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PERLGLOSSARY(1perl)    Perl Programmers Reference Guide	   PERLGLOSSARY(1perl)

       perlglossary - Perl Glossary

       A glossary of terms (technical and otherwise) used in the Perl
       documentation, derived from the Glossary of Programming Perl, Fourth
       Edition.	 Words or phrases in bold are defined elsewhere in this

       Other useful sources include the Unicode Glossary
       <>, the Free On-Line Dictionary of
       Computing <>, the Jargon File
       <>, and Wikipedia

       accessor methods
	   A method used to indirectly inspect or update an objectXs state
	   (its instance variables).

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

       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 hard reference, which is much safer than a memory address.

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

	   A nickname for something, which behaves in all ways as though youXd
	   used the original name instead of the nickname. Temporary aliases
	   are implicitly created in the loop variable for "foreach" loops, in
	   the $_ variable for "map" or "grep" operators, in $a and $b during
	   "sort"Xs comparison function, and in each element of @_ for the
	   actual arguments of a subroutine call. Permanent aliases are
	   explicitly created in packages by importing symbols or by
	   assignment to typeglobs. Lexically scoped aliases for package
	   variables are explicitly created by the "our" declaration.

	   The sort of characters we put into words. In Unicode, this is all
	   letters including all ideographs and certain diacritics, letter
	   numbers like Roman numerals, and various combining marks.

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

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

	   A bigger, fancier sort of program with a fancier name so people
	   donXt realize they are using a program.

	   The kind of computer youXre working on, where one Xkind of
	   computerX 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 itXs running on than programs in other languages, such
	   as C, that are compiled into machine code. See also platform and
	   operating system.

	   A piece of data supplied to a program, subroutine, function, or
	   method to tell it what itXs supposed to do. Also called a

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

       arithmetical operator
	   A symbol such as "+" or "/" that tells Perl to do the arithmetic
	   you were supposed to learn in grade school.

	   An ordered sequence of values, stored such that you can easily
	   access any of the values using an integer subscript that specifies
	   the valueXs offset in the sequence.

       array context
	   An archaic expression for what is more correctly referred to as
	   list context.

       Artistic License
	   The open source license that Larry Wall created for Perl,
	   maximizing PerlXs usefulness, availability, and modifiability. The
	   current version is 2.

	   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 Unicode.

	   A component of a 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 zero-width assertion.

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

       assignment operator
	   Either a regular assignment or a compound 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, "$a += 2" adds 2 to $a.

       associative array
	   See hash. Please. The term associative array is the old Perl 4 term
	   for a hash. Some languages call it a dictionary.

	   Determines whether you do the left operator first or the right
	   operator first when you have XA operator B operator CX, and the two
	   operators are of the same precedence. Operators like "+" are left
	   associative, while operators like "**" are right associative. See
	   Camel chapter 3, XUnary and Binary OperatorsX for a list of
	   operators and their associativity.

	   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 didnXt know when to expect.

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

       atomic operation
	   When Democritus gave the word XatomX to the indivisible bits of
	   matter, he meant literally something that could not be cut: X-
	   (not) + -XXXXX (cuttable). An atomic operation is an action that
	   canXt be interrupted, not one forbidden in a nuclear-free zone.

	   A new feature that allows the declaration of variables and
	   subroutines with modifiers, as in "sub foo : locked method". Also
	   another name for an instance variable of an object.

	   A feature of operator overloading of objects, whereby the behavior
	   of certain operators 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 Camel chapter 13, XOverloadingX.

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

	   To load on demand. (Also called XlazyX loading.)  Specifically, to
	   call an "AUTOLOAD" subroutine on behalf of an undefined subroutine.

	   To split a string automatically, as the Xa switch does when running
	   under Xp or Xn in order to emulate awk. (See also the "AutoSplit"
	   module, which has nothing to do with the "Xa" switch but a lot to
	   do with autoloading.)

	   A Graeco-Roman word meaning Xto bring oneself to lifeX.  In Perl,
	   storage locations (lvalues) spontaneously generate themselves as
	   needed, including the creation of any hard reference values to
	   point to the next level of storage. The assignment
	   "$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 donXt have to worry about it.

       AV  Short for Xarray valueX, which refers to one of PerlXs internal
	   data types that holds an array. The "AV" type is a subclass of SV.

       awk Descriptive editing termXshort for XawkwardX. Also coincidentally
	   refers to a venerable text-processing language from which Perl
	   derived some of its high-level ideas.

	   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.

	   The practice of saying, XIf I had to do it all over, IXd do it
	   differently,X and then actually going back and doing it all over
	   differently. Mathematically speaking, itXs 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 donXt pan out. See the section XThe Little
	   Engine That /Couldn(nXt)X in Camel chapter 5, XPattern MatchingX.

       backward compatibility
	   Means you can still run your old program because we didnXt break
	   any of the features or bugs it was relying on.

	   A word sufficiently ambiguous to be deemed illegal under "use
	   strict 'subs'". 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 XsuperclassX by people who respect their ancestors.

	   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.

	   Having to do with numbers represented in base 2. That means thereXs
	   basically two numbers: 0 and 1. Also used to describe a file of
	   XnontextX, 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.

	   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 XPieces of EightX comes from being able to split
	   the old Spanish dollar into 8 bits, each of which still counted for
	   money. ThatXs why a 25- cent piece today is still Xtwo bitsX.)

       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.

	   In corporate life, to grant official approval to a thing, as in,
	   XThe VP of Engineering has blessed our WebCruncher project.X
	   Similarly, in Perl, to grant official approval to a referent so
	   that it can function as an object, such as a WebCruncher object.
	   See the "bless" function in Camel chapter 27, XFunctionsX.

	   What a process does when it has to wait for something: XMy process
	   blocked waiting for the disk.X 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 2 such as 512 or 8192). Typically
	   refers to a chunk of data thatXs coming from or going to a disk

	   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 "BLOCK"s, for instance. Sometimes we also say
	   XblockX to mean a lexical scope; that is, a sequence of statements
	   that acts like a "BLOCK", such as within an "eval" or a file, even
	   though the statements arenXt 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.

	   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

	   A spot in your program where youXve told the debugger to stop
	   execution so you can poke around and see whether anything is wrong

	   To send a datagram to multiple destinations simultaneously.

       BSD A psychoactive drug, popular in the X80s, probably developed at UC
	   Berkeley or thereabouts. Similar in many ways to the prescription-
	   only medication called XSystem VX, but infinitely more useful. (Or,
	   at least, more fun.) The full chemical name is XBerkeley Standard

	   A location in a hash table containing (potentially) multiple
	   entries whose keys XhashX to the same hash value according to its
	   hash function. (As internal policy, you donXt have to worry about
	   it unless youXre into internals, or policy.)

	   A temporary holding location for data. Data that are Block
	   buffering means that the data is passed on to its destination
	   whenever the buffer is full. Line buffering means that itXs passed
	   on whenever a complete line is received. Command buffering means
	   that itXs 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.

	   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::" pseudopackage.

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

	   A piece of data worth eight bits in most places.

	   A pidgin-like lingo spoken among Xdroids when they donXt wish to
	   reveal their orientation (see endian). Named after some similar
	   languages spoken (for similar reasons) between compilers and
	   interpreters in the late 20XX century. These languages are
	   characterized by representing everything as a nonarchitecture-
	   dependent sequence of bytes.

       C   A language beloved by many for its inside-out type definitions,
	   inscrutable precedence rules, and heavy 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 itXs not surprising that Perl
	   borrowed a few ideas from it.

	   A data repository. Instead of computing expensive answers several
	   times, compute it once and save the result.

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

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

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

	   Reduced to a standard form to facilitate comparison.

       capture variables
	   The variablesXsuch as $1 and $2, and "%+" and %X Xthat hold the
	   text remembered in a pattern match. See Camel chapter 5, XPattern

	   The use of parentheses around a subpattern in a regular expression
	   to store the matched substring as a backreference. (Captured
	   strings are also returned as a list in list context.) See Camel
	   chapter 5, XPattern MatchingX.

       cargo cult
	   Copying and pasting code without understanding it, while
	   superstitiously believing in its value. This term originated from
	   preindustrial cultures dealing with the detritus of explorers and
	   colonizers of technologically advanced cultures. See The Gods Must
	   Be Crazy.

	   A property of certain characters. Originally, typesetter stored
	   capital letters in the upper of two cases and small letters in the
	   lower one. Unicode recognizes three cases: lowercase (character
	   property "\p{lower}"), titlecase ("\p{title}"), and uppercase
	   ("\p{upper}"). A fourth casemapping called foldcase is not itself a
	   distinct case, but it is used internally to implement casefolding.
	   Not all letters have case, and some nonletters have case.

	   Comparing or matching a string case-insensitively. In Perl, it is
	   implemented with the "/i" pattern modifier, the "fc" function, and
	   the "\F" double-quote translation escape.

	   The process of converting a string to one of the four Unicode
	   casemaps; in Perl, it is implemented with the "fc", "lc",
	   "ucfirst", and "uc" functions.

	   The smallest individual element of a string. Computers store
	   characters as integers, but Perl lets you operate on them as text.
	   The integer used to represent a particular character is called that
	   characterXs codepoint.

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

       character property
	   A predefined character class matchable by the "\p" or "\P"
	   metasymbol. Unicode defines hundreds of standard properties for
	   every possible codepoint, and Perl defines a few of its own, too.

       circumfix operator
	   An operator that surrounds its operand, like the angle operator, or
	   parentheses, or a hug.

	   A user-defined type, implemented in Perl via a package that
	   provides (either directly or by inheritance) methods (that is,
	   subroutines) to handle instances of the class (its objects). See
	   also inheritance.

       class method
	   A method whose invocant is a package name, not an object reference.
	   A method associated with the class as a whole. Also see instance

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

	   An anonymous subroutine that, when a reference to it is generated
	   at runtime, keeps track of the identities of externally visible
	   lexical variables, even after those lexical variables have
	   supposedly gone out of scope. TheyXre called XclosuresX because
	   this sort of behavior gives mathematicians a sense of closure.

	   A parenthesized subpattern used to group parts of a regular
	   expression into a single atom.

	   The word returned by the "ref" function when you apply it to a
	   reference to a subroutine. See also CV.

       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 program generator.

	   The integer a computer uses to represent a given character. ASCII
	   codepoints are in the range 0 to 127; Unicode codepoints are in the
	   range 0 to 0x1F_FFFF; and Perl codepoints are in the range 0 to
	   2XXX1 or 0 to 2XXX1, depending on your native integer size. In Perl
	   Culture, sometimes called ordinals.

       code subpattern
	   A regular expression subpattern whose real purpose is to execute
	   some Perl codeXfor example, the "(?{...})" and "(??{...})"

       collating sequence
	   The order into which characters sort. This is used by string
	   comparison routines to decide, for example, where in this glossary
	   to put Xcollating sequenceX.

