PERLGLOSSARY(1)

🌸 NAME 🌸

okay bestie, welcome to perlglossary(1) — the Perl Glossary 💅✨ This is the manual page from the Perl Programmers Reference Guide, and it's literally a whole glossary of terms.

perlglossary — Perl Glossary

✨ VERSION ✨

version 5.20250619

🦋 DESCRIPTION 🦋

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

Other useful sources include the Unicode Glossary (<http://unicode.org/glossary/>), the Free On-Line Dictionary of Computing (<http://foldoc.org/>), the Jargon File (<http://catb.org/~esr/jargon/>), and Wikipedia (<http://www.wikipedia.org/>). Go off, bestie 📚✨

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🌈 A 🌈

accessor methods

A method used to indirectly inspect or update an object’s state (its instance variables). 💅

actual arguments

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

address operator

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

algorithm

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

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 foreach loops, in the $_ variable for map or grep operators, in $a and $b during sort’s comparison function, and in each element of @_ for the actual arguments of a subroutine call. Permanent aliases are explicitly created in packages by importing symbols or by assignment to typeglobs. Lexically scoped aliases for package variables are explicitly created by the our declaration.

alphabetic

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

alternatives

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

anonymous

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

application

A bigger, fancier sort of program with a fancier name so people don’t realize they are using a program. not me clocking this 😭

architecture

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

argument

A piece of data supplied to a program, subroutine, function, or method to tell it what it’s supposed to do. Also called a “parameter”.

ARGV

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

arithmetical operator

A symbol such as + or / that tells Perl to do the arithmetic you were supposed to learn in grade school. the way that math class comes back to haunt you 😭

array

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

array context

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

Artistic License

The open source license that Larry Wall created for Perl, maximizing Perl’s usefulness, availability, and modifiability. The current version is 2. (<http://www.opensource.org/licenses/artistic-license.php>).

ASCII

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

assertion

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

assignment

An operator whose assigned mission in life is to change the value of a variable. fr fr, that’s the whole job 🎯

assignment operator

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

associative array

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

associativity

Determines whether you do the left operator first or the right operator first when you have “A operator B operator C”, and the two operators are of the same precedence. Operators like + are left associative, while operators like ** are right associative. See Camel chapter 3, “Unary and Binary Operators” for a list of operators and their associativity.

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. highkey relatable 💀

atom

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

atomic operation

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

attribute

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

autogeneration

A feature of operator overloading of objects, whereby the behavior of certain operators can be reasonably deduced using more fundamental operators. This assumes that the overloaded operators will often have the same relationships as the regular operators. See Camel chapter 13, “Overloading”.

autoincrement

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

autoload

To load on demand. (Also called “lazy” loading.) Specifically, to call an AUTOLOAD subroutine on behalf of an undefined subroutine. lazy girl loading, but make it Perl 🧚

autosplit

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

autovivification

A Graeco-Roman word meaning “to bring oneself to life”. In Perl, storage locations (lvalues) spontaneously generate themselves as needed, including the creation of any hard reference values to point to the next level of storage. The assignment $a[5][5][5][5][5] = "quintet" potentially creates five scalar storage locations, plus four references (in the first four scalar locations) pointing to four new anonymous arrays (to hold the last four scalar locations). But the point of autovivification is that you don’t have to worry about it. main character energy: it just shows up ✨

AV

Short for “array value”, which refers to one of Perl’s internal data types that holds an array. The AV type is a subclass of SV.

awk

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

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🎀 B 🎀

backreference

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

backtracking

The practice of saying, “If I had to do it all over, I’d do it differently,” and then actually going back and doing it all over differently. Mathematically speaking, it’s returning from an unsuccessful recursion on a tree of possibilities. Perl backtracks when it attempts to match patterns with a regular expression, and its earlier attempts don’t pan out. See the section “The Little Engine That /Couldn(n’t)” in Camel chapter 5, “Pattern Matching”. not the engine that could 😭💀

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. respecting the bugs is lowkey iconic 👑

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.

base class

A generic object type; that is, a class from which other, more specific classes are derived genetically by inheritance. Also called a “superclass” by people who respect their ancestors. 🫶

• big-endian — okay so picture this: someone who eats their eggs big end first (shoutout Swift for that one 🥚). It's also what you call a computer that stores the most significant byte of a word at a lower byte address than the least significant byte. These machines are often considered superior to little-endian ones. See also little-endian.
• binary — anything to do with numbers in base 2, which means bestie there's literally two numbers: 0 and 1. It also gets used to describe a file of "nontext", presumably because such a file makes full use of all the binary bits in its bytes. But with Unicode showing up, that distinction — already sus to begin with — loses even more of its meaning. 💀
• binary operator — an operator that takes two operands. Two. That's the whole vibe.
• bind — to assign a specific network address to a socket. Like giving your socket its own little address, slay.
• bit — an integer in the range from 0 to 1, inclusive. The smallest possible unit of information storage. An eighth of a byte, or an eighth of a dollar. 🪙 (Fun lore: the term "Pieces of Eight" comes from being able to split the old Spanish dollar into 8 bits, each of which still counted for money. That's literally why a 25-cent piece today is still called "two bits".)
• 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. Math but make it bitwise. ✨
• bit string — a sequence of bits that is actually being thought of as a sequence of bits, for once. Like, finally someone's being honest about it.
• bless — in corporate life, to grant official approval to a thing, as in "The VP of Engineering has blessed our WebCruncher project." Similarly in Perl: to grant official approval to a referent so that it can function as an object, such as a WebCruncher object. See the bless function in Camel chapter 27, "Functions". 👑
• block — what a process does when it has to wait for something: "My process blocked waiting for the disk." As a totally unrelated noun, it means a large chunk of data, of a size that the operating system likes to deal with (normally a power of 2 such as 512 or 8192). Typically it's a chunk of data coming from or going to a disk file.
• BLOCK — a syntactic construct made of a sequence of Perl statements delimited by braces. The if and while statements are defined in terms of BLOCKs, for instance. Sometimes we also say "block" to mean a lexical scope — that is, a sequence of statements that acts like a BLOCK, such as within an eval or a file, even though the statements aren't delimited by braces. Same word, two moods 🫶
• block buffering — a method of making input and output efficient by passing one block at a time. By default, Perl does block buffering to disk files. See buffer and command buffering.
• Boolean — a value that is either true or false. That's it. That's the whole entry. 🎀
• Boolean context — a special kind of scalar context used in conditionals to decide whether the scalar value returned by an expression is true or false. It does not evaluate as either a string or a number. See context.
• 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. It's giving detective era 🔍
• broadcast — to send a datagram to multiple destinations simultaneously. Group chat, but for packets.
• BSD — a psychoactive drug, popular in the '80s, probably developed at UC Berkeley or thereabouts. Similar in many ways to the prescription-only medication called "System V", but infinitely more useful. (Or, at least, more fun.) The full chemical name is "Berkeley Standard Distribution". 😭 iconic
• bucket — a location in a hash table containing (potentially) multiple entries whose keys "hash" to the same hash value according to its hash function. (As internal policy, you don't have to worry about it unless you're into internals, or policy.)
• buffer — a temporary holding location for data. Block buffering means the data is passed on to its destination whenever the buffer is full. Line buffering means it's passed on whenever a complete line is received. Command buffering means 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 — and ngl, that can be rather inefficient. 🙈
• built-in — a function that's predefined in the language. Even when it's hidden by overriding, you can always get at a built-in function by qualifying its name with the CORE:: pseudopackage. It's giving "you can't get rid of me" energy 💅
• bundle — a group of related modules on CPAN. (Also sometimes refers to a group of command-line switches grouped into one switch cluster.)
• byte — a piece of data worth eight bits in most places. Eight little bits, one iconic little unit 🍓
• bytecode — a pidgin-like lingo spoken among 'droids when they don't wish to reveal their orientation (see endian). 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 nonarchitecture-dependent sequence of bytes.

