1perlglossary(3)       User Contributed Perl Documentation      perlglossary(3)
2
3
4

NAME

6       perlglossary - Perl Glossary
7

VERSION

9       version 5.20180605
10

DESCRIPTION

12       A glossary of terms (technical and otherwise) used in the Perl
13       documentation, derived from the Glossary of Programming Perl, Fourth
14       Edition.  Words or phrases in bold are defined elsewhere in this
15       glossary.
16
17       Other useful sources include the Unicode Glossary
18       <http://unicode.org/glossary/>, the Free On-Line Dictionary of
19       Computing <http://foldoc.org/>, the Jargon File
20       <http://catb.org/~esr/jargon/>, and Wikipedia
21       <http://www.wikipedia.org/>.
22
23   A
24       accessor methods
25           A method used to indirectly inspect or update an object’s state
26           (its instance variables).
27
28       actual arguments
29           The scalar values that you supply to a function or subroutine when
30           you call it. For instance, when you call "power("puff")", the
31           string "puff" is the actual argument. See also argument and formal
32           arguments.
33
34       address operator
35           Some languages work directly with the memory addresses of values,
36           but this can be like playing with fire. Perl provides a set of
37           asbestos gloves for handling all memory management. The closest to
38           an address operator in Perl is the backslash operator, but it gives
39           you a hard reference, which is much safer than a memory address.
40
41       algorithm
42           A well-defined sequence of steps, explained clearly enough that
43           even a computer could do them.
44
45       alias
46           A nickname for something, which behaves in all ways as though you’d
47           used the original name instead of the nickname. Temporary aliases
48           are implicitly created in the loop variable for "foreach" loops, in
49           the $_ variable for "map" or "grep" operators, in $a and $b during
50           "sort"’s comparison function, and in each element of @_ for the
51           actual arguments of a subroutine call. Permanent aliases are
52           explicitly created in packages by importing symbols or by
53           assignment to typeglobs. Lexically scoped aliases for package
54           variables are explicitly created by the "our" declaration.
55
56       alphabetic
57           The sort of characters we put into words. In Unicode, this is all
58           letters including all ideographs and certain diacritics, letter
59           numbers like Roman numerals, and various combining marks.
60
61       alternatives
62           A list of possible choices from which you may select only one, as
63           in, “Would you like door A, B, or C?” Alternatives in regular
64           expressions are separated with a single vertical bar: "|".
65           Alternatives in normal Perl expressions are separated with a double
66           vertical bar: "||". Logical alternatives in Boolean expressions are
67           separated with either "||" or "or".
68
69       anonymous
70           Used to describe a referent that is not directly accessible through
71           a named variable. Such a referent must be indirectly accessible
72           through at least one hard reference. When the last hard reference
73           goes away, the anonymous referent is destroyed without pity.
74
75       application
76           A bigger, fancier sort of program with a fancier name so people
77           don’t realize they are using a program.
78
79       architecture
80           The kind of computer you’re working on, where one “kind of
81           computer” means all those computers sharing a compatible machine
82           language.  Since Perl programs are (typically) simple text files,
83           not executable images, a Perl program is much less sensitive to the
84           architecture it’s running on than programs in other languages, such
85           as C, that are compiled into machine code. See also platform and
86           operating system.
87
88       argument
89           A piece of data supplied to a program, subroutine, function, or
90           method to tell it what it’s supposed to do. Also called a
91           “parameter”.
92
93       ARGV
94           The name of the array containing the argument vector from the
95           command line. If you use the empty "<>" operator, "ARGV" is the
96           name of both the filehandle used to traverse the arguments and the
97           scalar containing the name of the current input file.
98
99       arithmetical operator
100           A symbol such as "+" or "/" that tells Perl to do the arithmetic
101           you were supposed to learn in grade school.
102
103       array
104           An ordered sequence of values, stored such that you can easily
105           access any of the values using an integer subscript that specifies
106           the value’s offset in the sequence.
107
108       array context
109           An archaic expression for what is more correctly referred to as
110           list context.
111
112       Artistic License
113           The open source license that Larry Wall created for Perl,
114           maximizing Perl’s usefulness, availability, and modifiability. The
115           current version is 2.
116           (<http://www.opensource.org/licenses/artistic-license.php>).
117
118       ASCII
119           The American Standard Code for Information Interchange (a 7-bit
120           character set adequate only for poorly representing English text).
121           Often used loosely to describe the lowest 128 values of the various
122           ISO-8859-X character sets, a bunch of mutually incompatible 8-bit
123           codes best described as half ASCII. See also Unicode.
124
125       assertion
126           A component of a regular expression that must be true for the
127           pattern to match but does not necessarily match any characters
128           itself. Often used specifically to mean a zero-width assertion.
129
130       assignment
131           An operator whose assigned mission in life is to change the value
132           of a variable.
133
134       assignment operator
135           Either a regular assignment or a compound operator composed of an
136           ordinary assignment and some other operator, that changes the value
137           of a variable in place; that is, relative to its old value. For
138           example, "$a += 2" adds 2 to $a.
139
140       associative array
141           See hash. Please. The term associative array is the old Perl 4 term
142           for a hash. Some languages call it a dictionary.
143
144       associativity
145           Determines whether you do the left operator first or the right
146           operator first when you have “A operator B operator C”, and the two
147           operators are of the same precedence. Operators like "+" are left
148           associative, while operators like "**" are right associative. See
149           Camel chapter 3, “Unary and Binary Operators” for a list of
150           operators and their associativity.
151
152       asynchronous
153           Said of events or activities whose relative temporal ordering is
154           indeterminate because too many things are going on at once. Hence,
155           an asynchronous event is one you didn’t know when to expect.
156
157       atom
158           A regular expression component potentially matching a substring
159           containing one or more characters and treated as an indivisible
160           syntactic unit by any following quantifier. (Contrast with an
161           assertion that matches something of zero width and may not be
162           quantified.)
163
164       atomic operation
165           When Democritus gave the word “atom” to the indivisible bits of
166           matter, he meant literally something that could not be cut: ἀ-
167           (not) + -τομος (cuttable). An atomic operation is an action that
168           can’t be interrupted, not one forbidden in a nuclear-free zone.
169
170       attribute
171           A new feature that allows the declaration of variables and
172           subroutines with modifiers, as in "sub foo : locked method". Also
173           another name for an instance variable of an object.
174
175       autogeneration
176           A feature of operator overloading of objects, whereby the behavior
177           of certain operators can be reasonably deduced using more
178           fundamental operators. This assumes that the overloaded operators
179           will often have the same relationships as the regular operators.
180           See Camel chapter 13, “Overloading”.
181
182       autoincrement
183           To add one to something automatically, hence the name of the "++"
184           operator. To instead subtract one from something automatically is
185           known as an “autodecrement”.
186
187       autoload
188           To load on demand. (Also called “lazy” loading.)  Specifically, to
189           call an "AUTOLOAD" subroutine on behalf of an undefined subroutine.
190
191       autosplit
192           To split a string automatically, as the –a switch does when running
193           under –p or –n in order to emulate awk. (See also the "AutoSplit"
194           module, which has nothing to do with the "–a" switch but a lot to
195           do with autoloading.)
196
197       autovivification
198           A Graeco-Roman word meaning “to bring oneself to life”.  In Perl,
199           storage locations (lvalues) spontaneously generate themselves as
200           needed, including the creation of any hard reference values to
201           point to the next level of storage. The assignment
202           "$a[5][5][5][5][5] = "quintet"" potentially creates five scalar
203           storage locations, plus four references (in the first four scalar
204           locations) pointing to four new anonymous arrays (to hold the last
205           four scalar locations). But the point of autovivification is that
206           you don’t have to worry about it.
207
208       AV  Short for “array value”, which refers to one of Perl’s internal
209           data types that holds an array. The "AV" type is a subclass of SV.
210
211       awk Descriptive editing term—short for “awkward”. Also coincidentally
212           refers to a venerable text-processing language from which Perl
213           derived some of its high-level ideas.
214
215   B
216       backreference
217           A substring captured by a subpattern within unadorned parentheses
218           in a regex. Backslashed decimal numbers ("\1", "\2", etc.) later in
219           the same pattern refer back to the corresponding subpattern in the
220           current match. Outside the pattern, the numbered variables ($1, $2,
221           etc.) continue to refer to these same values, as long as the
222           pattern was the last successful match of the current dynamic scope.
223
224       backtracking
225           The practice of saying, “If I had to do it all over, I’d do it
226           differently,” and then actually going back and doing it all over
227           differently. Mathematically speaking, it’s returning from an
228           unsuccessful recursion on a tree of possibilities. Perl backtracks
229           when it attempts to match patterns with a regular expression, and
230           its earlier attempts don’t pan out. See the section “The Little
231           Engine That /Couldn(n’t)” in Camel chapter 5, “Pattern Matching”.
232
233       backward compatibility
234           Means you can still run your old program because we didn’t break
235           any of the features or bugs it was relying on.
236
237       bareword
238           A word sufficiently ambiguous to be deemed illegal under "use
239           strict 'subs'". In the absence of that stricture, a bareword is
240           treated as if quotes were around it.
241
242       base class
243           A generic object type; that is, a class from which other, more
244           specific classes are derived genetically by inheritance. Also
245           called a “superclass” by people who respect their ancestors.
246
247       big-endian
248           From Swift: someone who eats eggs big end first. Also used of
249           computers that store the most significant byte of a word at a lower
250           byte address than the least significant byte. Often considered
251           superior to little-endian machines. See also little-endian.
252
253       binary
254           Having to do with numbers represented in base 2. That means there’s
255           basically two numbers: 0 and 1. Also used to describe a file of
256           “nontext”, presumably because such a file makes full use of all the
257           binary bits in its bytes. With the advent of Unicode, this
258           distinction, already suspect, loses even more of its meaning.
259
260       binary operator
261           An operator that takes two operands.
262
263       bind
264           To assign a specific network address to a socket.
265
266       bit An integer in the range from 0 to 1, inclusive. The smallest
267           possible unit of information storage. An eighth of a byte or of a
268           dollar.  (The term “Pieces of Eight” comes from being able to split
269           the old Spanish dollar into 8 bits, each of which still counted for
270           money. That’s why a 25- cent piece today is still “two bits”.)
271
272       bit shift
273           The movement of bits left or right in a computer word, which has
274           the effect of multiplying or dividing by a power of 2.
275
276       bit string
277           A sequence of bits that is actually being thought of as a sequence
278           of bits, for once.
279
280       bless
281           In corporate life, to grant official approval to a thing, as in,
282           “The VP of Engineering has blessed our WebCruncher project.”
283           Similarly, in Perl, to grant official approval to a referent so
284           that it can function as an object, such as a WebCruncher object.
285           See the "bless" function in Camel chapter 27, “Functions”.
286
287       block
288           What a process does when it has to wait for something: “My process
289           blocked waiting for the disk.” As an unrelated noun, it refers to a
290           large chunk of data, of a size that the operating system likes to
291           deal with (normally a power of 2 such as 512 or 8192). Typically
292           refers to a chunk of data that’s coming from or going to a disk
293           file.
294
295       BLOCK
296           A syntactic construct consisting of a sequence of Perl statements
297           that is delimited by braces.  The "if" and "while" statements are
298           defined in terms of "BLOCK"s, for instance. Sometimes we also say
299           “block” to mean a lexical scope; that is, a sequence of statements
300           that acts like a "BLOCK", such as within an "eval" or a file, even
301           though the statements aren’t delimited by braces.
302
303       block buffering
304           A method of making input and output efficient by passing one block
305           at a time. By default, Perl does block buffering to disk files. See
306           buffer and command buffering.
307
308       Boolean
309           A value that is either true or false.
310
311       Boolean context
312           A special kind of scalar context used in conditionals to decide
313           whether the scalar value returned by an expression is true or
314           false. Does not evaluate as either a string or a number. See
315           context.
316
317       breakpoint
318           A spot in your program where you’ve told the debugger to stop
319           execution so you can poke around and see whether anything is wrong
320           yet.
321
322       broadcast
323           To send a datagram to multiple destinations simultaneously.
324
325       BSD A psychoactive drug, popular in the ’80s, probably developed at UC
326           Berkeley or thereabouts. Similar in many ways to the prescription-
327           only medication called “System V”, but infinitely more useful. (Or,
328           at least, more fun.) The full chemical name is “Berkeley Standard
329           Distribution”.
330
331       bucket
332           A location in a hash table containing (potentially) multiple
333           entries whose keys “hash” to the same hash value according to its
334           hash function. (As internal policy, you don’t have to worry about
335           it unless you’re into internals, or policy.)
336
337       buffer
338           A temporary holding location for data. Data that are Block
339           buffering means that the data is passed on to its destination
340           whenever the buffer is full. Line buffering means that it’s passed
341           on whenever a complete line is received. Command buffering means
342           that it’s passed every time you do a "print" command (or
343           equivalent). If your output is unbuffered, the system processes it
344           one byte at a time without the use of a holding area. This can be
345           rather inefficient.
346
347       built-in
348           A function that is predefined in the language. Even when hidden by
349           overriding, you can always get at a built- in function by
350           qualifying its name with the "CORE::" pseudopackage.
351
352       bundle
353           A group of related modules on CPAN. (Also sometimes refers to a
354           group of command-line switches grouped into one switch cluster.)
355
356       byte
357           A piece of data worth eight bits in most places.
358
359       bytecode
360           A pidgin-like lingo spoken among ’droids when they don’t wish to
361           reveal their orientation (see endian). Named after some similar
362           languages spoken (for similar reasons) between compilers and
363           interpreters in the late 20ᵗʰ century. These languages are
364           characterized by representing everything as a nonarchitecture-
365           dependent sequence of bytes.
