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


       perlglossary - Perl Glossary


       version 5.20210411


       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. Pseudohashes 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 v5.34.0                      2021-05-04                 PERLGLOSSARY(1pm)

perl 5.34.0 - Generated Sat Feb 26 05:35:38 CST 2022
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