	   A person with permissions to index a namespace in PAUSE. Anyone can
	   upload any namespace, but only primary and co-maintainers get their
	   contributions indexed.

       combining character
	   Any character with the General Category of Combining Mark
	   ("\p{GC=M}"), which may be spacing or nonspacing. Some are even
	   invisible. A sequence of combining characters following a grapheme
	   base character together make up a single user-visible character
	   called a grapheme. Most but not all diacritics are combining
	   characters, and vice versa.

	   In 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 statement, which might start with a label and
	   typically ends with a semicolon.

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

       command-line arguments
	   The values you supply along with a program name when you tell a
	   shell to execute a command.	These values are passed to a Perl
	   program through @ARGV.

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

	   A remark that doesnXt affect the meaning of the program.  In Perl,
	   a comment is introduced by a "#" character and continues to the end
	   of the line.

       compilation unit
	   The file (or string, in the case of "eval") that is currently being

	   The process of turning source code into a machine-usable form. See
	   compile phase.

       compile phase
	   Any time before Perl starts running your main program. See also run
	   phase. Compile phase is mostly spent in compile time, but may also
	   be spent in runtime when "BEGIN" blocks, "use" or "no"
	   declarations, or constant subexpressions are being evaluated. The
	   startup and import code of any "use" declaration is also run during
	   compile phase.

	   Strictly speaking, a program that munches up another program and
	   spits out yet another file containing the program in a Xmore
	   executableX form, typically containing native machine instructions.
	   The 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 (syntax trees) within the perl process itself,
	   which the interpreter then interprets. There are, however,
	   extension modules to get Perl to act more like a XrealX compiler.
	   See Camel chapter 16, XCompilingX.

       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 runtime.

	   A XconstructorX for a referent that isnXt really an 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 the section
	   XCreating ReferencesX in Camel chapter 8, XReferencesX.

	   The process of gluing one catXs nose to another catXs tail. Also a
	   similar operation on two strings.

	   Something XiffyX. See Boolean context.

	   In telephony, the temporary electrical circuit between the callerXs
	   and the calleeXs phone. In networking, the same kind of temporary
	   circuit between a client and a server.

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

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

	   The surroundings or environment. The context given by the
	   surrounding code determines what kind of data a particular
	   expression is expected to return. The three primary contexts are
	   list context, scalar, and void context. Scalar context is sometimes
	   subdivided into Boolean context, numeric context, string context,
	   and void context. ThereXs also a XdonXt careX context (which is
	   dealt with in Camel chapter 2, XBits and PiecesX, if you care).

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

       core dump
	   The corpse of a process, in the form of a file left in the working
	   directory of the process, usually as a result of certain kinds of
	   fatal errors.

	   The Comprehensive Perl Archive Network. (See the Camel Preface and
	   Camel chapter 19, XCPANX for details.)

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

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

       currently selected output channel
	   The last filehandle that was designated with "select(FILEHANDLE)";
	   "STDOUT", if no filehandle has been selected.

       current package
	   The package in which the current statement is compiled. Scan
	   backward in the text of your program through the current lexical
	   scope or any enclosing lexical scopes until you find a package
	   declaration. ThatXs your current package name.

       current working directory
	   See working directory.

       CV  In academia, a curriculum vitae, a fancy kind of resume. In Perl,
	   an internal Xcode valueX typedef holding a subroutine. The "CV"
	   type is a subclass of SV.

       dangling statement
	   A bare, single statement, without any braces, hanging off an "if"
	   or "while" conditional. C allows them. Perl doesnXt.

	   A packet of data, such as a 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 IP
	   level, but stream protocols such as TCP hide this from your

       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 tree.

       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, as well
	   as various mathematical operations that you can do on the numbers,
	   but would make little sense on, say, a string such as "Kilroy".
	   Strings have their own operations, such as concatenation. Compound
	   types made of a number of smaller pieces generally have operations
	   to compose and decompose them, and perhaps to rearrange them.
	   Objects 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 "open_door" method.

       DBM Stands for XDatabase ManagementX routines, a set of routines that
	   emulate an 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 hash
	   across multiple invocations. You can "tie" your hash variables to
	   various DBM implementations.

	   An assertion that states something exists and perhaps describes
	   what itXs like, without giving any commitment as to how or where
	   youXll use it. A declaration is like the part of your recipe that
	   says, Xtwo cups flour, one large egg, four or five tadpolesXX See
	   statement for its opposite. Note that some declarations also
	   function as statements. Subroutine declarations also act as
	   definitions if a body is supplied.

	   Something that tells your program what sort of variable youXd like.
	   Perl doesnXt require you to declare variables, but you can use
	   "my", "our", or "state" to denote that you want something other
	   than the default.

	   To subtract a value from a variable, as in Xdecrement $xX (meaning
	   to remove 1 from its value) or Xdecrement $x by 3X.

	   A value chosen for you if you donXt supply a value of your own.

	   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 value and performing certain
	   operations on data that isnXt 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 false and the "defined" entry in Camel
	   chapter 27, XFunctionsX.

	   A character or string that sets bounds to an arbitrarily sized
	   textual object, not to be confused with a separator or terminator.
	   XTo delimitX really just means Xto surroundX or Xto encloseX (like
	   these parentheses are doing).

	   A fancy computer science term meaning Xto follow a reference to
	   what it points toX. The XdeX part of it refers to the fact that
	   youXre taking away one level of indirection.

       derived class
	   A class that defines some of its methods in terms of a more generic
	   class, called a base class. Note that classes arenXt 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.

	   See file descriptor.

	   To deallocate the memory of a referent (first triggering its
	   "DESTROY" method, if it has one).

	   A special method that is called when an object is thinking about
	   destroying itself. A Perl programXs "DESTROY" method doesnXt do the
	   actual destruction; Perl just triggers the method in case the class
	   wants to do any associated cleanup.

	   A whiz-bang hardware gizmo (like a disk or tape drive or a modem or
	   a joystick or a mouse) attached to your computer, which the
	   operating system tries to make look like a file (or a bunch of
	   files).  Under Unix, these fake files tend to live in the /dev

	   A pod directive. See Camel chapter 23, XPlain Old DocumentationX.

	   A special file that contains other files. Some operating systems
	   call these XfoldersX, XdrawersX, XcataloguesX, or XcatalogsX.

       directory handle
	   A name that represents a particular instance of opening a directory
	   to read it, until you close it. See the "opendir" function.

	   Some people need this and some people avoid it.  For Perl, itXs an
	   old way to say I/O layer.

	   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 references or, in the case of object methods, by
	   traversing the inheritance tree looking for the most specific
	   definition for the method.

	   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 Xbinary-onlyX distribution.

	   Some modules live both in the Standard Library and on CPAN. These
	   modules might be developed on two tracks as people modify either
	   version. The trend currently is to untangle these situations.

	   An enchantment, illusion, phantasm, or jugglery. Said when PerlXs
	   magical dwimmer effects donXt do what you expect, but rather seem
	   to be the product of arcane dweomercraft, sorcery, or wonder
	   working. [From Middle English.]

	   DWIM is an acronym for XDo What I MeanX, 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 XdwimmingX is a XdwimmerX.
	   Dwimming can require a great deal of behind-the-scenes magic, which
	   (if it doesnXt stay properly behind the scenes) is called a dweomer

       dynamic scoping
	   Dynamic scoping works over a dynamic scope, making variables
	   visible throughout the rest of the block in which they are first
	   used and in any subroutines that are called by the rest of the
	   block. Dynamically scoped variables can have their values
	   temporarily changed (and implicitly restored later) by a "local"
	   operator.  (Compare lexical scoping.) Used more loosely to mean how
	   a subroutine that is in the middle of calling another subroutine
	   XcontainsX that subroutine at runtime.

	   Derived from many sources. Some would say too many.

	   A basic building block. When youXre talking about an array, itXs
	   one of the items that make up the array.

	   When something is contained in something else, particularly when
	   that might be considered surprising: XIXve embedded a complete Perl
	   interpreter in my editor!X

       empty subclass test
	   The notion that an empty derived class should behave exactly like
	   its base class.

	   The veil of abstraction separating the interface from the
	   implementation (whether enforced or not), which mandates that all
	   access to an objectXs state be through methods alone.

	   See little-endian and big-endian.

       en passant
	   When you change a value as it is being copied. [From French Xin
	   passingX, as in the exotic pawn-capturing maneuver in chess.]

	   The collective set of environment variables your process inherits
	   from its parent. Accessed via %ENV.

       environment variable
	   A mechanism by which some high-level agent such as a user can pass
	   its preferences down to its future offspring (child processes,
	   grandchild processes, great-grandchild processes, and so on). Each
	   environment variable is a key/value pair, like one entry in a hash.

       EOF End of File. Sometimes used metaphorically as the terminating
	   string of a here document.

	   The error number returned by a syscall when it fails. Perl refers
	   to the error by the name $! (or $OS_ERROR if you use the English

	   See exception or fatal error.

       escape sequence
	   See metasymbol.

	   A fancy term for an error. See fatal error.

       exception handling
	   The way a program responds to an error. The exception-handling
	   mechanism in Perl is the "eval" operator.

	   To throw away the current processXs program and replace it with
	   another, without exiting the process or relinquishing any resources
	   held (apart from the old memory image).

       executable file
	   A file that is specially marked to tell the operating system that
	   itXs okay to run this file as a program.  Usually shortened to

	   To run a program or subroutine. (Has nothing to do with the "kill"
	   built-in, unless youXre trying to run a signal handler.)

       execute bit
	   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.

       exit status
	   See status.

	   Used as a noun in this case, this refers to a known way to
	   compromise a program to get it to do something the author didnXt
	   intend.  Your task is to write unexploitable programs.

	   To make symbols from a module available for import by other

	   Anything you can legally say in a spot where a value is required.
	   Typically composed of literals, variables, operators, functions,
	   and subroutine calls, not necessarily in that order.

	   A Perl module that also pulls in compiled C or C++ code. More
	   generally, any experimental option that can be compiled into Perl,
	   such as multithreading.

	   In Perl, any value that would look like "" or "0" if evaluated in a
	   string context. Since undefined values evaluate to "", all
	   undefined values are false, but not all false values are undefined.