366
367   C
368       C   A language beloved by many for its inside-out type definitions,
369           inscrutable precedence rules, and heavy overloading of the
370           function-call mechanism. (Well, actually, people first switched to
371           C because they found lowercase identifiers easier to read than
372           upper.) Perl is written in C, so it’s not surprising that Perl
373           borrowed a few ideas from it.
374
375       cache
376           A data repository. Instead of computing expensive answers several
377           times, compute it once and save the result.
378
379       callback
380           A handler that you register with some other part of your program in
381           the hope that the other part of your program will trigger your
382           handler when some event of interest transpires.
383
384       call by reference
385           An argument-passing mechanism in which the formal arguments refer
386           directly to the actual arguments, and the subroutine can change the
387           actual arguments by changing the formal arguments. That is, the
388           formal argument is an alias for the actual argument. See also call
389           by value.
390
391       call by value
392           An argument-passing mechanism in which the formal arguments refer
393           to a copy of the actual arguments, and the subroutine cannot change
394           the actual arguments by changing the formal arguments. See also
395           call by reference.
396
397       canonical
398           Reduced to a standard form to facilitate comparison.
399
400       capture variables
401           The variables—such as $1 and $2, and "%+" and "%– "—that hold the
402           text remembered in a pattern match. See Camel chapter 5, “Pattern
403           Matching”.
404
405       capturing
406           The use of parentheses around a subpattern in a regular expression
407           to store the matched substring as a backreference. (Captured
408           strings are also returned as a list in list context.) See Camel
409           chapter 5, “Pattern Matching”.
410
411       cargo cult
412           Copying and pasting code without understanding it, while
413           superstitiously believing in its value. This term originated from
414           preindustrial cultures dealing with the detritus of explorers and
415           colonizers of technologically advanced cultures. See The Gods Must
416           Be Crazy.
417
418       case
419           A property of certain characters. Originally, typesetter stored
420           capital letters in the upper of two cases and small letters in the
421           lower one. Unicode recognizes three cases: lowercase (character
422           property "\p{lower}"), titlecase ("\p{title}"), and uppercase
423           ("\p{upper}"). A fourth casemapping called foldcase is not itself a
424           distinct case, but it is used internally to implement casefolding.
425           Not all letters have case, and some nonletters have case.
426
427       casefolding
428           Comparing or matching a string case-insensitively. In Perl, it is
429           implemented with the "/i" pattern modifier, the "fc" function, and
430           the "\F" double-quote translation escape.
431
432       casemapping
433           The process of converting a string to one of the four Unicode
434           casemaps; in Perl, it is implemented with the "fc", "lc",
435           "ucfirst", and "uc" functions.
436
437       character
438           The smallest individual element of a string. Computers store
439           characters as integers, but Perl lets you operate on them as text.
440           The integer used to represent a particular character is called that
441           character’s codepoint.
442
443       character class
444           A square-bracketed list of characters used in a regular expression
445           to indicate that any character of the set may occur at a given
446           point. Loosely, any predefined set of characters so used.
447
448       character property
449           A predefined character class matchable by the "\p" or "\P"
450           metasymbol. Unicode defines hundreds of standard properties for
451           every possible codepoint, and Perl defines a few of its own, too.
452
453       circumfix operator
454           An operator that surrounds its operand, like the angle operator, or
455           parentheses, or a hug.
456
457       class
458           A user-defined type, implemented in Perl via a package that
459           provides (either directly or by inheritance) methods (that is,
460           subroutines) to handle instances of the class (its objects). See
461           also inheritance.
462
463       class method
464           A method whose invocant is a package name, not an object reference.
465           A method associated with the class as a whole. Also see instance
466           method.
467
468       client
469           In networking, a process that initiates contact with a server
470           process in order to exchange data and perhaps receive a service.
471
472       closure
473           An anonymous subroutine that, when a reference to it is generated
474           at runtime, keeps track of the identities of externally visible
475           lexical variables, even after those lexical variables have
476           supposedly gone out of scope. They’re called “closures” because
477           this sort of behavior gives mathematicians a sense of closure.
478
479       cluster
480           A parenthesized subpattern used to group parts of a regular
481           expression into a single atom.
482
483       CODE
484           The word returned by the "ref" function when you apply it to a
485           reference to a subroutine. See also CV.
486
487       code generator
488           A system that writes code for you in a low-level language, such as
489           code to implement the backend of a compiler. See program generator.
490
491       codepoint
492           The integer a computer uses to represent a given character. ASCII
493           codepoints are in the range 0 to 127; Unicode codepoints are in the
494           range 0 to 0x1F_FFFF; and Perl codepoints are in the range 0 to
495           2³²−1 or 0 to 2⁶⁴−1, depending on your native integer size. In Perl
496           Culture, sometimes called ordinals.
497
498       code subpattern
499           A regular expression subpattern whose real purpose is to execute
500           some Perl code—for example, the "(?{...})" and "(??{...})"
501           subpatterns.
502
503       collating sequence
504           The order into which characters sort. This is used by string
505           comparison routines to decide, for example, where in this glossary
506           to put “collating sequence”.
507
508       co-maintainer
509           A person with permissions to index a namespace in PAUSE. Anyone can
510           upload any namespace, but only primary and co-maintainers get their
511           contributions indexed.
512
513       combining character
514           Any character with the General Category of Combining Mark
515           ("\p{GC=M}"), which may be spacing or nonspacing. Some are even
516           invisible. A sequence of combining characters following a grapheme
517           base character together make up a single user-visible character
518           called a grapheme. Most but not all diacritics are combining
519           characters, and vice versa.
520
521       command
522           In shell programming, the syntactic combination of a program name
523           and its arguments. More loosely, anything you type to a shell (a
524           command interpreter) that starts it doing something. Even more
525           loosely, a Perl statement, which might start with a label and
526           typically ends with a semicolon.
527
528       command buffering
529           A mechanism in Perl that lets you store up the output of each Perl
530           command and then flush it out as a single request to the operating
531           system. It’s enabled by setting the $| ($AUTOFLUSH) variable to a
532           true value. It’s used when you don’t want data sitting around, not
533           going where it’s supposed to, which may happen because the default
534           on a file or pipe is to use block buffering.
535
536       command-line arguments
537           The values you supply along with a program name when you tell a
538           shell to execute a command.  These values are passed to a Perl
539           program through @ARGV.
540
541       command name
542           The name of the program currently executing, as typed on the
543           command line. In C, the command name is passed to the program as
544           the first command-line argument. In Perl, it comes in separately as
545           $0.
546
547       comment
548           A remark that doesn’t affect the meaning of the program.  In Perl,
549           a comment is introduced by a "#" character and continues to the end
550           of the line.
551
552       compilation unit
553           The file (or string, in the case of "eval") that is currently being
554           compiled.
555
556       compile
557           The process of turning source code into a machine-usable form. See
558           compile phase.
559
560       compile phase
561           Any time before Perl starts running your main program. See also run
562           phase. Compile phase is mostly spent in compile time, but may also
563           be spent in runtime when "BEGIN" blocks, "use" or "no"
564           declarations, or constant subexpressions are being evaluated. The
565           startup and import code of any "use" declaration is also run during
566           compile phase.
567
568       compiler
569           Strictly speaking, a program that munches up another program and
570           spits out yet another file containing the program in a “more
571           executable” form, typically containing native machine instructions.
572           The perl program is not a compiler by this definition, but it does
573           contain a kind of compiler that takes a program and turns it into a
574           more executable form (syntax trees) within the perl process itself,
575           which the interpreter then interprets. There are, however,
576           extension modules to get Perl to act more like a “real” compiler.
577           See Camel chapter 16, “Compiling”.
578
579       compile time
580           The time when Perl is trying to make sense of your code, as opposed
581           to when it thinks it knows what your code means and is merely
582           trying to do what it thinks your code says to do, which is runtime.
583
584       composer
585           A “constructor” for a referent that isn’t really an object, like an
586           anonymous array or a hash (or a sonata, for that matter).  For
587           example, a pair of braces acts as a composer for a hash, and a pair
588           of brackets acts as a composer for an array. See the section
589           “Creating References” in Camel chapter 8, “References”.
590
591       concatenation
592           The process of gluing one cat’s nose to another cat’s tail. Also a
593           similar operation on two strings.
594
595       conditional
596           Something “iffy”. See Boolean context.
597
598       connection
599           In telephony, the temporary electrical circuit between the caller’s
600           and the callee’s phone. In networking, the same kind of temporary
601           circuit between a client and a server.
602
603       construct
604           As a noun, a piece of syntax made up of smaller pieces. As a
605           transitive verb, to create an object using a constructor.
606
607       constructor
608           Any class method, instance, or subroutine that composes,
609           initializes, blesses, and returns an object. Sometimes we use the
610           term loosely to mean a composer.
611
612       context
613           The surroundings or environment. The context given by the
614           surrounding code determines what kind of data a particular
615           expression is expected to return. The three primary contexts are
616           list context, scalar, and void context. Scalar context is sometimes
617           subdivided into Boolean context, numeric context, string context,
618           and void context. There’s also a “don’t care” context (which is
619           dealt with in Camel chapter 2, “Bits and Pieces”, if you care).
620
621       continuation
622           The treatment of more than one physical line as a single logical
623           line. Makefile lines are continued by putting a backslash before
624           the newline. Mail headers, as defined by RFC 822, are continued by
625           putting a space or tab after the newline. In general, lines in Perl
626           do not need any form of continuation mark, because whitespace
627           (including newlines) is gleefully ignored. Usually.
628
629       core dump
630           The corpse of a process, in the form of a file left in the working
631           directory of the process, usually as a result of certain kinds of
632           fatal errors.
633
634       CPAN
635           The Comprehensive Perl Archive Network. (See the Camel Preface and
636           Camel chapter 19, “CPAN” for details.)
637
638       C preprocessor
639           The typical C compiler’s first pass, which processes lines
640           beginning with "#" for conditional compilation and macro
641           definition, and does various manipulations of the program text
642           based on the current definitions. Also known as cpp(1).
643
644       cracker
645           Someone who breaks security on computer systems. A cracker may be a
646           true hacker or only a script kiddie.
647
648       currently selected output channel
649           The last filehandle that was designated with "select(FILEHANDLE)";
650           "STDOUT", if no filehandle has been selected.
651
652       current package
653           The package in which the current statement is compiled. Scan
654           backward in the text of your program through the current lexical
655           scope or any enclosing lexical scopes until you find a package
656           declaration. That’s your current package name.
657
658       current working directory
659           See working directory.
660
661       CV  In academia, a curriculum vitæ, a fancy kind of résumé. In Perl, an
662           internal “code value” typedef holding a subroutine. The "CV" type
663           is a subclass of SV.
664
665   D
666       dangling statement
667           A bare, single statement, without any braces, hanging off an "if"
668           or "while" conditional. C allows them. Perl doesn’t.
669
670       datagram
671           A packet of data, such as a UDP message, that (from the viewpoint
672           of the programs involved) can be sent independently over the
673           network. (In fact, all packets are sent independently at the IP
674           level, but stream protocols such as TCP hide this from your
675           program.)
676
677       data structure
678           How your various pieces of data relate to each other and what shape
679           they make when you put them all together, as in a rectangular table
680           or a triangular tree.
681
682       data type
683           A set of possible values, together with all the operations that
684           know how to deal with those values. For example, a numeric data
685           type has a certain set of numbers that you can work with, as well
686           as various mathematical operations that you can do on the numbers,
687           but would make little sense on, say, a string such as "Kilroy".
688           Strings have their own operations, such as concatenation. Compound
689           types made of a number of smaller pieces generally have operations
690           to compose and decompose them, and perhaps to rearrange them.
691           Objects that model things in the real world often have operations
692           that correspond to real activities. For instance, if you model an
693           elevator, your elevator object might have an "open_door" method.
694
695       DBM Stands for “Database Management” routines, a set of routines that
696           emulate an associative array using disk files. The routines use a
697           dynamic hashing scheme to locate any entry with only two disk
698           accesses. DBM files allow a Perl program to keep a persistent hash
699           across multiple invocations. You can "tie" your hash variables to
700           various DBM implementations.
701
702       declaration
703           An assertion that states something exists and perhaps describes
704           what it’s like, without giving any commitment as to how or where
705           you’ll use it. A declaration is like the part of your recipe that
706           says, “two cups flour, one large egg, four or five tadpoles…” See
707           statement for its opposite. Note that some declarations also
708           function as statements. Subroutine declarations also act as
709           definitions if a body is supplied.
710
711       declarator
712           Something that tells your program what sort of variable you’d like.
713           Perl doesn’t require you to declare variables, but you can use
714           "my", "our", or "state" to denote that you want something other
715           than the default.
716
717       decrement
718           To subtract a value from a variable, as in “decrement $x” (meaning
719           to remove 1 from its value) or “decrement $x by 3”.
720
721       default
722           A value chosen for you if you don’t supply a value of your own.
723
724       defined
725           Having a meaning. Perl thinks that some of the things people try to
726           do are devoid of meaning; in particular, making use of variables
727           that have never been given a value and performing certain
728           operations on data that isn’t there. For example, if you try to
729           read data past the end of a file, Perl will hand you back an
730           undefined value. See also false and the "defined" entry in Camel
731           chapter 27, “Functions”.
732
733       delimiter
734           A character or string that sets bounds to an arbitrarily sized
735           textual object, not to be confused with a separator or terminator.
736           “To delimit” really just means “to surround” or “to enclose” (like
737           these parentheses are doing).
