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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" perlglossary \- Perl Glossary .SH "DESCRIPTION" .IX Header "DESCRIPTION" A glossary of terms (technical and otherwise) used in the Perl documentation. Other useful sources include the Free On-Line Dictionary of Computing , the Jargon File , and Wikipedia . .SS "A" .IX Subsection "A" .IP "accessor methods" 4 .IX Item "accessor methods" A \*(L"method\*(R" used to indirectly inspect or update an \*(L"object\*(R"'s state (its instance variables). .IP "actual arguments" 4 .IX Item "actual arguments" The scalar values that you supply to a \*(L"function\*(R" or \*(L"subroutine\*(R" when you call it. For instance, when you call \&\f(CW\*(C`power("puff")\*(C'\fR, the string \f(CW"puff"\fR is the actual argument. See also \*(L"argument\*(R" and \*(L"formal arguments\*(R". .IP "address operator" 4 .IX Item "address operator" Some languages work directly with the memory addresses of values, but this can be like playing with fire. Perl provides a set of asbestos gloves for handling all memory management. The closest to an address operator in Perl is the backslash operator, but it gives you a \*(L"hard reference\*(R", which is much safer than a memory address. .IP "algorithm" 4 .IX Item "algorithm" A well-defined sequence of steps, clearly enough explained that even a computer could do them. .IP "alias" 4 .IX Item "alias" A nickname for something, which behaves in all ways as though you'd used the original name instead of the nickname. Temporary aliases are implicitly created in the loop variable for \f(CW\*(C`foreach\*(C'\fR loops, in the \&\f(CW$_\fR variable for map or grep operators, in \f(CW$a\fR and \f(CW$b\fR during sort's comparison function, and in each element of \f(CW@_\fR for the \*(L"actual arguments\*(R" of a subroutine call. Permanent aliases are explicitly created in packages by importing symbols or by assignment to typeglobs. Lexically scoped aliases for package variables are explicitly created by the our declaration. .IP "alternatives" 4 .IX Item "alternatives" A list of possible choices from which you may select only one, as in \&\*(L"Would you like door A, B, or C?\*(R" Alternatives in regular expressions are separated with a single vertical bar: \f(CW\*(C`|\*(C'\fR. Alternatives in normal Perl expressions are separated with a double vertical bar: \&\f(CW\*(C`||\*(C'\fR. Logical alternatives in \*(L"Boolean\*(R" expressions are separated with either \f(CW\*(C`||\*(C'\fR or \f(CW\*(C`or\*(C'\fR. .IP "anonymous" 4 .IX Item "anonymous" Used to describe a \*(L"referent\*(R" that is not directly accessible through a named \*(L"variable\*(R". Such a referent must be indirectly accessible through at least one \*(L"hard reference\*(R". When the last hard reference goes away, the anonymous referent is destroyed without pity. .IP "architecture" 4 .IX Item "architecture" The kind of computer you're working on, where one \*(L"kind\*(R" of computer means all those computers sharing a compatible machine language. Since Perl programs are (typically) simple text files, not executable images, a Perl program is much less sensitive to the architecture it's running on than programs in other languages, such as C, that are compiled into machine code. See also \*(L"platform\*(R" and \*(L"operating system\*(R". .IP "argument" 4 .IX Item "argument" A piece of data supplied to a program, \&\*(L"subroutine\*(R", \*(L"function\*(R", or \*(L"method\*(R" to tell it what it's supposed to do. Also called a \*(L"parameter\*(R". .IP "\s-1ARGV\s0" 4 .IX Item "ARGV" The name of the array containing the \*(L"argument\*(R" \*(L"vector\*(R" from the command line. If you use the empty \f(CW\*(C`<>\*(C'\fR operator, \*(L"\s-1ARGV\s0\*(R" is the name of both the \*(L"filehandle\*(R" used to traverse the arguments and the \*(L"scalar\*(R" containing the name of the current input file. .IP "arithmetical operator" 4 .IX Item "arithmetical operator" A \*(L"symbol\*(R" such as \f(CW\*(C`+\*(C'\fR or \f(CW\*(C`/\*(C'\fR that tells Perl to do the arithmetic you were supposed to learn in grade school. .IP "array" 4 .IX Item "array" An ordered sequence of values, stored such that you can easily access any of the values using an integer \*(L"subscript\*(R" that specifies the value's \*(L"offset\*(R" in the sequence. .IP "array context" 4 .IX Item "array context" An archaic expression for what is more correctly referred to as \&\*(L"list context\*(R". .IP "\s-1ASCII\s0" 4 .IX Item "ASCII" The American Standard Code for Information Interchange (a 7\-bit character set adequate only for poorly representing English text). Often used loosely to describe the lowest 128 values of the various \&\s-1ISO\-8859\-X\s0 character sets, a bunch of mutually incompatible 8\-bit codes sometimes described as half \s-1ASCII\s0. See also \*(L"Unicode\*(R". .IP "assertion" 4 .IX Item "assertion" A component of a \*(L"regular expression\*(R" that must be true for the pattern to match but does not necessarily match any characters itself. Often used specifically to mean a \*(L"zero width\*(R" assertion. .IP "assignment" 4 .IX Item "assignment" An \*(L"operator\*(R" whose assigned mission in life is to change the value of a \*(L"variable\*(R". .IP "assignment operator" 4 .IX Item "assignment operator" Either a regular \*(L"assignment\*(R", or a compound \*(L"operator\*(R" composed of an ordinary assignment and some other operator, that changes the value of a variable in place, that is, relative to its old value. For example, \f(CW\*(C`$a += 2\*(C'\fR adds \f(CW2\fR to \f(CW$a\fR. .IP "associative array" 4 .IX Item "associative array" See \*(L"hash\*(R". Please. .IP "associativity" 4 .IX Item "associativity" Determines whether you do the left \*(L"operator\*(R" first or the right \&\*(L"operator\*(R" first when you have "A \*(L"operator\*(R" B \*(L"operator\*(R" C" and the two operators are of the same precedence. Operators like \f(CW\*(C`+\*(C'\fR are left associative, while operators like \f(CW\*(C`**\*(C'\fR are right associative. See perlop for a list of operators and their associativity. .IP "asynchronous" 4 .IX Item "asynchronous" Said of events or activities whose relative temporal ordering is indeterminate because too many things are going on at once. Hence, an asynchronous event is one you didn't know when to expect. .IP "atom" 4 .IX Item "atom" A \*(L"regular expression\*(R" component potentially matching a \&\*(L"substring\*(R" containing one or more characters and treated as an indivisible syntactic unit by any following \*(L"quantifier\*(R". (Contrast with an \*(L"assertion\*(R" that matches something of \*(L"zero width\*(R" and may not be quantified.) .IP "atomic operation" 4 .IX Item "atomic operation" When Democritus gave the word \*(L"atom\*(R" to the indivisible bits of matter, he meant literally something that could not be cut: \fIa\-\fR (not) + \fItomos\fR (cuttable). An atomic operation is an action that can't be interrupted, not one forbidden in a nuclear-free zone. .IP "attribute" 4 .IX Item "attribute" A new feature that allows the declaration of variables and subroutines with modifiers as in \f(CW\*(C`sub foo : locked method\*(C'\fR. Also, another name for an \*(L"instance variable\*(R" of an \&\*(L"object\*(R". .IP "autogeneration" 4 .IX Item "autogeneration" A feature of \*(L"operator overloading\*(R" of objects, whereby the behavior of certain operators can be reasonably deduced using more fundamental operators. This assumes that the overloaded operators will often have the same relationships as the regular operators. See perlop. .IP "autoincrement" 4 .IX Item "autoincrement" To add one to something automatically, hence the name of the \f(CW\*(C`++\*(C'\fR operator. To instead subtract one from something automatically is known as an \*(L"autodecrement\*(R". .IP "autoload" 4 .IX Item "autoload" To load on demand. (Also called \*(L"lazy\*(R" loading.) Specifically, to call an \s-1AUTOLOAD\s0 subroutine on behalf of an undefined subroutine. .IP "autosplit" 4 .IX Item "autosplit" To split a string automatically, as the \fB\-a\fR \*(L"switch\*(R" does when running under \fB\-p\fR or \fB\-n\fR in order to emulate \*(L"awk\*(R". (See also the AutoSplit module, which has nothing to do with the \fB\-a\fR switch, but a lot to do with autoloading.) .IP "autovivification" 4 .IX Item "autovivification" A Greco-Roman word meaning \*(L"to bring oneself to life\*(R". In Perl, storage locations (lvalues) spontaneously generate themselves as needed, including the creation of any \*(L"hard reference\*(R" values to point to the next level of storage. The assignment \&\f(CW\*(C`$a[5][5][5][5][5] = "quintet"\*(C'\fR potentially creates five scalar storage locations, plus four references (in the first four scalar locations) pointing to four new anonymous arrays (to hold the last four scalar locations). But the point of autovivification is that you don't have to worry about it. .IP "\s-1AV\s0" 4 .IX Item "AV" Short for \*(L"array value\*(R", which refers to one of Perl's internal data types that holds an \*(L"array\*(R". The \*(L"\s-1AV\s0\*(R" type is a subclass of \&\*(L"\s-1SV\s0\*(R". .IP "awk" 4 .IX Item "awk" Descriptive editing term\*(--short for \*(L"awkward\*(R". Also coincidentally refers to a venerable text-processing language from which Perl derived some of its high-level ideas. .SS "B" .IX Subsection "B" .IP "backreference" 4 .IX Item "backreference" A substring captured by a subpattern within unadorned parentheses in a \*(L"regex\*(R", also referred to as a capture group. The sequences (\f(CW\*(C`\eg1\*(C'\fR, \f(CW\*(C`\eg2\*(C'\fR, etc.) later in the same pattern refer back to the corresponding subpattern in the current match. Outside the pattern, the numbered variables (\f(CW$1\fR, \f(CW$2\fR, etc.) continue to refer to these same values, as long as the pattern was the last successful match of the current dynamic scope. \f(CW\*(C`\eg{\-1}\*(C'\fR can be used to refer to a group by relative rather than absolute position; and groups can be also be named, and referred to later by name rather than number. See \*(L"Capture groups\*(R" in perlre. .IP "backtracking" 4 .IX Item "backtracking" The practice of saying, \*(L"If I had to do it all over, I'd do it differently,\*(R" and then actually going back and doing it all over differently. Mathematically speaking, it's returning from an unsuccessful recursion on a tree of possibilities. Perl backtracks when it attempts to match patterns with a \*(L"regular expression\*(R", and its earlier attempts don't pan out. See \*(L"Backtracking\*(R" in perlre. .IP "backward compatibility" 4 .IX Item "backward compatibility" Means you can still run your old program because we didn't break any of the features or bugs it was relying on. .IP "bareword" 4 .IX Item "bareword" A word sufficiently ambiguous to be deemed illegal under use strict \&'subs'. In the absence of that stricture, a bareword is treated as if quotes were around it. .IP "base class" 4 .IX Item "base class" A generic \*(L"object\*(R" type; that is, a \*(L"class\*(R" from which other, more specific classes are derived genetically by \*(L"inheritance\*(R". Also called a \*(L"superclass\*(R" by people who respect their ancestors. .IP "big-endian" 4 .IX Item "big-endian" From Swift: someone who eats eggs big end first. Also used of computers that store the most significant \*(L"byte\*(R" of a word at a lower byte address than the least significant byte. Often considered superior to little-endian machines. See also \*(L"little-endian\*(R". .IP "binary" 4 .IX Item "binary" Having to do with numbers represented in base 2. That means there's basically two numbers, 0 and 1. Also used to describe a \*(L"non-text file\*(R", presumably because such a file makes full use of all the binary bits in its bytes. With the advent of \*(L"Unicode\*(R", this distinction, already suspect, loses even more of its meaning. .IP "binary operator" 4 .IX Item "binary operator" An \*(L"operator\*(R" that takes two operands. .IP "bind" 4 .IX Item "bind" To assign a specific \*(L"network address\*(R" to a \*(L"socket\*(R". .IP "bit" 4 .IX Item "bit" An integer in the range from 0 to 1, inclusive. The smallest possible unit of information storage. An eighth of a \*(L"byte\*(R" or of a dollar. (The term \*(L"Pieces of Eight\*(R" comes from being able to split the old Spanish dollar into 8 bits, each of which still counted for money. That's why a 25\-cent piece today is still \*(L"two bits\*(R".) .IP "bit shift" 4 .IX Item "bit shift" The movement of bits left or right in a computer word, which has the effect of multiplying or dividing by a power of 2. .IP "bit string" 4 .IX Item "bit string" A sequence of bits that is actually being thought of as a sequence of bits, for once. .IP "bless" 4 .IX Item "bless" In corporate life, to grant official approval to a thing, as in, \*(L"The \&\s-1VP\s0 of Engineering has blessed our WebCruncher project.\*(R" Similarly in Perl, to grant official approval to a \*(L"referent\*(R" so that it can function as an \*(L"object\*(R", such as a WebCruncher object. See \&\*(L"bless\*(R" in perlfunc. .IP "block" 4 .IX Item "block" What a \*(L"process\*(R" does when it has to wait for something: \*(L"My process blocked waiting for the disk.\*(R" As an unrelated noun, it refers to a large chunk of data, of a size that the \*(L"operating system\*(R" likes to deal with (normally a power of two such as 512 or 8192). Typically refers to a chunk of data that's coming from or going to a disk file. .IP "\s-1BLOCK\s0" 4 .IX Item "BLOCK" A syntactic construct consisting of a sequence of Perl statements that is delimited by braces. The \f(CW\*(C`if\*(C'\fR and \&\f(CW\*(C`while\*(C'\fR statements are defined in terms of BLOCKs, for instance. Sometimes we also say \*(L"block\*(R" to mean a lexical scope; that is, a sequence of statements that act like a \*(L"\s-1BLOCK\s0\*(R", such as within an eval or a file, even though the statements aren't delimited by braces. .IP "block buffering" 4 .IX Item "block buffering" A method of making input and output efficient by passing one \*(L"block\*(R" at a time. By default, Perl does block buffering to disk files. See \&\*(L"buffer\*(R" and \*(L"command buffering\*(R". .IP "Boolean" 4 .IX Item "Boolean" A value that is either \*(L"true\*(R" or \*(L"false\*(R". .IP "Boolean context" 4 .IX Item "Boolean context" A special kind of \*(L"scalar context\*(R" used in conditionals to decide whether the \*(L"scalar value\*(R" returned by an expression is \*(L"true\*(R" or \&\*(L"false\*(R". Does not evaluate as either a string or a number. See \&\*(L"context\*(R". .IP "breakpoint" 4 .IX Item "breakpoint" A spot in your program where you've told the debugger to stop execution so you can poke around and see whether anything is wrong yet. .IP "broadcast" 4 .IX Item "broadcast" To send a \*(L"datagram\*(R" to multiple destinations simultaneously. .IP "\s-1BSD\s0" 4 .IX Item "BSD" A psychoactive drug, popular in the 80s, probably developed at U. C. Berkeley or thereabouts. Similar in many ways to the prescription-only medication called \*(L"System V\*(R", but infinitely more useful. (Or, at least, more fun.) The full chemical name is \&\*(L"Berkeley Standard Distribution\*(R". .IP "bucket" 4 .IX Item "bucket" A location in a \*(L"hash table\*(R" containing (potentially) multiple entries whose keys \*(L"hash\*(R" to the same hash value according to its hash function. (As internal policy, you don't have to worry about it, unless you're into internals, or policy.) .IP "buffer" 4 .IX Item "buffer" A temporary holding location for data. Block buffering means that the data is passed on to its destination whenever the buffer is full. Line buffering means that it's passed on whenever a complete line is received. Command buffering means that it's passed every time you do a print command (or equivalent). If your output is unbuffered, the system processes it one byte at a time without the use of a holding area. This can be rather inefficient. .IP "built-in" 4 .IX Item "built-in" A \*(L"function\*(R" that is predefined in the language. Even when hidden by \*(L"overriding\*(R", you can always get at a built-in function by qualifying its name with the \f(CW\*(C`CORE::\*(C'\fR pseudo-package. .IP "bundle" 4 .IX Item "bundle" A group of related modules on \*(L"\s-1CPAN\s0\*(R". (Also, sometimes refers to a group of command-line switches grouped into one \*(L"switch cluster\*(R".) .IP "byte" 4 .IX Item "byte" A piece of data worth eight bits in most places. .IP "bytecode" 4 .IX Item "bytecode" A pidgin-like language spoken among 'droids when they don't wish to reveal their orientation (see \*(L"endian\*(R"). Named after some similar languages spoken (for similar reasons) between compilers and interpreters in the late 20th century. These languages are characterized by representing everything as a non-architecture-dependent sequence of bytes. .SS "C" .IX Subsection "C" .IP "C" 4 .IX Item "C" A language beloved by many for its inside-out \*(L"type\*(R" definitions, inscrutable \*(L"precedence\*(R" rules, and heavy \*(L"overloading\*(R" of the function-call mechanism. (Well, actually, people first switched to C because they found lowercase identifiers easier to read than upper.) Perl is written in C, so it's not surprising that Perl borrowed a few ideas from it. .IP "C preprocessor" 4 .IX Item "C preprocessor" The typical C compiler's first pass, which processes lines beginning with \f(CW\*(C`#\*(C'\fR for conditional compilation and macro definition and does various manipulations of the program text based on the current definitions. Also known as \fIcpp\fR(1). .IP "call by reference" 4 .IX Item "call by reference" An \*(L"argument\*(R"\-passing mechanism in which the \*(L"formal arguments\*(R" refer directly to the \*(L"actual arguments\*(R", and the \*(L"subroutine\*(R" can change the actual arguments by changing the formal arguments. That is, the formal argument is an \*(L"alias\*(R" for the actual argument. See also \*(L"call by value\*(R". .IP "call by value" 4 .IX Item "call by value" An \*(L"argument\*(R"\-passing mechanism in which the \*(L"formal arguments\*(R" refer to a copy of the \*(L"actual arguments\*(R", and the \*(L"subroutine\*(R" cannot change the actual arguments by changing the formal arguments. See also \*(L"call by reference\*(R". .IP "callback" 4 .IX Item "callback" A \*(L"handler\*(R" that you register with some other part of your program in the hope that the other part of your program will \*(L"trigger\*(R" your handler when some event of interest transpires. .IP "canonical" 4 .IX Item "canonical" Reduced to a standard form to facilitate comparison. .IP "capture buffer, capture group" 4 .IX Item "capture buffer, capture group" These two terms are synonymous: a captured substring by a regex subpattern. .IP "capturing" 4 .IX Item "capturing" The use of parentheses around a \*(L"subpattern\*(R" in a \*(L"regular expression\*(R" to store the matched \*(L"substring\*(R" as a \*(L"backreference\*(R" or capture group. (Captured strings are also returned as a list in \*(L"list context\*(R".) .IP "character" 4 .IX Item "character" A small integer representative of a unit of orthography. Historically, characters were usually stored as fixed-width integers (typically in a byte, or maybe two, depending on the character set), but with the advent of \s-1UTF\-8\s0, characters are often stored in a variable number of bytes depending on the size of the integer that represents the character. Perl manages this transparently for you, for the most part. .IP "character class" 4 .IX Item "character class" A square-bracketed list of characters used in a \*(L"regular expression\*(R" to indicate that any character of the set may occur at a given point. Loosely, any predefined set of characters so used. .IP "character property" 4 .IX Item "character property" A predefined \*(L"character class\*(R" matchable by the \f(CW\*(C`\ep\*(C'\fR \&\*(L"metasymbol\*(R". Many standard properties are defined for \*(L"Unicode\*(R". .IP "circumfix operator" 4 .IX Item "circumfix operator" An \*(L"operator\*(R" that surrounds its \*(L"operand\*(R", like the angle operator, or parentheses, or a hug. .IP "class" 4 .IX Item "class" A user-defined \*(L"type\*(R", implemented in Perl via a \*(L"package\*(R" that provides (either directly or by inheritance) methods (that is, subroutines) to handle instances of the class (its objects). See also \*(L"inheritance\*(R". .IP "class method" 4 .IX Item "class method" A \*(L"method\*(R" whose \*(L"invocant\*(R" is a \*(L"package\*(R" name, not an \&\*(L"object\*(R" reference. A method associated with the class as a whole. .IP "client" 4 .IX Item "client" In networking, a \*(L"process\*(R" that initiates contact with a \*(L"server\*(R" process in order to exchange data and perhaps receive a service. .IP "cloister" 4 .IX Item "cloister" A \*(L"cluster\*(R" used to restrict the scope of a \*(L"regular expression modifier\*(R". .IP "closure" 4 .IX Item "closure" An \*(L"anonymous\*(R" subroutine that, when a reference to it is generated at run time, keeps track of the identities of externally visible lexical variables even after those lexical variables have supposedly gone out of \*(L"scope\*(R". They're called \&\*(L"closures\*(R" because this sort of behavior gives mathematicians a sense of closure. .IP "cluster" 4 .IX Item "cluster" A parenthesized \*(L"subpattern\*(R" used to group parts of a \*(L"regular expression\*(R" into a single \*(L"atom\*(R". .IP "\s-1CODE\s0" 4 .IX Item "CODE" The word returned by the ref function when you apply it to a reference to a subroutine. See also \*(L"\s-1CV\s0\*(R". .IP "code generator" 4 .IX Item "code generator" A system that writes code for you in a low-level language, such as code to implement the backend of a compiler. See \*(L"program generator\*(R". .IP "code point" 4 .IX Item "code point" The position of a character in a character set encoding. The character \&\f(CW\*(C`NULL\*(C'\fR is almost certainly at the zeroth position in all character sets, so its code point is 0. The code point for the \f(CW\*(C`SPACE\*(C'\fR character in the \s-1ASCII\s0 character set is 0x20, or 32 decimal; in \s-1EBCDIC\s0 it is 0x40, or 64 decimal. The ord function returns the code point of a character. .Sp \&\*(L"code position\*(R" and \*(L"ordinal\*(R" mean the same thing as \*(L"code point\*(R". .IP "code subpattern" 4 .IX Item "code subpattern" A \*(L"regular expression\*(R" subpattern whose real purpose is to execute some Perl code, for example, the \f(CW\*(C`(?