🔤 C 🔤

• C — a language beloved by many for its inside-out type definitions, inscrutable precedence rules, and heavy overloading of the function-call mechanism. (Well, actually, people first switched to C because they found lowercase identifiers easier to read than upper.) Perl is written in C, so it's not surprising that Perl borrowed a few ideas from it. Respect where respect is due 🫡
• cache — a data repository. Instead of computing expensive answers several times, compute it once and save the result. Work smarter, not harder, bestie.
• callback — a handler that you register with some other part of your program in the hope that the other part of your program will trigger your handler when some event of interest transpires. It's like leaving a "text me when you get there" with your own code 🫶
• call by reference — an argument-passing mechanism in which the formal arguments refer directly to the actual arguments, and the subroutine can change the actual arguments by changing the formal arguments. That is, the formal argument is an alias for the actual argument. See also call by value.
• call by value — an argument-passing mechanism in which the formal arguments refer to a copy of the actual arguments, and the subroutine cannot change the actual arguments by changing the formal arguments. See also call by reference.
• canonical — reduced to a standard form to facilitate comparison. Everything matching, nothing out of place, we love a consistent queen ✨
• capture variables — the variables — such as $1 and $2, and %+ and %– — that hold the text remembered in a pattern match. See Camel chapter 5, "Pattern Matching".
• capturing — the use of parentheses around a subpattern in a regular expression to store the matched substring as a backreference. (Captured strings are also returned as a list in list context.) See Camel chapter 5, "Pattern Matching".
• cargo cult — copying and pasting code without understanding it, while superstitiously believing in its value. This term originated from preindustrial cultures dealing with the detritus of explorers and colonizers of technologically advanced cultures. See The Gods Must Be Crazy. 💀 we've all been there
• case — a property of certain characters. Originally, typesetters stored capital letters in the upper of two cases and small letters in the lower one. Unicode recognizes three cases: lowercase (character property \p{lower}), titlecase (\p{title}), and uppercase (\p{upper}). A fourth casemapping called foldcase is not itself a distinct case, but it is used internally to implement casefolding. Not all letters have case, and some nonletters have case. Chaotic, honestly.
• casefolding — comparing or matching a string case-insensitively. In Perl, it is implemented with the /i pattern modifier, the fc function, and the \F double-quote translation escape.
• casemapping — the process of converting a string to one of the four Unicode casemaps; in Perl, it is implemented with the fc, lc, ucfirst, and uc functions. Glow-up, but make it typographic 💅
• character — the smallest individual element of a string. Computers store characters as integers, but Perl lets you operate on them as text. The integer used to represent a particular character is called that character's codepoint.
• character class — a square-bracketed list of characters used in a regular expression to indicate that any character of the set may occur at a given point. Loosely, any predefined set of characters so used.
• character property — a predefined character class matchable by the \p or \P metasymbol. Unicode defines hundreds of standard properties for every possible codepoint, and Perl defines a few of its own, too. Overachievers 💖
• circumfix operator — an operator that surrounds its operand, like the angle operator, or parentheses, or a hug. Yes, a hug is an operator now, it's canon 🫂
• class — a user-defined type, implemented in Perl via a package that provides (either directly or by inheritance) methods (that is, subroutines) to handle instances of the class (its objects). See also inheritance.
• class method — a method whose invocant is a package name, not an object reference. A method associated with the class as a whole. Also see instance method.
• client — in networking, a process that initiates contact with a server process in order to exchange data and perhaps receive a service. The one who texts first, fr fr 📱
• closure — an anonymous subroutine that, when a reference to it is generated at runtime, keeps track of the identities of externally visible lexical variables, even after those lexical variables have supposedly gone out of scope. They're called "closures" because this sort of behavior gives mathematicians a sense of closure. 😭 the way that's so real
• cluster — a parenthesized subpattern used to group parts of a regular expression into a single atom.
• CODE — the word returned by the ref function when you apply it to a reference to a subroutine. See also CV.
• code generator — a system that writes code for you in a low-level language, such as code to implement the backend of a compiler. See program generator.
• codepoint — the integer a computer uses to represent a given character. ASCII codepoints are in the range 0 to 127; Unicode codepoints are in the range 0 to 0x10_FFFF; and Perl codepoints are in the range 0 to 2³²−1 or 0 to 2⁶⁴−1, depending on your native integer size. In Perl Culture, sometimes called ordinals. 🔢

okay so code subpattern is a regex subpattern whose whole actual job is to run some Perl code — think (?{...}) and (??{...}).

collating sequence — the order into which characters sort. String comparison routines use it to decide stuff like where in this very glossary to put “collating sequence”. 💅

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

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

command — in shell programming, the syntactic combination of a program name and its arguments. More loosely, anything you type to a shell (a command interpreter) that starts it doing something. Even more loosely, a Perl statement, which might start with a label and typically ends with a semicolon.

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

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

command name — the name of the program currently executing, as typed on the command line. In C, the command name is passed to the program as the first command-line argument. In Perl, it comes in separately as $0.

comment — a remark that doesn’t affect the meaning of the program. In Perl, a comment is introduced by a # character and continues to the end of the line.

compilation unit — the file (or string, in the case of eval) that is currently being compiled.

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

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

compiler — strictly speaking, a program that munches up another program and spits out yet another file containing the program in a “more executable” form, typically containing native machine instructions. The perl program is not a compiler by this definition, but it does contain a kind of compiler that takes a program and turns it into a more executable form (syntax trees) within the perl process itself, which the interpreter then interprets. There are, however, extension modules to get Perl to act more like a “real” compiler. See Camel chapter 16, “Compiling”.

compile time — the time when Perl is trying to make sense of your code, as opposed to when it thinks it knows what your code means and is merely trying to do what it thinks your code says to do, which is runtime. 😌

composer — a “constructor” for a referent that isn’t really an object, like an anonymous array or a hash (or a sonata, for that matter). For example, a pair of braces acts as a composer for a hash, and a pair of brackets acts as a composer for an array. See the section “Creating References” in Camel chapter 8, “References”. 🎀

concatenation — the process of gluing one cat’s nose to another cat’s tail. Also a similar operation on two strings.

conditional — something “iffy”. See Boolean context.

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 client and a server.

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

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

context — the surroundings or environment. The context given by the surrounding code determines what kind of data a particular expression is expected to return. The three primary contexts are list context, scalar, and void context. Scalar context is sometimes subdivided into Boolean context, numeric context, string context, and void context. There’s also a “don’t care” context (which is dealt with in Camel chapter 2, “Bits and Pieces”, if you care). 🦋

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

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

CPAN — the Comprehensive Perl Archive Network. (See the Camel Preface and Camel chapter 19, “CPAN” for details.)

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

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

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

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

current working directory — see working directory.

CV — in academia, a curriculum vitæ, a fancy kind of résumé. In Perl, an internal “code value” typedef holding a subroutine. The CV type is a subclass of SV. 👑

💀 D 💀

dangling statement — a bare, single statement, without any braces, hanging off an if or while conditional. C allows them. Perl doesn’t. periodt.

datagram — a packet of data, such as a UDP message, that (from the viewpoint of the programs involved) can be sent independently over the network. (In fact, all packets are sent independently at the IP level, but stream protocols such as TCP hide this from your program.)

data structure — how your various pieces of data relate to each other and what shape they make when you put them all together, as in a rectangular table or a triangular tree. 🌈

data type — a set of possible values, together with all the operations that know how to deal with those values. For example, a numeric data type has a certain set of numbers that you can work with, as well as various mathematical operations that you can do on the numbers, but would make little sense on, say, a string such as "Kilroy". Strings have their own operations, such as concatenation. Compound types made of a number of smaller pieces generally have operations to compose and decompose them, and perhaps to rearrange them. Objects that model things in the real world often have operations that correspond to real activities. For instance, if you model an elevator, your elevator object might have an open_door method.

DBM — stands for “Database Management” routines, a set of routines that emulate an associative array using disk files. The routines use a dynamic hashing scheme to locate any entry with only two disk accesses. DBM files allow a Perl program to keep a persistent hash across multiple invocations. You can tie your hash variables to various DBM implementations.

declaration — an assertion 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, “two cups flour, one large egg, four or five tadpoles…” See statement for its opposite. Note that some declarations also function as statements. Subroutine declarations also act as definitions if a body is supplied. 🍓

declarator — something that tells your program what sort of variable you’d like. Perl doesn’t require you to declare variables, but you can use my, our, or state to denote that you want something other than the default.

decrement — to subtract a value from a variable, as in “decrement $x” (meaning to remove 1 from its value) or “decrement $x by 3”.

default — a value chosen for you if you don’t supply a value of your own.