738
739       dereference
740           A fancy computer science term meaning “to follow a reference to
741           what it points to”. The “de” part of it refers to the fact that
742           you’re taking away one level of indirection.
743
744       derived class
745           A class that defines some of its methods in terms of a more generic
746           class, called a base class. Note that classes aren’t classified
747           exclusively into base classes or derived classes: a class can
748           function as both a derived class and a base class simultaneously,
749           which is kind of classy.
750
751       descriptor
752           See file descriptor.
753
754       destroy
755           To deallocate the memory of a referent (first triggering its
756           "DESTROY" method, if it has one).
757
758       destructor
759           A special method that is called when an object is thinking about
760           destroying itself. A Perl program’s "DESTROY" method doesn’t do the
761           actual destruction; Perl just triggers the method in case the class
762           wants to do any associated cleanup.
763
764       device
765           A whiz-bang hardware gizmo (like a disk or tape drive or a modem or
766           a joystick or a mouse) attached to your computer, which the
767           operating system tries to make look like a file (or a bunch of
768           files).  Under Unix, these fake files tend to live in the /dev
769           directory.
770
771       directive
772           A pod directive. See Camel chapter 23, “Plain Old Documentation”.
773
774       directory
775           A special file that contains other files. Some operating systems
776           call these “folders”, “drawers”, “catalogues”, or “catalogs”.
777
778       directory handle
779           A name that represents a particular instance of opening a directory
780           to read it, until you close it. See the "opendir" function.
781
782       discipline
783           Some people need this and some people avoid it.  For Perl, it’s an
784           old way to say I/O layer.
785
786       dispatch
787           To send something to its correct destination. Often used
788           metaphorically to indicate a transfer of programmatic control to a
789           destination selected algorithmically, often by lookup in a table of
790           function references or, in the case of object methods, by
791           traversing the inheritance tree looking for the most specific
792           definition for the method.
793
794       distribution
795           A standard, bundled release of a system of software. The default
796           usage implies source code is included. If that is not the case, it
797           will be called a “binary-only” distribution.
798
799       dual-lived
800           Some modules live both in the Standard Library and on CPAN. These
801           modules might be developed on two tracks as people modify either
802           version. The trend currently is to untangle these situations.
803
804       dweomer
805           An enchantment, illusion, phantasm, or jugglery. Said when Perl’s
806           magical dwimmer effects don’t do what you expect, but rather seem
807           to be the product of arcane dweomercraft, sorcery, or wonder
808           working. [From Middle English.]
809
810       dwimmer
811           DWIM is an acronym for “Do What I Mean”, the principle that
812           something should just do what you want it to do without an undue
813           amount of fuss. A bit of code that does “dwimming” is a “dwimmer”.
814           Dwimming can require a great deal of behind-the-scenes magic, which
815           (if it doesn’t stay properly behind the scenes) is called a dweomer
816           instead.
817
818       dynamic scoping
819           Dynamic scoping works over a dynamic scope, making variables
820           visible throughout the rest of the block in which they are first
821           used and in any subroutines that are called by the rest of the
822           block. Dynamically scoped variables can have their values
823           temporarily changed (and implicitly restored later) by a "local"
824           operator.  (Compare lexical scoping.) Used more loosely to mean how
825           a subroutine that is in the middle of calling another subroutine
826           “contains” that subroutine at runtime.
827
828   E
829       eclectic
830           Derived from many sources. Some would say too many.
831
832       element
833           A basic building block. When you’re talking about an array, it’s
834           one of the items that make up the array.
835
836       embedding
837           When something is contained in something else, particularly when
838           that might be considered surprising: “I’ve embedded a complete Perl
839           interpreter in my editor!”
840
841       empty subclass test
842           The notion that an empty derived class should behave exactly like
843           its base class.
844
845       encapsulation
846           The veil of abstraction separating the interface from the
847           implementation (whether enforced or not), which mandates that all
848           access to an object’s state be through methods alone.
849
850       endian
851           See little-endian and big-endian.
852
853       en passant
854           When you change a value as it is being copied. [From French “in
855           passing”, as in the exotic pawn-capturing maneuver in chess.]
856
857       environment
858           The collective set of environment variables your process inherits
859           from its parent. Accessed via %ENV.
860
861       environment variable
862           A mechanism by which some high-level agent such as a user can pass
863           its preferences down to its future offspring (child processes,
864           grandchild processes, great-grandchild processes, and so on). Each
865           environment variable is a key/value pair, like one entry in a hash.
866
867       EOF End of File. Sometimes used metaphorically as the terminating
868           string of a here document.
869
870       errno
871           The error number returned by a syscall when it fails. Perl refers
872           to the error by the name $! (or $OS_ERROR if you use the English
873           module).
874
875       error
876           See exception or fatal error.
877
878       escape sequence
879           See metasymbol.
880
881       exception
882           A fancy term for an error. See fatal error.
883
884       exception handling
885           The way a program responds to an error. The exception-handling
886           mechanism in Perl is the "eval" operator.
887
888       exec
889           To throw away the current process’s program and replace it with
890           another, without exiting the process or relinquishing any resources
891           held (apart from the old memory image).
892
893       executable file
894           A file that is specially marked to tell the operating system that
895           it’s okay to run this file as a program.  Usually shortened to
896           “executable”.
897
898       execute
899           To run a program or subroutine. (Has nothing to do with the "kill"
900           built-in, unless you’re trying to run a signal handler.)
901
902       execute bit
903           The special mark that tells the operating system it can run this
904           program. There are actually three execute bits under Unix, and
905           which bit gets used depends on whether you own the file singularly,
906           collectively, or not at all.
907
908       exit status
909           See status.
910
911       exploit
912           Used as a noun in this case, this refers to a known way to
913           compromise a program to get it to do something the author didn’t
914           intend.  Your task is to write unexploitable programs.
915
916       export
917           To make symbols from a module available for import by other
918           modules.
919
920       expression
921           Anything you can legally say in a spot where a value is required.
922           Typically composed of literals, variables, operators, functions,
923           and subroutine calls, not necessarily in that order.
924
925       extension
926           A Perl module that also pulls in compiled C or C++ code. More
927           generally, any experimental option that can be compiled into Perl,
928           such as multithreading.
929
930   F
931       false
932           In Perl, any value that would look like "" or "0" if evaluated in a
933           string context. Since undefined values evaluate to "", all
934           undefined values are false, but not all false values are undefined.
935
936       FAQ Frequently Asked Question (although not necessarily frequently
937           answered, especially if the answer appears in the Perl FAQ shipped
938           standard with Perl).
939
940       fatal error
941           An uncaught exception, which causes termination of the process
942           after printing a message on your standard error stream. Errors that
943           happen inside an "eval" are not fatal. Instead, the "eval"
944           terminates after placing the exception message in the $@
945           ($EVAL_ERROR) variable.  You can try to provoke a fatal error with
946           the "die" operator (known as throwing or raising an exception), but
947           this may be caught by a dynamically enclosing "eval". If not
948           caught, the "die" becomes a fatal error.
949
950       feeping creaturism
951           A spoonerism of “creeping featurism”, noting the biological urge to
952           add just one more feature to a program.
953
954       field
955           A single piece of numeric or string data that is part of a longer
956           string, record, or line. Variable-width fields are usually split up
957           by separators (so use "split" to extract the fields), while fixed-
958           width fields are usually at fixed positions (so use "unpack").
959           Instance variables are also known as “fields”.
960
961       FIFO
962           First In, First Out. See also LIFO. Also a nickname for a named
963           pipe.
964
965       file
966           A named collection of data, usually stored on disk in a directory
967           in a filesystem. Roughly like a document, if you’re into office
968           metaphors. In modern filesystems, you can actually give a file more
969           than one name. Some files have special properties, like directories
970           and devices.
971
972       file descriptor
973           The little number the operating system uses to keep track of which
974           opened file you’re talking about.  Perl hides the file descriptor
975           inside a standard I/O stream and then attaches the stream to a
976           filehandle.
977
978       fileglob
979           A “wildcard” match on filenames. See the "glob" function.
980
981       filehandle
982           An identifier (not necessarily related to the real name of a file)
983           that represents a particular instance of opening a file, until you
984           close it. If you’re going to open and close several different files
985           in succession, it’s fine to open each of them with the same
986           filehandle, so you don’t have to write out separate code to process
987           each file.
988
989       filename
990           One name for a file. This name is listed in a directory. You can
991           use it in an "open" to tell the operating system exactly which file
992           you want to open, and associate the file with a filehandle, which
993           will carry the subsequent identity of that file in your program,
994           until you close it.
995
996       filesystem
997           A set of directories and files residing on a partition of the disk.
998           Sometimes known as a “partition”. You can change the file’s name or
999           even move a file around from directory to directory within a
1000           filesystem without actually moving the file itself, at least under
1001           Unix.
1002
1003       file test operator
1004           A built-in unary operator that you use to determine whether
1005           something is true about a file, such as "–o $filename" to test
1006           whether you’re the owner of the file.
1007
1008       filter
1009           A program designed to take a stream of input and transform it into
1010           a stream of output.
1011
1012       first-come
1013           The first PAUSE author to upload a namespace automatically becomes
1014           the primary maintainer for that namespace. The “first come”
1015           permissions distinguish a primary maintainer who was assigned that
1016           role from one who received it automatically.
1017
1018       flag
1019           We tend to avoid this term because it means so many things.  It may
1020           mean a command-line switch that takes no argument itself (such as
1021           Perl’s "–n" and "–p" flags) or, less frequently, a single-bit
1022           indicator (such as the "O_CREAT" and "O_EXCL" flags used in
1023           "sysopen"). Sometimes informally used to refer to certain regex
1024           modifiers.
1025
1026       floating point
1027           A method of storing numbers in “scientific notation”, such that the
1028           precision of the number is independent of its magnitude (the
1029           decimal point “floats”). Perl does its numeric work with floating-
1030           point numbers (sometimes called “floats”) when it can’t get away
1031           with using integers. Floating-point numbers are mere approximations
1032           of real numbers.
1033
1034       flush
1035           The act of emptying a buffer, often before it’s full.
1036
1037       FMTEYEWTK
1038           Far More Than Everything You Ever Wanted To Know. An exhaustive
1039           treatise on one narrow topic, something of a super-FAQ. See Tom for
1040           far more.
1041
1042       foldcase
1043           The casemap used in Unicode when comparing or matching without
1044           regard to case. Comparing lower-, title-, or uppercase are all
1045           unreliable due to Unicode’s complex, one-to-many case mappings.
1046           Foldcase is a lowercase variant (using a partially decomposed
1047           normalization form for certain codepoints) created specifically to
1048           resolve this.
1049
1050       fork
1051           To create a child process identical to the parent process at its
1052           moment of conception, at least until it gets ideas of its own. A
1053           thread with protected memory.
1054
1055       formal arguments
1056           The generic names by which a subroutine knows its arguments. In
1057           many languages, formal arguments are always given individual names;
1058           in Perl, the formal arguments are just the elements of an array.
1059           The formal arguments to a Perl program are $ARGV[0], $ARGV[1], and
1060           so on. Similarly, the formal arguments to a Perl subroutine are
1061           $_[0], $_[1], and so on. You may give the arguments individual
1062           names by assigning the values to a "my" list. See also actual
1063           arguments.
1064
1065       format
1066           A specification of how many spaces and digits and things to put
1067           somewhere so that whatever you’re printing comes out nice and
1068           pretty.
1069
1070       freely available
1071           Means you don’t have to pay money to get it, but the copyright on
1072           it may still belong to someone else (like Larry).
1073
1074       freely redistributable
1075           Means you’re not in legal trouble if you give a bootleg copy of it
1076           to your friends and we find out about it. In fact, we’d rather you
1077           gave a copy to all your friends.
1078
1079       freeware
1080           Historically, any software that you give away, particularly if you
1081           make the source code available as well. Now often called open
1082           source software. Recently there has been a trend to use the term in
1083           contradistinction to open source software, to refer only to free
1084           software released under the Free Software Foundation’s GPL (General
1085           Public License), but this is difficult to justify etymologically.
1086
1087       function
1088           Mathematically, a mapping of each of a set of input values to a
1089           particular output value. In computers, refers to a subroutine or
1090           operator that returns a value. It may or may not have input values
1091           (called arguments).
1092
1093       funny character
1094           Someone like Larry, or one of his peculiar friends. Also refers to
1095           the strange prefixes that Perl requires as noun markers on its
1096           variables.
1097
1098   G
1099       garbage collection
1100           A misnamed feature—it should be called, “expecting your mother to
1101           pick up after you”. Strictly speaking, Perl doesn’t do this, but it
1102           relies on a reference-counting mechanism to keep things tidy.
1103           However, we rarely speak strictly and will often refer to the
1104           reference-counting scheme as a form of garbage collection. (If it’s
1105           any comfort, when your interpreter exits, a “real” garbage
1106           collector runs to make sure everything is cleaned up if you’ve been
1107           messy with circular references and such.)
1108
1109       GID Group ID—in Unix, the numeric group ID that the operating system
1110           uses to identify you and members of your group.
1111
1112       glob
1113           Strictly, the shell’s "*" character, which will match a “glob” of
1114           characters when you’re trying to generate a list of filenames.
1115           Loosely, the act of using globs and similar symbols to do pattern
1116           matching.  See also fileglob and typeglob.
1117
1118       global
1119           Something you can see from anywhere, usually used of variables and
1120           subroutines that are visible everywhere in your program.  In Perl,
1121           only certain special variables are truly global—most variables (and
1122           all subroutines) exist only in the current package.  Global
1123           variables can be declared with "our". See “Global Declarations” in
1124           Camel chapter 4, “Statements and Declarations”.
1125
1126       global destruction
1127           The garbage collection of globals (and the running of any
1128           associated object destructors) that takes place when a Perl
1129           interpreter is being shut down. Global destruction should not be
1130           confused with the Apocalypse, except perhaps when it should.