{...})\*(C'\fR and \f(CW\*(C`(??{...})\*(C'\fR subpatterns. .IP "collating sequence" 4 .IX Item "collating sequence" The order into which characters sort. This is used by \&\*(L"string\*(R" comparison routines to decide, for example, where in this glossary to put \*(L"collating sequence\*(R". .IP "command" 4 .IX Item "command" In \*(L"shell\*(R" programming, the syntactic combination of a program name and its arguments. More loosely, anything you type to a shell (a command interpreter) that starts it doing something. Even more loosely, a Perl \*(L"statement\*(R", which might start with a \*(L"label\*(R" and typically ends with a semicolon. .IP "command buffering" 4 .IX Item "command buffering" A mechanism in Perl that lets you store up the output of each Perl \&\*(L"command\*(R" and then flush it out as a single request to the \&\*(L"operating system\*(R". It's enabled by setting the \f(CW$|\fR (\f(CW$AUTOFLUSH\fR) variable to a true value. It's used when you don't want data sitting around not going where it's supposed to, which may happen because the default on a \*(L"file\*(R" or \*(L"pipe\*(R" is to use \&\*(L"block buffering\*(R". .IP "command name" 4 .IX Item "command name" The name of the program currently executing, as typed on the command line. In C, the \*(L"command\*(R" name is passed to the program as the first command-line argument. In Perl, it comes in separately as \&\f(CW$0\fR. .IP "command-line arguments" 4 .IX Item "command-line arguments" The values you supply along with a program name when you tell a \*(L"shell\*(R" to execute a \*(L"command\*(R". These values are passed to a Perl program through \f(CW@ARGV\fR. .IP "comment" 4 .IX Item "comment" A remark that doesn't affect the meaning of the program. In Perl, a comment is introduced by a \f(CW\*(C`#\*(C'\fR character and continues to the end of the line. .IP "compilation unit" 4 .IX Item "compilation unit" The \*(L"file\*(R" (or \*(L"string\*(R", in the case of eval) that is currently being compiled. .IP "compile phase" 4 .IX Item "compile phase" Any time before Perl starts running your main program. See also \&\*(L"run phase\*(R". Compile phase is mostly spent in \*(L"compile time\*(R", but may also be spent in \*(L"run time\*(R" when \f(CW\*(C`BEGIN\*(C'\fR blocks, use declarations, or constant subexpressions are being evaluated. The startup and import code of any use declaration is also run during compile phase. .IP "compile time" 4 .IX Item "compile time" The time when Perl is trying to make sense of your code, as opposed to when it thinks it knows what your code means and is merely trying to do what it thinks your code says to do, which is \*(L"run time\*(R". .IP "compiler" 4 .IX Item "compiler" Strictly speaking, a program that munches up another program and spits out yet another file containing the program in a \*(L"more executable\*(R" form, typically containing native machine instructions. The \fIperl\fR program is not a compiler by this definition, but it does contain a kind of compiler that takes a program and turns it into a more executable form (syntax trees) within the \fIperl\fR process itself, which the \*(L"interpreter\*(R" then interprets. There are, however, extension modules to get Perl to act more like a \&\*(L"real\*(R" compiler. See O. .IP "composer" 4 .IX Item "composer" A \*(L"constructor\*(R" for a \*(L"referent\*(R" that isn't really an \*(L"object\*(R", like an anonymous array or a hash (or a sonata, for that matter). For example, a pair of braces acts as a composer for a hash, and a pair of brackets acts as a composer for an array. See \*(L"Making References\*(R" in perlref. .IP "concatenation" 4 .IX Item "concatenation" The process of gluing one cat's nose to another cat's tail. Also, a similar operation on two strings. .IP "conditional" 4 .IX Item "conditional" Something \*(L"iffy\*(R". See \*(L"Boolean context\*(R". .IP "connection" 4 .IX Item "connection" In telephony, the temporary electrical circuit between the caller's and the callee's phone. In networking, the same kind of temporary circuit between a \*(L"client\*(R" and a \*(L"server\*(R". .IP "construct" 4 .IX Item "construct" As a noun, a piece of syntax made up of smaller pieces. As a transitive verb, to create an \*(L"object\*(R" using a \*(L"constructor\*(R". .IP "constructor" 4 .IX Item "constructor" Any \*(L"class method\*(R", instance \*(L"method\*(R", or \*(L"subroutine\*(R" that composes, initializes, blesses, and returns an \*(L"object\*(R". Sometimes we use the term loosely to mean a \*(L"composer\*(R". .IP "context" 4 .IX Item "context" The surroundings, or environment. The context given by the surrounding code determines what kind of data a particular \&\*(L"expression\*(R" is expected to return. The three primary contexts are \&\*(L"list context\*(R", \*(L"scalar context\*(R", and \*(L"void context\*(R". Scalar context is sometimes subdivided into \*(L"Boolean context\*(R", \*(L"numeric context\*(R", \*(L"string context\*(R", and \*(L"void context\*(R". There's also a \&\*(L"don't care\*(R" scalar context (which is dealt with in Programming Perl, Third Edition, Chapter 2, \*(L"Bits and Pieces\*(R" if you care). .IP "continuation" 4 .IX Item "continuation" The treatment of more than one physical \*(L"line\*(R" as a single logical line. \*(L"Makefile\*(R" lines are continued by putting a backslash before the \*(L"newline\*(R". Mail headers as defined by \s-1RFC\s0 822 are continued by putting a space or tab \fIafter\fR the newline. In general, lines in Perl do not need any form of continuation mark, because \*(L"whitespace\*(R" (including newlines) is gleefully ignored. Usually. .IP "core dump" 4 .IX Item "core dump" The corpse of a \*(L"process\*(R", in the form of a file left in the \&\*(L"working directory\*(R" of the process, usually as a result of certain kinds of fatal error. .IP "\s-1CPAN\s0" 4 .IX Item "CPAN" The Comprehensive Perl Archive Network. (See \*(L"What modules and extensions are available for Perl? What is \s-1CPAN\s0? What does CPAN/src/... mean?\*(R" in perlfaq2). .IP "cracker" 4 .IX Item "cracker" Someone who breaks security on computer systems. A cracker may be a true \*(L"hacker\*(R" or only a \*(L"script kiddie\*(R". .IP "current package" 4 .IX Item "current package" The \*(L"package\*(R" in which the current statement is compiled. Scan backwards in the text of your program through the current lexical scope or any enclosing lexical scopes till you find a package declaration. That's your current package name. .IP "current working directory" 4 .IX Item "current working directory" See \*(L"working directory\*(R". .IP "currently selected output channel" 4 .IX Item "currently selected output channel" The last \*(L"filehandle\*(R" that was designated with select(\f(CW\*(C`FILEHANDLE\*(C'\fR); \*(L"\s-1STDOUT\s0\*(R", if no filehandle has been selected. .IP "\s-1CV\s0" 4 .IX Item "CV" An internal \*(L"code value\*(R" typedef, holding a \*(L"subroutine\*(R". The \*(L"\s-1CV\s0\*(R" type is a subclass of \*(L"\s-1SV\s0\*(R". .SS "D" .IX Subsection "D" .IP "dangling statement" 4 .IX Item "dangling statement" A bare, single \*(L"statement\*(R", without any braces, hanging off an \f(CW\*(C`if\*(C'\fR or \f(CW\*(C`while\*(C'\fR conditional. C allows them. Perl doesn't. .IP "data structure" 4 .IX Item "data structure" How your various pieces of data relate to each other and what shape they make when you put them all together, as in a rectangular table or a triangular-shaped tree. .IP "data type" 4 .IX Item "data type" A set of possible values, together with all the operations that know how to deal with those values. For example, a numeric data type has a certain set of numbers that you can work with and various mathematical operations that you can do on the numbers but would make little sense on, say, a string such as \f(CW"Kilroy"\fR. Strings have their own operations, such as \*(L"concatenation\*(R". Compound types made of a number of smaller pieces generally have operations to compose and decompose them, and perhaps to rearrange them. Objects that model things in the real world often have operations that correspond to real activities. For instance, if you model an elevator, your elevator object might have an \f(CW\*(C`open_door()\*(C'\fR \&\*(L"method\*(R". .IP "datagram" 4 .IX Item "datagram" A packet of data, such as a \*(L"\s-1UDP\s0\*(R" message, that (from the viewpoint of the programs involved) can be sent independently over the network. (In fact, all packets are sent independently at the \*(L"\s-1IP\s0\*(R" level, but \&\*(L"stream\*(R" protocols such as \*(L"\s-1TCP\s0\*(R" hide this from your program.) .IP "\s-1DBM\s0" 4 .IX Item "DBM" Stands for \*(L"Data Base Management\*(R" routines, a set of routines that emulate an \*(L"associative array\*(R" using disk files. The routines use a dynamic hashing scheme to locate any entry with only two disk accesses. \s-1DBM\s0 files allow a Perl program to keep a persistent \&\*(L"hash\*(R" across multiple invocations. You can tie your hash variables to various \s-1DBM\s0 implementations\*(--see AnyDBM_File and DB_File. .IP "declaration" 4 .IX Item "declaration" An \*(L"assertion\*(R" that states something exists and perhaps describes what it's like, without giving any commitment as to how or where you'll use it. A declaration is like the part of your recipe that says, \*(L"two cups flour, one large egg, four or five tadpoles...