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 value 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 false and the defined entry in Camel chapter 27, “Functions”. 😭

delimiter — a character or string that sets bounds to an arbitrarily sized textual object, not to be confused with a separator or terminator. “To delimit” really just means “to surround” or “to enclose” (like these parentheses are doing). 💅

dereference

Okay so this is a fancy computer-science term that literally just means "to follow a reference to what it points to." The "de" part of it is doing the heavy lifting here — it's referring to the fact that you're taking away one level of indirection. One layer gone, bestie. 💅

derived class

A class that defines some of its methods in terms of a more generic class, which we call a base class. And no, classes aren't sorted exclusively into base classes or derived classes — a class can function as both a derived class and a base class at the same time, which is, and I quote, "kind of classy." 👑

descriptor

See file descriptor. (Yes, it's giving "see attached." 🙈)

destroy

To deallocate the memory of a referent — and before that happens, it first triggers its DESTROY method, if it has one. Cleanup era. 🧹

destructor

A special method that gets called when an object is thinking about destroying itself. Important nuance though: a Perl program's DESTROY method doesn't do the actual destruction. Perl just triggers the method in case the class wants to do any associated cleanup. Literally "not me doing the work, just showing up in case you need me." 💀

device

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

directive

A pod directive. See Camel chapter 23, "Plain Old Documentation".

directory

A special file that contains other files. Some operating systems call these "folders", "drawers", "catalogues", or "catalogs" — same energy, different branding. 🎀

directory handle

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

discipline

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

dispatch

To send something to its correct destination. It's often used metaphorically to indicate a transfer of programmatic control to a destination that's selected algorithmically — usually 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. Finding the right one like it's a group chat with 40 members. 📨

distribution

A standard, bundled release of a system of software. The default usage implies source code is included. If that's not the case, it'll be called a "binary-only" distribution.

dual-lived

Some modules live both in the Standard Library and on CPAN. These modules might be developed on two separate tracks as people modify either version. The trend currently is to untangle these situations. Two homes, one module — icon behavior honestly. 🦋

dweomer

An enchantment, illusion, phantasm, or jugglery. You say it when Perl's magical dwimmer effects don't do what you expect, but rather seem to be the product of arcane dweomercraft, sorcery, or wonder working. [From Middle English.] ✨🔮

dwimmer

So DWIM is an acronym for "Do What I Mean" — 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 "dwimming" is a "dwimmer". Fair warning tho: dwimming can require a great deal of behind-the-scenes magic, which — if it doesn't stay properly behind the scenes — is called a dweomer instead. 🙈

dynamic scoping

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

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🌸 E 🌸

eclectic

Derived from many sources. Some would say too many. 😭

element

A basic building block. When you're talking about an array, it's one of the items that make up the array. 🧱

embedding

When something is contained in something else — particularly when that might be considered surprising: "I've embedded a complete Perl interpreter in my editor!" Main character energy fr. 👑

empty subclass test

The notion that an empty derived class should behave exactly like its base class. Vibe check passed. ✅

encapsulation

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

endian

See little-endian and big-endian.

en passant

When you change a value as it's being copied. [From French "in passing", as in the exotic pawn-capturing maneuver in chess.] 🍓

environment

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

environment variable

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

EOF

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

errno

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

error

See exception or fatal error.

escape sequence

See metasymbol.

exception

A fancy term for an error. See fatal error.

exception handling

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

exec

To throw away the current process's program and replace it with another — without exiting the process or relinquishing any resources held (apart from the old memory image). Full identity swap, no goodbye. 💅

executable file

A file that's specially marked to tell the operating system that it's okay to run this file as a program. Usually shortened to "executable".

execute

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

execute bit

The special mark that tells the operating system it can run this program. There are actually three execute bits under Unix, and which bit gets used depends on whether you own the file singularly, collectively, or not at all.

exit status

See status.

exploit

Used as a noun in this case, this refers to a known way to compromise a program to get it to do something the author didn't intend. Your task is to write unexploitable programs. That's the assignment. 🔥

export

To make symbols from a module available for import by other modules.

expression

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

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.

---

🔥 F 🔥

false

In Perl, any value that would look like "" or "0" if evaluated in a string context. And since undefined values evaluate to "", all undefined values are false — but not all false values are undefined. Read that twice, bestie. 😭

FAQ

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

fatal error

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

feeping creaturism

A spoonerism of "creeping featurism", noting the biological urge to add just one more feature to a program. Just one more. Just one more. 🧚

field

A single piece of numeric or string data that's part of a longer string, record, or line. Variable-width fields are usually split up by separators (so use split to extract the fields), while fixed-width fields are usually at fixed positions (so use unpack). Also, instance variables are known as "fields" too. Two meanings, both valid, we contain multitudes. 🌈

FIFO

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

file

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

file descriptor

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

fileglob

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

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. And here's the slay: 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. Efficiency icon. ⭐

filename

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

filesystem

A set of directories and files residing on a partition of the disk. Sometimes known as a "partition". 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. Moving without moving, we love a loophole. 🦋

file test operator

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

filter

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

first-come

The first PAUSE author to upload a namespace automatically becomes the primary maintainer for that namespace, no vote no nothing 💅. The "first come" permissions are how you tell apart a primary maintainer who was assigned that role by hand from one who just got it automatically by being first. iykyk.

flag

Okay so we lowkey try to avoid this word because it means like… everything 😭. It can mean a command-line switch that takes no argument itself — think Perl's -n and -p flags — or, less often, a single-bit indicator, like the O_CREAT and O_EXCL flags you use in sysopen. Sometimes people informally use it for certain regex modifiers too. It's giving chaotic neutral.

floating point

A way of storing numbers in "scientific notation" so that the precision of the number is independent of its magnitude — the decimal point literally "floats" 🦋. Perl does its numeric work with floating-point numbers (sometimes just called "floats") whenever it can't get away with using integers. Real talk though: floating-point numbers are mere approximations of real numbers. Not the real thing, just vibes.

flush

The act of emptying a buffer — often before it's even full. Like clearing your camera roll mid-scroll 🫶.

FMTEYEWTK

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

foldcase

The casemap used in Unicode when you're comparing or matching without regard to case. Comparing lowercase, title case, or uppercase are all unreliable because Unicode's case mappings are complex and one-to-many 😭. Foldcase is a lowercase variant (using a partially decomposed normalization form for certain codepoints) made specifically to resolve this. Iconic problem-solving tbh.

fork

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

formal arguments

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

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 ✨. It's giving aesthetic.

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) 👑.

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. Share the wealth, bestie.

freeware

Historically, any software that you give away, especially if you also make the source code available. Now often called open source software. Recently there's been a trend to use the term in contradistinction to open source software — meaning only free software released under the Free Software Foundation's GPL (General Public License) — but that's difficult to justify etymologically 💀.

function

Mathematically: a mapping of each of a set of input values to a particular output value. In computers: a subroutine or operator that returns a value. It may or may not have input values (those are called arguments). Slay either way.

funny character

Someone like Larry, or one of his peculiar friends 🌈. Also refers to the strange prefixes Perl requires as noun markers on its variables. Both meanings, same energy.

---

✨ G ✨

garbage collection

A misnamed feature — it should really be called "expecting your mother to pick up after you" 😭. Strictly speaking, Perl doesn't do this; it relies on a reference-counting mechanism to keep things tidy. But we rarely speak strictly and will often call the reference-counting scheme a form of garbage collection. (If it's any comfort: when your interpreter exits, a "real" garbage collector runs to make sure everything gets cleaned up — you know, if you've been messy with circular references and such 🙈.)