       FAQ Frequently Asked Question (although not necessarily frequently
	   answered, especially if the answer appears in the Perl FAQ shipped
	   standard with Perl).

       fatal error
	   An uncaught exception, which causes termination of the process
	   after printing a message on your standard error stream. Errors that
	   happen inside an "eval" are not fatal. Instead, the "eval"
	   terminates after placing the exception message in the $@
	   ($EVAL_ERROR) variable.  You can try to provoke a fatal error with
	   the "die" operator (known as throwing or raising an exception), but
	   this may be caught by a dynamically enclosing "eval". If not
	   caught, the "die" becomes a fatal error.

       feeping creaturism
	   A spoonerism of Xcreeping featurismX, noting the biological urge to
	   add just one more feature to a program.

	   A single piece of numeric or string data that is part of a longer
	   string, record, or line. Variable-width fields are usually split up
	   by separators (so use "split" to extract the fields), while fixed-
	   width fields are usually at fixed positions (so use "unpack").
	   Instance variables are also known as XfieldsX.

	   First In, First Out. See also LIFO. Also a nickname for a named

	   A named collection of data, usually stored on disk in a directory
	   in a filesystem. Roughly like a document, if youXre into office
	   metaphors. In modern filesystems, you can actually give a file more
	   than one name. Some files have special properties, like directories
	   and devices.

       file descriptor
	   The little number the operating system uses to keep track of which
	   opened file youXre talking about.  Perl hides the file descriptor
	   inside a standard I/O stream and then attaches the stream to a

	   A XwildcardX match on filenames. See the "glob" function.

	   An identifier (not necessarily related to the real name of a file)
	   that represents a particular instance of opening a file, until you
	   close it. If youXre going to open and close several different files
	   in succession, itXs fine to open each of them with the same
	   filehandle, so you donXt have to write out separate code to process
	   each file.

	   One name for a file. This name is listed in a directory. You can
	   use it in an "open" to tell the operating system exactly which file
	   you want to open, and associate the file with a filehandle, which
	   will carry the subsequent identity of that file in your program,
	   until you close it.

	   A set of directories and files residing on a partition of the disk.
	   Sometimes known as a XpartitionX. You can change the fileXs name or
	   even move a file around from directory to directory within a
	   filesystem without actually moving the file itself, at least under

       file test operator
	   A built-in unary operator that you use to determine whether
	   something is true about a file, such as "Xo $filename" to test
	   whether youXre the owner of the file.

	   A program designed to take a stream of input and transform it into
	   a stream of output.

	   The first PAUSE author to upload a namespace automatically becomes
	   the primary maintainer for that namespace. The Xfirst comeX
	   permissions distinguish a primary maintainer who was assigned that
	   role from one who received it automatically.

	   We tend to avoid this term because it means so many things.	It may
	   mean a command-line switch that takes no argument itself (such as
	   PerlXs "Xn" and "Xp" flags) or, less frequently, a single-bit
	   indicator (such as the "O_CREAT" and "O_EXCL" flags used in
	   "sysopen"). Sometimes informally used to refer to certain regex

       floating point
	   A method of storing numbers in Xscientific notationX, such that the
	   precision of the number is independent of its magnitude (the
	   decimal point XfloatsX). Perl does its numeric work with floating-
	   point numbers (sometimes called XfloatsX) when it canXt get away
	   with using integers. Floating-point numbers are mere approximations
	   of real numbers.

	   The act of emptying a buffer, often before itXs full.

	   Far More Than Everything You Ever Wanted To Know. An exhaustive
	   treatise on one narrow topic, something of a super-FAQ. See Tom for
	   far more.

	   The casemap used in Unicode when comparing or matching without
	   regard to case. Comparing lower-, title-, or uppercase are all
	   unreliable due to UnicodeXs complex, one-to-many case mappings.
	   Foldcase is a lowercase variant (using a partially decomposed
	   normalization form for certain codepoints) created specifically to
	   resolve this.

	   To create a child process identical to the parent process at its
	   moment of conception, at least until it gets ideas of its own. A
	   thread with protected memory.

       formal arguments
	   The generic names by which a subroutine knows its arguments. In
	   many languages, formal arguments are always given individual names;
	   in Perl, the formal arguments are just the elements of an array.
	   The formal arguments to a Perl program are $ARGV[0], $ARGV[1], and
	   so on. Similarly, the formal arguments to a Perl subroutine are
	   $_[0], $_[1], and so on. You may give the arguments individual
	   names by assigning the values to a "my" list. See also actual

	   A specification of how many spaces and digits and things to put
	   somewhere so that whatever youXre printing comes out nice and

       freely available
	   Means you donXt have to pay money to get it, but the copyright on
	   it may still belong to someone else (like Larry).

       freely redistributable
	   Means youXre not in legal trouble if you give a bootleg copy of it
	   to your friends and we find out about it. In fact, weXd rather you
	   gave a copy to all your friends.

	   Historically, any software that you give away, particularly if you
	   make the source code available as well. Now often called open
	   source software. Recently there has been a trend to use the term in
	   contradistinction to open source software, to refer only to free
	   software released under the Free Software FoundationXs GPL (General
	   Public License), but this is difficult to justify etymologically.

	   Mathematically, a mapping of each of a set of input values to a
	   particular output value. In computers, refers to a subroutine or
	   operator that returns a value. It may or may not have input values
	   (called arguments).

       funny character
	   Someone like Larry, or one of his peculiar friends. Also refers to
	   the strange prefixes that Perl requires as noun markers on its

       garbage collection
	   A misnamed featureXit should be called, Xexpecting your mother to
	   pick up after youX. Strictly speaking, Perl doesnXt do this, but it
	   relies on a reference-counting mechanism to keep things tidy.
	   However, we rarely speak strictly and will often refer to the
	   reference-counting scheme as a form of garbage collection. (If itXs
	   any comfort, when your interpreter exits, a XrealX garbage
	   collector runs to make sure everything is cleaned up if youXve been
	   messy with circular references and such.)

       GID Group IDXin Unix, the numeric group ID that the operating system
	   uses to identify you and members of your group.

	   Strictly, the shellXs "*" character, which will match a XglobX of
	   characters when youXre trying to generate a list of filenames.
	   Loosely, the act of using globs and similar symbols to do pattern
	   matching.  See also fileglob and typeglob.

	   Something you can see from anywhere, usually used of variables and
	   subroutines that are visible everywhere in your program.  In Perl,
	   only certain special variables are truly globalXmost variables (and
	   all subroutines) exist only in the current package.	Global
	   variables can be declared with "our". See XGlobal DeclarationsX in
	   Camel chapter 4, XStatements and DeclarationsX.

       global destruction
	   The garbage collection of globals (and the running of any
	   associated object destructors) that takes place when a Perl
	   interpreter is being shut down. Global destruction should not be
	   confused with the Apocalypse, except perhaps when it should.

       glue language
	   A language such as Perl that is good at hooking things together
	   that werenXt intended to be hooked together.

	   The size of the pieces youXre dealing with, mentally speaking.

	   A graphene is an allotrope of carbon arranged in a hexagonal
	   crystal lattice one atom thick. A grapheme, or more fully, a
	   grapheme cluster string is a single user-visible character, which
	   may in turn be several characters (codepoints) long. For example, a
	   carriage return plus a line feed is a single grapheme but two
	   characters, while a XXX is a single grapheme but one, two, or even
	   three characters, depending on normalization.

	   A subpattern whose quantifier wants to match as many things as

	   Originally from the old Unix editor command for XGlobally search
	   for a Regular Expression and Print itX, now used in the general
	   sense of any kind of search, especially text searches. Perl has a
	   built-in "grep" function that searches a list for elements matching
	   any given criterion, whereas the grep(1) program searches for lines
	   matching a regular expression in one or more files.

	   A set of users of which you are a member. In some operating systems
	   (like Unix), you can give certain file access permissions to other
	   members of your group.

       GV  An internal Xglob valueX typedef, holding a typeglob. The "GV" type
	   is a subclass of SV.

	   Someone who is brilliantly persistent in solving technical
	   problems, whether these involve golfing, fighting orcs, or
	   programming.	 Hacker is a neutral term, morally speaking. Good
	   hackers are not to be confused with evil crackers or clueless
	   script kiddies. If you confuse them, we will presume that you are
	   either evil or clueless.

	   A subroutine or method that Perl calls when your program needs to
	   respond to some internal event, such as a signal, or an encounter
	   with an operator subject to operator overloading. See also

       hard reference
	   A scalar value containing the actual address of a referent, such
	   that the referentXs reference count accounts for it. (Some hard
	   references are held internally, such as the implicit reference from
	   one of a typeglobXs variable slots to its corresponding referent.)
	   A hard reference is different from a symbolic reference.

	   An unordered association of key/value pairs, stored such that you
	   can easily use a string key to look up its associated data value.
	   This glossary is like a hash, where the word to be defined is the
	   key and the definition is the value. A hash is also sometimes
	   septisyllabically called an Xassociative arrayX, which is a pretty
	   good reason for simply calling it a XhashX instead.

       hash table
	   A data structure used internally by Perl for implementing
	   associative arrays (hashes) efficiently. See also bucket.

       header file
	   A file containing certain required definitions that you must
	   include XaheadX of the rest of your program to do certain obscure
	   operations. A C header file has a .h extension. Perl doesnXt really
	   have header files, though historically Perl has sometimes used
	   translated .h files with a .ph extension. See "require" in Camel
	   chapter 27, XFunctionsX. (Header files have been superseded by the
	   module mechanism.)

       here document
	   So called because of a similar construct in shells that pretends
	   that the lines following the command are a separate file to be fed
	   to the command, up to some terminating string. In Perl, however,
	   itXs just a fancy form of quoting.

	   A number in base 16, XhexX for short. The digits for 10 through 15
	   are customarily represented by the letters "a" through "f".
	   Hexadecimal constants in Perl start with "0x". See also the "hex"
	   function in Camel chapter 27, XFunctionsX.

       home directory
	   The directory you are put into when you log in. On a Unix system,
	   the name is often placed into $ENV{HOME} or $ENV{LOGDIR} by login,
	   but you can also find it with "(get""pwuid($<))[7]". (Some
	   platforms do not have a concept of a home directory.)

	   The computer on which a program or other data resides.

	   Excessive pride, the sort of thing for which Zeus zaps you.	Also
	   the quality that makes you write (and maintain) programs that other
	   people wonXt want to say bad things about. Hence, the third great
	   virtue of a programmer. See also laziness and impatience.

       HV  Short for a Xhash valueX typedef, which holds PerlXs internal
	   representation of a hash. The "HV" type is a subclass of SV.

	   A legally formed name for most anything in which a computer program
	   might be interested. Many languages (including Perl) allow
	   identifiers to start with an alphabetic character, and then contain
	   alphabetics and digits. Perl also allows connector punctuation like
	   the underscore character wherever it allows alphabetics. (Perl also
	   has more complicated names, like qualified names.)