\*(R" See \&\*(L"statement\*(R" for its opposite. Note that some declarations also function as statements. Subroutine declarations also act as definitions if a body is supplied. .IP "decrement" 4 .IX Item "decrement" To subtract a value from a variable, as in "decrement \f(CW$x\fR\*(L" (meaning to remove 1 from its value) or \*(R"decrement \f(CW$x\fR by 3". .IP "default" 4 .IX Item "default" A \*(L"value\*(R" chosen for you if you don't supply a value of your own. .IP "defined" 4 .IX Item "defined" Having a meaning. Perl thinks that some of the things people try to do are devoid of meaning, in particular, making use of variables that have never been given a \*(L"value\*(R" and performing certain operations on data that isn't there. For example, if you try to read data past the end of a file, Perl will hand you back an undefined value. See also \&\*(L"false\*(R" and \*(L"defined\*(R" in perlfunc. .IP "delimiter" 4 .IX Item "delimiter" A \*(L"character\*(R" or \*(L"string\*(R" that sets bounds to an arbitrarily-sized textual object, not to be confused with a \*(L"separator\*(R" or \&\*(L"terminator\*(R". \*(L"To delimit\*(R" really just means \*(L"to surround\*(R" or \*(L"to enclose\*(R" (like these parentheses are doing). .IP "deprecated modules and features" 4 .IX Item "deprecated modules and features" Deprecated modules and features are those which were part of a stable release, but later found to be subtly flawed, and which should be avoided. They are subject to removal and/or bug-incompatible reimplementation in the next major release (but they will be preserved through maintenance releases). Deprecation warnings are issued under \fB\-w\fR or \f(CW\*(C`use diagnostics\*(C'\fR, and notices are found in perldeltas, as well as various other PODs. Coding practices that misuse features, such as \f(CW\*(C`my $foo if 0\*(C'\fR, can also be deprecated. .IP "dereference" 4 .IX Item "dereference" A fancy computer science term meaning "to follow a \*(L"reference\*(R" to what it points to\*(L". The \*(R"de" part of it refers to the fact that you're taking away one level of \*(L"indirection\*(R". .IP "derived class" 4 .IX Item "derived class" A \*(L"class\*(R" that defines some of its methods in terms of a more generic class, called a \*(L"base class\*(R". Note that classes aren't classified exclusively into base classes or derived classes: a class can function as both a derived class and a base class simultaneously, which is kind of classy. .IP "descriptor" 4 .IX Item "descriptor" See \*(L"file descriptor\*(R". .IP "destroy" 4 .IX Item "destroy" To deallocate the memory of a \*(L"referent\*(R" (first triggering its \&\f(CW\*(C`DESTROY\*(C'\fR method, if it has one). .IP "destructor" 4 .IX Item "destructor" A special \*(L"method\*(R" that is called when an \*(L"object\*(R" is thinking about destroying itself. A Perl program's \f(CW\*(C`DESTROY\*(C'\fR method doesn't do the actual destruction; Perl just triggers the method in case the \*(L"class\*(R" wants to do any associated cleanup. .IP "device" 4 .IX Item "device" A whiz-bang hardware gizmo (like a disk or tape drive or a modem or a joystick or a mouse) attached to your computer, that the \*(L"operating system\*(R" tries to make look like a \*(L"file\*(R" (or a bunch of files). Under Unix, these fake files tend to live in the \fI/dev\fR directory. .IP "directive" 4 .IX Item "directive" A \*(L"pod\*(R" directive. See perlpod. .IP "directory" 4 .IX Item "directory" A special file that contains other files. Some operating systems call these \*(L"folders\*(R", \*(L"drawers\*(R", or \&\*(L"catalogs\*(R". .IP "directory handle" 4 .IX Item "directory handle" A name that represents a particular instance of opening a directory to read it, until you close it. See the opendir function. .IP "dispatch" 4 .IX Item "dispatch" To send something to its correct destination. Often used metaphorically to indicate a transfer of programmatic control to a destination selected algorithmically, often by lookup in a table of function references or, in the case of object methods, by traversing the inheritance tree looking for the most specific definition for the method. .IP "distribution" 4 .IX Item "distribution" A standard, bundled release of a system of software. The default usage implies source code is included. If that is not the case, it will be called a \*(L"binary-only\*(R" distribution. .IP "(to be) dropped modules" 4 .IX Item "(to be) dropped modules" When Perl 5 was first released (see perlhist), several modules were included, which have now fallen out of common use. It has been suggested that these modules should be removed, since the distribution became rather large, and the common criterion for new module additions is now limited to modules that help to build, test, and extend perl itself. Furthermore, the \s-1CPAN\s0 (which didn't exist at the time of Perl 5.0) can become the new home of dropped modules. Dropping modules is currently not an option, but further developments may clear the last barriers. .IP "dweomer" 4 .IX Item "dweomer" An enchantment, illusion, phantasm, or jugglery. Said when Perl's magical \*(L"dwimmer\*(R" effects don't do what you expect, but rather seem to be the product of arcane dweomercraft, sorcery, or wonder working. [From Old English] .IP "dwimmer" 4 .IX Item "dwimmer" \&\s-1DWIM\s0 is an acronym for \*(L"Do What I Mean\*(R", the principle that something should just do what you want it to do without an undue amount of fuss. A bit of code that does \*(L"dwimming\*(R" is a \*(L"dwimmer\*(R". Dwimming can require a great deal of behind-the-scenes magic, which (if it doesn't stay properly behind the scenes) is called a \*(L"dweomer\*(R" instead. .IP "dynamic scoping" 4 .IX Item "dynamic scoping" Dynamic scoping works over a dynamic scope, making variables visible throughout the rest of the \*(L"block\*(R" in which they are first used and in any subroutines that are called by the rest of the block. Dynamically scoped variables can have their values temporarily changed (and implicitly restored later) by a local operator. (Compare \*(L"lexical scoping\*(R".) Used more loosely to mean how a subroutine that is in the middle of calling another subroutine \&\*(L"contains\*(R" that subroutine at \*(L"run time\*(R". .SS "E" .IX Subsection "E" .IP "eclectic" 4 .IX Item "eclectic" Derived from many sources. Some would say \fItoo\fR many. .IP "element" 4 .IX Item "element" A basic building block. When you're talking about an \*(L"array\*(R", it's one of the items that make up the array. .IP "embedding" 4 .IX Item "embedding" When something is contained in something else, particularly when that might be considered surprising: \*(L"I've embedded a complete Perl interpreter in my editor!\*(R" .IP "empty subclass test" 4 .IX Item "empty subclass test" The notion that an empty \*(L"derived class\*(R" should behave exactly like its \*(L"base class\*(R". .IP "en passant" 4 .IX Item "en passant" When you change a \*(L"value\*(R" as it is being copied. [From French, \*(L"in passing\*(R", as in the exotic pawn-capturing maneuver in chess.] .IP "encapsulation" 4 .IX Item "encapsulation" The veil of abstraction separating the \*(L"interface\*(R" from the \&\*(L"implementation\*(R" (whether enforced or not), which mandates that all access to an \*(L"object\*(R"'s state be through methods alone. .IP "endian" 4 .IX Item "endian" See \*(L"little-endian\*(R" and \*(L"big-endian\*(R". .IP "environment" 4 .IX Item "environment" The collective set of environment variables your \*(L"process\*(R" inherits from its parent. Accessed via \f(CW%ENV\fR. .IP "environment variable" 4 .IX Item "environment variable" A mechanism by which some high-level agent such as a user can pass its preferences down to its future offspring (child processes, grandchild processes, great-grandchild processes, and so on). Each environment variable is a \*(L"key\*(R"/\*(L"value\*(R" pair, like one entry in a \&\*(L"hash\*(R". .IP "\s-1EOF\s0" 4 .IX Item "EOF" End of File. Sometimes used metaphorically as the terminating string of a \*(L"here document\*(R". .IP "errno" 4 .IX Item "errno" The error number returned by a \*(L"syscall\*(R" when it fails. Perl refers to the error by the name \f(CW$!\fR (or \f(CW$OS_ERROR\fR if you use the English module). .IP "error" 4 .IX Item "error" See \*(L"exception\*(R" or \*(L"fatal error\*(R". .IP "escape sequence" 4 .IX Item "escape sequence" See \*(L"metasymbol\*(R". .IP "exception" 4 .IX Item "exception" A fancy term for an error. See \*(L"fatal error\*(R". .IP "exception handling" 4 .IX Item "exception handling" The way a program responds to an error. The exception handling mechanism in Perl is the eval operator. .IP "exec" 4 .IX Item "exec" To throw away the current \*(L"process\*(R"'s program and replace it with another without exiting the process or relinquishing any resources held (apart from the old memory image). .IP "executable file" 4 .IX Item "executable file" A \*(L"file\*(R" that is specially marked to tell the \*(L"operating system\*(R" that it's okay to run this file as a program. Usually shortened to \&\*(L"executable\*(R". .IP "execute" 4 .IX Item "execute" To run a program or \*(L"subroutine\*(R". (Has nothing to do with the kill built-in, unless you're trying to run a \*(L"signal handler\*(R".) .IP "execute bit" 4 .IX Item "execute bit" The special mark that tells the operating system it can run this program. There are actually three execute bits under Unix, and which bit gets used depends on whether you own the file singularly, collectively, or not at all. .IP "exit status" 4 .IX Item "exit status" See \*(L"status\*(R". .IP "export" 4 .IX Item "export" To make symbols from a \*(L"module\*(R" available for \*(L"import\*(R" by other modules. .IP "expression" 4 .IX Item "expression" Anything you can legally say in a spot where a \*(L"value\*(R" is required. Typically composed of literals, variables, operators, functions, and \*(L"subroutine\*(R" calls, not necessarily in that order. .IP "extension" 4 .IX Item "extension" A Perl module that also pulls in compiled C or \*(C+ code. More generally, any experimental option that can be compiled into Perl, such as multithreading. .SS "F" .IX Subsection "F" .IP "false" 4 .IX Item "false" In Perl, any value that would look like \f(CW""\fR or \f(CW"0"\fR if evaluated in a string context. Since undefined values evaluate to \f(CW""\fR, all undefined values are false, but not all false values are undefined. .IP "\s-1FAQ\s0" 4 .IX Item "FAQ" Frequently Asked Question (although not necessarily frequently answered, especially if the answer appears in the Perl \s-1FAQ\s0 shipped standard with Perl). .IP "fatal error" 4 .IX Item "fatal error" An uncaught \*(L"exception\*(R", which causes termination of the \*(L"process\*(R" after printing a message on your \*(L"standard error\*(R" stream. Errors that happen inside an eval are not fatal. Instead, the eval terminates after placing the exception message in the \f(CW$@\fR (\f(CW$EVAL_ERROR\fR) variable. You can try to provoke a fatal error with the die operator (known as throwing or raising an exception), but this may be caught by a dynamically enclosing