GID

Group ID — in Unix, the numeric group ID the operating system uses to identify you and the members of your group 💜.

glob

Strictly? The shell's * character, which matches a "glob" 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 fileglob and typeglob.

global

Something you can see from anywhere — usually said 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 package. Global variables can be declared with our. See "Global Declarations" in Camel chapter 4, "Statements and Declarations" ✨.

global destruction

The garbage collection of globals (plus the running of any associated object destructors) that happens when a Perl interpreter is being shut down 💀. Global destruction should not be confused with the Apocalypse — except perhaps when it should 😭.

glue language

A language such as Perl that's good at hooking things together that weren't intended to be hooked together. Bestie matchmaker energy fr fr 🫶.

granularity

The size of the pieces you're dealing with, mentally speaking. Big picture or tiny details, pick your vibe.

grapheme

A graphene is an allotrope of carbon arranged in a hexagonal crystal lattice one atom thick (lol not that one). A grapheme — or more fully, a grapheme cluster string — is a single user-visible character, which may in turn be several characters (codepoints) long 🌸. For example: a carriage return plus a line feed is a single grapheme but two characters, while a "ȫ" is a single grapheme but one, two, or even three characters, depending on normalization. Absolutely unhinged and I respect it.

greedy

A subpattern whose quantifier wants to match as many things as possible. It's giving "no thoughts just consume everything" 😭.

grep

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

group

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

GV

An internal "glob value" typedef, holding a typeglob. The GV type is a subclass of SV 🌈.

---

🦋 H 🦋

hacker

Someone who is brilliantly persistent in solving technical problems — whether those 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. No cap.

handler

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

hard reference

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

hash

An unordered association of key/value pairs, stored so you can easily use a string key to look up its associated data value 💖. This glossary is literally like a hash: the word being defined is the key, the definition is the value. A hash is also sometimes septisyllabically called an "associative array" — which is a pretty good reason for simply calling it a "hash" instead 😭.

hash table

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

header file

A file containing certain required definitions that you must include "ahead" of the rest of your program to do certain obscure operations. A C header file has a .h extension. Perl doesn't really have header files, though historically Perl has sometimes used translated .h files with a .ph extension 🦋. See require in Camel chapter 27, "Functions". (Header files have been superseded by the module mechanism.)

here document

So called because of a similar construct in shells that pretends the lines following the command are a separate file to be fed to the command, up to some terminating string ✨. In Perl, though? It's just a fancy form of quoting. Periodt.

hexadecimal

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

home directory

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

host

The computer on which a program or other data resides 💻.

hubris

Excessive pride — the sort of thing for which Zeus zaps you ⚡. 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 laziness and impatience.

HV

Short for a "hash value" typedef, which holds Perl's internal representation of a hash. The HV type is a subclass of SV 🌈.

---

🎀 I 🎀

identifier

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

impatience

The rage you feel when the computer is being a lazy little gremlin 😤. This is the energy that makes you write programs that don't just react to your needs but straight-up anticipate them — or at minimum, pretend to 🙈. Hence: the second great virtue of a programmer. See also laziness and hubris.

implementation

How a piece of code actually goes about doing its job. Real talk: users of the code should not count on implementation details staying the same unless those details are part of the published interface. iykyk 💅

import

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

increment

To increase the value of something by 1 (or by some other number, if so specified). Little bump, big vibes ✨

indexing

Back in olden days, this was the act of looking up a key in an actual index (like a phone book 📖). But now it's merely the act of using any kind of key or position to find the corresponding value, even if no index is involved at all. Things have degenerated so hard that Perl's "index" function merely locates the position (index) of one string in another 💀

indirect filehandle

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

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.

indirect object

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

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

indirect object slot

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

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

infix

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

inheritance

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

instance

Short for "an instance of a class", meaning an object of that class.

instance data

See instance variable.

instance method

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

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

instance variable

An attribute of an object; data stored with the particular object rather than with the class as a whole. It's giving personal stash 🎀

integer

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

interface

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

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 "LIST".

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 perl process itself, which the Perl runtime system then interprets. Plot twist 😭

invocant

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

invocation

The act of calling up a deity, daemon, program, method, subroutine, or function to get it to do what you think it's supposed to do 🙏. We usually "call" subroutines but "invoke" methods, since it sounds cooler. periodt 💅

I/O

Input from, or output to, a file or device.

IO

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

I/O layer

One of the filters between the data and what you get as input or what you end up with as output. Little middlemen 🧚

IPA

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

IP

Internet Protocol, or Intellectual Property.

IPC

Interprocess Communication.

is-a

A relationship between two objects in which one object is considered to be a more specific version of the other, generic object: "A camel is a mammal." Since the generic object really only exists in a Platonic sense, we usually add a little abstraction to the notion of objects and think of the relationship as being between a generic base class and a specific derived class. Oddly enough, Platonic classes don't always have Platonic relationships — see inheritance 💀

iteration

Doing something repeatedly. Again. And again. And again 🔁

iterator

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

IV

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

---

J

JAPH

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

K

key

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

keyword

See reserved words.

L

label

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

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 then 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 impatience and hubris.

leftmost longest

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

left shift

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

lexeme

Fancy term for a token.

lexer

Fancy term for a tokener.

lexical analysis

Fancy term for tokenizing. We love a fancy rebrand 🎀

lexical scoping

Looking at your Oxford English Dictionary through a microscope 🔬. (Also known as static scoping, 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. static scoping. —Ant. dynamic scoping.

lexical variable

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

library

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

LIFO

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

line

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

linebreak

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

line buffering

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

line number

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

link

Used as a noun, a name in a directory that represents a file. 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 👀

• LIST — bestie, this is a syntactic construct, okay? It's a comma-separated list of expressions that gets evaluated to produce a list value. Every single expression inside a LIST gets evaluated in list context and then interpolated into the list value. That's the whole vibe. ✨
• list — literally just an ordered set of scalar values. That's it. That's the entry. 💅
• list context — the situation where an expression's surroundings (aka the code calling it) expects it to hand back a list of values instead of just one lonely little value. Functions that want a LIST of arguments straight-up tell those arguments "hey, produce a list value for me." See also context. 🫶
• list operator — an operator that does stuff with a list of values, like join or grep. Usually this term is used for the named built-in operators (think print, unlink, and system) that don't require parentheses around their argument list. Iconic, honestly. 👑
• list value — an unnamed list of temporary scalar values that can get passed around inside your program, from any list-generating function to any function or construct that provides a list context. Very main character energy, no name needed. 🦋
• literal — a token in a programming language, like a number or a string, that gives you an actual value instead of just representing possible values the way a variable does. It's giving "what you see is what you get." ⭐
• little-endian — okay so, from Swift: someone who eats eggs little end first 🥚. It's also used for computers that store the least significant byte of a word at a lower byte address than the most significant byte. Often considered superior to big-endian machines. See also big-endian. Not me picking sides but 💅
• local — the word does NOT mean the same thing everywhere, and that's the trap, bestie. A global variable in Perl can be localized inside a dynamic scope via the local operator. That's it. That's what it means here. 🙈
• logical operator — symbols representing the concepts "and", "or", "xor", and "not". The little logic gremlins. 🔥
• lookahead — an assertion that peeks at the string to the right of the current match location. Just a lil sneak peek bestie 👀
• lookbehind — an assertion that peeks at the string to the left of the current match location. Same sneak peek, other direction. 🎀
• loop — a construct that performs something repeatedly, like a roller coaster. 🎢
• loop control statement — any statement inside the body of a loop that can make the loop stop early or skip an iteration. Generally, you shouldn't try this on roller coasters. 😭 (safety first, queen)
• loop label — a kind of key or name attached to a loop (or roller coaster) so that loop control statements can specify which loop they want to control. Gotta name your rides, iykyk. 🎡
• lowercase — in Unicode, this is NOT just characters with the General Category of Lowercase Letter. It's any character with the Lowercase property, which includes Modifier Letters, Letter Numbers, some Other Symbols, and one Combining Mark. Unicode said "we contain multitudes" and honestly? Slay. 🌈
• lvaluable — able to serve as an lvalue. Short entry, big power. ✨
• lvalue — a term used by language lawyers for a storage location you can assign a new value to, like a variable or an element of an array. The "l" is short for "left", as in the left side of an assignment, which is a typical place to find lvalues. An lvaluable function or expression is one you can assign a value to, as in pos($x) = 10. Lowkey iconic. 💜
• lvalue modifier — an adjectival pseudofunction that warps the meaning of an lvalue in some declarative fashion. Currently there are exactly three lvalue modifiers: my, our, and local. The whole squad. 🫶