1131
1132       glue language
1133           A language such as Perl that is good at hooking things together
1134           that weren’t intended to be hooked together.
1135
1136       granularity
1137           The size of the pieces you’re dealing with, mentally speaking.
1138
1139       grapheme
1140           A graphene is an allotrope of carbon arranged in a hexagonal
1141           crystal lattice one atom thick. A grapheme, or more fully, a
1142           grapheme cluster string is a single user-visible character, which
1143           may in turn be several characters (codepoints) long. For example, a
1144           carriage return plus a line feed is a single grapheme but two
1145           characters, while a “ȫ” is a single grapheme but one, two, or even
1146           three characters, depending on normalization.
1147
1148       greedy
1149           A subpattern whose quantifier wants to match as many things as
1150           possible.
1151
1152       grep
1153           Originally from the old Unix editor command for “Globally search
1154           for a Regular Expression and Print it”, now used in the general
1155           sense of any kind of search, especially text searches. Perl has a
1156           built-in "grep" function that searches a list for elements matching
1157           any given criterion, whereas the grep(1) program searches for lines
1158           matching a regular expression in one or more files.
1159
1160       group
1161           A set of users of which you are a member. In some operating systems
1162           (like Unix), you can give certain file access permissions to other
1163           members of your group.
1164
1165       GV  An internal “glob value” typedef, holding a typeglob. The "GV" type
1166           is a subclass of SV.
1167
1168   H
1169       hacker
1170           Someone who is brilliantly persistent in solving technical
1171           problems, whether these involve golfing, fighting orcs, or
1172           programming.  Hacker is a neutral term, morally speaking. Good
1173           hackers are not to be confused with evil crackers or clueless
1174           script kiddies. If you confuse them, we will presume that you are
1175           either evil or clueless.
1176
1177       handler
1178           A subroutine or method that Perl calls when your program needs to
1179           respond to some internal event, such as a signal, or an encounter
1180           with an operator subject to operator overloading. See also
1181           callback.
1182
1183       hard reference
1184           A scalar value containing the actual address of a referent, such
1185           that the referent’s reference count accounts for it. (Some hard
1186           references are held internally, such as the implicit reference from
1187           one of a typeglob’s variable slots to its corresponding referent.)
1188           A hard reference is different from a symbolic reference.
1189
1190       hash
1191           An unordered association of key/value pairs, stored such that you
1192           can easily use a string key to look up its associated data value.
1193           This glossary is like a hash, where the word to be defined is the
1194           key and the definition is the value. A hash is also sometimes
1195           septisyllabically called an “associative array”, which is a pretty
1196           good reason for simply calling it a “hash” instead.
1197
1198       hash table
1199           A data structure used internally by Perl for implementing
1200           associative arrays (hashes) efficiently. See also bucket.
1201
1202       header file
1203           A file containing certain required definitions that you must
1204           include “ahead” of the rest of your program to do certain obscure
1205           operations. A C header file has a .h extension. Perl doesn’t really
1206           have header files, though historically Perl has sometimes used
1207           translated .h files with a .ph extension. See "require" in Camel
1208           chapter 27, “Functions”. (Header files have been superseded by the
1209           module mechanism.)
1210
1211       here document
1212           So called because of a similar construct in shells that pretends
1213           that the lines following the command are a separate file to be fed
1214           to the command, up to some terminating string. In Perl, however,
1215           it’s just a fancy form of quoting.
1216
1217       hexadecimal
1218           A number in base 16, “hex” for short. The digits for 10 through 15
1219           are customarily represented by the letters "a" through "f".
1220           Hexadecimal constants in Perl start with "0x". See also the "hex"
1221           function in Camel chapter 27, “Functions”.
1222
1223       home directory
1224           The directory you are put into when you log in. On a Unix system,
1225           the name is often placed into $ENV{HOME} or $ENV{LOGDIR} by login,
1226           but you can also find it with "(get""pwuid($<))[7]". (Some
1227           platforms do not have a concept of a home directory.)
1228
1229       host
1230           The computer on which a program or other data resides.
1231
1232       hubris
1233           Excessive pride, the sort of thing for which Zeus zaps you.  Also
1234           the quality that makes you write (and maintain) programs that other
1235           people won’t want to say bad things about. Hence, the third great
1236           virtue of a programmer. See also laziness and impatience.
1237
1238       HV  Short for a “hash value” typedef, which holds Perl’s internal
1239           representation of a hash. The "HV" type is a subclass of SV.
1240
1241   I
1242       identifier
1243           A legally formed name for most anything in which a computer program
1244           might be interested. Many languages (including Perl) allow
1245           identifiers to start with an alphabetic character, and then contain
1246           alphabetics and digits. Perl also allows connector punctuation like
1247           the underscore character wherever it allows alphabetics. (Perl also
1248           has more complicated names, like qualified names.)
1249
1250       impatience
1251           The anger you feel when the computer is being lazy.  This makes you
1252           write programs that don’t just react to your needs, but actually
1253           anticipate them. Or at least that pretend to. Hence, the second
1254           great virtue of a programmer. See also laziness and hubris.
1255
1256       implementation
1257           How a piece of code actually goes about doing its job. Users of the
1258           code should not count on implementation details staying the same
1259           unless they are part of the published interface.
1260
1261       import
1262           To gain access to symbols that are exported from another module.
1263           See "use" in Camel chapter 27, “Functions”.
1264
1265       increment
1266           To increase the value of something by 1 (or by some other number,
1267           if so specified).
1268
1269       indexing
1270           In olden days, the act of looking up a key in an actual index (such
1271           as a phone book). But now it's merely the act of using any kind of
1272           key or position to find the corresponding value, even if no index
1273           is involved. Things have degenerated to the point that Perl’s
1274           "index" function merely locates the position (index) of one string
1275           in another.
1276
1277       indirect filehandle
1278           An expression that evaluates to something that can be used as a
1279           filehandle: a string (filehandle name), a typeglob, a typeglob
1280           reference, or a low-level IO object.
1281
1282       indirection
1283           If something in a program isn’t the value you’re looking for but
1284           indicates where the value is, that’s indirection. This can be done
1285           with either symbolic references or hard.
1286
1287       indirect object
1288           In English grammar, a short noun phrase between a verb and its
1289           direct object indicating the beneficiary or recipient of the
1290           action. In Perl, "print STDOUT "$foo\n";" can be understood as
1291           “verb indirect-object object”, where "STDOUT" is the recipient of
1292           the "print" action, and "$foo" is the object being printed.
1293           Similarly, when invoking a method, you might place the invocant in
1294           the dative slot between the method and its arguments:
1295
1296               $gollum = new Pathetic::Creature "Sméagol";
1297               give $gollum "Fisssssh!";
1298               give $gollum "Precious!";
1299
1300       indirect object slot
1301           The syntactic position falling between a method call and its
1302           arguments when using the indirect object invocation syntax. (The
1303           slot is distinguished by the absence of a comma between it and the
1304           next argument.) "STDERR" is in the indirect object slot here:
1305
1306               print STDERR "Awake! Awake! Fear, Fire, Foes! Awake!\n";
1307
1308       infix
1309           An operator that comes in between its operands, such as
1310           multiplication in "24 * 7".
1311
1312       inheritance
1313           What you get from your ancestors, genetically or otherwise. If you
1314           happen to be a class, your ancestors are called base classes and
1315           your descendants are called derived classes. See single inheritance
1316           and multiple inheritance.
1317
1318       instance
1319           Short for “an instance of a class”, meaning an object of that
1320           class.
1321
1322       instance data
1323           See instance variable.
1324
1325       instance method
1326           A method of an object, as opposed to a class method.
1327
1328           A method whose invocant is an object, not a package name. Every
1329           object of a class shares all the methods of that class, so an
1330           instance method applies to all instances of the class, rather than
1331           applying to a particular instance. Also see class method.
1332
1333       instance variable
1334           An attribute of an object; data stored with the particular object
1335           rather than with the class as a whole.
1336
1337       integer
1338           A number with no fractional (decimal) part. A counting number, like
1339           1, 2, 3, and so on, but including 0 and the negatives.
1340
1341       interface
1342           The services a piece of code promises to provide forever, in
1343           contrast to its implementation, which it should feel free to change
1344           whenever it likes.
1345
1346       interpolation
1347           The insertion of a scalar or list value somewhere in the middle of
1348           another value, such that it appears to have been there all along.
1349           In Perl, variable interpolation happens in double-quoted strings
1350           and patterns, and list interpolation occurs when constructing the
1351           list of values to pass to a list operator or other such construct
1352           that takes a "LIST".
1353
1354       interpreter
1355           Strictly speaking, a program that reads a second program and does
1356           what the second program says directly without turning the program
1357           into a different form first, which is what compilers do. Perl is
1358           not an interpreter by this definition, because it contains a kind
1359           of compiler that takes a program and turns it into a more
1360           executable form (syntax trees) within the perl process itself,
1361           which the Perl runtime system then interprets.
1362
1363       invocant
1364           The agent on whose behalf a method is invoked. In a class method,
1365           the invocant is a package name. In an instance method, the invocant
1366           is an object reference.
1367
1368       invocation
1369           The act of calling up a deity, daemon, program, method, subroutine,
1370           or function to get it to do what you think it’s supposed to do.  We
1371           usually “call” subroutines but “invoke” methods, since it sounds
1372           cooler.
1373
1374       I/O Input from, or output to, a file or device.
1375
1376       IO  An internal I/O object. Can also mean indirect object.
1377
1378       I/O layer
1379           One of the filters between the data and what you get as input or
1380           what you end up with as output.
1381
1382       IPA India Pale Ale. Also the International Phonetic Alphabet, the
1383           standard alphabet used for phonetic notation worldwide. Draws
1384           heavily on Unicode, including many combining characters.
1385
1386       IP  Internet Protocol, or Intellectual Property.
1387
1388       IPC Interprocess Communication.
1389
1390       is-a
1391           A relationship between two objects in which one object is
1392           considered to be a more specific version of the other, generic
1393           object: “A camel is a mammal.” Since the generic object really only
1394           exists in a Platonic sense, we usually add a little abstraction to
1395           the notion of objects and think of the relationship as being
1396           between a generic base class and a specific derived class. Oddly
1397           enough, Platonic classes don’t always have Platonic relationships—
1398           see inheritance.
1399
1400       iteration
1401           Doing something repeatedly.
1402
1403       iterator
1404           A special programming gizmo that keeps track of where you are in
1405           something that you’re trying to iterate over. The "foreach" loop in
1406           Perl contains an iterator; so does a hash, allowing you to "each"
1407           through it.
1408
1409       IV  The integer four, not to be confused with six, Tom’s favorite
1410           editor. IV also means an internal Integer Value of the type a
1411           scalar can hold, not to be confused with an NV.
1412
1413   J
1414       JAPH
1415           “Just Another Perl Hacker”, a clever but cryptic bit of Perl code
1416           that, when executed, evaluates to that string. Often used to
1417           illustrate a particular Perl feature, and something of an ongoing
1418           Obfuscated Perl Contest seen in USENET signatures.
1419
1420   K
1421       key The string index to a hash, used to look up the value associated
1422           with that key.
1423
1424       keyword
1425           See reserved words.
1426
1427   L
1428       label
1429           A name you give to a statement so that you can talk about that
1430           statement elsewhere in the program.
1431
1432       laziness
1433           The quality that makes you go to great effort to reduce overall
1434           energy expenditure. It makes you write labor-saving programs that
1435           other people will find useful, and then document what you wrote so
1436           you don’t have to answer so many questions about it. Hence, the
1437           first great virtue of a programmer. Also hence, this book. See also
1438           impatience and hubris.
1439
1440       leftmost longest
1441           The preference of the regular expression engine to match the
1442           leftmost occurrence of a pattern, then given a position at which a
1443           match will occur, the preference for the longest match (presuming
1444           the use of a greedy quantifier). See Camel chapter 5, “Pattern
1445           Matching” for much more on this subject.
1446
1447       left shift
1448           A bit shift that multiplies the number by some power of 2.
1449
1450       lexeme
1451           Fancy term for a token.
1452
1453       lexer
1454           Fancy term for a tokener.
1455
1456       lexical analysis
1457           Fancy term for tokenizing.
1458
1459       lexical scoping
1460           Looking at your Oxford English Dictionary through a microscope.
1461           (Also known as static scoping, because dictionaries don’t change
1462           very fast.) Similarly, looking at variables stored in a private
1463           dictionary (namespace) for each scope, which are visible only from
1464           their point of declaration down to the end of the lexical scope in
1465           which they are declared. —Syn.  static scoping. —Ant. dynamic
1466           scoping.
1467
1468       lexical variable
1469           A variable subject to lexical scoping, declared by "my". Often just
1470           called a “lexical”. (The "our" declaration declares a lexically
1471           scoped name for a global variable, which is not itself a lexical
1472           variable.)
1473
1474       library
1475           Generally, a collection of procedures. In ancient days, referred to
1476           a collection of subroutines in a .pl file. In modern times, refers
1477           more often to the entire collection of Perl modules on your system.
1478
1479       LIFO
1480           Last In, First Out. See also FIFO. A LIFO is usually called a
1481           stack.
1482
1483       line
1484           In Unix, a sequence of zero or more nonnewline characters
1485           terminated with a newline character. On non-Unix machines, this is
1486           emulated by the C library even if the underlying operating system
1487           has different ideas.
1488
1489       linebreak
1490           A grapheme consisting of either a carriage return followed by a
1491           line feed or any character with the Unicode Vertical Space
1492           character property.