eval. If not caught, the die becomes a fatal error. .IP "field" 4 .IX Item "field" A single piece of numeric or string data that is part of a longer \&\*(L"string\*(R", \*(L"record\*(R", or \*(L"line\*(R". Variable-width fields are usually split up by separators (so use split to extract the fields), while fixed-width fields are usually at fixed positions (so use unpack). Instance variables are also known as fields. .IP "\s-1FIFO\s0" 4 .IX Item "FIFO" First In, First Out. See also \*(L"\s-1LIFO\s0\*(R". Also, a nickname for a \&\*(L"named pipe\*(R". .IP "file" 4 .IX Item "file" A named collection of data, usually stored on disk in a \*(L"directory\*(R" in a \*(L"filesystem\*(R". Roughly like a document, if you're into office metaphors. In modern filesystems, you can actually give a file more than one name. Some files have special properties, like directories and devices. .IP "file descriptor" 4 .IX Item "file descriptor" The little number the \*(L"operating system\*(R" uses to keep track of which opened \*(L"file\*(R" you're talking about. Perl hides the file descriptor inside a \*(L"standard I/O\*(R" stream and then attaches the stream to a \*(L"filehandle\*(R". .IP "file test operator" 4 .IX Item "file test operator" A built-in unary operator that you use to determine whether something is \*(L"true\*(R" about a file, such as \f(CW\*(C`\-o $filename\*(C'\fR to test whether you're the owner of the file. .IP "fileglob" 4 .IX Item "fileglob" A \*(L"wildcard\*(R" match on filenames. See the glob function. .IP "filehandle" 4 .IX Item "filehandle" An identifier (not necessarily related to the real name of a file) that represents a particular instance of opening a file until you close it. If you're going to open and close several different files in succession, it's fine to open each of them with the same filehandle, so you don't have to write out separate code to process each file. .IP "filename" 4 .IX Item "filename" One name for a file. This name is listed in a \*(L"directory\*(R", and you can use it in an open to tell the \*(L"operating system\*(R" exactly which file you want to open, and associate the file with a \*(L"filehandle\*(R" which will carry the subsequent identity of that file in your program, until you close it. .IP "filesystem" 4 .IX Item "filesystem" A set of directories and files residing on a partition of the disk. Sometimes known as a \*(L"partition\*(R". You can change the file's name or even move a file around from directory to directory within a filesystem without actually moving the file itself, at least under Unix. .IP "filter" 4 .IX Item "filter" A program designed to take a \*(L"stream\*(R" of input and transform it into a stream of output. .IP "flag" 4 .IX Item "flag" We tend to avoid this term because it means so many things. It may mean a command-line \*(L"switch\*(R" that takes no argument itself (such as Perl's \fB\-n\fR and \fB\-p\fR flags) or, less frequently, a single-bit indicator (such as the \&\f(CW\*(C`O_CREAT\*(C'\fR and \f(CW\*(C`O_EXCL\*(C'\fR flags used in sysopen). .IP "floating point" 4 .IX Item "floating point" A method of storing numbers in \*(L"scientific notation\*(R", such that the precision of the number is independent of its magnitude (the decimal point \*(L"floats\*(R"). Perl does its numeric work with floating-point numbers (sometimes called \*(L"floats\*(R"), when it can't get away with using integers. Floating-point numbers are mere approximations of real numbers. .IP "flush" 4 .IX Item "flush" The act of emptying a \*(L"buffer\*(R", often before it's full. .IP "\s-1FMTEYEWTK\s0" 4 .IX Item "FMTEYEWTK" Far More Than Everything You Ever Wanted To Know. An exhaustive treatise on one narrow topic, something of a super\-\*(L"\s-1FAQ\s0\*(R". See Tom for far more. .IP "fork" 4 .IX Item "fork" To create a child \*(L"process\*(R" identical to the parent process at its moment of conception, at least until it gets ideas of its own. A thread with protected memory. .IP "formal arguments" 4 .IX Item "formal arguments" The generic names by which a \*(L"subroutine\*(R" knows its arguments. In many languages, formal arguments are always given individual names, but in Perl, the formal arguments are just the elements of an array. The formal arguments to a Perl program are \f(CW$ARGV[0]\fR, \f(CW$ARGV[1]\fR, and so on. Similarly, the formal arguments to a Perl subroutine are \f(CW$_[0]\fR, \f(CW$_[1]\fR, and so on. You may give the arguments individual names by assigning the values to a my list. See also \*(L"actual arguments\*(R". .IP "format" 4 .IX Item "format" A specification of how many spaces and digits and things to put somewhere so that whatever you're printing comes out nice and pretty. .IP "freely available" 4 .IX Item "freely available" Means you don't have to pay money to get it, but the copyright on it may still belong to someone else (like Larry). .IP "freely redistributable" 4 .IX Item "freely redistributable" Means you're not in legal trouble if you give a bootleg copy of it to your friends and we find out about it. In fact, we'd rather you gave a copy to all your friends. .IP "freeware" 4 .IX Item "freeware" Historically, any software that you give away, particularly if you make the source code available as well. Now often called \f(CW\*(C`open source software\*(C'\fR. Recently there has been a trend to use the term in contradistinction to \*(L"open source software\*(R", to refer only to free software released under the Free Software Foundation's \s-1GPL\s0 (General Public License), but this is difficult to justify etymologically. .IP "function" 4 .IX Item "function" Mathematically, a mapping of each of a set of input values to a particular output value. In computers, refers to a \*(L"subroutine\*(R" or \&\*(L"operator\*(R" that returns a \*(L"value\*(R". It may or may not have input values (called arguments). .IP "funny character" 4 .IX Item "funny character" Someone like Larry, or one of his peculiar friends. Also refers to the strange prefixes that Perl requires as noun markers on its variables. .SS "G" .IX Subsection "G" .IP "garbage collection" 4 .IX Item "garbage collection" A misnamed feature\*(--it should be called, \*(L"expecting your mother to pick up after you\*(R". Strictly speaking, Perl doesn't do this, but it relies on a reference-counting mechanism to keep things tidy. However, we rarely speak strictly and will often refer to the reference-counting scheme as a form of garbage collection. (If it's any comfort, when your interpreter exits, a \*(L"real\*(R" garbage collector runs to make sure everything is cleaned up if you've been messy with circular references and such.) .IP "\s-1GID\s0" 4 .IX Item "GID" Group ID\*(--in Unix, the numeric group \s-1ID\s0 that the \*(L"operating system\*(R" uses to identify you and members of your \*(L"group\*(R". .IP "glob" 4 .IX Item "glob" Strictly, the shell's \f(CW\*(C`*\*(C'\fR character, which will match a \*(L"glob\*(R" of characters when you're trying to generate a list of filenames. Loosely, the act of using globs and similar symbols to do pattern matching. See also \*(L"fileglob\*(R" and \*(L"typeglob\*(R". .IP "global" 4 .IX Item "global" Something you can see from anywhere, usually used of variables and subroutines that are visible everywhere in your program. In Perl, only certain special variables are truly global\*(--most variables (and all subroutines) exist only in the current \*(L"package\*(R". Global variables can be declared with our. See \*(L"our\*(R" in perlfunc. .IP "global destruction" 4 .IX Item "global destruction" The \*(L"garbage collection\*(R" of globals (and the running of any associated object destructors) that takes place when a Perl \&\*(L"interpreter\*(R" is being shut down. Global destruction should not be confused with the Apocalypse, except perhaps when it should. .IP "glue language" 4 .IX Item "glue language" A language such as Perl that is good at hooking things together that weren't intended to be hooked together. .IP "granularity" 4 .IX Item "granularity" The size of the pieces you're dealing with, mentally speaking. .IP "greedy" 4 .IX Item "greedy" A \*(L"subpattern\*(R" whose \*(L"quantifier\*(R" wants to match as many things as possible. .IP "grep" 4 .IX Item "grep" Originally from the old Unix editor command for \*(L"Globally search for a Regular Expression and Print it\*(R", now used in the general sense of any kind of search, especially text searches. Perl has a built-in grep function that searches a list for elements matching any given criterion, whereas the \fIgrep\fR(1) program searches for lines matching a \*(L"regular expression\*(R" in one or more files. .IP "group" 4 .IX Item "group" A set of users of which you are a member. In some operating systems (like Unix), you can give certain file access permissions to other members of your group. .IP "\s-1GV\s0" 4 .IX Item "GV" An internal \*(L"glob value\*(R" typedef, holding a \*(L"typeglob\*(R". The \*(L"\s-1GV\s0\*(R" type is a subclass of \*(L"\s-1SV\s0\*(R". .SS "H" .IX Subsection "H" .IP "hacker" 4 .IX Item "hacker" Someone who is brilliantly persistent in solving technical problems, whether these involve golfing, fighting orcs, or programming. Hacker is a neutral term, morally speaking. Good hackers are not to be confused with evil crackers or clueless script kiddies. If you confuse them, we will presume that you are either evil or clueless. .IP "handler" 4 .IX Item "handler" A \*(L"subroutine\*(R" or \*(L"method\*(R" that is called by Perl when your program needs to respond to some internal event, such as a \*(L"signal\*(R", or an encounter with an operator subject to \*(L"operator overloading\*(R". See also \*(L"callback\*(R". .IP "hard reference" 4 .IX Item "hard reference" A \*(L"scalar\*(R" \*(L"value\*(R" containing the actual address of a \&\*(L"referent\*(R", such that the referent's \*(L"reference\*(R" count accounts for it. (Some hard references are held internally, such as the implicit reference from one of a \*(L"typeglob\*(R"'s variable slots to its corresponding referent.) A hard reference is different from a \&\*(L"symbolic reference\*(R". .IP "hash" 4 .IX Item "hash" An unordered association of \*(L"key\*(R"/\*(L"value\*(R" pairs, stored such that you can easily use a string \*(L"key\*(R" to look up its associated data \&\*(L"value\*(R". This glossary is like a hash, where the word to be defined is the key, and the definition is the value. A hash is also sometimes septisyllabically called an \*(L"associative array\*(R", which is a pretty good reason for simply calling it a \*(L"hash\*(R" instead. .IP "hash table" 4 .IX Item "hash table" A data structure used internally by Perl for implementing associative arrays (hashes) efficiently. See also \*(L"bucket\*(R". .IP "header file" 4 .IX Item "header file" A