	   The anger you feel when the computer is being lazy.	This makes you
	   write programs that donXt just react to your needs, but actually
	   anticipate them. Or at least that pretend to. Hence, the second
	   great virtue of a programmer. See also laziness and hubris.

	   How a piece of code actually goes about doing its job. Users of the
	   code should not count on implementation details staying the same
	   unless they are part of the published interface.

	   To gain access to symbols that are exported from another module.
	   See "use" in Camel chapter 27, XFunctionsX.

	   To increase the value of something by 1 (or by some other number,
	   if so specified).

	   In olden days, the act of looking up a key in an actual index (such
	   as a phone book). But now it's merely the act of using any kind of
	   key or position to find the corresponding value, even if no index
	   is involved. Things have degenerated to the point that PerlXs
	   "index" function merely locates the position (index) of one string
	   in another.

       indirect filehandle
	   An expression that evaluates to something that can be used as a
	   filehandle: a string (filehandle name), a typeglob, a typeglob
	   reference, or a low-level IO object.

	   If something in a program isnXt the value youXre looking for but
	   indicates where the value is, thatXs indirection. This can be done
	   with either symbolic references or hard.

       indirect object
	   In English grammar, a short noun phrase between a verb and its
	   direct object indicating the beneficiary or recipient of the
	   action. In Perl, "print STDOUT "$foo\n";" can be understood as
	   Xverb indirect-object objectX, where "STDOUT" is the recipient of
	   the "print" action, and "$foo" is the object being printed.
	   Similarly, when invoking a method, you might place the invocant in
	   the dative slot between the method and its arguments:

	       $gollum = new Pathetic::Creature "Smeagol";
	       give $gollum "Fisssssh!";
	       give $gollum "Precious!";

       indirect object slot
	   The syntactic position falling between a method call and its
	   arguments when using the indirect object invocation syntax. (The
	   slot is distinguished by the absence of a comma between it and the
	   next argument.) "STDERR" is in the indirect object slot here:

	       print STDERR "Awake! Awake! Fear, Fire, Foes! Awake!\n";

	   An operator that comes in between its operands, such as
	   multiplication in "24 * 7".

	   What you get from your ancestors, genetically or otherwise. If you
	   happen to be a class, your ancestors are called base classes and
	   your descendants are called derived classes. See single inheritance
	   and multiple inheritance.

	   Short for Xan instance of a classX, meaning an object of that

       instance data
	   See instance variable.

       instance method
	   A method of an object, as opposed to a class method.

	   A method whose invocant is an object, not a package name. Every
	   object of a class shares all the methods of that class, so an
	   instance method applies to all instances of the class, rather than
	   applying to a particular instance. Also see class method.

       instance variable
	   An attribute of an object; data stored with the particular object
	   rather than with the class as a whole.

	   A number with no fractional (decimal) part. A counting number, like
	   1, 2, 3, and so on, but including 0 and the negatives.

	   The services a piece of code promises to provide forever, in
	   contrast to its implementation, which it should feel free to change
	   whenever it likes.

	   The insertion of a scalar or list value somewhere in the middle of
	   another value, such that it appears to have been there all along.
	   In Perl, variable interpolation happens in double-quoted strings
	   and patterns, and list interpolation occurs when constructing the
	   list of values to pass to a list operator or other such construct
	   that takes a "LIST".

	   Strictly speaking, a program that reads a second program and does
	   what the second program says directly without turning the program
	   into a different form first, which is what compilers do. Perl is
	   not an interpreter by this definition, because it contains a kind
	   of compiler that takes a program and turns it into a more
	   executable form (syntax trees) within the perl process itself,
	   which the Perl runtime system then interprets.

	   The agent on whose behalf a method is invoked. In a class method,
	   the invocant is a package name. In an instance method, the invocant
	   is an object reference.

	   The act of calling up a deity, daemon, program, method, subroutine,
	   or function to get it to do what you think itXs supposed to do.  We
	   usually XcallX subroutines but XinvokeX methods, since it sounds

       I/O Input from, or output to, a file or device.

       IO  An internal I/O object. Can also mean indirect object.

       I/O layer
	   One of the filters between the data and what you get as input or
	   what you end up with as output.

       IPA India Pale Ale. Also the International Phonetic Alphabet, the
	   standard alphabet used for phonetic notation worldwide. Draws
	   heavily on Unicode, including many combining characters.

       IP  Internet Protocol, or Intellectual Property.

       IPC Interprocess Communication.

	   A relationship between two objects in which one object is
	   considered to be a more specific version of the other, generic
	   object: XA camel is a mammal.X Since the generic object really only
	   exists in a Platonic sense, we usually add a little abstraction to
	   the notion of objects and think of the relationship as being
	   between a generic base class and a specific derived class. Oddly
	   enough, Platonic classes donXt always have Platonic
	   relationshipsXsee inheritance.

	   Doing something repeatedly.

	   A special programming gizmo that keeps track of where you are in
	   something that youXre trying to iterate over. The "foreach" loop in
	   Perl contains an iterator; so does a hash, allowing you to "each"
	   through it.

       IV  The integer four, not to be confused with six, TomXs favorite
	   editor. IV also means an internal Integer Value of the type a
	   scalar can hold, not to be confused with an NV.

	   XJust Another Perl HackerX, a clever but cryptic bit of Perl code
	   that, when executed, evaluates to that string. Often used to
	   illustrate a particular Perl feature, and something of an ongoing
	   Obfuscated Perl Contest seen in USENET signatures.

       key The string index to a hash, used to look up the value associated
	   with that key.

	   See reserved words.

	   A name you give to a statement so that you can talk about that
	   statement elsewhere in the program.

	   The quality that makes you go to great effort to reduce overall
	   energy expenditure. It makes you write labor-saving programs that
	   other people will find useful, and then document what you wrote so
	   you donXt have to answer so many questions about it. Hence, the
	   first great virtue of a programmer. Also hence, this book. See also
	   impatience and hubris.

       leftmost longest
	   The preference of the regular expression engine to match the
	   leftmost occurrence of a pattern, then given a position at which a
	   match will occur, the preference for the longest match (presuming
	   the use of a greedy quantifier). See Camel chapter 5, XPattern
	   MatchingX for much more on this subject.

       left shift
	   A bit shift that multiplies the number by some power of 2.

	   Fancy term for a token.

	   Fancy term for a tokener.

       lexical analysis
	   Fancy term for tokenizing.

       lexical scoping
	   Looking at your Oxford English Dictionary through a microscope.
	   (Also known as static scoping, because dictionaries donXt change
	   very fast.) Similarly, looking at variables stored in a private
	   dictionary (namespace) for each scope, which are visible only from
	   their point of declaration down to the end of the lexical scope in
	   which they are declared. XSyn.  static scoping. XAnt. dynamic

       lexical variable
	   A variable subject to lexical scoping, declared by "my". Often just
	   called a XlexicalX. (The "our" declaration declares a lexically
	   scoped name for a global variable, which is not itself a lexical

	   Generally, a collection of procedures. In ancient days, referred to
	   a collection of subroutines in a .pl file. In modern times, refers
	   more often to the entire collection of Perl modules on your system.

	   Last In, First Out. See also FIFO. A LIFO is usually called a

	   In Unix, a sequence of zero or more nonnewline characters
	   terminated with a newline character. On non-Unix machines, this is
	   emulated by the C library even if the underlying operating system
	   has different ideas.

	   A grapheme consisting of either a carriage return followed by a
	   line feed or any character with the Unicode Vertical Space
	   character property.

       line buffering
	   Used by a standard I/O output stream that flushes its buffer after
	   every newline. Many standard I/O libraries automatically set up
	   line buffering on output that is going to the terminal.

       line number
	   The number of lines read previous to this one, plus 1. Perl keeps a
	   separate line number for each source or input file it opens. The
	   current source fileXs line number is represented by "__LINE__". The
	   current input line number (for the file that was most recently read
	   via "<FH>") is represented by the $. ($INPUT_LINE_NUMBER) variable.
	   Many error messages report both values, if available.

	   Used as a noun, a name in a directory that represents a file. A
	   given file can have multiple links to it. ItXs like having the same
	   phone number listed in the phone directory under different names.
	   As a verb, to resolve a partially compiled fileXs unresolved
	   symbols into a (nearly) executable image. Linking can generally be
	   static or dynamic, which has nothing to do with static or dynamic

	   A syntactic construct representing a comma- separated list of
	   expressions, evaluated to produce a list value.  Each expression in
	   a "LIST" is evaluated in list context and interpolated into the
	   list value.

	   An ordered set of scalar values.

       list context
	   The situation in which an expression is expected by its
	   surroundings (the code calling it) to return a list of values
	   rather than a single value. Functions that want a "LIST" of
	   arguments tell those arguments that they should produce a list
	   value. See also context.

       list operator
	   An operator that does something with a list of values, such as
	   "join" or "grep". Usually used for named built-in operators (such
	   as "print", "unlink", and "system") that do not require parentheses
	   around their argument list.

       list value
	   An unnamed list of temporary scalar values that may be passed
	   around within a program from any list-generating function to any
	   function or construct that provides a list context.

	   A token in a programming language, such as a number or string, that
	   gives you an actual value instead of merely representing possible
	   values as a variable does.

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

	   Not meaning the same thing everywhere. A global variable in Perl
	   can be localized inside a dynamic scope via the "local" operator.

       logical operator
	   Symbols representing the concepts XandX, XorX, XxorX, and XnotX.

	   An assertion that peeks at the string to the right of the current
	   match location.

	   An assertion that peeks at the string to the left of the current
	   match location.

	   A construct that performs something repeatedly, like a roller

       loop control statement
	   Any statement within the body of a loop that can make a loop
	   prematurely stop looping or skip an iteration. Generally, you
	   shouldnXt try this on roller coasters.

       loop label
	   A kind of key or name attached to a loop (or roller coaster) so
	   that loop control statements can talk about which loop they want to

	   In Unicode, not just characters with the General Category of
	   Lowercase Letter, but any character with the Lowercase property,
	   including Modifier Letters, Letter Numbers, some Other Symbols, and
	   one Combining Mark.

	   Able to serve as an lvalue.

	   Term used by language lawyers for a storage location you can assign
	   a new value to, such as a variable or an element of an array. The
	   XlX is short for XleftX, as in the left side of an assignment, a
	   typical place for lvalues. An lvaluable function or expression is
	   one to which a value may be assigned, as in "pos($x) = 10".

       lvalue modifier
	   An adjectival pseudofunction that warps the meaning of an lvalue in
	   some declarative fashion. Currently there are three lvalue
	   modifiers: "my", "our", and "local".