1493
1494       line buffering
1495           Used by a standard I/O output stream that flushes its buffer after
1496           every newline. Many standard I/O libraries automatically set up
1497           line buffering on output that is going to the terminal.
1498
1499       line number
1500           The number of lines read previous to this one, plus 1. Perl keeps a
1501           separate line number for each source or input file it opens. The
1502           current source file’s line number is represented by "__LINE__". The
1503           current input line number (for the file that was most recently read
1504           via "<FH>") is represented by the $. ($INPUT_LINE_NUMBER) variable.
1505           Many error messages report both values, if available.
1506
1507       link
1508           Used as a noun, a name in a directory that represents a file. A
1509           given file can have multiple links to it. It’s like having the same
1510           phone number listed in the phone directory under different names.
1511           As a verb, to resolve a partially compiled file’s unresolved
1512           symbols into a (nearly) executable image. Linking can generally be
1513           static or dynamic, which has nothing to do with static or dynamic
1514           scoping.
1515
1516       LIST
1517           A syntactic construct representing a comma- separated list of
1518           expressions, evaluated to produce a list value.  Each expression in
1519           a "LIST" is evaluated in list context and interpolated into the
1520           list value.
1521
1522       list
1523           An ordered set of scalar values.
1524
1525       list context
1526           The situation in which an expression is expected by its
1527           surroundings (the code calling it) to return a list of values
1528           rather than a single value. Functions that want a "LIST" of
1529           arguments tell those arguments that they should produce a list
1530           value. See also context.
1531
1532       list operator
1533           An operator that does something with a list of values, such as
1534           "join" or "grep". Usually used for named built-in operators (such
1535           as "print", "unlink", and "system") that do not require parentheses
1536           around their argument list.
1537
1538       list value
1539           An unnamed list of temporary scalar values that may be passed
1540           around within a program from any list-generating function to any
1541           function or construct that provides a list context.
1542
1543       literal
1544           A token in a programming language, such as a number or string, that
1545           gives you an actual value instead of merely representing possible
1546           values as a variable does.
1547
1548       little-endian
1549           From Swift: someone who eats eggs little end first. Also used of
1550           computers that store the least significant byte of a word at a
1551           lower byte address than the most significant byte. Often considered
1552           superior to big-endian machines. See also big-endian.
1553
1554       local
1555           Not meaning the same thing everywhere. A global variable in Perl
1556           can be localized inside a dynamic scope via the "local" operator.
1557
1558       logical operator
1559           Symbols representing the concepts “and”, “or”, “xor”, and “not”.
1560
1561       lookahead
1562           An assertion that peeks at the string to the right of the current
1563           match location.
1564
1565       lookbehind
1566           An assertion that peeks at the string to the left of the current
1567           match location.
1568
1569       loop
1570           A construct that performs something repeatedly, like a roller
1571           coaster.
1572
1573       loop control statement
1574           Any statement within the body of a loop that can make a loop
1575           prematurely stop looping or skip an iteration. Generally, you
1576           shouldn’t try this on roller coasters.
1577
1578       loop label
1579           A kind of key or name attached to a loop (or roller coaster) so
1580           that loop control statements can talk about which loop they want to
1581           control.
1582
1583       lowercase
1584           In Unicode, not just characters with the General Category of
1585           Lowercase Letter, but any character with the Lowercase property,
1586           including Modifier Letters, Letter Numbers, some Other Symbols, and
1587           one Combining Mark.
1588
1589       lvaluable
1590           Able to serve as an lvalue.
1591
1592       lvalue
1593           Term used by language lawyers for a storage location you can assign
1594           a new value to, such as a variable or an element of an array. The
1595           “l” is short for “left”, as in the left side of an assignment, a
1596           typical place for lvalues. An lvaluable function or expression is
1597           one to which a value may be assigned, as in "pos($x) = 10".
1598
1599       lvalue modifier
1600           An adjectival pseudofunction that warps the meaning of an lvalue in
1601           some declarative fashion. Currently there are three lvalue
1602           modifiers: "my", "our", and "local".
1603
1604   M
1605       magic
1606           Technically speaking, any extra semantics attached to a variable
1607           such as $!, $0, %ENV, or %SIG, or to any tied variable.  Magical
1608           things happen when you diddle those variables.
1609
1610       magical increment
1611           An increment operator that knows how to bump up ASCII alphabetics
1612           as well as numbers.
1613
1614       magical variables
1615           Special variables that have side effects when you access them or
1616           assign to them. For example, in Perl, changing elements of the %ENV
1617           array also changes the corresponding environment variables that
1618           subprocesses will use. Reading the $!  variable gives you the
1619           current system error number or message.
1620
1621       Makefile
1622           A file that controls the compilation of a program. Perl programs
1623           don’t usually need a Makefile because the Perl compiler has plenty
1624           of self-control.
1625
1626       man The Unix program that displays online documentation (manual pages)
1627           for you.
1628
1629       manpage
1630           A “page” from the manuals, typically accessed via the man(1)
1631           command. A manpage contains a SYNOPSIS, a DESCRIPTION, a list of
1632           BUGS, and so on, and is typically longer than a page. There are
1633           manpages documenting commands, syscalls, library functions,
1634           devices, protocols, files, and such. In this book, we call any
1635           piece of standard Perl documentation (like perlop or perldelta) a
1636           manpage, no matter what format it’s installed in on your system.
1637
1638       matching
1639           See pattern matching.
1640
1641       member data
1642           See instance variable.
1643
1644       memory
1645           This always means your main memory, not your disk.  Clouding the
1646           issue is the fact that your machine may implement virtual memory;
1647           that is, it will pretend that it has more memory than it really
1648           does, and it’ll use disk space to hold inactive bits. This can make
1649           it seem like you have a little more memory than you really do, but
1650           it’s not a substitute for real memory. The best thing that can be
1651           said about virtual memory is that it lets your performance degrade
1652           gradually rather than suddenly when you run out of real memory. But
1653           your program can die when you run out of virtual memory, too—if you
1654           haven’t thrashed your disk to death first.
1655
1656       metacharacter
1657           A character that is not supposed to be treated normally. Which
1658           characters are to be treated specially as metacharacters varies
1659           greatly from context to context. Your shell will have certain
1660           metacharacters, double-quoted Perl strings have other
1661           metacharacters, and regular expression patterns have all the
1662           double-quote metacharacters plus some extra ones of their own.
1663
1664       metasymbol
1665           Something we’d call a metacharacter except that it’s a sequence of
1666           more than one character.  Generally, the first character in the
1667           sequence must be a true metacharacter to get the other characters
1668           in the metasymbol to misbehave along with it.
1669
1670       method
1671           A kind of action that an object can take if you tell it to. See
1672           Camel chapter 12, “Objects”.
1673
1674       method resolution order
1675           The path Perl takes through @INC. By default, this is a double
1676           depth first search, once looking for defined methods and once for
1677           "AUTOLOAD". However, Perl lets you configure this with "mro".
1678
1679       minicpan
1680           A CPAN mirror that includes just the latest versions for each
1681           distribution, probably created with "CPAN::Mini". See Camel chapter
1682           19, “CPAN”.
1683
1684       minimalism
1685           The belief that “small is beautiful”. Paradoxically, if you say
1686           something in a small language, it turns out big, and if you say it
1687           in a big language, it turns out small. Go figure.
1688
1689       mode
1690           In the context of the stat(2) syscall, refers to the field holding
1691           the permission bits and the type of the file.
1692
1693       modifier
1694           See statement modifier, regular expression, and lvalue, not
1695           necessarily in that order.
1696
1697       module
1698           A file that defines a package of (almost) the same name, which can
1699           either export symbols or function as an object class.  (A module’s
1700           main .pm file may also load in other files in support of the
1701           module.) See the "use" built-in.
1702
1703       modulus
1704           An integer divisor when you’re interested in the remainder instead
1705           of the quotient.
1706
1707       mojibake
1708           When you speak one language and the computer thinks you’re speaking
1709           another. You’ll see odd translations when you send UTF‑8, for
1710           instance, but the computer thinks you sent Latin-1, showing all
1711           sorts of weird characters instead. The term is written
1712           「文字化け」in Japanese and means “character rot”, an apt
1713           description. Pronounced ["modʑibake"] in standard IPA phonetics, or
1714           approximately “moh-jee-bah-keh”.
1715
1716       monger
1717           Short for one member of Perl mongers, a purveyor of Perl.
1718
1719       mortal
1720           A temporary value scheduled to die when the current statement
1721           finishes.
1722
1723       mro See method resolution order.
1724
1725       multidimensional array
1726           An array with multiple subscripts for finding a single element.
1727           Perl implements these using references—see Camel chapter 9, “Data
1728           Structures”.
1729
1730       multiple inheritance
1731           The features you got from your mother and father, mixed together
1732           unpredictably. (See also inheritance and single inheritance.) In
1733           computer languages (including Perl), it is the notion that a given
1734           class may have multiple direct ancestors or base classes.
1735
1736   N
1737       named pipe
1738           A pipe with a name embedded in the filesystem so that it can be
1739           accessed by two unrelated processes.
1740
1741       namespace
1742           A domain of names. You needn’t worry about whether the names in one
1743           such domain have been used in another. See package.
1744
1745       NaN Not a number. The value Perl uses for certain invalid or
1746           inexpressible floating-point operations.
1747
1748       network address
1749           The most important attribute of a socket, like your telephone’s
1750           telephone number. Typically an IP address. See also port.
1751
1752       newline
1753           A single character that represents the end of a line, with the
1754           ASCII value of 012 octal under Unix (but 015 on a Mac), and
1755           represented by "\n" in Perl strings. For Windows machines writing
1756           text files, and for certain physical devices like terminals, the
1757           single newline gets automatically translated by your C library into
1758           a line feed and a carriage return, but normally, no translation is
1759           done.
1760
1761       NFS Network File System, which allows you to mount a remote filesystem
1762           as if it were local.
1763
1764       normalization
1765           Converting a text string into an alternate but equivalent canonical
1766           (or compatible) representation that can then be compared for
1767           equivalence. Unicode recognizes four different normalization forms:
1768           NFD, NFC, NFKD, and NFKC.
1769
1770       null character
1771           A character with the numeric value of zero. It’s used by C to
1772           terminate strings, but Perl allows strings to contain a null.
1773
1774       null list
1775           A list value with zero elements, represented in Perl by "()".
1776
1777       null string
1778           A string containing no characters, not to be confused with a string
1779           containing a null character, which has a positive length and is
1780           true.
1781
1782       numeric context
1783           The situation in which an expression is expected by its
1784           surroundings (the code calling it) to return a number.  See also
1785           context and string context.
1786
1787       numification
1788           (Sometimes spelled nummification and nummify.) Perl lingo for
1789           implicit conversion into a number; the related verb is numify.
1790           Numification is intended to rhyme with mummification, and numify
1791           with mummify. It is unrelated to English numen, numina, numinous.
1792           We originally forgot the extra m a long time ago, and some people
1793           got used to our funny spelling, and so just as with
1794           "HTTP_REFERER"’s own missing letter, our weird spelling has stuck
1795           around.
1796
1797       NV  Short for Nevada, no part of which will ever be confused with
1798           civilization. NV also means an internal floating- point Numeric
1799           Value of the type a scalar can hold, not to be confused with an IV.
1800
1801       nybble
1802           Half a byte, equivalent to one hexadecimal digit, and worth four
1803           bits.
1804
1805   O
1806       object
1807           An instance of a class. Something that “knows” what user-defined
1808           type (class) it is, and what it can do because of what class it is.
1809           Your program can request an object to do things, but the object
1810           gets to decide whether it wants to do them or not. Some objects are
1811           more accommodating than others.
1812
1813       octal
1814           A number in base 8. Only the digits 0 through 7 are allowed. Octal
1815           constants in Perl start with 0, as in 013. See also the "oct"
1816           function.
1817
1818       offset
1819           How many things you have to skip over when moving from the
1820           beginning of a string or array to a specific position within it.
1821           Thus, the minimum offset is zero, not one, because you don’t skip
1822           anything to get to the first item.
1823
1824       one-liner
1825           An entire computer program crammed into one line of text.
1826
1827       open source software
1828           Programs for which the source code is freely available and freely
1829           redistributable, with no commercial strings attached.  For a more
1830           detailed definition, see <http://www.opensource.org/osd.html>.
1831
1832       operand
1833           An expression that yields a value that an operator operates on. See
1834           also precedence.
1835
1836       operating system
1837           A special program that runs on the bare machine and hides the gory
1838           details of managing processes and devices.  Usually used in a
1839           looser sense to indicate a particular culture of programming. The
1840           loose sense can be used at varying levels of specificity.  At one
1841           extreme, you might say that all versions of Unix and Unix-
1842           lookalikes are the same operating system (upsetting many people,
1843           especially lawyers and other advocates). At the other extreme, you
1844           could say this particular version of this particular vendor’s
1845           operating system is different from any other version of this or any
1846           other vendor’s operating system. Perl is much more portable across
1847           operating systems than many other languages. See also architecture
1848           and platform.
1849
1850       operator
1851           A gizmo that transforms some number of input values to some number
1852           of output values, often built into a language with a special syntax
1853           or symbol. A given operator may have specific expectations about
1854           what types of data you give as its arguments (operands) and what
1855           type of data you want back from it.
1856
1857       operator overloading
1858           A kind of overloading that you can do on built-in operators to make
1859           them work on objects as if the objects were ordinary scalar values,
1860           but with the actual semantics supplied by the object class. This is
1861           set up with the overload pragma—see Camel chapter 13,
1862           “Overloading”.