🌸 M 🌸

• magic — technically speaking, any extra semantics attached to a variable, like $!, $0, %ENV, or %SIG, or to any tied variable. Magical things happen when you diddle those variables. Yes, "diddle" is the technical term here. 💀
• magical increment — an increment operator that knows how to bump up ASCII alphabetics as well as numbers. It's got range. ✨
• magical variables — special variables that have side effects when you access them or assign to them. For example, in Perl, changing elements of the %ENV array also changes the corresponding environment variables that subprocesses will use. And reading the $! variable gives you the current system error number or message. Handle with care, bestie 🫶
• Makefile — a file that controls the compilation of a program. Perl programs don't usually need a Makefile because the Perl compiler has plenty of self-control. 💅
• man — the Unix program that displays online documentation (manual pages) for you. The OG help menu. 📖
• manpage — a "page" from the manuals, typically accessed via the man(1) command. A manpage contains a SYNOPSIS, a DESCRIPTION, a list of BUGS, and so on, and is typically longer than a page. There are manpages documenting commands, syscalls, library functions, devices, protocols, files, and such. In this book, we call any piece of standard Perl documentation (like perlop or perldelta) a manpage, no matter what format it's installed in on your system. 🎀
• matching — see pattern matching.
• member data — see instance variable.
• memory — this always means your main memory, not your disk. Clouding the issue (lol, cloud) is the fact that your machine may implement virtual memory; that is, it'll pretend 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 is 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. 😭💀
• metacharacter — a character that is not supposed to be treated normally. Which characters count as special metacharacters varies greatly from context to context. Your shell has its own metacharacters, double-quoted Perl strings have other metacharacters, and regular expression patterns have all the double-quote metacharacters plus some extra ones of their own. Rude little gremlins, all of them. 🔥
• metasymbol — something we'd call a metacharacter 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. Peer pressure, but make it syntax. 💀
• method — a kind of action that an object can take if you tell it to. See Camel chapter 12, "Objects". 🦋
• method resolution order — the path Perl takes through @INC. By default, this is a double depth first search — once looking for defined methods and once for AUTOLOAD. However, Perl lets you configure this with mro. Very customizable, very demure. 👑
• minicpan — a CPAN mirror that includes just the latest versions for each distribution, probably created with CPAN::Mini. See Camel chapter 19, "CPAN". Small but mighty. 🍓
• minimalism — the belief that "small is beautiful". 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. 🤷‍♀️
• mode — in the context of the stat(2) syscall, this refers to the field holding the permission bits and the type of the file. 🔐
• modifier — see statement modifier, regular expression, and lvalue — not necessarily in that order. 😌
• module — a file that defines a package of (almost) the same name, which can either export symbols or function as an object class. (A module's main .pm file may also load in other files in support of the module.) See the use built-in. 📦
• modulus — an integer divisor when you're interested in the remainder instead of the quotient. Math but make it ✨spicy✨
• mojibake — when you speak one language and the computer thinks you're speaking another. You'll see odd translations when you send UTF‑8, for instance, but the computer thinks you sent Latin-1, showing all sorts of weird characters instead. The term is written 「文字化け」 in Japanese and means "character rot", an apt description. Pronounced ["modʑibake"] in standard IPA phonetics, or approximately "moh-jee-bah-keh". 😭 A whole mood.
• monger — short for one member of Perl mongers, a purveyor of Perl. 🛍️
• mortal — a temporary value scheduled to die when the current statement finishes. RIP bestie, see you never 🌸💀
• mro — see method resolution order.
• multidimensional array — an array with multiple subscripts for finding a single element. Perl implements these using references — see Camel chapter 9, "Data Structures". 🧚
• multiple inheritance — the features you got from your mother and father, mixed together unpredictably. (See also inheritance and single inheritance.) In computer languages (including Perl), it's the notion that a given class may have multiple direct ancestors or base classes. Family drama, but in code. 🫶

🦋 N 🦋

• named pipe — a pipe with a name embedded in the filesystem so that two unrelated processes can access it. Networking but make it filesystem 💅
• namespace — a domain of names. You needn't worry about whether the names in one such domain have been used in another. See package. 🌐
• NaN — Not a number. The value Perl uses for certain invalid or inexpressible floating-point operations. Math said "no ❤️". 😭
• network address — the most important attribute of a socket, like your telephone's telephone number. Typically an IP address. See also port. 📞
• newline — a single character that represents the end of a line, with the ASCII value of 012 octal under Unix (but 015 on a Mac), and represented by "\n" in Perl strings. For Windows machines writing text files, and for certain physical devices like terminals, the single newline gets automatically translated by your C library into a line feed and a carriage return — but normally, no translation is done. ⭐
• NFS — Network File System, which allows you to mount a remote filesystem as if it were local. Distance? Never heard of her. 🦋
• normalization — converting a text string into an alternate but equivalent canonical (or compatible) representation that can then be compared for equivalence. Unicode recognizes four different normalization forms: NFD, NFC, NFKD, and NFKC. Collect all four 🎀
• null character — a character with the numeric value of zero. It's used by C to terminate strings, but Perl allows strings to contain a null. Perl said "we don't do that here." 💅
• null list — a list value with zero elements, represented in Perl by (). Empty but valid. She contains nothing and that's her power. ✨
• null string — a string containing no characters, not to be confused with a string containing a null character, which has a positive length and is true. Do not mix these up bestie, I'm begging 🙈
• numeric context — the situation in which an expression is expected by its surroundings (the code calling it) to return a number. See also context and string context. 🔢

numification

Okay so numification is Perl lingo for implicit conversion into a number — and the related verb is numify. It’s sometimes spelled nummification and nummify, bestie. The whole thing is intended to rhyme with mummification and mummify. It is unrelated to English numen, numina, numinous. We originally forgot the extra m a long time ago, and some people got used to our funny spelling, and so just as with HTTP_REFERER’s own missing letter, our weird spelling has stuck around. 💅

NV

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

nybble

Half a byte, equivalent to one hexadecimal digit, and worth four bits. Tiny little icon behavior. 🎀

---

🍊 O

object

An instance of a class. Something that “knows” 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. 😭

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.

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. No cap.

one-liner

An entire computer program crammed into one line of text. Main character energy, honestly. ✨

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 <http://www.opensource.org/osd.html>.

operand

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

operating system

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

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.

operator overloading

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

options

See either switches or regular expression modifiers.

ordinal

An abstract character’s integer value. Same thing as codepoint.

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 context. 🫶

overriding

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

owner

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

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🍑 P

package

A namespace for global variables, subroutines, and the like, such that they can be kept separate from like-named symbols in other namespaces. In a sense, only the package is global, since the symbols in the 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. Organized queen behavior 👑.

pad

Short for scratchpad.

parameter

See argument.

parent class

See base class.

parse tree

See syntax tree.

parsing

The subtle but sometimes brutal art of attempting to turn your possibly malformed program into a valid syntax tree. It’s giving “make it make sense” 😭.

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 patch(1) program when you want to fix a bug or upgrade your old version.

PATH

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

pathname

A fully qualified filename such as /usr/bin/perl. Sometimes confused with PATH. Very “same vibe, different thing” energy.

pattern

A template used in pattern matching.

pattern matching

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

PAUSE

The Perl Authors Upload SErver (<http://pause.perl.org>), the gateway for modules on their way to CPAN.