file containing certain required definitions that you must include \&\*(L"ahead\*(R" of the rest of your program to do certain obscure operations. A C header file has a \fI.h\fR extension. Perl doesn't really have header files, though historically Perl has sometimes used translated \&\fI.h\fR files with a \fI.ph\fR extension. See \*(L"require\*(R" in perlfunc. (Header files have been superseded by the \*(L"module\*(R" mechanism.) .IP "here document" 4 .IX Item "here document" So called because of a similar construct in shells that pretends that the lines following the \*(L"command\*(R" are a separate \*(L"file\*(R" to be fed to the command, up to some terminating string. In Perl, however, it's just a fancy form of quoting. .IP "hexadecimal" 4 .IX Item "hexadecimal" A number in base 16, \*(L"hex\*(R" for short. The digits for 10 through 16 are customarily represented by the letters \f(CW\*(C`a\*(C'\fR through \f(CW\*(C`f\*(C'\fR. Hexadecimal constants in Perl start with \f(CW\*(C`0x\*(C'\fR. See also \&\*(L"hex\*(R" in perlfunc. .IP "home directory" 4 .IX Item "home directory" The directory you are put into when you log in. On a Unix system, the name is often placed into \f(CW$ENV{HOME}\fR or \f(CW$ENV{LOGDIR}\fR by \&\fIlogin\fR, but you can also find it with \f(CW\*(C`(getpwuid($<))[7]\*(C'\fR. (Some platforms do not have a concept of a home directory.) .IP "host" 4 .IX Item "host" The computer on which a program or other data resides. .IP "hubris" 4 .IX Item "hubris" Excessive pride, the sort of thing Zeus zaps you for. Also the quality that makes you write (and maintain) programs that other people won't want to say bad things about. Hence, the third great virtue of a programmer. See also \*(L"laziness\*(R" and \*(L"impatience\*(R". .IP "\s-1HV\s0" 4 .IX Item "HV" Short for a \*(L"hash value\*(R" typedef, which holds Perl's internal representation of a hash. The \*(L"\s-1HV\s0\*(R" type is a subclass of \*(L"\s-1SV\s0\*(R". .SS "I" .IX Subsection "I" .IP "identifier" 4 .IX Item "identifier" A legally formed name for most anything in which a computer program might be interested. Many languages (including Perl) allow identifiers that start with a letter and contain letters and digits. Perl also counts the underscore character as a valid letter. (Perl also has more complicated names, such as \*(L"qualified\*(R" names.) .IP "impatience" 4 .IX Item "impatience" The anger you feel when the computer is being lazy. This makes you write programs that don't just react to your needs, but actually anticipate them. Or at least that pretend to. Hence, the second great virtue of a programmer. See also \*(L"laziness\*(R" and \*(L"hubris\*(R". .IP "implementation" 4 .IX Item "implementation" How a piece of code actually goes about doing its job. Users of the code should not count on implementation details staying the same unless they are part of the published \*(L"interface\*(R". .IP "import" 4 .IX Item "import" To gain access to symbols that are exported from another module. See \&\*(L"use\*(R" in perlfunc. .IP "increment" 4 .IX Item "increment" To increase the value of something by 1 (or by some other number, if so specified). .IP "indexing" 4 .IX Item "indexing" In olden days, the act of looking up a \*(L"key\*(R" in an actual index (such as a phone book), but now merely the act of using any kind of key or position to find the corresponding \*(L"value\*(R", even if no index is involved. Things have degenerated to the point that Perl's index function merely locates the position (index) of one string in another. .IP "indirect filehandle" 4 .IX Item "indirect filehandle" An \*(L"expression\*(R" that evaluates to something that can be used as a \&\*(L"filehandle\*(R": a \*(L"string\*(R" (filehandle name), a \*(L"typeglob\*(R", a typeglob \*(L"reference\*(R", or a low-level \*(L"\s-1IO\s0\*(R" object. .IP "indirect object" 4 .IX Item "indirect object" In English grammar, a short noun phrase between a verb and its direct object indicating the beneficiary or recipient of the action. In Perl, \f(CW\*(C`print STDOUT "$foo\en";\*(C'\fR can be understood as \*(L"verb indirect-object object\*(R" where \*(L"\s-1STDOUT\s0\*(R" is the recipient of the print action, and \f(CW"$foo"\fR is the object being printed. Similarly, when invoking a \*(L"method\*(R", you might place the invocant between the method and its arguments: .Sp .Vb 3 \& $gollum = new Pathetic::Creature "Smeagol"; \& give $gollum "Fisssssh!"; \& give $gollum "Precious!"; .Ve .Sp In modern Perl, calling methods this way is often considered bad practice and to be avoided. .IP "indirect object slot" 4 .IX Item "indirect object slot" The syntactic position falling between a method call and its arguments when using the indirect object invocation syntax. (The slot is distinguished by the absence of a comma between it and the next argument.) \*(L"\s-1STDERR\s0\*(R" is in the indirect object slot here: .Sp .Vb 2 \& print STDERR "Awake! Awake! Fear, Fire, \& Foes! Awake!\en"; .Ve .IP "indirection" 4 .IX Item "indirection" If something in a program isn't the value you're looking for but indicates where the value is, that's indirection. This can be done with either symbolic references or hard references. .IP "infix" 4 .IX Item "infix" An \*(L"operator\*(R" that comes in between its operands, such as multiplication in \f(CW\*(C`24 * 7\*(C'\fR. .IP "inheritance" 4 .IX Item "inheritance" What you get from your ancestors, genetically or otherwise. If you happen to be a \*(L"class\*(R", your ancestors are called base classes and your descendants are called derived classes. See \*(L"single inheritance\*(R" and \*(L"multiple inheritance\*(R". .IP "instance" 4 .IX Item "instance" Short for \*(L"an instance of a class\*(R", meaning an \*(L"object\*(R" of that \*(L"class\*(R". .IP "instance variable" 4 .IX Item "instance variable" An \*(L"attribute\*(R" of an \*(L"object\*(R"; data stored with the particular object rather than with the class as a whole. .IP "integer" 4 .IX Item "integer" A number with no fractional (decimal) part. A counting number, like 1, 2, 3, and so on, but including 0 and the negatives. .IP "interface" 4 .IX Item "interface" The services a piece of code promises to provide forever, in contrast to its \*(L"implementation\*(R", which it should feel free to change whenever it likes. .IP "interpolation" 4 .IX Item "interpolation" The insertion of a scalar or list value somewhere in the middle of another value, such that it appears to have been there all along. In Perl, variable interpolation happens in double-quoted strings and patterns, and list interpolation occurs when constructing the list of values to pass to a list operator or other such construct that takes a \&\*(L"\s-1LIST\s0\*(R". .IP "interpreter" 4 .IX Item "interpreter" Strictly speaking, a program that reads a second program and does what the second program says directly without turning the program into a different form first, which is what compilers do. Perl is not an interpreter by this definition, because it contains a kind of compiler that takes a program and turns it into a more executable form (syntax trees) within the \fIperl\fR process itself, which the Perl \*(L"run time\*(R" system then interprets. .IP "invocant" 4 .IX Item "invocant" The agent on whose behalf a \*(L"method\*(R" is invoked. In a \*(L"class\*(R" method, the invocant is a package name. In an \*(L"instance\*(R" method, the invocant is an object reference. .IP "invocation" 4 .IX Item "invocation" The act of calling up a deity, daemon, program, method, subroutine, or function to get it do what you think it's supposed to do. We usually \&\*(L"call\*(R" subroutines but \*(L"invoke\*(R" methods, since it sounds cooler. .IP "I/O" 4 .IX Item "I/O" Input from, or output to, a \*(L"file\*(R" or \*(L"device\*(R". .IP "\s-1IO\s0" 4 .IX Item "IO" An internal I/O object. Can also mean \*(L"indirect object\*(R". .IP "\s-1IP\s0" 4 .IX Item "IP" Internet Protocol, or Intellectual Property. .IP "\s-1IPC\s0" 4 .IX Item "IPC" Interprocess Communication. .IP "is-a" 4 .IX Item "is-a" A relationship between two objects in which one object is considered to be a more specific version of the other, generic object: \&\*(L"A camel is a mammal.\*(R" Since the generic object really only exists in a Platonic sense, we usually add a little abstraction to the notion of objects and think of the relationship as being between a generic \&\*(L"base class\*(R" and a specific \*(L"derived class\*(R". Oddly enough, Platonic classes don't always have Platonic relationships\*(--see \&\*(L"inheritance\*(R". .IP "iteration" 4 .IX Item "iteration" Doing something repeatedly. .IP "iterator" 4 .IX Item "iterator" A special programming gizmo that keeps track of where you are in something that you're trying to iterate over. The \f(CW\*(C`foreach\*(C'\fR loop in Perl contains an iterator; so does a hash, allowing you to each through it. .IP "\s-1IV\s0" 4 .IX Item "IV" The integer four, not to be confused with six, Tom's favorite editor. \&\s-1IV\s0 also means an internal Integer Value of the type a \*(L"scalar\*(R" can hold, not to be confused with an \*(L"\s-1NV\s0\*(R". .SS "J" .IX Subsection "J" .IP "\s-1JAPH\s0" 4 .IX Item "JAPH" \&\*(L"Just Another Perl Hacker,\*(R" a clever but cryptic bit of Perl code that when executed, evaluates to that string. Often used to illustrate a particular Perl feature, and something of an ongoing Obfuscated Perl Contest seen in Usenix signatures. .SS "K" .IX Subsection "K" .IP "key" 4 .IX Item "key" The string index to a \*(L"hash\*(R", used to look up the \*(L"value\*(R" associated with that key. .IP "keyword" 4 .IX Item "keyword" See \*(L"reserved words\*(R". .SS "L" .IX Subsection "L" .IP "label" 4 .IX Item "label" A name you give to a \*(L"statement\*(R" so that you can talk about that statement elsewhere in the program. .IP "laziness" 4 .IX Item "laziness" The quality that makes you go to great effort to reduce overall energy expenditure. It makes you write labor-saving programs that other people will find useful, and document what you wrote so you don't have to answer so many questions about it. Hence, the first great virtue of a programmer. Also hence, this book. See also \*(L"impatience\*(R" and \&\*(L"hubris\*(R". .IP "left shift" 4 .IX Item "left shift" A \*(L"bit shift\*(R" that multiplies the number by some power of 2. .IP "leftmost longest" 4 .IX Item "leftmost longest" The preference of the \*(L"regular expression\*(R" engine to match the leftmost occurrence of a \*(L"pattern\*(R", then given a position at which a match will occur, the preference for the longest match (presuming the use of a \*(L"greedy\*(R" quantifier). See perlre for \fImuch\fR more on this subject. .IP "lexeme" 4 .IX Item "lexeme" Fancy term for a \*(L"token\*(R". .IP "lexer" 