1863
1864       options
1865           See either switches or regular expression modifiers.
1866
1867       ordinal
1868           An abstract character’s integer value. Same thing as codepoint.
1869
1870       overloading
1871           Giving additional meanings to a symbol or construct.  Actually, all
1872           languages do overloading to one extent or another, since people are
1873           good at figuring out things from context.
1874
1875       overriding
1876           Hiding or invalidating some other definition of the same name. (Not
1877           to be confused with overloading, which adds definitions that must
1878           be disambiguated some other way.) To confuse the issue further, we
1879           use the word with two overloaded definitions: to describe how you
1880           can define your own subroutine to hide a built-in function of the
1881           same name (see the section “Overriding Built-in Functions” in Camel
1882           chapter 11, “Modules”), and to describe how you can define a
1883           replacement method in a derived class to hide a base class’s method
1884           of the same name (see Camel chapter 12, “Objects”).
1885
1886       owner
1887           The one user (apart from the superuser) who has absolute control
1888           over a file. A file may also have a group of users who may exercise
1889           joint ownership if the real owner permits it. See permission bits.
1890
1891   P
1892       package
1893           A namespace for global variables, subroutines, and the like, such
1894           that they can be kept separate from like-named symbols in other
1895           namespaces. In a sense, only the package is global, since the
1896           symbols in the package’s symbol table are only accessible from code
1897           compiled outside the package by naming the package. But in another
1898           sense, all package symbols are also globals—they’re just well-
1899           organized globals.
1900
1901       pad Short for scratchpad.
1902
1903       parameter
1904           See argument.
1905
1906       parent class
1907           See base class.
1908
1909       parse tree
1910           See syntax tree.
1911
1912       parsing
1913           The subtle but sometimes brutal art of attempting to turn your
1914           possibly malformed program into a valid syntax tree.
1915
1916       patch
1917           To fix by applying one, as it were. In the realm of hackerdom, a
1918           listing of the differences between two versions of a program as
1919           might be applied by the patch(1) program when you want to fix a bug
1920           or upgrade your old version.
1921
1922       PATH
1923           The list of directories the system searches to find a program you
1924           want to execute.  The list is stored as one of your environment
1925           variables, accessible in Perl as $ENV{PATH}.
1926
1927       pathname
1928           A fully qualified filename such as /usr/bin/perl. Sometimes
1929           confused with "PATH".
1930
1931       pattern
1932           A template used in pattern matching.
1933
1934       pattern matching
1935           Taking a pattern, usually a regular expression, and trying the
1936           pattern various ways on a string to see whether there’s any way to
1937           make it fit. Often used to pick interesting tidbits out of a file.
1938
1939       PAUSE
1940           The Perl Authors Upload SErver (<http://pause.perl.org>), the
1941           gateway for modules on their way to CPAN.
1942
1943       Perl mongers
1944           A Perl user group, taking the form of its name from the New York
1945           Perl mongers, the first Perl user group. Find one near you at
1946           <http://www.pm.org>.
1947
1948       permission bits
1949           Bits that the owner of a file sets or unsets to allow or disallow
1950           access to other people. These flag bits are part of the mode word
1951           returned by the "stat" built-in when you ask about a file. On Unix
1952           systems, you can check the ls(1) manpage for more information.
1953
1954       Pern
1955           What you get when you do "Perl++" twice. Doing it only once will
1956           curl your hair. You have to increment it eight times to shampoo
1957           your hair. Lather, rinse, iterate.
1958
1959       pipe
1960           A direct connection that carries the output of one process to the
1961           input of another without an intermediate temporary file.  Once the
1962           pipe is set up, the two processes in question can read and write as
1963           if they were talking to a normal file, with some caveats.
1964
1965       pipeline
1966           A series of processes all in a row, linked by pipes, where each
1967           passes its output stream to the next.
1968
1969       platform
1970           The entire hardware and software context in which a program runs. A
1971           program written in a platform-dependent language might break if you
1972           change any of the following: machine, operating system, libraries,
1973           compiler, or system configuration. The perl interpreter has to be
1974           compiled differently for each platform because it is implemented in
1975           C, but programs written in the Perl language are largely platform
1976           independent.
1977
1978       pod The markup used to embed documentation into your Perl code. Pod
1979           stands for “Plain old documentation”. See Camel chapter 23, “Plain
1980           Old Documentation”.
1981
1982       pod command
1983           A sequence, such as "=head1", that denotes the start of a pod
1984           section.
1985
1986       pointer
1987           A variable in a language like C that contains the exact memory
1988           location of some other item. Perl handles pointers internally so
1989           you don’t have to worry about them. Instead, you just use symbolic
1990           pointers in the form of keys and variable names, or hard
1991           references, which aren’t pointers (but act like pointers and do in
1992           fact contain pointers).
1993
1994       polymorphism
1995           The notion that you can tell an object to do something generic, and
1996           the object will interpret the command in different ways depending
1997           on its type. [< Greek πολυ- + μορϕή, many forms.]
1998
1999       port
2000           The part of the address of a TCP or UDP socket that directs packets
2001           to the correct process after finding the right machine, something
2002           like the phone extension you give when you reach the company
2003           operator. Also the result of converting code to run on a different
2004           platform than originally intended, or the verb denoting this
2005           conversion.
2006
2007       portable
2008           Once upon a time, C code compilable under both BSD and SysV. In
2009           general, code that can be easily converted to run on another
2010           platform, where “easily” can be defined however you like, and
2011           usually is.  Anything may be considered portable if you try hard
2012           enough, such as a mobile home or London Bridge.
2013
2014       porter
2015           Someone who “carries” software from one platform to another.
2016           Porting programs written in platform-dependent languages such as C
2017           can be difficult work, but porting programs like Perl is very much
2018           worth the agony.
2019
2020       possessive
2021           Said of quantifiers and groups in patterns that refuse to give up
2022           anything once they’ve gotten their mitts on it. Catchier and easier
2023           to say than the even more formal nonbacktrackable.
2024
2025       POSIX
2026           The Portable Operating System Interface specification.
2027
2028       postfix
2029           An operator that follows its operand, as in "$x++".
2030
2031       pp  An internal shorthand for a “push- pop” code; that is, C code
2032           implementing Perl’s stack machine.
2033
2034       pragma
2035           A standard module whose practical hints and suggestions are
2036           received (and possibly ignored) at compile time. Pragmas are named
2037           in all lowercase.
2038
2039       precedence
2040           The rules of conduct that, in the absence of other guidance,
2041           determine what should happen first.  For example, in the absence of
2042           parentheses, you always do multiplication before addition.
2043
2044       prefix
2045           An operator that precedes its operand, as in "++$x".
2046
2047       preprocessing
2048           What some helper process did to transform the incoming data into a
2049           form more suitable for the current process. Often done with an
2050           incoming pipe. See also C preprocessor.
2051
2052       primary maintainer
2053           The author that PAUSE allows to assign co-maintainer permissions to
2054           a namespace. A primary maintainer can give up this distinction by
2055           assigning it to another PAUSE author. See Camel chapter 19, “CPAN”.
2056
2057       procedure
2058           A subroutine.
2059
2060       process
2061           An instance of a running program. Under multitasking systems like
2062           Unix, two or more separate processes could be running the same
2063           program independently at the same time—in fact, the "fork" function
2064           is designed to bring about this happy state of affairs. Under other
2065           operating systems, processes are sometimes called “threads”,
2066           “tasks”, or “jobs”, often with slight nuances in meaning.
2067
2068       program
2069           See script.
2070
2071       program generator
2072           A system that algorithmically writes code for you in a high-level
2073           language. See also code generator.
2074
2075       progressive matching
2076           Pattern matching  matching>that picks up where it left off before.
2077
2078       property
2079           See either instance variable or character property.
2080
2081       protocol
2082           In networking, an agreed-upon way of sending messages back and
2083           forth so that neither correspondent will get too confused.
2084
2085       prototype
2086           An optional part of a subroutine declaration telling the Perl
2087           compiler how many and what flavor of arguments may be passed as
2088           actual arguments, so you can write subroutine calls that parse much
2089           like built-in functions. (Or don’t parse, as the case may be.)
2090
2091       pseudofunction
2092           A construct that sometimes looks like a function but really isn’t.
2093           Usually reserved for lvalue modifiers like "my", for context
2094           modifiers like "scalar", and for the pick-your-own-quotes
2095           constructs, "q//", "qq//", "qx//", "qw//", "qr//", "m//", "s///",
2096           "y///", and "tr///".
2097
2098       pseudohash
2099           Formerly, a reference to an array whose initial element happens to
2100           hold a reference to a hash. You used to be able to treat a
2101           pseudohash reference as either an array reference or a hash
2102           reference. Pseduohashes are no longer supported.
2103
2104       pseudoliteral
2105           An operator X"that looks something like a literal, such as the
2106           output-grabbing operator, <literal moreinfo="none""`>"command""`".
2107
2108       public domain
2109           Something not owned by anybody. Perl is copyrighted and is thus not
2110           in the public domain—it’s just freely available and freely
2111           redistributable.
2112
2113       pumpkin
2114           A notional “baton” handed around the Perl community indicating who
2115           is the lead integrator in some arena of development.
2116
2117       pumpking
2118           A pumpkin holder, the person in charge of pumping the pump, or at
2119           least priming it. Must be willing to play the part of the Great
2120           Pumpkin now and then.
2121
2122       PV  A “pointer value”, which is Perl Internals Talk for a "char*".
2123
2124   Q
2125       qualified
2126           Possessing a complete name. The symbol $Ent::moot is qualified;
2127           $moot is unqualified. A fully qualified filename is specified from
2128           the top-level directory.
2129
2130       quantifier
2131           A component of a regular expression specifying how many times the
2132           foregoing atom may occur.
2133
2134   R
2135       race condition
2136           A race condition exists when the result of several interrelated
2137           events depends on the ordering of those events, but that order
2138           cannot be guaranteed due to nondeterministic timing effects. If two
2139           or more programs, or parts of the same program, try to go through
2140           the same series of events, one might interrupt the work of the
2141           other. This is a good way to find an exploit.
2142
2143       readable
2144           With respect to files, one that has the proper permission bit set
2145           to let you access the file. With respect to computer programs, one
2146           that’s written well enough that someone has a chance of figuring
2147           out what it’s trying to do.
2148
2149       reaping
2150           The last rites performed by a parent process on behalf of a
2151           deceased child process so that it doesn’t remain a zombie.  See the
2152           "wait" and "waitpid" function calls.
2153
2154       record
2155           A set of related data values in a file or stream, often associated
2156           with a unique key field. In Unix, often commensurate with a line,
2157           or a blank-line–terminated set of lines (a “paragraph”).  Each line
2158           of the /etc/passwd file is a record, keyed on login name,
2159           containing information about that user.
2160
2161       recursion
2162           The art of defining something (at least partly) in terms of itself,
2163           which is a naughty no-no in dictionaries but often works out okay
2164           in computer programs if you’re careful not to recurse forever
2165           (which is like an infinite loop with more spectacular failure
2166           modes).
2167
2168       reference
2169           Where you look to find a pointer to information somewhere else.
2170           (See indirection.) References come in two flavors: symbolic
2171           references and hard references.
2172
2173       referent
2174           Whatever a reference refers to, which may or may not have a name.
2175           Common types of referents include scalars, arrays, hashes, and
2176           subroutines.
2177
2178       regex
2179           See regular expression.
2180
2181       regular expression
2182           A single entity with various interpretations, like an elephant. To
2183           a computer scientist, it’s a grammar for a little language in which
2184           some strings are legal and others aren’t. To normal people, it’s a
2185           pattern you can use to find what you’re looking for when it varies
2186           from case to case. Perl’s regular expressions are far from regular
2187           in the theoretical sense, but in regular use they work quite well.
2188           Here’s a regular expression: "/Oh s.*t./". This will match strings
2189           like “"Oh say can you see by the dawn's early light"” and “"Oh
2190           sit!"”. See Camel chapter 5, “Pattern Matching”.
2191
2192       regular expression modifier
2193           An option on a pattern or substitution, such as "/i" to render the
2194           pattern case- insensitive.
2195
2196       regular file
2197           A file that’s not a directory, a device, a named pipe or socket, or
2198           a symbolic link. Perl uses the "–f" file test operator to identify
2199           regular files. Sometimes called a “plain” file.
2200
2201       relational operator
2202           An operator that says whether a particular ordering relationship is
2203           true about a pair of operands. Perl has both numeric and string
2204           relational operators. See collating sequence.
2205
2206       reserved words
2207           A word with a specific, built-in meaning to a compiler, such as
2208           "if" or "delete". In many languages (not Perl), it’s illegal to use
2209           reserved words to name anything else. (Which is why they’re
2210           reserved, after all.) In Perl, you just can’t use them to name
2211           labels or filehandles. Also called “keywords”.
2212
2213       return value
2214           The value produced by a subroutine or expression when evaluated. In
2215           Perl, a return value may be either a list or a scalar.
2216
2217       RFC Request For Comment, which despite the timid connotations is the
2218           name of a series of important standards documents.
2219
2220       right shift
2221           A bit shift that divides a number by some power of 2.
2222
2223       role
2224           A name for a concrete set of behaviors. A role is a way to add
2225           behavior to a class without inheritance.
2226
2227       root
2228           The superuser ("UID" == 0). Also the top-level directory of the
2229           filesystem.
2230
2231       RTFM
2232           What you are told when someone thinks you should Read The Fine
2233           Manual.
2234
2235       run phase
2236           Any time after Perl starts running your main program.  See also
2237           compile phase. Run phase is mostly spent in runtime but may also be
2238           spent in compile time when "require", "do" "FILE", or "eval"
2239           "STRING" operators are executed, or when a substitution uses the
2240           "/ee" modifier.