Perl mongers

A Perl user group, taking the form of its name from the New York Perl mongers, the first Perl user group. Find one near you at <http://www.pm.org>. Bestie meetup potential: high. 🦋

permission bits

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

Pern

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

phaser

The lifetime (execution timeline) of a program is broken up into phases. A phaser is a block of code called during a specific execution phase.

pipe

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

pipeline

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

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 the following: machine, operating system, libraries, compiler, or system configuration. The perl interpreter has to be compiled differently for each platform because it is implemented in C, but programs written in the Perl language are largely platform independent. Slay, portability. 🌈

pod

The markup used to embed documentation into your Perl code. Pod stands for “Plain old documentation”. See Camel chapter 23, “Plain Old Documentation”.

pod command

A sequence, such as =head1, that denotes the start of a pod section.

pointer

A variable 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 variable names, or hard references, which aren’t pointers (but act like pointers and do in fact contain pointers). Iconic “it’s complicated” situation 💅.

polymorphism

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

port

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

portable

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

porter

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

possessive

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

POSIX

The Portable Operating System Interface specification.

postfix

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

pp

An internal shorthand for a “push-pop” code; that is, C code implementing Perl’s stack machine.

pragma

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

• precedence — okay so these are the rules of conduct that, when nothing else is guiding you, decide what should happen first. Like no parentheses? You always do multiplication before addition, bestie. 💅
• prefix — an operator that comes before its operand, as in ++$x. It’s giving “I go first” energy. ✨
• preprocessing — what some helper process did to transform the incoming data into a form more suitable for the current process. Often done with an incoming pipe. See also C preprocessor.
• primary maintainer — the author that PAUSE allows to assign co-maintainer permissions to a namespace. A primary maintainer can give up this distinction by assigning it to another PAUSE author. See Camel chapter 19, “CPAN”. 🎀
• procedure — a subroutine. That’s it. That’s the whole vibe. 🫶
• process — an instance of a running program. Under multitasking systems like Unix, two or more separate processes could be running the same program independently at the same time—in fact, the fork function is designed to bring about this happy state of affairs. Under other operating systems, processes are sometimes called “threads”, “tasks”, or “jobs”, often with slight nuances in meaning. 💖
• program — see script.
• program generator — a system that algorithmically writes code for you in a high-level language. See also code generator. It’s literally the “write my essay for me” of code, but algorithmic. 😭
• progressive matching — pattern matching that picks up where it left off before. No cap, it just resumes the hunt. 🔥
• property — see either instance variable or character property. Pick your fighter. 🦋
• protocol — in networking, an agreed-upon way of sending messages back and forth so that neither correspondent will get too confused. It’s giving polite group-chat rules, but for packets. 💅
• prototype — an optional part of a subroutine declaration telling the Perl compiler how many and what flavor of arguments may be passed as actual arguments, so you can write subroutine calls that parse much like built-in functions. (Or don’t parse, as the case may be.) 🙈
• pseudofunction — a construct that sometimes looks like a function but really isn’t. Usually reserved for lvalue modifiers like my, for context modifiers like scalar, and for the pick-your-own-quotes constructs, q//, qq//, qx//, qw//, qr//, m//, s///, y///, and tr///. Fake function energy, but iconic. 👑
• pseudohash — formerly, a reference to an array whose initial element happens to hold a reference to a hash. You used to be able to treat a pseudohash reference as either an array reference or a hash reference. Pseudohashes are no longer supported. Periodt. 💀
• pseudoliteral — an operator that looks something like a literal, such as the output-grabbing operator, `command`. It’s cosplaying as a literal, iykyk. 🎀
• public domain — something not owned by anybody. Perl is copyrighted and is thus not in the public domain—it’s just freely available and freely redistributable. Bestie, free to use does not mean unowned. 💖
• pumpkin — a notional “baton” handed around the Perl community indicating who is the lead integrator in some arena of development. Main character baton energy. 🎃
• pumpking — a pumpkin holder, the person in charge of pumping the pump, or at least priming it. Must be willing to play the part of the Great Pumpkin now and then. 👑
• PV — a “pointer value”, which is Perl Internals Talk for a char*. Lowkey internal slang, highkey important. ✨

💖 Q 💖

• qualified — possessing a complete name. The symbol $Ent::moot is qualified; $moot is unqualified. A fully qualified filename is specified from the top-level directory. It’s giving full government name vs. nickname. 💅
• quantifier — a component of a regular expression specifying how many times the foregoing atom may occur. It’s literally “how many times though?” in regex form. 🔥

🌈 R 🌈

• race condition — a race condition exists when the result of several interrelated events depends on the ordering of those events, but that order cannot be guaranteed due to nondeterministic timing effects. If two or more programs, or parts of the same program, try to go through the same series of events, one might interrupt the work of the other. This is a good way to find an exploit. ⚠️ Not cute, not slay, very much a security vibe check fail. 💀
• readable — with respect to files, one that has the proper permission bit set to let you access the file. With respect to computer programs, one that’s written well enough that someone has a chance of figuring out what it’s trying to do. Two very different kinds of “can I read this?” bestie. 📖
• reaping — the last rites performed by a parent process on behalf of a deceased child process so that it doesn’t remain a zombie. See the wait and waitpid function calls. Parent process doing cleanup duty fr fr. 🧚
• record — a set of related data values in a file or stream, often associated with a unique key field. In Unix, often commensurate with a line, or a blank-line–terminated set of lines (a “paragraph”). Each line of the /etc/passwd file is a record, keyed on login name, containing information about that user. It’s giving one contact card in a giant address book. 💖
• recursion — the art of defining something (at least partly) in terms of itself, which is a naughty no-no in dictionaries but often works out okay in computer programs if you’re careful not to recurse forever (which is like an infinite loop with more spectacular failure modes). Not me defining recursion by saying recursion. 😭
• reference — where you look to find a pointer to information somewhere else. (See indirection.) References come in two flavors: symbolic references and hard references. Two flavors, one iconic concept. 🍓
• referent — whatever a reference refers to, which may or may not have a name. Common types of referents include scalars, arrays, hashes, and subroutines. It’s the thing behind the thing. 🦋
• regex — see regular expression.
• regular expression — a single entity with various interpretations, like an elephant. To a computer scientist, it’s a grammar for a little language in which some strings are legal and others aren’t. To normal people, it’s a pattern you can use to find what you’re looking for when it varies from case to case. Perl’s regular expressions are far from regular in the theoretical sense, but in regular use they work quite well. Here’s a regular expression: /Oh s.*t./. This will match strings like “Oh say can you see by the dawn's early light” and “Oh sit!”. See Camel chapter 5, “Pattern Matching”. 🔥
• regular expression modifier — an option on a pattern or substitution, such as /i to render the pattern case-insensitive. Tiny flag, big mood. 💅
• regular file — a file that’s not a directory, a device, a named pipe or socket, or a symbolic link. Perl uses the -f file test operator to identify regular files. Sometimes called a “plain” file. Just a normal file living its normal file life. 🎀
• relational operator — an operator that says whether a particular ordering relationship is true about a pair of operands. Perl has both numeric and string relational operators. See collating sequence. It’s giving “who comes first?” but for values. ✨
• reserved words — a word with a specific, built-in meaning to a compiler, such as if or delete. In many languages (not Perl), it’s illegal to use reserved words to name anything else. (Which is why they’re reserved, after all.) In Perl, you just can’t use them to name labels or filehandles. Also called “keywords”. They already have main character energy in the compiler. 👑
• return value — the value produced by a subroutine or expression when evaluated. In Perl, a return value may be either a list or a scalar. It’s what the code hands back to you. 🫶
• RFC — Request For Comment, which despite the timid connotations is the name of a series of important standards documents. Do not let the soft name fool you, bestie. 📜
• right shift — a bit shift that divides a number by some power of 2. Math but make it bitwise. ✨
• role — a name for a concrete set of behaviors. A role is a way to add behavior to a class without inheritance. It’s giving “I can do this vibe” without the whole family tree. 💖
• root — the superuser (UID == 0). Also the top-level directory of the filesystem. Same word, two absolute icons. 👑
• RTFM — what you are told when someone thinks you should Read The Fine Manual. Not me being told this constantly. 🙈
• run phase — any time after Perl starts running your main program. See also compile phase. Run phase is mostly spent in runtime but may also be spent in compile time when require, do FILE, or eval STRING operators are executed, or when a substitution uses the /ee modifier. 🔥
• runtime — the time when Perl is actually doing what your code says to do, as opposed to the earlier period of time when it was trying to figure out whether what you said made any sense whatsoever, which is compile time. The “doing the thing” era. 💅
• runtime pattern — a pattern that contains one or more variables to be interpolated before parsing the pattern as a regular expression, and that therefore cannot be analyzed at compile time, but must be reanalyzed each time the pattern match operator is evaluated. Runtime patterns are useful but expensive. Highkey useful, lowkey pricey. 💸
• RV — a recreational vehicle, not to be confused with vehicular recreation. RV also means an internal Reference Value of the type a scalar can hold. See also IV and NV if you’re not confused yet. 😭
• rvalue — a value that you might find on the right side of an assignment. See also lvalue. Right side bestie. ✨