4 .IX Item "lexer" Fancy term for a \*(L"tokener\*(R". .IP "lexical analysis" 4 .IX Item "lexical analysis" Fancy term for \*(L"tokenizing\*(R". .IP "lexical scoping" 4 .IX Item "lexical scoping" Looking at your \fIOxford English Dictionary\fR through a microscope. (Also known as \*(L"static scoping\*(R", because dictionaries don't change very fast.) Similarly, looking at variables stored in a private dictionary (namespace) for each scope, which are visible only from their point of declaration down to the end of the lexical scope in which they are declared. \-\-Syn. \*(L"static scoping\*(R". \&\-\-Ant. \*(L"dynamic scoping\*(R". .IP "lexical variable" 4 .IX Item "lexical variable" A \*(L"variable\*(R" subject to \*(L"lexical scoping\*(R", declared by my. Often just called a \*(L"lexical\*(R". (The our declaration declares a lexically scoped name for a global variable, which is not itself a lexical variable.) .IP "library" 4 .IX Item "library" Generally, a collection of procedures. In ancient days, referred to a collection of subroutines in a \fI.pl\fR file. In modern times, refers more often to the entire collection of Perl modules on your system. .IP "\s-1LIFO\s0" 4 .IX Item "LIFO" Last In, First Out. See also \*(L"\s-1FIFO\s0\*(R". A \s-1LIFO\s0 is usually called a \&\*(L"stack\*(R". .IP "line" 4 .IX Item "line" In Unix, a sequence of zero or more non-newline characters terminated with a \*(L"newline\*(R" character. On non-Unix machines, this is emulated by the C library even if the underlying \*(L"operating system\*(R" has different ideas. .IP "line buffering" 4 .IX Item "line buffering" Used by a \*(L"standard I/O\*(R" output stream that flushes its \&\*(L"buffer\*(R" after every \*(L"newline\*(R". Many standard I/O libraries automatically set up line buffering on output that is going to the terminal. .IP "line number" 4 .IX Item "line number" The number of lines read previous to this one, plus 1. Perl keeps a separate line number for each source or input file it opens. The current source file's line number is represented by \f(CW\*(C`_\|_LINE_\|_\*(C'\fR. The current input line number (for the file that was most recently read via \f(CW\*(C`\*(C'\fR) is represented by the \f(CW$.\fR (\f(CW$INPUT_LINE_NUMBER\fR) variable. Many error messages report both values, if available. .IP "link" 4 .IX Item "link" Used as a noun, a name in a \*(L"directory\*(R", representing a \*(L"file\*(R". A given file can have multiple links to it. It's like having the same phone number listed in the phone directory under different names. As a verb, to resolve a partially compiled file's unresolved symbols into a (nearly) executable image. Linking can generally be static or dynamic, which has nothing to do with static or dynamic scoping. .IP "\s-1LIST\s0" 4 .IX Item "LIST" A syntactic construct representing a comma-separated list of expressions, evaluated to produce a \*(L"list value\*(R". Each \&\*(L"expression\*(R" in a \*(L"\s-1LIST\s0\*(R" is evaluated in \*(L"list context\*(R" and interpolated into the list value. .IP "list" 4 .IX Item "list" An ordered set of scalar values. .IP "list context" 4 .IX Item "list context" The situation in which an \*(L"expression\*(R" is expected by its surroundings (the code calling it) to return a list of values rather than a single value. Functions that want a \*(L"\s-1LIST\s0\*(R" of arguments tell those arguments that they should produce a list value. See also \&\*(L"context\*(R". .IP "list operator" 4 .IX Item "list operator" An \*(L"operator\*(R" that does something with a list of values, such as join or grep. Usually used for named built-in operators (such as print, unlink, and system) that do not require parentheses around their \*(L"argument\*(R" list. .IP "list value" 4 .IX Item "list value" An unnamed list of temporary scalar values that may be passed around within a program from any list-generating function to any function or construct that provides a \*(L"list context\*(R". .IP "literal" 4 .IX Item "literal" A token in a programming language such as a number or \*(L"string\*(R" that gives you an actual \*(L"value\*(R" instead of merely representing possible values as a \*(L"variable\*(R" does. .IP "little-endian" 4 .IX Item "little-endian" From Swift: someone who eats eggs little end first. Also used of computers that store the least significant \*(L"byte\*(R" of a word at a lower byte address than the most significant byte. Often considered superior to big-endian machines. See also \*(L"big-endian\*(R". .IP "local" 4 .IX Item "local" Not meaning the same thing everywhere. A global variable in Perl can be localized inside a dynamic scope via the local operator. .IP "logical operator" 4 .IX Item "logical operator" Symbols representing the concepts \*(L"and\*(R", \*(L"or\*(R", \*(L"xor\*(R", and \*(L"not\*(R". .IP "lookahead" 4 .IX Item "lookahead" An \*(L"assertion\*(R" that peeks at the string to the right of the current match location. .IP "lookbehind" 4 .IX Item "lookbehind" An \*(L"assertion\*(R" that peeks at the string to the left of the current match location. .IP "loop" 4 .IX Item "loop" A construct that performs something repeatedly, like a roller coaster. .IP "loop control statement" 4 .IX Item "loop control statement" Any statement within the body of a loop that can make a loop prematurely stop looping or skip an \*(L"iteration\*(R". Generally you shouldn't try this on roller coasters. .IP "loop label" 4 .IX Item "loop label" A kind of key or name attached to a loop (or roller coaster) so that loop control statements can talk about which loop they want to control. .IP "lvaluable" 4 .IX Item "lvaluable" Able to serve as an \*(L"lvalue\*(R". .IP "lvalue" 4 .IX Item "lvalue" Term used by language lawyers for a storage location you can assign a new \*(L"value\*(R" to, such as a \*(L"variable\*(R" or an element of an \&\*(L"array\*(R". The \*(L"l\*(R" is short for \*(L"left\*(R", as in the left side of an assignment, a typical place for lvalues. An \*(L"lvaluable\*(R" function or expression is one to which a value may be assigned, as in \f(CW\*(C`pos($x) = 10\*(C'\fR. .IP "lvalue modifier" 4 .IX Item "lvalue modifier" An adjectival pseudofunction that warps the meaning of an \*(L"lvalue\*(R" in some declarative fashion. Currently there are three lvalue modifiers: my, our, and local. .SS "M" .IX Subsection "M" .IP "magic" 4 .IX Item "magic" Technically speaking, any extra semantics attached to a variable such as \f(CW$!\fR, \f(CW$0\fR, \f(CW%ENV\fR, or \f(CW%SIG\fR, or to any tied variable. Magical things happen when you diddle those variables. .IP "magical increment" 4 .IX Item "magical increment" An \*(L"increment\*(R" operator that knows how to bump up alphabetics as well as numbers. .IP "magical variables" 4 .IX Item "magical variables" Special variables that have side effects when you access them or assign to them. For example, in Perl, changing elements of the \&\f(CW%ENV\fR array also changes the corresponding environment variables that subprocesses will use. Reading the \f(CW$!\fR variable gives you the current system error number or message. .IP "Makefile" 4 .IX Item "Makefile" A file that controls the compilation of a program. Perl programs don't usually need a \*(L"Makefile\*(R" because the Perl compiler has plenty of self-control. .IP "man" 4 .IX Item "man" The Unix program that displays online documentation (manual pages) for you. .IP "manpage" 4 .IX Item "manpage" A \*(L"page\*(R" from the manuals, typically accessed via the \fIman\fR(1) command. A manpage contains a \s-1SYNOPSIS\s0, a \s-1DESCRIPTION\s0, a list of \&\s-1BUGS\s0, and so on, and is typically longer than a page. There are manpages documenting commands, syscalls, \&\*(L"library\*(R" functions, devices, protocols, files, and such. In this book, we call any piece of standard Perl documentation (like \fIperlop\fR or \&\fIperldelta\fR) a manpage, no matter what format it's installed in on your system. .IP "matching" 4 .IX Item "matching" See \*(L"pattern matching\*(R". .IP "member data" 4 .IX Item "member data" See \*(L"instance variable\*(R". .IP "memory" 4 .IX Item "memory" This always means your main memory, not your disk. Clouding the issue is the fact that your machine may implement \*(L"virtual\*(R" memory; that is, it will pretend that it has more memory than it really does, and it'll use disk space to hold inactive bits. This can make it seem like you have a little more memory than you really do, but it's not a substitute for real memory. The best thing that can be said about virtual memory is that it lets your performance degrade gradually rather than suddenly when you run out of real memory. But your program can die when you run out of virtual memory too, if you haven't thrashed your disk to death first. .IP "metacharacter" 4 .IX Item "metacharacter" A \*(L"character\*(R" that is \fInot\fR supposed to be treated normally. Which characters are to be treated specially as metacharacters varies greatly from context to context. Your \*(L"shell\*(R" will have certain metacharacters, double-quoted Perl strings have other metacharacters, and \*(L"regular expression\*(R" patterns have all the double-quote metacharacters plus some extra ones of their own. .IP "metasymbol" 4 .IX Item "metasymbol" Something we'd call a \*(L"metacharacter\*(R" except that it's a sequence of more than one character. Generally, the first character in the sequence must be a true metacharacter to get the other characters in the metasymbol to misbehave along with it. .IP "method" 4 .IX Item "method" A kind of action that an \*(L"object\*(R" can take if you tell it to. See perlobj. .IP "minimalism" 4 .IX Item "minimalism" The belief that \*(L"small is beautiful.