2241
2242       runtime
2243           The time when Perl is actually doing what your code says to do, as
2244           opposed to the earlier period of time when it was trying to figure
2245           out whether what you said made any sense whatsoever, which is
2246           compile time.
2247
2248       runtime pattern
2249           A pattern that contains one or more variables to be interpolated
2250           before parsing the pattern as a regular expression, and that
2251           therefore cannot be analyzed at compile time, but must be
2252           reanalyzed each time the pattern match operator is evaluated.
2253           Runtime patterns are useful but expensive.
2254
2255       RV  A recreational vehicle, not to be confused with vehicular
2256           recreation. RV also means an internal Reference Value of the type a
2257           scalar can hold. See also IV and NV if you’re not confused yet.
2258
2259       rvalue
2260           A value that you might find on the right side of an assignment. See
2261           also lvalue.
2262
2263   S
2264       sandbox
2265           A walled off area that’s not supposed to affect beyond its walls.
2266           You let kids play in the sandbox instead of running in the road.
2267           See Camel chapter 20, “Security”.
2268
2269       scalar
2270           A simple, singular value; a number, string, or reference.
2271
2272       scalar context
2273           The situation in which an expression is expected by its
2274           surroundings (the code calling it) to return a single value rather
2275           than a list of values. See also context and list context. A scalar
2276           context sometimes imposes additional constraints on the return
2277           value—see string context and numeric context. Sometimes we talk
2278           about a Boolean context inside conditionals, but this imposes no
2279           additional constraints, since any scalar value, whether numeric or
2280           string, is already true or false.
2281
2282       scalar literal
2283           A number or quoted string—an actual value in the text of your
2284           program, as opposed to a variable.
2285
2286       scalar value
2287           A value that happens to be a scalar as opposed to a list.
2288
2289       scalar variable
2290           A variable prefixed with "$" that holds a single value.
2291
2292       scope
2293           From how far away you can see a variable, looking through one. Perl
2294           has two visibility mechanisms. It does dynamic scoping of "local"
2295           variables, meaning that the rest of the block, and any subroutines
2296           that are called by the rest of the block, can see the variables
2297           that are local to the block. Perl does lexical scoping of "my"
2298           variables, meaning that the rest of the block can see the variable,
2299           but other subroutines called by the block cannot see the variable.
2300
2301       scratchpad
2302           The area in which a particular invocation of a particular file or
2303           subroutine keeps some of its temporary values, including any
2304           lexically scoped variables.
2305
2306       script
2307           A text file that is a program intended to be executed directly
2308           rather than compiled to another form of file before execution.
2309
2310           Also, in the context of Unicode, a writing system for a particular
2311           language or group of languages, such as Greek, Bengali, or Tengwar.
2312
2313       script kiddie
2314           A cracker who is not a hacker but knows just enough to run canned
2315           scripts. A cargo-cult programmer.
2316
2317       sed A venerable Stream EDitor from which Perl derives some of its
2318           ideas.
2319
2320       semaphore
2321           A fancy kind of interlock that prevents multiple threads or
2322           processes from using up the same resources simultaneously.
2323
2324       separator
2325           A character or string that keeps two surrounding strings from being
2326           confused with each other. The "split" function works on separators.
2327           Not to be confused with delimiters or terminators. The “or” in the
2328           previous sentence separated the two alternatives.
2329
2330       serialization
2331           Putting a fancy data structure into linear order so that it can be
2332           stored as a string in a disk file or database, or sent through a
2333           pipe. Also called marshalling.
2334
2335       server
2336           In networking, a process that either advertises a service or just
2337           hangs around at a known location and waits for clients who need
2338           service to get in touch with it.
2339
2340       service
2341           Something you do for someone else to make them happy, like giving
2342           them the time of day (or of their life). On some machines, well-
2343           known services are listed by the "getservent" function.
2344
2345       setgid
2346           Same as setuid, only having to do with giving away group
2347           privileges.
2348
2349       setuid
2350           Said of a program that runs with the privileges of its owner rather
2351           than (as is usually the case) the privileges of whoever is running
2352           it. Also describes the bit in the mode word (permission bits) that
2353           controls the feature. This bit must be explicitly set by the owner
2354           to enable this feature, and the program must be carefully written
2355           not to give away more privileges than it ought to.
2356
2357       shared memory
2358           A piece of memory accessible by two different processes who
2359           otherwise would not see each other’s memory.
2360
2361       shebang
2362           Irish for the whole McGillicuddy. In Perl culture, a portmanteau of
2363           “sharp” and “bang”, meaning the "#!" sequence that tells the system
2364           where to find the interpreter.
2365
2366       shell
2367           A command-line interpreter. The program that interactively gives
2368           you a prompt, accepts one or more lines of input, and executes the
2369           programs you mentioned, feeding each of them their proper arguments
2370           and input data. Shells can also execute scripts containing such
2371           commands. Under Unix, typical shells include the Bourne shell
2372           (/bin/sh), the C shell (/bin/csh), and the Korn shell (/bin/ksh).
2373           Perl is not strictly a shell because it’s not interactive (although
2374           Perl programs can be interactive).
2375
2376       side effects
2377           Something extra that happens when you evaluate an expression.
2378           Nowadays it can refer to almost anything. For example, evaluating a
2379           simple assignment statement typically has the “side effect” of
2380           assigning a value to a variable. (And you thought assigning the
2381           value was your primary intent in the first place!) Likewise,
2382           assigning a value to the special variable $| ($AUTOFLUSH) has the
2383           side effect of forcing a flush after every "write" or "print" on
2384           the currently selected filehandle.
2385
2386       sigil
2387           A glyph used in magic. Or, for Perl, the symbol in front of a
2388           variable name, such as "$", "@", and "%".
2389
2390       signal
2391           A bolt out of the blue; that is, an event triggered by the
2392           operating system, probably when you’re least expecting it.
2393
2394       signal handler
2395           A subroutine that, instead of being content to be called in the
2396           normal fashion, sits around waiting for a bolt out of the blue
2397           before it will deign to execute. Under Perl, bolts out of the blue
2398           are called signals, and you send them with the "kill" built-in. See
2399           the %SIG hash in Camel chapter 25, “Special Names” and the section
2400           “Signals” in Camel chapter 15, “Interprocess Communication”.
2401
2402       single inheritance
2403           The features you got from your mother, if she told you that you
2404           don’t have a father. (See also inheritance and multiple
2405           inheritance.) In computer languages, the idea that classes
2406           reproduce asexually so that a given class can only have one direct
2407           ancestor or base class. Perl supplies no such restriction, though
2408           you may certainly program Perl that way if you like.
2409
2410       slice
2411           A selection of any number of elements from a list, array, or hash.
2412
2413       slurp
2414           To read an entire file into a string in one operation.
2415
2416       socket
2417           An endpoint for network communication among multiple processes that
2418           works much like a telephone or a post office box. The most
2419           important thing about a socket is its network address (like a phone
2420           number). Different kinds of sockets have different kinds of
2421           addresses—some look like filenames, and some don’t.
2422
2423       soft reference
2424           See symbolic reference.
2425
2426       source filter
2427           A special kind of module that does preprocessing on your script
2428           just before it gets to the tokener.
2429
2430       stack
2431           A device you can put things on the top of, and later take them back
2432           off in the opposite order in which you put them on. See LIFO.
2433
2434       standard
2435           Included in the official Perl distribution, as in a standard
2436           module, a standard tool, or a standard Perl manpage.
2437
2438       standard error
2439           The default output stream for nasty remarks that don’t belong in
2440           standard output. Represented within a Perl program by the output>
2441           filehandle "STDERR". You can use this stream explicitly, but the
2442           "die" and "warn" built-ins write to your standard error stream
2443           automatically (unless trapped or otherwise intercepted).
2444
2445       standard input
2446           The default input stream for your program, which if possible
2447           shouldn’t care where its data is coming from. Represented within a
2448           Perl program by the filehandle "STDIN".
2449
2450       standard I/O
2451           A standard C library for doing buffered input and output to the
2452           operating system. (The “standard” of standard I/O is at most
2453           marginally related to the “standard” of standard input and output.)
2454           In general, Perl relies on whatever implementation of standard I/O
2455           a given operating system supplies, so the buffering characteristics
2456           of a Perl program on one machine may not exactly match those on
2457           another machine.  Normally this only influences efficiency, not
2458           semantics. If your standard I/O package is doing block buffering
2459           and you want it to flush the buffer more often, just set the $|
2460           variable to a true value.
2461
2462       Standard Library
2463           Everything that comes with the official perl distribution. Some
2464           vendor versions of perl change their distributions, leaving out
2465           some parts or including extras. See also dual-lived.
2466
2467       standard output
2468           The default output stream for your program, which if possible
2469           shouldn’t care where its data is going. Represented within a Perl
2470           program by the filehandle "STDOUT".
2471
2472       statement
2473           A command to the computer about what to do next, like a step in a
2474           recipe: “Add marmalade to batter and mix until mixed.” A statement
2475           is distinguished from a declaration, which doesn’t tell the
2476           computer to do anything, but just to learn something.
2477
2478       statement modifier
2479           A conditional or loop that you put after the statement instead of
2480           before, if you know what we mean.
2481
2482       static
2483           Varying slowly compared to something else. (Unfortunately,
2484           everything is relatively stable compared to something else, except
2485           for certain elementary particles, and we’re not so sure about
2486           them.) In computers, where things are supposed to vary rapidly,
2487           “static” has a derogatory connotation, indicating a slightly
2488           dysfunctional variable, subroutine, or method. In Perl culture, the
2489           word is politely avoided.
2490
2491           If you’re a C or C++ programmer, you might be looking for Perl’s
2492           "state" keyword.
2493
2494       static method
2495           No such thing. See class method.
2496
2497       static scoping
2498           No such thing. See lexical scoping.
2499
2500       static variable
2501           No such thing. Just use a lexical variable in a scope larger than
2502           your subroutine, or declare it with "state" instead of with "my".
2503
2504       stat structure
2505           A special internal spot in which Perl keeps the information about
2506           the last file on which you requested information.
2507
2508       status
2509           The value returned to the parent process when one of its child
2510           processes dies. This value is placed in the special variable $?.
2511           Its upper eight bits are the exit status of the defunct process,
2512           and its lower eight bits identify the signal (if any) that the
2513           process died from. On Unix systems, this status value is the same
2514           as the status word returned by wait(2). See "system" in Camel
2515           chapter 27, “Functions”.
2516
2517       STDERR
2518           See standard error.
2519
2520       STDIN
2521           See standard input.
2522
2523       STDIO
2524           See standard I/O.
2525
2526       STDOUT
2527           See standard output.
2528
2529       stream
2530           A flow of data into or out of a process as a steady sequence of
2531           bytes or characters, without the appearance of being broken up into
2532           packets. This is a kind of interface—the underlying implementation
2533           may well break your data up into separate packets for delivery, but
2534           this is hidden from you.
2535
2536       string
2537           A sequence of characters such as “He said !@#*&%@#*?!”.  A string
2538           does not have to be entirely printable.
2539
2540       string context
2541           The situation in which an expression is expected by its
2542           surroundings (the code calling it) to return a string.  See also
2543           context and numeric context.
2544
2545       stringification
2546           The process of producing a string representation of an abstract
2547           object.
2548
2549       struct
2550           C keyword introducing a structure definition or name.
2551
2552       structure
2553           See data structure.
2554
2555       subclass
2556           See derived class.
2557
2558       subpattern
2559           A component of a regular expression pattern.
2560
2561       subroutine
2562           A named or otherwise accessible piece of program that can be
2563           invoked from elsewhere in the program in order to accomplish some
2564           subgoal of the program. A subroutine is often parameterized to
2565           accomplish different but related things depending on its input
2566           arguments. If the subroutine returns a meaningful value, it is also
2567           called a function.
2568
2569       subscript
2570           A value that indicates the position of a particular array element
2571           in an array.
2572
2573       substitution
2574           Changing parts of a string via the "s///" operator. (We avoid use
2575           of this term to mean variable interpolation.)
2576
2577       substring
2578           A portion of a string, starting at a certain character position
2579           (offset) and proceeding for a certain number of characters.
2580
2581       superclass
2582           See base class.
2583
2584       superuser
2585           The person whom the operating system will let do almost anything.
2586           Typically your system administrator or someone pretending to be
2587           your system administrator. On Unix systems, the root user. On
2588           Windows systems, usually the Administrator user.
2589
2590       SV  Short for “scalar value”. But within the Perl interpreter, every
2591           referent is treated as a member of a class derived from SV, in an
2592           object-oriented sort of way. Every value inside Perl is passed
2593           around as a C language "SV*" pointer. The SV struct knows its own
2594           “referent type”, and the code is smart enough (we hope) not to try
2595           to call a hash function on a subroutine.
2596
2597       switch
2598           An option you give on a command line to influence the way your
2599           program works, usually introduced with a minus sign.  The word is
2600           also used as a nickname for a switch statement.
2601
2602       switch cluster
2603           The combination of multiple command- line switches (e.g., "–a –b
2604           –c") into one switch (e.g., "–abc").  Any switch with an additional
2605           argument must be the last switch in a cluster.
2606
2607       switch statement
2608           A program technique that lets you evaluate an expression and then,
2609           based on the value of the expression, do a multiway branch to the
2610           appropriate piece of code for that value. Also called a “case
2611           structure”, named after the similar Pascal construct. Most switch
2612           statements in Perl are spelled "given". See “The "given" statement”
2613           in Camel chapter 4, “Statements and Declarations”.