🦋 S 🦋

• sandbox — a walled off area that’s not supposed to affect beyond its walls. You let kids play in the sandbox instead of running in the road. See Camel chapter 20, “Security”. Cute contained chaos. 🎀
• scalar — a simple, singular value; a number, string, or reference. One value, one vibe. 💅
• scalar context — the situation in which an expression is expected by its surroundings (the code calling it) to return a single value rather than a list of values. See also context and list context. A scalar context sometimes imposes additional constraints on the return value—see string context and numeric context. Sometimes we talk about a Boolean context inside conditionals, but this imposes no additional constraints, since any scalar value, whether numeric or string, is already true or false. One value only, bestie. 🫶
• scalar literal — a number or quoted string—an actual value in the text of your program, as opposed to a variable. It’s literally right there in the code. ✨
• scalar value — a value that happens to be a scalar as opposed to a list. Singular value energy. 🎀
• scalar variable — a variable prefixed with $ that holds a single value. The $ is the little crown. 👑
• scope — from how far away you can see a variable, looking through one. Perl has two visibility mechanisms. It does dynamic scoping of local variables, meaning that the rest of the block, and any subroutines that are called by the rest of the block, can see the variables that are local to the block. Perl does lexical scoping of my variables, meaning that the rest of the block can see the variable, but other subroutines called by the block cannot see the variable. Visibility rules, but make it Perl. 💖
• scratchpad — the area in which a particular invocation of a particular file or subroutine keeps some of its temporary values, including any lexically scoped variables. It’s the little private notes app for that exact invocation. 🎀

🎀 script 🎀

A text file that is a program, bestie — like, you run it directly instead of compiling it into some other kind of file first. No glow-up phase, it just goes.

Also! In the Unicode world, a "script" is a writing system for a particular language or group of languages — Greek, Bengali, Tengwar, the whole aesthetic. Two totally different meanings, both iconic.

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💀 script kiddie

A cracker who is not a hacker but knows just enough to run canned scripts. A cargo-cult programmer. It's giving "copied the answer but can't explain it." 🙈

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sed

A venerable Stream EDitor from which Perl derives some of its ideas. Respect the ancestors, fr fr. 👑

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semaphore

A fancy kind of interlock that stops multiple threads or processes from using up the same resources simultaneously. Think of it as the bouncer at the club door — only so many get in at once. 🚪✨

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separator

A character or string that keeps two surrounding strings from being confused with each other. The split function works on separators. Not to be confused with delimiters or terminators, okay? The "or" in the previous sentence separated the two alternatives — see what she did there. 💅

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serialization

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

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server

In networking, a process that either advertises a service or just hangs around at a known location and waits for clients who need service to get in touch with it. Main character energy: it doesn't chase, it waits. 👑

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service

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

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setgid

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

---

setuid

Said of a program that runs with the privileges of its owner rather than (as is usually the case) the privileges of whoever is running it. Also describes the bit in the mode word (permission bits) that controls the feature.

Buckle up, because this is the serious part: this bit must be explicitly set by the owner to enable the feature, and the program must be carefully written not to give away more privileges than it ought to. No cap — that's a whole security thing. 🔥

---

shared memory

A piece of memory accessible by two different processes who otherwise would not see each other's memory. It's giving "we share a Notes app." 💜

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shebang

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

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shell

A command-line interpreter. The program that interactively gives you a prompt, accepts one or more lines of input, and executes the programs you mentioned, feeding each of them their proper arguments and input data. Shells can also execute scripts containing such commands.

Under Unix, typical shells include the Bourne shell (/bin/sh), the C shell (/bin/csh), and the Korn shell (/bin/ksh).

Perl is not strictly a shell because it's not interactive (although Perl programs can be interactive). So close, but no. ✨

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side effects

Something extra that happens when you evaluate an expression. Nowadays it can refer to almost anything. Like — evaluating a simple assignment statement typically has the "side effect" of assigning a value to a variable. (And you thought assigning the value was your primary intent in the first place! 😭)

Likewise, assigning a value to the special variable $| ($AUTOFLUSH) has the side effect of forcing a flush after every write or print on the currently selected filehandle. Sneaky little icon.

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sigil

A glyph used in magic. Or, for Perl, the symbol in front of a variable name — such as $, @, and %. Witchcraft, but make it syntax. 🧚

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signal

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

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signal handler

A subroutine that, instead of being content to be called in the normal fashion, sits around waiting for a bolt out of the blue before it will deign to execute. So dramatic, we love her. 🎀

Under Perl, bolts out of the blue are called signals, and you send them with the kill built-in. See the %SIG hash in Camel chapter 25, "Special Names" and the section "Signals" in Camel chapter 15, "Interprocess Communication".

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single inheritance

The features you got from your mother, if she told you that you don't have a father. (See also inheritance and multiple inheritance.) In computer languages, the idea that classes reproduce asexually so that a given class can only have one direct ancestor or base class.

Perl supplies no such restriction, though you may certainly program Perl that way if you like. Live your truth. 🌈

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slice

A selection of any number of elements from a list, array, or hash. Just a little piece, cut cute. 🍰

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slurp

To read an entire file into a string in one operation. No chewing, just vibes. 🥤

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socket

An endpoint for network communication among multiple processes that works much like a telephone or a post office box. The most important thing about a socket is its network address (like a phone number). Different kinds of sockets have different kinds of addresses — some look like filenames, and some don't. 💅

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soft reference

See symbolic reference.

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source filter

A special kind of module that does preprocessing on your script just before it gets to the tokener. Backstage pass energy. 🎟️

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stack

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

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standard

Included in the official Perl distribution — as in a standard module, a standard tool, or a standard Perl manpage. Certified canon. 👑

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standard error

The default output stream for nasty remarks that don't belong in standard output. Represented within a Perl program by the filehandle STDERR.

You can use this stream explicitly, but the die and warn built-ins write to your standard error stream automatically (unless trapped or otherwise intercepted). 😭 so true

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standard input

The default input stream for your program, which if possible shouldn't care where its data is coming from. Represented within a Perl program by the filehandle STDIN.

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standard I/O

A standard C library for doing buffered input and output to the operating system. (The "standard" of standard I/O is at most marginally related to the "standard" of standard input and output — don't get it twisted. 💀)

In general, Perl relies on whatever implementation of standard I/O a given operating system supplies, so the buffering characteristics of a Perl program on one machine may not exactly match those on another machine. Normally this only influences efficiency, not semantics.

If your standard I/O package is doing block buffering and you want it to flush the buffer more often, just set the $| variable to a true value. Little fix, big slay. ✨

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Standard Library

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

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standard output

The default output stream for your program, which if possible shouldn't care where its data is going. Represented within a Perl program by the filehandle STDOUT. 🫶

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statement

A command to the computer about what to do next, like a step in a recipe: "Add marmalade to batter and mix until mixed." 🍓

A statement is distinguished from a declaration, which doesn't tell the computer to do anything, but just to learn something.

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statement modifier

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

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static

Varying slowly compared to something else. (Unfortunately, everything is relatively stable compared to something else, except for certain elementary particles, and we're not so sure about them. 😭)

In computers, where things are supposed to vary rapidly, "static" has a derogatory connotation, indicating a slightly dysfunctional variable, subroutine, or method. In Perl culture, the word is politely avoided. 🙈

If you're a C or C++ programmer, you might be looking for Perl's state keyword.

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static method

No such thing. See class method.

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static scoping

No such thing. See lexical scoping.

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static variable

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

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stat structure

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

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status

The value returned to the parent process when one of its child processes dies. This value is placed in the special variable $?.

Its upper eight bits are the exit status of the defunct process, and its lower eight bits identify the signal (if any) that the process died from. On Unix systems, this status value is the same as the status word returned by wait(2). See system in Camel chapter 27, "Functions". 🔥

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STDERR

See standard error.

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STDIN

See standard input.

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STDIO

See standard I/O.

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STDOUT

See standard output.

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stream

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

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string

A sequence of characters such as "He said !@#&%@#?!". A string does not have to be entirely printable. 💀 accurate

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string context

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

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stringification

The process of producing a string representation of an abstract object. Turning vibes into text. 🎀

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struct

C keyword introducing a structure definition or name.

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structure

See data structure.

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subclass

See derived class.

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subpattern

A component of a regular expression pattern. A little pattern inside the pattern, iykyk. 🦋

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subroutine

A named or otherwise accessible piece of program that can be invoked from elsewhere in the program in order to accomplish some subgoal of the program. A subroutine is often parameterized to accomplish different but related things depending on its input arguments.