	   Technically speaking, any extra semantics attached to a variable
	   such as $!, $0, %ENV, or %SIG, or to any tied variable.  Magical
	   things happen when you diddle those variables.

       magical increment
	   An increment operator that knows how to bump up ASCII alphabetics
	   as well as numbers.

       magical variables
	   Special variables that have side effects when you access them or
	   assign to them. For example, in Perl, changing elements of the %ENV
	   array also changes the corresponding environment variables that
	   subprocesses will use. Reading the $!  variable gives you the
	   current system error number or message.

	   A file that controls the compilation of a program. Perl programs
	   donXt usually need a Makefile because the Perl compiler has plenty
	   of self-control.

       man The Unix program that displays online documentation (manual pages)
	   for you.

	   A XpageX from the manuals, typically accessed via the man(1)
	   command. A manpage contains a SYNOPSIS, a DESCRIPTION, a list of
	   BUGS, and so on, and is typically longer than a page. There are
	   manpages documenting commands, syscalls, library functions,
	   devices, protocols, files, and such. In this book, we call any
	   piece of standard Perl documentation (like perlop or perldelta) a
	   manpage, no matter what format itXs installed in on your system.

	   See pattern matching.

       member data
	   See instance variable.

	   This always means your main memory, not your disk.  Clouding the
	   issue is the fact that your machine may implement virtual memory;
	   that is, it will pretend that it has more memory than it really
	   does, and itXll use disk space to hold inactive bits. This can make
	   it seem like you have a little more memory than you really do, but
	   itXs not a substitute for real memory. The best thing that can be
	   said about virtual memory is that it lets your performance degrade
	   gradually rather than suddenly when you run out of real memory. But
	   your program can die when you run out of virtual memory, tooXif you
	   havenXt thrashed your disk to death first.

	   A character that is not supposed to be treated normally. Which
	   characters are to be treated specially as metacharacters varies
	   greatly from context to context. Your shell will have certain
	   metacharacters, double-quoted Perl strings have other
	   metacharacters, and regular expression patterns have all the
	   double-quote metacharacters plus some extra ones of their own.

	   Something weXd call a metacharacter except that itXs a sequence of
	   more than one character.  Generally, the first character in the
	   sequence must be a true metacharacter to get the other characters
	   in the metasymbol to misbehave along with it.

	   A kind of action that an object can take if you tell it to. See
	   Camel chapter 12, XObjectsX.

       method resolution order
	   The path Perl takes through @INC. By default, this is a double
	   depth first search, once looking for defined methods and once for
	   "AUTOLOAD". However, Perl lets you configure this with "mro".

	   A CPAN mirror that includes just the latest versions for each
	   distribution, probably created with "CPAN::Mini". See Camel chapter
	   19, XCPANX.

	   The belief that Xsmall is beautifulX. Paradoxically, if you say
	   something in a small language, it turns out big, and if you say it
	   in a big language, it turns out small. Go figure.

	   In the context of the stat(2) syscall, refers to the field holding
	   the permission bits and the type of the file.

	   See statement modifier, regular expression, and lvalue, not
	   necessarily in that order.

	   A file that defines a package of (almost) the same name, which can
	   either export symbols or function as an object class.  (A moduleXs
	   main .pm file may also load in other files in support of the
	   module.) See the "use" built-in.

	   An integer divisor when youXre interested in the remainder instead
	   of the quotient.

	   When you speak one language and the computer thinks youXre speaking
	   another. YouXll see odd translations when you send UTFX8, for
	   instance, but the computer thinks you sent Latin-1, showing all
	   sorts of weird characters instead. The term is written XXXXXXin
	   Japanese and means Xcharacter rotX, an apt description. Pronounced
	   ["modXibake"] in standard IPA phonetics, or approximately Xmoh-jee-

	   Short for one member of Perl mongers, a purveyor of Perl.

	   A temporary value scheduled to die when the current statement

       mro See method resolution order.

       multidimensional array
	   An array with multiple subscripts for finding a single element.
	   Perl implements these using referencesXsee Camel chapter 9, XData

       multiple inheritance
	   The features you got from your mother and father, mixed together
	   unpredictably. (See also inheritance and single inheritance.) In
	   computer languages (including Perl), it is the notion that a given
	   class may have multiple direct ancestors or base classes.

       named pipe
	   A pipe with a name embedded in the filesystem so that it can be
	   accessed by two unrelated processes.

	   A domain of names. You neednXt worry about whether the names in one
	   such domain have been used in another. See package.

       NaN Not a number. The value Perl uses for certain invalid or
	   inexpressible floating-point operations.

       network address
	   The most important attribute of a socket, like your telephoneXs
	   telephone number. Typically an IP address. See also port.

	   A single character that represents the end of a line, with the
	   ASCII value of 012 octal under Unix (but 015 on a Mac), and
	   represented by "\n" in Perl strings. For Windows machines writing
	   text files, and for certain physical devices like terminals, the
	   single newline gets automatically translated by your C library into
	   a line feed and a carriage return, but normally, no translation is

       NFS Network File System, which allows you to mount a remote filesystem
	   as if it were local.

	   Converting a text string into an alternate but equivalent canonical
	   (or compatible) representation that can then be compared for
	   equivalence. Unicode recognizes four different normalization forms:
	   NFD, NFC, NFKD, and NFKC.

       null character
	   A character with the numeric value of zero. ItXs used by C to
	   terminate strings, but Perl allows strings to contain a null.

       null list
	   A list value with zero elements, represented in Perl by "()".

       null string
	   A string containing no characters, not to be confused with a string
	   containing a null character, which has a positive length and is

       numeric context
	   The situation in which an expression is expected by its
	   surroundings (the code calling it) to return a number.  See also
	   context and string context.

	   (Sometimes spelled nummification and nummify.) Perl lingo for
	   implicit conversion into a number; the related verb is numify.
	   Numification is intended to rhyme with mummification, and numify
	   with mummify. It is unrelated to English numen, numina, numinous.
	   We originally forgot the extra m a long time ago, and some people
	   got used to our funny spelling, and so just as with
	   "HTTP_REFERER"Xs own missing letter, our weird spelling has stuck

       NV  Short for Nevada, no part of which will ever be confused with
	   civilization. NV also means an internal floating- point Numeric
	   Value of the type a scalar can hold, not to be confused with an IV.

	   Half a byte, equivalent to one hexadecimal digit, and worth four

	   An instance of a class. Something that XknowsX what user-defined
	   type (class) it is, and what it can do because of what class it is.
	   Your program can request an object to do things, but the object
	   gets to decide whether it wants to do them or not. Some objects are
	   more accommodating than others.

	   A number in base 8. Only the digits 0 through 7 are allowed. Octal
	   constants in Perl start with 0, as in 013. See also the "oct"

	   How many things you have to skip over when moving from the
	   beginning of a string or array to a specific position within it.
	   Thus, the minimum offset is zero, not one, because you donXt skip
	   anything to get to the first item.

	   An entire computer program crammed into one line of text.

       open source software
	   Programs for which the source code is freely available and freely
	   redistributable, with no commercial strings attached.  For a more
	   detailed definition, see <>.

	   An expression that yields a value that an operator operates on. See
	   also precedence.

       operating system
	   A special program that runs on the bare machine and hides the gory
	   details of managing processes and devices.  Usually used in a
	   looser sense to indicate a particular culture of programming. The
	   loose sense can be used at varying levels of specificity.  At one
	   extreme, you might say that all versions of Unix and Unix-
	   lookalikes are the same operating system (upsetting many people,
	   especially lawyers and other advocates). At the other extreme, you
	   could say this particular version of this particular vendorXs
	   operating system is different from any other version of this or any
	   other vendorXs operating system. Perl is much more portable across
	   operating systems than many other languages. See also architecture
	   and platform.

	   A gizmo that transforms some number of input values to some number
	   of output values, often built into a language with a special syntax
	   or symbol. A given operator may have specific expectations about
	   what types of data you give as its arguments (operands) and what
	   type of data you want back from it.

       operator overloading
	   A kind of overloading that you can do on built-in operators to make
	   them work on objects as if the objects were ordinary scalar values,
	   but with the actual semantics supplied by the object class. This is
	   set up with the overload pragmaXsee Camel chapter 13,

	   See either switches or regular expression modifiers.

	   An abstract characterXs integer value. Same thing as codepoint.

	   Giving additional meanings to a symbol or construct.	 Actually, all
	   languages do overloading to one extent or another, since people are
	   good at figuring out things from context.

	   Hiding or invalidating some other definition of the same name. (Not
	   to be confused with overloading, which adds definitions that must
	   be disambiguated some other way.) To confuse the issue further, we
	   use the word with two overloaded definitions: to describe how you
	   can define your own subroutine to hide a built-in function of the
	   same name (see the section XOverriding Built-in FunctionsX in Camel
	   chapter 11, XModulesX), and to describe how you can define a
	   replacement method in a derived class to hide a base classXs method
	   of the same name (see Camel chapter 12, XObjectsX).

	   The one user (apart from the superuser) who has absolute control
	   over a file. A file may also have a group of users who may exercise
	   joint ownership if the real owner permits it. See permission bits.

	   A namespace for global variables, subroutines, and the like, such
	   that they can be kept separate from like-named symbols in other
	   namespaces. In a sense, only the package is global, since the
	   symbols in the packageXs symbol table are only accessible from code
	   compiled outside the package by naming the package. But in another
	   sense, all package symbols are also globalsXtheyXre just well-
	   organized globals.

       pad Short for scratchpad.

	   See argument.

       parent class
	   See base class.

       parse tree
	   See syntax tree.

	   The subtle but sometimes brutal art of attempting to turn your
	   possibly malformed program into a valid syntax tree.

	   To fix by applying one, as it were. In the realm of hackerdom, a
	   listing of the differences between two versions of a program as
	   might be applied by the patch(1) program when you want to fix a bug
	   or upgrade your old version.

	   The list of directories the system searches to find a program you
	   want to execute.  The list is stored as one of your environment
	   variables, accessible in Perl as $ENV{PATH}.

	   A fully qualified filename such as /usr/bin/perl. Sometimes
	   confused with "PATH".

	   A template used in pattern matching.

       pattern matching
	   Taking a pattern, usually a regular expression, and trying the
	   pattern various ways on a string to see whether thereXs any way to
	   make it fit. Often used to pick interesting tidbits out of a file.

	   The Perl Authors Upload SErver (<>), the
	   gateway for modules on their way to CPAN.

       Perl mongers
	   A Perl user group, taking the form of its name from the New York
	   Perl mongers, the first Perl user group. Find one near you at

       permission bits
	   Bits that the owner of a file sets or unsets to allow or disallow
	   access to other people. These flag bits are part of the mode word
	   returned by the "stat" built-in when you ask about a file. On Unix
	   systems, you can check the ls(1) manpage for more information.