\*(R" Paradoxically, if you say something in a small language, it turns out big, and if you say it in a big language, it turns out small. Go figure. .IP "mode" 4 .IX Item "mode" In the context of the stat syscall, refers to the field holding the \*(L"permission bits\*(R" and the type of the \*(L"file\*(R". .IP "modifier" 4 .IX Item "modifier" See \*(L"statement modifier\*(R", \*(L"regular expression modifier\*(R", and \&\*(L"lvalue modifier\*(R", not necessarily in that order. .IP "module" 4 .IX Item "module" A \*(L"file\*(R" that defines a \*(L"package\*(R" of (almost) the same name, which can either \*(L"export\*(R" symbols or function as an \*(L"object\*(R" class. (A module's main \fI.pm\fR file may also load in other files in support of the module.) See the use built-in. .IP "modulus" 4 .IX Item "modulus" An integer divisor when you're interested in the remainder instead of the quotient. .IP "monger" 4 .IX Item "monger" Short for Perl Monger, a purveyor of Perl. .IP "mortal" 4 .IX Item "mortal" A temporary value scheduled to die when the current statement finishes. .IP "multidimensional array" 4 .IX Item "multidimensional array" An array with multiple subscripts for finding a single element. Perl implements these using references\-\-see perllol and perldsc. .IP "multiple inheritance" 4 .IX Item "multiple inheritance" The features you got from your mother and father, mixed together unpredictably. (See also \*(L"inheritance\*(R", and \*(L"single inheritance\*(R".) In computer languages (including Perl), the notion that a given class may have multiple direct ancestors or base classes. .SS "N" .IX Subsection "N" .IP "named pipe" 4 .IX Item "named pipe" A \*(L"pipe\*(R" with a name embedded in the \*(L"filesystem\*(R" so that it can be accessed by two unrelated processes. .IP "namespace" 4 .IX Item "namespace" A domain of names. You needn't worry about whether the names in one such domain have been used in another. See \*(L"package\*(R". .IP "network address" 4 .IX Item "network address" The most important attribute of a socket, like your telephone's telephone number. Typically an \s-1IP\s0 address. See also \*(L"port\*(R". .IP "newline" 4 .IX Item "newline" A single character that represents the end of a line, with the \s-1ASCII\s0 value of 012 octal under Unix (but 015 on a Mac), and represented by \&\f(CW\*(C`\en\*(C'\fR in Perl strings. For Windows machines writing text files, and for certain physical devices like terminals, the single newline gets automatically translated by your C library into a line feed and a carriage return, but normally, no translation is done. .IP "\s-1NFS\s0" 4 .IX Item "NFS" Network File System, which allows you to mount a remote filesystem as if it were local. .IP "null character" 4 .IX Item "null character" A character with the \s-1ASCII\s0 value of zero. It's used by C to terminate strings, but Perl allows strings to contain a null. .IP "null list" 4 .IX Item "null list" A \*(L"list value\*(R" with zero elements, represented in Perl by \f(CW\*(C`()\*(C'\fR. .IP "null string" 4 .IX Item "null string" A \*(L"string\*(R" containing no characters, not to be confused with a string containing a \*(L"null character\*(R", which has a positive length and is \*(L"true\*(R". .IP "numeric context" 4 .IX Item "numeric context" The situation in which an expression is expected by its surroundings (the code calling it) to return a number. See also \*(L"context\*(R" and \&\*(L"string context\*(R". .IP "\s-1NV\s0" 4 .IX Item "NV" Short for Nevada, no part of which will ever be confused with civilization. \s-1NV\s0 also means an internal floating-point Numeric Value of the type a \*(L"scalar\*(R" can hold, not to be confused with an \*(L"\s-1IV\s0\*(R". .IP "nybble" 4 .IX Item "nybble" Half a \*(L"byte\*(R", equivalent to one \*(L"hexadecimal\*(R" digit, and worth four bits. .SS "O" .IX Subsection "O" .IP "object" 4 .IX Item "object" An \*(L"instance\*(R" of a \*(L"class\*(R". Something that \*(L"knows\*(R" what user-defined type (class) it is, and what it can do because of what class it is. Your program can request an object to do things, but the object gets to decide whether it wants to do them or not. Some objects are more accommodating than others. .IP "octal" 4 .IX Item "octal" A number in base 8. Only the digits 0 through 7 are allowed. Octal constants in Perl start with 0, as in 013. See also the oct function. .IP "offset" 4 .IX Item "offset" How many things you have to skip over when moving from the beginning of a string or array to a specific position within it. Thus, the minimum offset is zero, not one, because you don't skip anything to get to the first item. .IP "one-liner" 4 .IX Item "one-liner" An entire computer program crammed into one line of text. .IP "open source software" 4 .IX Item "open source software" Programs for which the source code is freely available and freely redistributable, with no commercial strings attached. For a more detailed definition, see . .IP "operand" 4 .IX Item "operand" An \*(L"expression\*(R" that yields a \*(L"value\*(R" that an \*(L"operator\*(R" operates on. See also \*(L"precedence\*(R". .IP "operating system" 4 .IX Item "operating system" A special program that runs on the bare machine and hides the gory details of managing processes and devices. Usually used in a looser sense to indicate a particular culture of programming. The loose sense can be used at varying levels of specificity. At one extreme, you might say that all versions of Unix and Unix-lookalikes are the same operating system (upsetting many people, especially lawyers and other advocates). At the other extreme, you could say this particular version of this particular vendor's operating system is different from any other version of this or any other vendor's operating system. Perl is much more portable across operating systems than many other languages. See also \&\*(L"architecture\*(R" and \*(L"platform\*(R". .IP "operator" 4 .IX Item "operator" A gizmo that transforms some number of input values to some number of output values, often built into a language with a special syntax or symbol. A given operator may have specific expectations about what types of data you give as its arguments (operands) and what type of data you want back from it. .IP "operator overloading" 4 .IX Item "operator overloading" A kind of \*(L"overloading\*(R" that you can do on built-in operators to make them work on objects as if the objects were ordinary scalar values, but with the actual semantics supplied by the object class. This is set up with the overload \&\*(L"pragma\*(R". .IP "options" 4 .IX Item "options" See either switches or \*(L"regular expression modifier\*(R". .IP "ordinal" 4 .IX Item "ordinal" Another name for \*(L"code point\*(R" .IP "overloading" 4 .IX Item "overloading" Giving additional meanings to a symbol or construct. Actually, all languages do overloading to one extent or another, since people are good at figuring out things from \*(L"context\*(R". .IP "overriding" 4 .IX Item "overriding" Hiding or invalidating some other definition of the same name. (Not to be confused with \*(L"overloading\*(R", which adds definitions that must be disambiguated some other way.) To confuse the issue further, we use the word with two overloaded definitions: to describe how you can define your own \*(L"subroutine\*(R" to hide a built-in \*(L"function\*(R" of the same name (see \*(L"Overriding Built-in Functions\*(R" in perlsub) and to describe how you can define a replacement \*(L"method\*(R" in a \*(L"derived class\*(R" to hide a \*(L"base class\*(R"'s method of the same name (see perlobj). .IP "owner" 4 .IX Item "owner" The one user (apart from the superuser) who has absolute control over a \*(L"file\*(R". A file may also have a \*(L"group\*(R" of users who may exercise joint ownership if the real owner permits it. See \&\*(L"permission bits\*(R". .SS "P" .IX Subsection "P" .IP "package" 4 .IX Item "package" A \*(L"namespace\*(R" for global variables, subroutines, and the like, such that they can be kept separate from like-named symbols in other namespaces. In a sense, only the package is global, since the symbols in the package's symbol table are only accessible from code compiled outside the package by naming the package. But in another sense, all package symbols are also globals\*(--they're just well-organized globals. .IP "pad" 4 .IX Item "pad" Short for \*(L"scratchpad\*(R". .IP "parameter" 4 .IX Item "parameter" See \*(L"argument\*(R". .IP "parent class" 4 .IX Item "parent class" See \*(L"base class\*(R". .IP "parse tree" 4 .IX Item "parse tree" See \*(L"syntax tree\*(R". .IP "parsing" 4 .IX Item "parsing" The subtle but sometimes brutal art of attempting to turn your possibly malformed program into a valid \*(L"syntax tree\*(R". .IP "patch" 4 .IX Item "patch" To fix by applying one, as it were. In the realm of hackerdom, a listing of the differences between two versions of a program as might be applied by the \fIpatch\fR(1) program when you want to fix a bug or upgrade your old version. .IP "\s-1PATH\s0" 4 .IX Item "PATH" The list of directories the system searches to find a program you want to \*(L"execute\*(R". The list is stored as one of your environment variables, accessible in Perl as \&\f(CW$ENV{PATH}\fR. .IP "pathname" 4 .IX Item "pathname" A fully qualified filename such as \fI/usr/bin/perl\fR. Sometimes confused with \*(L"\s-1PATH\s0\*(R". .IP "pattern" 4 .IX Item "pattern" A template used in \*(L"pattern matching\*(R". .IP "pattern matching" 4 .IX Item "pattern matching" Taking a pattern, usually a \*(L"regular expression\*(R", and trying the pattern various ways on a string to see whether there's any way to make it fit. Often used to pick interesting tidbits out of a file. .IP "permission bits" 4 .IX Item "permission bits" Bits that the \*(L"owner\*(R" of a file sets or unsets to allow or disallow access to other people. These flag bits are part of the \*(L"mode\*(R" word returned by the stat built-in when you ask about a file. On Unix systems, you can check the \fIls\fR(1) manpage for more information. .IP "Pern" 4 .IX Item "Pern" What you get when you do \f(CW\*(C`Perl++\*(C'\fR twice. Doing it only once will curl your hair. You have to increment it eight times to shampoo your hair. Lather, rinse, iterate. .IP "pipe" 4 .IX Item "pipe" A direct \*(L"connection\*(R" that carries the output of one \*(L"process\*(R" to the input of another without an intermediate temporary file. Once the pipe is set up, the two processes in question can read and write as if they were talking to a normal file, with some caveats. .IP "pipeline" 4 .IX Item "pipeline" A series of processes all in a row, linked by pipes, where each passes its output stream to the next. .IP "platform" 4 .IX Item "platform" The entire hardware and software context in which a program runs. A program written in a platform-dependent language might break if you change any of: machine, operating system, libraries, compiler, or system configuration. The \fIperl\fR interpreter has to be compiled differently for each platform because it is implemented in C, but programs written in the Perl language are largely platform-independent. .IP "pod" 4 .IX Item "pod" The markup used to embed documentation into your Perl code. See perlpod. .IP "pointer" 4 .IX Item "pointer" A \*(L"variable\*(R" in a language like C that contains the exact memory location of some other item. Perl handles pointers internally so you don't have to worry about them. Instead, you just use symbolic pointers in the form of keys and \*(L"variable\*(R" names, or hard references, which aren't pointers (but act like pointers and do in fact contain pointers). .IP "polymorphism" 4 .IX Item "polymorphism" The notion that you can tell an \*(L"object\*(R" to do something generic, and the object will interpret the command in different ways depending on its type. [