ARGV> is
the name of both the L</filehandle> used to traverse the arguments and
the L</scalar> containing the name of the current input file.

=item arithmetical operator

A L</symbol> such as C<+> or C</> that tells Perl to do the arithmetic
you were supposed to learn in grade school.

=item array

An ordered sequence of L<values|/value>, stored such that you can
easily access any of the values using an integer L</subscript>
that specifies the value's L</offset> in the sequence.

=item array context

An archaic expression for what is more correctly referred to as
L</list context>.

=item ASCII

The American Standard Code for Information Interchange (a 7-bit
character set adequate only for poorly representing English text).
Often used loosely to describe the lowest 128 values of the various
ISO-8859-X character sets, a bunch of mutually incompatible 8-bit
codes best described as half ASCII.  See also L</Unicode>.

=item assertion

A component of a L</regular expression> that must be true for the
pattern to match but does not necessarily match any characters itself.
Often used specifically to mean a L</zero width> assertion.

=item assignment

An L</operator> whose assigned mission in life is to change the value
of a L</variable>.

=item assignment operator

Either a regular L</assignment>, or a compound L</operator> composed
of an ordinary assignment and some other operator, that changes the
value of a variable in place, that is, relative to its old value.  For
example, C<$a += 2> adds C<2> to C<$a>.

=item associative array

See L</hash>.  Please.

=item associativity

Determines whether you do the left L</operator> first or the right
L</operator> first when you have "A L</operator> B L</operator> C" and
the two operators are of the same precedence.  Operators like C<+> are
left associative, while operators like C<**> are right associative.
See L<perlop> for a list of operators and their associativity.

=item asynchronous

Said of events or activities whose relative temporal ordering is
indeterminate because too many things are going on at once.  Hence, an
asynchronous event is one you didn't know when to expect.

=item atom

A L</regular expression> component potentially matching a
L</substring> containing one or more characters and treated as an
indivisible syntactic unit by any following L</quantifier>.  (Contrast
with an L</assertion> that matches something of L</zero width> and may
not be quantified.)

=item atomic operation

When Democritus gave the word "atom" to the indivisible bits of
matter, he meant literally something that could not be cut: I<a->
(not) + I<tomos> (cuttable).  An atomic operation is an action that
can't be interrupted, not one forbidden in a nuclear-free zone.

=item attribute

A new feature that allows the declaration of L<variables|/variable>
and L<subroutines|/subroutine> with modifiers as in C<sub foo : locked
method>.  Also, another name for an L</instance variable> of an
L</object>.

=item autogeneration

A feature of L</operator overloading> of L<objects|/object>, whereby
the behavior of certain L<operators|/operator> can be reasonably
deduced using more fundamental operators.  This assumes that the
overloaded operators will often have the same relationships as the
regular operators.  See L<perlop>.

=item autoincrement

To add one to something automatically, hence the name of the C<++>
operator.  To instead subtract one from something automatically is
known as an "autodecrement".

=item autoload

To load on demand.  (Also called "lazy" loading.)  Specifically, to
call an L<AUTOLOAD|perlsub/Autoloading> subroutine on behalf of an
undefined subroutine.

=item autosplit

To split a string automatically, as the B<-a> L</switch> does when
running under B<-p> or B<-n> in order to emulate L</awk>.  (See also
the L<AutoSplit> module, which has nothing to do with the B<-a>
switch, but a lot to do with autoloading.)

=item autovivification

A Greco-Roman word meaning "to bring oneself to life".  In Perl,
storage locations (L<lvalues|/lvalue>) spontaneously generate
themselves as needed, including the creation of any L</hard reference>
values to point to the next level of storage.  The assignment
C<$a[5][5][5][5][5] = "quintet"> potentially creates five scalar
storage locations, plus four references (in the first four scalar
locations) pointing to four new anonymous arrays (to hold the last
four scalar locations).  But the point of autovivification is that you
don't have to worry about it.

=item AV

Short for "array value", which refers to one of Perl's internal data
types that holds an L</array>.  The L</AV> type is a subclass of
L</SV>.

=item awk

Descriptive editing term--short for "awkward".  Also coincidentally
refers to a venerable text-processing language from which Perl derived
some of its high-level ideas.

=back

=head2 B

=over 4

=item backreference

A substring L<captured|/capturing> by a subpattern within
unadorned parentheses in a L</regex>.  Backslashed decimal numbers
(C<\1>, C<\2>, etc.)  later in the same pattern refer back to the
corresponding subpattern in the current match.  Outside the pattern,
the numbered variables (C<$1>, C<$2>, etc.) continue to refer to these
same values, as long as the pattern was the last successful match of
the current dynamic scope.

=item 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 L</regular expression>, and
its earlier attempts don't pan out.  See L<perlre/Backtracking>.

=item 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.

=item bareword

A word sufficiently ambiguous to be deemed illegal under L<use strict
'subs'|strict/strict subs>.  In the absence of that stricture, a
bareword is treated as if quotes were around it.

=item base class

A generic L</object> type; that is, a L</class> from which other, more
specific classes are derived genetically by L</inheritance>.  Also
called a "superclass" by people who respect their ancestors.

=item big-endian

From Swift: someone who eats eggs big end first.  Also used of
computers that store the most significant L</byte> of a word at a
lower byte address than the least significant byte.  Often considered
superior to little-endian machines.  See also L</little-endian>.

=item 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 L</Unicode>, this distinction,
already suspect, loses even more of its meaning.

=item binary operator

An L</operator> that takes two L<operands|/operand>.

=item bind

To assign a specific L</network address> to a L</socket>.

=item bit

An integer in the range from 0 to 1, inclusive.  The smallest possible
unit of information storage.  An eighth of a L</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".)

=item 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.

=item bit string

A sequence of L<bits|/bit> that is actually being thought of as a
sequence of bits, for once.

=item 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 L</referent> so that it can
function as an L</object>, such as a WebCruncher object.  See
L<perlfunc/"bless">.

=item block

What a L</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 L</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.

=item BLOCK

A syntactic construct consisting of a sequence of Perl
L<statements|/statement> that is delimited by braces.  The C<if> and
C<while> statements are defined in terms of L<BLOCKs|/BLOCK>, for instance.
Sometimes we also say "block" to mean a lexical scope; that is, a
sequence of statements that act like a L</BLOCK>, such as within an
L<eval|perlfunc/eval> or a file, even though the statements aren't
delimited by braces.

=item block buffering

A method of making input and output efficient by passing one L</block>
at a time.  By default, Perl does block buffering to disk files.  See
L</buffer> and L</command buffering>.

=item Boolean

A value that is either L</true> or L</false>.

=item Boolean context

A special kind of L</scalar context> used in conditionals to decide
whether the L</scalar value> returned by an expression is L</true> or
L</false>.  Does not evaluate as either a string or a number.  See
L</context>.

=item breakpoint

A spot in your program where you've told the debugger to stop
L<execution|/execute> so you can poke around and see whether anything
is wrong yet.

=item broadcast

To send a L</datagram> to multiple destinations simultaneously.

=item 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".

=item bucket

A location in a L</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.)

=item buffer

A temporary holding location for data.  L<Block buffering|/block
buffering> means that the data is passed on to its destination
whenever the buffer is full.  L<Line buffering|/line buffering> means
that it's passed on whenever a complete line is received.  L<Command
buffering|/command buffering> means that it's passed every time you do
a L<print|perlfunc/print> command (or equivalent).  If your output is