	   What you get when you do "Perl++" twice. Doing it only once will
	   curl your hair. You have to increment it eight times to shampoo
	   your hair. Lather, rinse, iterate.

	   A direct connection that carries the output of one process to the
	   input of another without an intermediate temporary file.  Once the
	   pipe is set up, the two processes in question can read and write as
	   if they were talking to a normal file, with some caveats.

	   A series of processes all in a row, linked by pipes, where each
	   passes its output stream to the next.

	   The entire hardware and software context in which a program runs. A
	   program written in a platform-dependent language might break if you
	   change any of the following: machine, operating system, libraries,
	   compiler, or system configuration. The perl interpreter has to be
	   compiled differently for each platform because it is implemented in
	   C, but programs written in the Perl language are largely platform

       pod The markup used to embed documentation into your Perl code. Pod
	   stands for XPlain old documentationX. See Camel chapter 23, XPlain
	   Old DocumentationX.

       pod command
	   A sequence, such as "=head1", that denotes the start of a pod

	   A variable in a language like C that contains the exact memory
	   location of some other item. Perl handles pointers internally so
	   you donXt have to worry about them. Instead, you just use symbolic
	   pointers in the form of keys and variable names, or hard
	   references, which arenXt pointers (but act like pointers and do in
	   fact contain pointers).

	   The notion that you can tell an object to do something generic, and
	   the object will interpret the command in different ways depending
	   on its type. [< Greek XXXX- + XXXXX, many forms.]

	   The part of the address of a TCP or UDP socket that directs packets
	   to the correct process after finding the right machine, something
	   like the phone extension you give when you reach the company
	   operator. Also the result of converting code to run on a different
	   platform than originally intended, or the verb denoting this

	   Once upon a time, C code compilable under both BSD and SysV. In
	   general, code that can be easily converted to run on another
	   platform, where XeasilyX can be defined however you like, and
	   usually is.	Anything may be considered portable if you try hard
	   enough, such as a mobile home or London Bridge.

	   Someone who XcarriesX software from one platform to another.
	   Porting programs written in platform-dependent languages such as C
	   can be difficult work, but porting programs like Perl is very much
	   worth the agony.

	   Said of quantifiers and groups in patterns that refuse to give up
	   anything once theyXve gotten their mitts on it. Catchier and easier
	   to say than the even more formal nonbacktrackable.

	   The Portable Operating System Interface specification.

	   An operator that follows its operand, as in "$x++".

       pp  An internal shorthand for a Xpush- popX code; that is, C code
	   implementing PerlXs stack machine.

	   A standard module whose practical hints and suggestions are
	   received (and possibly ignored) at compile time. Pragmas are named
	   in all lowercase.

	   The rules of conduct that, in the absence of other guidance,
	   determine what should happen first.	For example, in the absence of
	   parentheses, you always do multiplication before addition.

	   An operator that precedes its operand, as in "++$x".

	   What some helper process did to transform the incoming data into a
	   form more suitable for the current process. Often done with an
	   incoming pipe. See also C preprocessor.

       primary maintainer
	   The author that PAUSE allows to assign co-maintainer permissions to
	   a namespace. A primary maintainer can give up this distinction by
	   assigning it to another PAUSE author. See Camel chapter 19, XCPANX.

	   A subroutine.

	   An instance of a running program. Under multitasking systems like
	   Unix, two or more separate processes could be running the same
	   program independently at the same timeXin fact, the "fork" function
	   is designed to bring about this happy state of affairs. Under other
	   operating systems, processes are sometimes called XthreadsX,
	   XtasksX, or XjobsX, often with slight nuances in meaning.

	   See script.

       program generator
	   A system that algorithmically writes code for you in a high-level
	   language. See also code generator.

       progressive matching
	   Pattern matching  matching>that picks up where it left off before.

	   See either instance variable or character property.

	   In networking, an agreed-upon way of sending messages back and
	   forth so that neither correspondent will get too confused.

	   An optional part of a subroutine declaration telling the Perl
	   compiler how many and what flavor of arguments may be passed as
	   actual arguments, so you can write subroutine calls that parse much
	   like built-in functions. (Or donXt parse, as the case may be.)

	   A construct that sometimes looks like a function but really isnXt.
	   Usually reserved for lvalue modifiers like "my", for context
	   modifiers like "scalar", and for the pick-your-own-quotes
	   constructs, "q//", "qq//", "qx//", "qw//", "qr//", "m//", "s///",
	   "y///", and "tr///".

	   Formerly, a reference to an array whose initial element happens to
	   hold a reference to a hash. You used to be able to treat a
	   pseudohash reference as either an array reference or a hash
	   reference. Pseduohashes are no longer supported.

	   An operator X"that looks something like a literal, such as the
	   output-grabbing operator, <literal moreinfo="none""`>"command""`".

       public domain
	   Something not owned by anybody. Perl is copyrighted and is thus not
	   in the public domainXitXs just freely available and freely

	   A notional XbatonX handed around the Perl community indicating who
	   is the lead integrator in some arena of development.

	   A pumpkin holder, the person in charge of pumping the pump, or at
	   least priming it. Must be willing to play the part of the Great
	   Pumpkin now and then.

       PV  A Xpointer valueX, which is Perl Internals Talk for a "char*".

	   Possessing a complete name. The symbol $Ent::moot is qualified;
	   $moot is unqualified. A fully qualified filename is specified from
	   the top-level directory.

	   A component of a regular expression specifying how many times the
	   foregoing atom may occur.

       race condition
	   A race condition exists when the result of several interrelated
	   events depends on the ordering of those events, but that order
	   cannot be guaranteed due to nondeterministic timing effects. If two
	   or more programs, or parts of the same program, try to go through
	   the same series of events, one might interrupt the work of the
	   other. This is a good way to find an exploit.

	   With respect to files, one that has the proper permission bit set
	   to let you access the file. With respect to computer programs, one
	   thatXs written well enough that someone has a chance of figuring
	   out what itXs trying to do.

	   The last rites performed by a parent process on behalf of a
	   deceased child process so that it doesnXt remain a zombie.  See the
	   "wait" and "waitpid" function calls.

	   A set of related data values in a file or stream, often associated
	   with a unique key field. In Unix, often commensurate with a line,
	   or a blank-lineXterminated set of lines (a XparagraphX).  Each line
	   of the /etc/passwd file is a record, keyed on login name,
	   containing information about that user.

	   The art of defining something (at least partly) in terms of itself,
	   which is a naughty no-no in dictionaries but often works out okay
	   in computer programs if youXre careful not to recurse forever
	   (which is like an infinite loop with more spectacular failure

	   Where you look to find a pointer to information somewhere else.
	   (See indirection.) References come in two flavors: symbolic
	   references and hard references.

	   Whatever a reference refers to, which may or may not have a name.
	   Common types of referents include scalars, arrays, hashes, and

	   See regular expression.

       regular expression
	   A single entity with various interpretations, like an elephant. To
	   a computer scientist, itXs a grammar for a little language in which
	   some strings are legal and others arenXt. To normal people, itXs a
	   pattern you can use to find what youXre looking for when it varies
	   from case to case. PerlXs regular expressions are far from regular
	   in the theoretical sense, but in regular use they work quite well.
	   HereXs a regular expression: "/Oh s.*t./". This will match strings
	   like X"Oh say can you see by the dawn's early light"X and X"Oh
	   sit!"X. See Camel chapter 5, XPattern MatchingX.

       regular expression modifier
	   An option on a pattern or substitution, such as "/i" to render the
	   pattern case- insensitive.

       regular file
	   A file thatXs not a directory, a device, a named pipe or socket, or
	   a symbolic link. Perl uses the "Xf" file test operator to identify
	   regular files. Sometimes called a XplainX file.

       relational operator
	   An operator that says whether a particular ordering relationship is
	   true about a pair of operands. Perl has both numeric and string
	   relational operators. See collating sequence.

       reserved words
	   A word with a specific, built-in meaning to a compiler, such as
	   "if" or "delete". In many languages (not Perl), itXs illegal to use
	   reserved words to name anything else. (Which is why theyXre
	   reserved, after all.) In Perl, you just canXt use them to name
	   labels or filehandles. Also called XkeywordsX.

       return value
	   The value produced by a subroutine or expression when evaluated. In
	   Perl, a return value may be either a list or a scalar.

       RFC Request For Comment, which despite the timid connotations is the
	   name of a series of important standards documents.

       right shift
	   A bit shift that divides a number by some power of 2.

	   A name for a concrete set of behaviors. A role is a way to add
	   behavior to a class without inheritance.

	   The superuser ("UID" == 0). Also the top-level directory of the

	   What you are told when someone thinks you should Read The Fine

       run phase
	   Any time after Perl starts running your main program.  See also
	   compile phase. Run phase is mostly spent in runtime but may also be
	   spent in compile time when "require", "do" "FILE", or "eval"
	   "STRING" operators are executed, or when a substitution uses the
	   "/ee" modifier.

	   The time when Perl is actually doing what your code says to do, as
	   opposed to the earlier period of time when it was trying to figure
	   out whether what you said made any sense whatsoever, which is
	   compile time.

       runtime pattern
	   A pattern that contains one or more variables to be interpolated
	   before parsing the pattern as a regular expression, and that
	   therefore cannot be analyzed at compile time, but must be
	   reanalyzed each time the pattern match operator is evaluated.
	   Runtime patterns are useful but expensive.

       RV  A recreational vehicle, not to be confused with vehicular
	   recreation. RV also means an internal Reference Value of the type a
	   scalar can hold. See also IV and NV if youXre not confused yet.

	   A value that you might find on the right side of an assignment. See
	   also lvalue.

	   A walled off area thatXs not supposed to affect beyond its walls.
	   You let kids play in the sandbox instead of running in the road.
	   See Camel chapter 20, XSecurityX.

	   A simple, singular value; a number, string, or reference.

       scalar context
	   The situation in which an expression is expected by its
	   surroundings (the code calling it) to return a single value rather
	   than a list of values. See also context and list context. A scalar
	   context sometimes imposes additional constraints on the return
	   valueXsee string context and numeric context. Sometimes we talk
	   about a Boolean context inside conditionals, but this imposes no
	   additional constraints, since any scalar value, whether numeric or
	   string, is already true or false.

       scalar literal
	   A number or quoted stringXan actual value in the text of your
	   program, as opposed to a variable.

       scalar value
	   A value that happens to be a scalar as opposed to a list.

       scalar variable
	   A variable prefixed with "$" that holds a single value.

	   From how far away you can see a variable, looking through one. Perl
	   has two visibility mechanisms. It does dynamic scoping of "local"
	   variables, meaning that the rest of the block, and any subroutines
	   that are called by the rest of the block, can see the variables
	   that are local to the block. Perl does lexical scoping of "my"
	   variables, meaning that the rest of the block can see the variable,
	   but other subroutines called by the block cannot see the variable.