If the subroutine returns a meaningful value, it is also called a function. 🫶

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subscript

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

substitution 💖

Changing parts of a string via the s/// operator. (We avoid using this term to mean variable interpolation, okay? That’s a whole different vibe.)

substring 🎀

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

superclass ✨

See base class.

superuser 👑

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

SV 💅

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

switch 🔥

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

switch cluster 🦋

The combination of multiple command-line switches (e.g., –a –b –c) into one switch (e.g., –abc). Any switch with an additional argument must be the last switch in a cluster.

switch statement 🌈

A program technique that lets you evaluate an expression and then, based on the value of the expression, do a multiway branch to the appropriate piece of code for that value. Also called a “case structure”, named after the similar Pascal construct. Most switch statements in Perl are spelled given. See “The given statement” in Camel chapter 4, “Statements and Declarations”.

The given, when keywords and the smartmatch (~~) operator will be removed in Perl 5.42. 💀

symbol ⭐

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

symbolic debugger 🧚

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

symbolic link 🌸

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

symbolic reference 🪄

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

symbol table 🍓

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

synchronous ⏳

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

syntactic sugar 🍬

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

syntax 📝

From Greek σύνταξις, “with-arrangement”. How things (particularly symbols) are put together with each other.

syntax tree 🌳

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

syscall 🖥️

A function call directly to the operating system. Many of the important subroutines and functions you use aren’t direct system calls, but are built up in one or more layers above the system call level. In general, Perl programmers don’t need to worry about the distinction. However, if you do happen to know which Perl functions are really syscalls, you can predict which of these will set the $! ($ERRNO) variable on failure. Unfortunately, beginning programmers often confusingly employ the term “system call” to mean what happens when you call the Perl system function, which actually involves many syscalls. To avoid any confusion, we nearly always say “syscall” for something you could call indirectly via Perl’s syscall function, and never for something you would call with Perl’s system function.

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✨ T ✨

taint checks 🛡️

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

tainted 🙈

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

taint mode 🚨

Running under the –T switch, marking all external data as suspect and refusing to use it with system commands. See Camel chapter 20, “Security”.

TCP 🌐

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

term 🍃

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

terminator 🛑

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

ternary 🔺

An operator taking three operands. Sometimes pronounced trinary.

text 📄

A string or file containing primarily printable characters.

thread 🧵

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

tie 🎀

The bond between a magical variable and its implementation class. See the tie function in Camel chapter 27, “Functions” and Camel chapter 14, “Tied Variables”.

titlecase 🔠

The case used for capitals that are followed by lowercase characters instead of by more capitals. Sometimes called sentence case or headline case. English doesn’t use Unicode titlecase, but casing rules for English titles are more complicated than simply capitalizing each word’s first character.

TMTOWTDI 💫

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

token 🪙

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

tokener 🧩

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

tokenizing ✂️

Splitting up a program text into tokens. Also known as “lexing”, in which case you get “lexemes” instead of tokens.

toolbox approach 🧰

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

topic 🎯

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

transliterate 🔄

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

trigger ⚡

An event that causes a handler to be run.

trinary 🔺

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

troff 🖨️

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

true ✅

Any scalar value that doesn’t evaluate to 0 or "".

truncating 🗑️

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

type 🏷️

See data type and class.

type casting 🎭

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

typedef 🧱

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

typed lexical 🐴

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

typeglob 🌟

Use of a single identifier, prefixed with *. For example, *name stands for any or all of $name, @name, %name, &name, or just name. How you use it determines whether it is interpreted as all or only one of them. See “Typeglobs and Filehandles” in Camel chapter 2, “Bits and Pieces”.

typemap 🗺️

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

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💜 U 💜

UDP 📡

User Datagram Protocol, the typical way to send datagrams over the Internet.

UID 🆔

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

umask 🔐

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

unary operator

An operator with only one operand, like ! or chdir. Unary operators are usually prefix operators, meaning they come before their operand. The ++ and -- operators can be either prefix or postfix — and yes, their position does change their meanings. 💅

Unicode

A character set that includes basically all the major character sets of the world, more or less. Go look at http://www.unicode.org for the whole vibe. 🌈

Unix

Okay so Unix is a very large and constantly evolving language with several alternative syntaxes that are largely incompatible with each other. In it, anyone can define anything any way they choose, and usually do. People who speak it think it’s easy to learn because it’s so easily twisted to their own ends, but dialectical differences make tribal intercommunication nearly impossible, and travelers often get reduced to a pidgin-like subset of the language. To be universally understood, a Unix shell programmer has to spend years studying the art. Many have abandoned this discipline and now communicate through an Esperanto-like language called Perl. 🦋

Back in ancient times, Unix also referred to some code that a couple of people at Bell Labs wrote to make use of a PDP-7 computer that wasn’t doing much of anything else at the time. Iconic behavior, honestly. 👑

uppercase

In Unicode, this isn’t just characters with the General Category of Uppercase Letter — it’s any character with the Uppercase property, including some Letter Numbers and Symbols. Do not confuse it with titlecase, bestie. 🎀

UTF-8 string

A string whose ordinals represent a valid sequence of UTF-8 bytes. Sometimes called a UTF-8 encoded string. ✨

IMPORTANT: This is unrelated to Perl’s internal “UTF8 flag”, which only Perl itself should usually care about. UTF-8 strings may have that flag set or unset. 🫶

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✨ V ✨

value

The actual piece of data — as opposed to all the variables, references, keys, indices, operators, and whatnot you need to access the value. It’s giving “the real thing versus the whole scavenger hunt.” 💖

variable

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

variable interpolation

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

variadic

Said of a function that happily receives an indeterminate number of actual arguments. It’s like “bring whoever, I’m not counting.” 💅

vector

Mathematical jargon for a list of scalar values. Math girlies stay winning. 🌸

virtual

Providing the appearance of something without the reality — like virtual memory is not real memory. (See also memory.) The opposite of “virtual” is “transparent”, which means providing the reality of something without the appearance, like how Perl handles the variable-length UTF-8 character encoding transparently. 🦋

void context

A form of scalar context in which an expression isn’t expected to return any value at all and is evaluated for its side effects alone. No return value, just vibes. 💀

v-string

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

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🌟 W 🌟

warning

A message printed to the STDERR stream to the effect that something might be wrong but isn’t worth blowing up over. Peep warn in Camel chapter 27, “Functions”, and the warnings pragma in Camel chapter 28, “Pragmantic Modules”. 🫶

watch expression

An expression which, when its value changes, causes a breakpoint in the Perl debugger. It’s basically the debugger saying “not me watching this value like a hawk.” 👀

weak reference

A reference that doesn’t get counted normally. When all the normal references to data disappear, the data disappears. These are useful for circular references that would never disappear otherwise. Circular-reference cleanup realness. 🔥

whitespace

A character that moves your cursor but doesn’t otherwise put anything on your screen. Typically refers to any of: space, tab, line feed, carriage return, or form feed. In Unicode, it matches many other characters that Unicode considers whitespace, including the ɴ-ʙʀ. 💜

word

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

working directory

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

wrapper

A program or subroutine that runs some other program or subroutine for you, modifying some of its input or output to better suit your purposes. It’s giving “I got you, bestie.” 💖

WYSIWYG

What You See Is What You Get. Usually used when something that appears on the screen matches how it will eventually look, like Perl’s format declarations. Also used to mean the opposite of magic because everything works exactly as it appears, as in the three-argument form of open. No cap, what you see is what you get. 👑

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💥 X 💥

XS

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

XSUB

An external subroutine defined in XS. Short, sweet, iconic. 💅

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🌈 Y 🌈

yacc

Yet Another Compiler Compiler. A parser generator without which Perl probably would not have existed. See the file perly.y in the Perl source distribution. Thank you for your service, yacc. 🫶

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⭐ Z ⭐

zero width

A subpattern assertion matching the null string between characters. Tiny, invisible, lowkey powerful. 🦋

zombie

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

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👑 AUTHOR AND COPYRIGHT 👑

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

That’s the whole glossary, bestie! This iconic page is PERLGLOSSARY(1), from perl v5.42.3, dated 2026-11-03. Periodt. ✨🎀💅