2614
2615       symbol
2616           Generally, any token or metasymbol. Often used more specifically to
2617           mean the sort of name you might find in a symbol table.
2618
2619       symbolic debugger
2620           A program that lets you step through the execution of your program,
2621           stopping or printing things out here and there to see whether
2622           anything has gone wrong, and, if so, what. The “symbolic” part just
2623           means that you can talk to the debugger using the same symbols with
2624           which your program is written.
2625
2626       symbolic link
2627           An alternate filename that points to the real filename, which in
2628           turn points to the real file. Whenever the operating system is
2629           trying to parse a pathname containing a symbolic link, it merely
2630           substitutes the new name and continues parsing.
2631
2632       symbolic reference
2633           A variable whose value is the name of another variable or
2634           subroutine. By dereferencing the first variable, you can get at the
2635           second one. Symbolic references are illegal under "use strict
2636           "refs"".
2637
2638       symbol table
2639           Where a compiler remembers symbols. A program like Perl must
2640           somehow remember all the names of all the variables, filehandles,
2641           and subroutines you’ve used. It does this by placing the names in a
2642           symbol table, which is implemented in Perl using a hash table.
2643           There is a separate symbol table for each package to give each
2644           package its own namespace.
2645
2646       synchronous
2647           Programming in which the orderly sequence of events can be
2648           determined; that is, when things happen one after the other, not at
2649           the same time.
2650
2651       syntactic sugar
2652           An alternative way of writing something more easily; a shortcut.
2653
2654       syntax
2655           From Greek σύνταξις, “with-arrangement”. How things (particularly
2656           symbols) are put together with each other.
2657
2658       syntax tree
2659           An internal representation of your program wherein lower-level
2660           constructs dangle off the higher-level constructs enclosing them.
2661
2662       syscall
2663           A function call directly to the operating system. Many of the
2664           important subroutines and functions you use aren’t direct system
2665           calls, but are built up in one or more layers above the system call
2666           level. In general, Perl programmers don’t need to worry about the
2667           distinction. However, if you do happen to know which Perl functions
2668           are really syscalls, you can predict which of these will set the $!
2669           ($ERRNO) variable on failure. Unfortunately, beginning programmers
2670           often confusingly employ the term “system call” to mean what
2671           happens when you call the Perl "system" function, which actually
2672           involves many syscalls. To avoid any confusion, we nearly always
2673           say “syscall” for something you could call indirectly via Perl’s
2674           "syscall" function, and never for something you would call with
2675           Perl’s "system" function.
2676
2677   T
2678       taint checks
2679           The special bookkeeping Perl does to track the flow of external
2680           data through your program and disallow their use in system
2681           commands.
2682
2683       tainted
2684           Said of data derived from the grubby hands of a user, and thus
2685           unsafe for a secure program to rely on. Perl does taint checks if
2686           you run a setuid (or setgid) program, or if you use the "–T"
2687           switch.
2688
2689       taint mode
2690           Running under the "–T" switch, marking all external data as suspect
2691           and refusing to use it with system commands. See Camel chapter 20,
2692           “Security”.
2693
2694       TCP Short for Transmission Control Protocol. A protocol wrapped around
2695           the Internet Protocol to make an unreliable packet transmission
2696           mechanism appear to the application program to be a reliable stream
2697           of bytes.  (Usually.)
2698
2699       term
2700           Short for a “terminal”—that is, a leaf node of a syntax tree. A
2701           thing that functions grammatically as an operand for the operators
2702           in an expression.
2703
2704       terminator
2705           A character or string that marks the end of another string. The $/
2706           variable contains the string that terminates a "readline"
2707           operation, which "chomp" deletes from the end. Not to be confused
2708           with delimiters or separators. The period at the end of this
2709           sentence is a terminator.
2710
2711       ternary
2712           An operator taking three operands. Sometimes pronounced trinary.
2713
2714       text
2715           A string or file containing primarily printable characters.
2716
2717       thread
2718           Like a forked process, but without fork’s inherent memory
2719           protection. A thread is lighter weight than a full process, in that
2720           a process could have multiple threads running around in it, all
2721           fighting over the same process’s memory space unless steps are
2722           taken to protect threads from one another.
2723
2724       tie The bond between a magical variable and its implementation class.
2725           See the "tie" function in Camel chapter 27, “Functions” and Camel
2726           chapter 14, “Tied Variables”.
2727
2728       titlecase
2729           The case used for capitals that are followed by lowercase
2730           characters instead of by more capitals.  Sometimes called sentence
2731           case or headline case. English doesn’t use Unicode titlecase, but
2732           casing rules for English titles are more complicated than simply
2733           capitalizing each word’s first character.
2734
2735       TMTOWTDI
2736           There’s More Than One Way To Do It, the Perl Motto. The notion that
2737           there can be more than one valid path to solving a programming
2738           problem in context. (This doesn’t mean that more ways are always
2739           better or that all possible paths are equally desirable—just that
2740           there need not be One True Way.)
2741
2742       token
2743           A morpheme in a programming language, the smallest unit of text
2744           with semantic significance.
2745
2746       tokener
2747           A module that breaks a program text into a sequence of tokens for
2748           later analysis by a parser.
2749
2750       tokenizing
2751           Splitting up a program text into tokens. Also known as “lexing”, in
2752           which case you get “lexemes” instead of tokens.
2753
2754       toolbox approach
2755           The notion that, with a complete set of simple tools that work well
2756           together, you can build almost anything you want. Which is fine if
2757           you’re assembling a tricycle, but if you’re building a
2758           defranishizing comboflux regurgalator, you really want your own
2759           machine shop in which to build special tools. Perl is sort of a
2760           machine shop.
2761
2762       topic
2763           The thing you’re working on. Structures like "while(<>)", "for",
2764           "foreach", and "given" set the topic for you by assigning to $_,
2765           the default (topic) variable.
2766
2767       transliterate
2768           To turn one string representation into another by mapping each
2769           character of the source string to its corresponding character in
2770           the result string. Not to be confused with translation: for
2771           example, Greek πολύχρωμος transliterates into polychromos but
2772           translates into many-colored. See the "tr///" operator in Camel
2773           chapter 5, “Pattern Matching”.
2774
2775       trigger
2776           An event that causes a handler to be run.
2777
2778       trinary
2779           Not a stellar system with three stars, but an operator taking three
2780           operands. Sometimes pronounced ternary.
2781
2782       troff
2783           A venerable typesetting language from which Perl derives the name
2784           of its $% variable and which is secretly used in the production of
2785           Camel books.
2786
2787       true
2788           Any scalar value that doesn’t evaluate to 0 or "".
2789
2790       truncating
2791           Emptying a file of existing contents, either automatically when
2792           opening a file for writing or explicitly via the "truncate"
2793           function.
2794
2795       type
2796           See data type and class.
2797
2798       type casting
2799           Converting data from one type to another. C permits this.  Perl
2800           does not need it. Nor want it.
2801
2802       typedef
2803           A type definition in the C and C++ languages.
2804
2805       typed lexical
2806           A lexical variable  lexical>that is declared with a class type: "my
2807           Pony $bill".
2808
2809       typeglob
2810           Use of a single identifier, prefixed with "*". For example, *name
2811           stands for any or all of $name, @name, %name, &name, or just
2812           "name". How you use it determines whether it is interpreted as all
2813           or only one of them. See “Typeglobs and Filehandles” in Camel
2814           chapter 2, “Bits and Pieces”.
2815
2816       typemap
2817           A description of how C types may be transformed to and from Perl
2818           types within an extension module written in XS.
2819
2820   U
2821       UDP User Datagram Protocol, the typical way to send datagrams over the
2822           Internet.
2823
2824       UID A user ID. Often used in the context of file or process ownership.
2825
2826       umask
2827           A mask of those permission bits that should be forced off when
2828           creating files or directories, in order to establish a policy of
2829           whom you’ll ordinarily deny access to. See the "umask" function.
2830
2831       unary operator
2832           An operator with only one operand, like "!" or "chdir". Unary
2833           operators are usually prefix operators; that is, they precede their
2834           operand. The "++" and "––" operators can be either prefix or
2835           postfix. (Their position does change their meanings.)
2836
2837       Unicode
2838           A character set comprising all the major character sets of the
2839           world, more or less. See <http://www.unicode.org>.
2840
2841       Unix
2842           A very large and constantly evolving language with several
2843           alternative and largely incompatible syntaxes, in which anyone can
2844           define anything any way they choose, and usually do. Speakers of
2845           this language think it’s easy to learn because it’s so easily
2846           twisted to one’s own ends, but dialectical differences make tribal
2847           intercommunication nearly impossible, and travelers are often
2848           reduced to a pidgin-like subset of the language. To be universally
2849           understood, a Unix shell programmer must spend years of study in
2850           the art. Many have abandoned this discipline and now communicate
2851           via an Esperanto-like language called Perl.
2852
2853           In ancient times, Unix was also used to refer to some code that a
2854           couple of people at Bell Labs wrote to make use of a PDP-7 computer
2855           that wasn’t doing much of anything else at the time.
2856
2857       uppercase
2858           In Unicode, not just characters with the General Category of
2859           Uppercase Letter, but any character with the Uppercase property,
2860           including some Letter Numbers and Symbols. Not to be confused with
2861           titlecase.
2862
2863   V
2864       value
2865           An actual piece of data, in contrast to all the variables,
2866           references, keys, indices, operators, and whatnot that you need to
2867           access the value.
2868
2869       variable
2870           A named storage location that can hold any of various kinds of
2871           value, as your program sees fit.
2872
2873       variable interpolation
2874           The interpolation of a scalar or array variable into a string.
2875
2876       variadic
2877           Said of a function that happily receives an indeterminate number of
2878           actual arguments.
2879
2880       vector
2881           Mathematical jargon for a list of scalar values.
2882
2883       virtual
2884           Providing the appearance of something without the reality, as in:
2885           virtual memory is not real memory. (See also memory.) The opposite
2886           of “virtual” is “transparent”, which means providing the reality of
2887           something without the appearance, as in: Perl handles the variable-
2888           length UTF‑8 character encoding transparently.
2889
2890       void context
2891           A form of scalar context in which an expression is not expected to
2892           return any value at all and is evaluated for its side effects
2893           alone.
2894
2895       v-string
2896           A “version” or “vector” string specified with a "v" followed by a
2897           series of decimal integers in dot notation, for instance,
2898           "v1.20.300.4000". Each number turns into a character with the
2899           specified ordinal value. (The "v" is optional when there are at
2900           least three integers.)
2901
2902   W
2903       warning
2904           A message printed to the "STDERR" stream to the effect that
2905           something might be wrong but isn’t worth blowing up over. See
2906           "warn" in Camel chapter 27, “Functions” and the "warnings" pragma
2907           in Camel chapter 28, “Pragmantic Modules”.
2908
2909       watch expression
2910           An expression which, when its value changes, causes a breakpoint in
2911           the Perl debugger.
2912
2913       weak reference
2914           A reference that doesn’t get counted normally. When all the normal
2915           references to data disappear, the data disappears. These are useful
2916           for circular references that would never disappear otherwise.
2917
2918       whitespace
2919           A character that moves your cursor but doesn’t otherwise put
2920           anything on your screen. Typically refers to any of: space, tab,
2921           line feed, carriage return, or form feed. In Unicode, matches many
2922           other characters that Unicode considers whitespace, including the
2923           ɴ-ʙʀ .
2924
2925       word
2926           In normal “computerese”, the piece of data of the size most
2927           efficiently handled by your computer, typically 32 bits or so, give
2928           or take a few powers of 2. In Perl culture, it more often refers to
2929           an alphanumeric identifier (including underscores), or to a string
2930           of nonwhitespace characters bounded by whitespace or string
2931           boundaries.
2932
2933       working directory
2934           Your current directory, from which relative pathnames are
2935           interpreted by the operating system. The operating system knows
2936           your current directory because you told it with a "chdir", or
2937           because you started out in the place where your parent process was
2938           when you were born.
2939
2940       wrapper
2941           A program or subroutine that runs some other program or subroutine
2942           for you, modifying some of its input or output to better suit your
2943           purposes.
2944
2945       WYSIWYG
2946           What You See Is What You Get. Usually used when something that
2947           appears on the screen matches how it will eventually look, like
2948           Perl’s "format" declarations. Also used to mean the opposite of
2949           magic because everything works exactly as it appears, as in the
2950           three- argument form of "open".
2951
2952   X
2953       XS  An extraordinarily exported, expeditiously excellent, expressly
2954           eXternal Subroutine, executed in existing C or C++ or in an
2955           exciting extension language called (exasperatingly) XS.
2956
2957       XSUB
2958           An external subroutine defined in XS.
2959
2960   Y
2961       yacc
2962           Yet Another Compiler Compiler. A parser generator without which
2963           Perl probably would not have existed. See the file perly.y in the
2964           Perl source distribution.
2965
2966   Z
2967       zero width
2968           A subpattern assertion matching the null string between characters.
2969
2970       zombie
2971           A process that has died (exited) but whose parent has not yet
2972           received proper notification of its demise by virtue of having
2973           called "wait" or "waitpid". If you "fork", you must clean up after
2974           your child processes when they exit; otherwise, the process table
2975           will fill up and your system administrator will Not Be Happy with
2976           you.
2977
2979       Based on the Glossary of Programming Perl, Fourth Edition, by Tom
2980       Christiansen, brian d foy, Larry Wall, & Jon Orwant.  Copyright (c)
2981       2000, 1996, 1991, 2012 O'Reilly Media, Inc.  This document may be
2982       distributed under the same terms as Perl itself.
2983
2984
2985
2986perl v5.26.3                      2018-06-05                   perlglossary(3)
Impressum