	   The area in which a particular invocation of a particular file or
	   subroutine keeps some of its temporary values, including any
	   lexically scoped variables.

	   A text file that is a program intended to be executed directly
	   rather than compiled to another form of file before execution.

	   Also, in the context of Unicode, a writing system for a particular
	   language or group of languages, such as Greek, Bengali, or Tengwar.

       script kiddie
	   A cracker who is not a hacker but knows just enough to run canned
	   scripts. A cargo-cult programmer.

       sed A venerable Stream EDitor from which Perl derives some of its

	   A fancy kind of interlock that prevents multiple threads or
	   processes from using up the same resources simultaneously.

	   A character or string that keeps two surrounding strings from being
	   confused with each other. The "split" function works on separators.
	   Not to be confused with delimiters or terminators. The XorX in the
	   previous sentence separated the two alternatives.

	   Putting a fancy data structure into linear order so that it can be
	   stored as a string in a disk file or database, or sent through a
	   pipe. Also called marshalling.

	   In networking, a process that either advertises a service or just
	   hangs around at a known location and waits for clients who need
	   service to get in touch with it.

	   Something you do for someone else to make them happy, like giving
	   them the time of day (or of their life). On some machines, well-
	   known services are listed by the "getservent" function.

	   Same as setuid, only having to do with giving away group

	   Said of a program that runs with the privileges of its owner rather
	   than (as is usually the case) the privileges of whoever is running
	   it. Also describes the bit in the mode word (permission bits) that
	   controls the feature. This bit must be explicitly set by the owner
	   to enable this feature, and the program must be carefully written
	   not to give away more privileges than it ought to.

       shared memory
	   A piece of memory accessible by two different processes who
	   otherwise would not see each otherXs memory.

	   Irish for the whole McGillicuddy. In Perl culture, a portmanteau of
	   XsharpX and XbangX, meaning the "#!" sequence that tells the system
	   where to find the interpreter.

	   A command-line interpreter. The program that interactively gives
	   you a prompt, accepts one or more lines of input, and executes the
	   programs you mentioned, feeding each of them their proper arguments
	   and input data. Shells can also execute scripts containing such
	   commands. Under Unix, typical shells include the Bourne shell
	   (/bin/sh), the C shell (/bin/csh), and the Korn shell (/bin/ksh).
	   Perl is not strictly a shell because itXs not interactive (although
	   Perl programs can be interactive).

       side effects
	   Something extra that happens when you evaluate an expression.
	   Nowadays it can refer to almost anything. For example, evaluating a
	   simple assignment statement typically has the Xside effectX of
	   assigning a value to a variable. (And you thought assigning the
	   value was your primary intent in the first place!) Likewise,
	   assigning a value to the special variable $| ($AUTOFLUSH) has the
	   side effect of forcing a flush after every "write" or "print" on
	   the currently selected filehandle.

	   A glyph used in magic. Or, for Perl, the symbol in front of a
	   variable name, such as "$", "@", and "%".

	   A bolt out of the blue; that is, an event triggered by the
	   operating system, probably when youXre least expecting it.

       signal handler
	   A subroutine that, instead of being content to be called in the
	   normal fashion, sits around waiting for a bolt out of the blue
	   before it will deign to execute. Under Perl, bolts out of the blue
	   are called signals, and you send them with the "kill" built-in. See
	   the %SIG hash in Camel chapter 25, XSpecial NamesX and the section
	   XSignalsX in Camel chapter 15, XInterprocess CommunicationX.

       single inheritance
	   The features you got from your mother, if she told you that you
	   donXt have a father. (See also inheritance and multiple
	   inheritance.) In computer languages, the idea that classes
	   reproduce asexually so that a given class can only have one direct
	   ancestor or base class. Perl supplies no such restriction, though
	   you may certainly program Perl that way if you like.

	   A selection of any number of elements from a list, array, or hash.

	   To read an entire file into a string in one operation.

	   An endpoint for network communication among multiple processes that
	   works much like a telephone or a post office box. The most
	   important thing about a socket is its network address (like a phone
	   number). Different kinds of sockets have different kinds of
	   addressesXsome look like filenames, and some donXt.

       soft reference
	   See symbolic reference.

       source filter
	   A special kind of module that does preprocessing on your script
	   just before it gets to the tokener.

	   A device you can put things on the top of, and later take them back
	   off in the opposite order in which you put them on. See LIFO.

	   Included in the official Perl distribution, as in a standard
	   module, a standard tool, or a standard Perl manpage.

       standard error
	   The default output stream for nasty remarks that donXt belong in
	   standard output. Represented within a Perl program by the output>
	   filehandle "STDERR". You can use this stream explicitly, but the
	   "die" and "warn" built-ins write to your standard error stream
	   automatically (unless trapped or otherwise intercepted).

       standard input
	   The default input stream for your program, which if possible
	   shouldnXt care where its data is coming from. Represented within a
	   Perl program by the filehandle "STDIN".

       standard I/O
	   A standard C library for doing buffered input and output to the
	   operating system. (The XstandardX of standard I/O is at most
	   marginally related to the XstandardX of standard input and output.)
	   In general, Perl relies on whatever implementation of standard I/O
	   a given operating system supplies, so the buffering characteristics
	   of a Perl program on one machine may not exactly match those on
	   another machine.  Normally this only influences efficiency, not
	   semantics. If your standard I/O package is doing block buffering
	   and you want it to flush the buffer more often, just set the $|
	   variable to a true value.

       Standard Library
	   Everything that comes with the official perl distribution. Some
	   vendor versions of perl change their distributions, leaving out
	   some parts or including extras. See also dual-lived.

       standard output
	   The default output stream for your program, which if possible
	   shouldnXt care where its data is going. Represented within a Perl
	   program by the filehandle "STDOUT".

	   A command to the computer about what to do next, like a step in a
	   recipe: XAdd marmalade to batter and mix until mixed.X A statement
	   is distinguished from a declaration, which doesnXt tell the
	   computer to do anything, but just to learn something.

       statement modifier
	   A conditional or loop that you put after the statement instead of
	   before, if you know what we mean.

	   Varying slowly compared to something else. (Unfortunately,
	   everything is relatively stable compared to something else, except
	   for certain elementary particles, and weXre not so sure about
	   them.) In computers, where things are supposed to vary rapidly,
	   XstaticX has a derogatory connotation, indicating a slightly
	   dysfunctional variable, subroutine, or method. In Perl culture, the
	   word is politely avoided.

	   If youXre a C or C++ programmer, you might be looking for PerlXs
	   "state" keyword.

       static method
	   No such thing. See class method.

       static scoping
	   No such thing. See lexical scoping.

       static variable
	   No such thing. Just use a lexical variable in a scope larger than
	   your subroutine, or declare it with "state" instead of with "my".

       stat structure
	   A special internal spot in which Perl keeps the information about
	   the last file on which you requested information.

	   The value returned to the parent process when one of its child
	   processes dies. This value is placed in the special variable $?.
	   Its upper eight bits are the exit status of the defunct process,
	   and its lower eight bits identify the signal (if any) that the
	   process died from. On Unix systems, this status value is the same
	   as the status word returned by wait(2). See "system" in Camel
	   chapter 27, XFunctionsX.

	   See standard error.

	   See standard input.

	   See standard I/O.

	   See standard output.

	   A flow of data into or out of a process as a steady sequence of
	   bytes or characters, without the appearance of being broken up into
	   packets. This is a kind of interfaceXthe underlying implementation
	   may well break your data up into separate packets for delivery, but
	   this is hidden from you.

	   A sequence of characters such as XHe said !@#*&%@#*?!X.  A string
	   does not have to be entirely printable.

       string context
	   The situation in which an expression is expected by its
	   surroundings (the code calling it) to return a string.  See also
	   context and numeric context.

	   The process of producing a string representation of an abstract

	   C keyword introducing a structure definition or name.

	   See data structure.

	   See derived class.

	   A component of a regular expression pattern.

	   A named or otherwise accessible piece of program that can be
	   invoked from elsewhere in the program in order to accomplish some
	   subgoal of the program. A subroutine is often parameterized to
	   accomplish different but related things depending on its input
	   arguments. If the subroutine returns a meaningful value, it is also
	   called a function.

	   A value that indicates the position of a particular array element
	   in an array.

	   Changing parts of a string via the "s///" operator. (We avoid use
	   of this term to mean variable interpolation.)

	   A portion of a string, starting at a certain character position
	   (offset) and proceeding for a certain number of characters.

	   See base class.

	   The person whom the operating system will let do almost anything.
	   Typically your system administrator or someone pretending to be
	   your system administrator. On Unix systems, the root user. On
	   Windows systems, usually the Administrator user.

       SV  Short for Xscalar valueX. But within the Perl interpreter, every
	   referent is treated as a member of a class derived from SV, in an
	   object-oriented sort of way. Every value inside Perl is passed
	   around as a C language "SV*" pointer. The SV struct knows its own
	   Xreferent typeX, and the code is smart enough (we hope) not to try
	   to call a hash function on a subroutine.

	   An option you give on a command line to influence the way your
	   program works, usually introduced with a minus sign.	 The word is
	   also used as a nickname for a switch statement.

       switch cluster
	   The combination of multiple command- line switches (e.g., "Xa Xb
	   Xc") into one switch (e.g., "Xabc").	 Any switch with an additional
	   argument must be the last switch in a cluster.

       switch statement
	   A program technique that lets you evaluate an expression and then,
	   based on the value of the expression, do a multiway branch to the
	   appropriate piece of code for that value. Also called a Xcase
	   structureX, named after the similar Pascal construct. Most switch
	   statements in Perl are spelled "given". See XThe "given" statementX
	   in Camel chapter 4, XStatements and DeclarationsX.

	   Generally, any token or metasymbol. Often used more specifically to
	   mean the sort of name you might find in a symbol table.

       symbolic debugger
	   A program that lets you step through the execution of your program,
	   stopping or printing things out here and there to see whether
	   anything has gone wrong, and, if so, what. The XsymbolicX part just
	   means that you can talk to the debugger using the same symbols with
	   which your program is written.

       symbolic link
	   An alternate filename that points to the real filename, which in
	   turn points to the real file. Whenever the operating system is
	   trying to parse a pathname containing a symbolic link, it merely
	   substitutes the new name and continues parsing.

       symbolic reference
	   A variable whose value is the name of another variable or
	   subroutine. By dereferencing the first variable, you can get at the
	   second one. Symbolic references are illegal under "use strict

       symbol table
	   Where a compiler remembers symbols. A program like Perl must
	   somehow remember all the names of all the variables, filehandles,
	   and subroutines youXve used. It does this by placing the names in a
	   symbol table, which is implemented in Perl using a hash table.
	   There is a separate symbol table for each package to give each
	   package its own namespace.

	   Programming in which the orderly sequence of events can be
	   determined; that is, when things happen one after the other, not at
	   the same time.

       syntactic sugar
	   An alternative way of writing something more easily; a shortcut.

	   From Greek XXXXXXXX, Xwith-arrangementX. How things (particularly
	   symbols) are put together with each other.

       syntax tree
	   An internal representation of your program wherein lower-level
	   constructs dangle off the higher-level constructs enclosing them.

	   A function call directly to the operating system. Many of the
	   important subroutines and functions you use arenXt direct system
	   calls, but are built up in one or more layers above the system call
	   level. In general, Perl programmers donXt need to worry about the
	   distinction. However, if you do happen to know which Perl functions
	   are really syscalls, you can predict which of these will set the $!
	   ($ERRNO) variable on failure. Unfortunately, beginning programmers
	   often confusingly employ the term Xsystem callX to mean what
	   happens when you call the Perl "system" function, which actually
	   involves many syscalls. To avoid any confusion, we nearly always
	   say XsyscallX for something you could call indirectly via PerlXs
	   "syscall" function, and never for something you would call with
	   PerlXs "system" function.

       taint checks
	   The special bookkeeping Perl does to track the flow of external
	   data through your program and disallow their use in system

	   Said of data derived from the grubby hands of a user, and thus
	   unsafe for a secure program to rely on. Perl does taint checks if
	   you run a setuid (or setgid) program, or if you use the "XT"

       taint mode
	   Running under the "XT" switch, marking all external data as suspect
	   and refusing to use it with system commands. See Camel chapter 20,

       TCP Short for Transmission Control Protocol. A protocol wrapped around
	   the Internet Protocol to make an unreliable packet transmission
	   mechanism appear to the application program to be a reliable stream
	   of bytes.  (Usually.)

	   Short for a XterminalXXthat is, a leaf node of a syntax tree. A
	   thing that functions grammatically as an operand for the operators
	   in an expression.

	   A character or string that marks the end of another string. The $/
	   variable contains the string that terminates a "readline"
	   operation, which "chomp" deletes from the end. Not to be confused
	   with delimiters or separators. The period at the end of this
	   sentence is a terminator.

	   An operator taking three operands. Sometimes pronounced trinary.

	   A string or file containing primarily printable characters.

	   Like a forked process, but without forkXs inherent memory
	   protection. A thread is lighter weight than a full process, in that
	   a process could have multiple threads running around in it, all
	   fighting over the same processXs memory space unless steps are
	   taken to protect threads from one another.

       tie The bond between a magical variable and its implementation class.
	   See the "tie" function in Camel chapter 27, XFunctionsX and Camel
	   chapter 14, XTied VariablesX.

	   The case used for capitals that are followed by lowercase
	   characters instead of by more capitals.  Sometimes called sentence
	   case or headline case. English doesnXt use Unicode titlecase, but
	   casing rules for English titles are more complicated than simply
	   capitalizing each wordXs first character.

	   ThereXs More Than One Way To Do It, the Perl Motto. The notion that
	   there can be more than one valid path to solving a programming
	   problem in context. (This doesnXt mean that more ways are always
	   better or that all possible paths are equally desirableXjust that
	   there need not be One True Way.)

	   A morpheme in a programming language, the smallest unit of text
	   with semantic significance.

	   A module that breaks a program text into a sequence of tokens for
	   later analysis by a parser.

	   Splitting up a program text into tokens. Also known as XlexingX, in
	   which case you get XlexemesX instead of tokens.

       toolbox approach
	   The notion that, with a complete set of simple tools that work well
	   together, you can build almost anything you want. Which is fine if
	   youXre assembling a tricycle, but if youXre building a
	   defranishizing comboflux regurgalator, you really want your own
	   machine shop in which to build special tools. Perl is sort of a
	   machine shop.

	   The thing youXre working on. Structures like "while(<>)", "for",
	   "foreach", and "given" set the topic for you by assigning to $_,
	   the default (topic) variable.

	   To turn one string representation into another by mapping each
	   character of the source string to its corresponding character in
	   the result string. Not to be confused with translation: for
	   example, Greek XXXXXXXXXX transliterates into polychromos but
	   translates into many-colored. See the "tr///" operator in Camel
	   chapter 5, XPattern MatchingX.

	   An event that causes a handler to be run.

	   Not a stellar system with three stars, but an operator taking three
	   operands. Sometimes pronounced ternary.

	   A venerable typesetting language from which Perl derives the name
	   of its $% variable and which is secretly used in the production of
	   Camel books.

	   Any scalar value that doesnXt evaluate to 0 or "".

	   Emptying a file of existing contents, either automatically when
	   opening a file for writing or explicitly via the "truncate"

	   See data type and class.

       type casting
	   Converting data from one type to another. C permits this.  Perl
	   does not need it. Nor want it.

	   A type definition in the C and C++ languages.

       typed lexical
	   A lexical variable  lexical>that is declared with a class type: "my
	   Pony $bill".

	   Use of a single identifier, prefixed with "*". For example, *name
	   stands for any or all of $name, @name, %name, &name, or just
	   "name". How you use it determines whether it is interpreted as all
	   or only one of them. See XTypeglobs and FilehandlesX in Camel
	   chapter 2, XBits and PiecesX.

	   A description of how C types may be transformed to and from Perl
	   types within an extension module written in XS.

       UDP User Datagram Protocol, the typical way to send datagrams over the

       UID A user ID. Often used in the context of file or process ownership.

	   A mask of those permission bits that should be forced off when
	   creating files or directories, in order to establish a policy of
	   whom youXll ordinarily deny access to. See the "umask" function.

       unary operator
	   An operator with only one operand, like "!" or "chdir". Unary
	   operators are usually prefix operators; that is, they precede their
	   operand. The "++" and "XX" operators can be either prefix or
	   postfix. (Their position does change their meanings.)

	   A character set comprising all the major character sets of the
	   world, more or less. See <>.

	   A very large and constantly evolving language with several
	   alternative and largely incompatible syntaxes, in which anyone can
	   define anything any way they choose, and usually do. Speakers of
	   this language think itXs easy to learn because itXs so easily
	   twisted to oneXs own ends, but dialectical differences make tribal
	   intercommunication nearly impossible, and travelers are often
	   reduced to a pidgin-like subset of the language. To be universally
	   understood, a Unix shell programmer must spend years of study in
	   the art. Many have abandoned this discipline and now communicate
	   via an Esperanto-like language called Perl.

	   In ancient times, Unix was also used to refer to some code that a
	   couple of people at Bell Labs wrote to make use of a PDP-7 computer
	   that wasnXt doing much of anything else at the time.

	   In Unicode, not just characters with the General Category of
	   Uppercase Letter, but any character with the Uppercase property,
	   including some Letter Numbers and Symbols. Not to be confused with

	   An actual piece of data, in contrast to all the variables,
	   references, keys, indices, operators, and whatnot that you need to
	   access the value.

	   A named storage location that can hold any of various kinds of
	   value, as your program sees fit.

       variable interpolation
	   The interpolation of a scalar or array variable into a string.

	   Said of a function that happily receives an indeterminate number of
	   actual arguments.

	   Mathematical jargon for a list of scalar values.

	   Providing the appearance of something without the reality, as in:
	   virtual memory is not real memory. (See also memory.) The opposite
	   of XvirtualX is XtransparentX, which means providing the reality of
	   something without the appearance, as in: Perl handles the variable-
	   length UTFX8 character encoding transparently.

       void context
	   A form of scalar context in which an expression is not expected to
	   return any value at all and is evaluated for its side effects

	   A XversionX or XvectorX string specified with a "v" followed by a
	   series of decimal integers in dot notation, for instance,
	   "v1.20.300.4000". Each number turns into a character with the
	   specified ordinal value. (The "v" is optional when there are at
	   least three integers.)

	   A message printed to the "STDERR" stream to the effect that
	   something might be wrong but isnXt worth blowing up over. See
	   "warn" in Camel chapter 27, XFunctionsX and the "warnings" pragma
	   in Camel chapter 28, XPragmantic ModulesX.

       watch expression
	   An expression which, when its value changes, causes a breakpoint in
	   the Perl debugger.

       weak reference
	   A reference that doesnXt get counted normally. When all the normal
	   references to data disappear, the data disappears. These are useful
	   for circular references that would never disappear otherwise.

	   A character that moves your cursor but doesnXt otherwise put
	   anything on your screen. Typically refers to any of: space, tab,
	   line feed, carriage return, or form feed. In Unicode, matches many
	   other characters that Unicode considers whitespace, including the
	   X-XX .

	   In normal XcomputereseX, the piece of data of the size most
	   efficiently handled by your computer, typically 32 bits or so, give
	   or take a few powers of 2. In Perl culture, it more often refers to
	   an alphanumeric identifier (including underscores), or to a string
	   of nonwhitespace characters bounded by whitespace or string

       working directory
	   Your current directory, from which relative pathnames are
	   interpreted by the operating system. The operating system knows
	   your current directory because you told it with a "chdir", or
	   because you started out in the place where your parent process was
	   when you were born.

	   A program or subroutine that runs some other program or subroutine
	   for you, modifying some of its input or output to better suit your

	   What You See Is What You Get. Usually used when something that
	   appears on the screen matches how it will eventually look, like
	   PerlXs "format" declarations. Also used to mean the opposite of
	   magic because everything works exactly as it appears, as in the
	   three- argument form of "open".

       XS  An extraordinarily exported, expeditiously excellent, expressly
	   eXternal Subroutine, executed in existing C or C++ or in an
	   exciting extension language called (exasperatingly) XS.

	   An external subroutine defined in XS.

	   Yet Another Compiler Compiler. A parser generator without which
	   Perl probably would not have existed. See the file perly.y in the
	   Perl source distribution.

       zero width
	   A subpattern assertion matching the null string between characters.

	   A process that has died (exited) but whose parent has not yet
	   received proper notification of its demise by virtue of having
	   called "wait" or "waitpid". If you "fork", you must clean up after
	   your child processes when they exit; otherwise, the process table
	   will fill up and your system administrator will Not Be Happy with

       Based on the Glossary of Programming Perl, Fourth Edition, by Tom
       Christiansen, brian d foy, Larry Wall, & Jon Orwant.  Copyright (c)
       2000, 1996, 1991, 2012 O'Reilly Media, Inc.  This document may be
       distributed under the same terms as Perl itself.

perl v5.18.2			  2014-01-06		   PERLGLOSSARY(1perl)

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