SPECIAL-PURPOSE IPv4 BLOCKS
14 blocks that belong to no host on the internet — 13.8 % of the address space, of which exactly one eighth is multicast and reserved
IPv6 ADDRESS NOTATION
eight groups of sixteen bits, the double colon, and one canonical spelling out of thousands
JAVASCRIPT vs GO
seven questions, the same to both, and the document each answer is written in
JAVASCRIPT vs RUST
seven questions, the same to both, and the document each answer is written in
KANBAN
the board, the limit on work in progress, and the four metrics that measure flow
LANGUAGE CODES
487 rows in ISO 639-2; 183 languages also have a two-letter code and 20 have two three-letter ones — and the tag is always the shortest
LIFE CYCLE MODELS
the same steps arranged five ways: the document, the year, and what one turn of the loop covers
LOGIC GATES
Seven digital-logic symbols — and how to build six of them from a single element, NAND
MARKDOWN SYNTAX
headings, emphasis, lists, links and code per the CommonMark 0.31.2 specification — the core all dialects share
MEDIA TYPES
2322 registered subtypes under 11 top-level types, and how to read one you have never seen
THE MIDI PROTOCOL
one top bit separates status from data, seven commands per channel, and how much time a serial wire actually takes
THE FLAGS OF OPEN()
FIVE flags of creating a file — and why O_CREAT|O_EXCL is not a faster check but a check and a creation joined into one indivisible act
${…}: FOUR MODIFICATIONS
The colon asks about emptiness too: in the column of the empty variable it changes the answer four times out of four, and in the other two columns none
${…}: TRIMMING BY PATTERN
The sign says from which end to cut and doubling it says how much: from the same path the same pair of patterns takes away either one character or fifteen
POSIX SIGNALS
Twenty-seven signals, five default actions — and two that cannot be caught, ignored or blocked
PYTHON vs GO
seven questions, the same to both, and the document each answer is written in
PYTHON vs JAVASCRIPT
seven questions, the same to both, and the document each answer is written in
PYTHON vs RUST
seven questions, the same to both, and the document each answer is written in
THE ORDER OF REDIRECTIONS
Redirections are done from left to right, and “2>&1” copies where the output points at that very moment: the file first — and it holds two lines; the copy first — one
REGULAR EXPRESSIONS
anchors, classes, quantifiers and groups: what a pattern is made of and how it reads, token by token
TIMESTAMPS
date, time and offset from UTC in one string: what it is made of and what it is not
SEMANTIC VERSIONING
what each of the three numbers means, what may follow them, and the order versions stand in
QUOTING IN THE SHELL
29 characters named by the standard, 4 ways to take the meaning off them — and the 3 characters where double quotes stop
read: A LINE INTO VARIABLES
The last variable takes the whole rest of the line, inner spaces and all; without -r the backslash disappears, and a line with no final newline gives status 1 — although the variable is already full
INSERTION SORT
the way cards are ordered in the hand · the trace of one real run
QUICKSORT
splitting around a pivot · the trace of one real run
TWO-CAMERA SPEAKER SETUP
the lighting triangle and where each of the 2 cameras stands · the floor plan from above
THREE-CAMERA SPEAKER SETUP
the lighting triangle and where each of the 3 cameras stands · the floor plan from above
THE SELECT STATEMENT
8 clauses in the order you write them — and the order they take effect in
SUBNET MASKS
from /0 to /32: the mask, how many addresses a block holds, and how many of them go to hosts
THE CONDITIONS OF TRAP
FIVE conditions from the standard — EXIT and four signals — and three extensions a conformant shell refuses
THE UMASK
The file mode creation mask: the nine bits it clears, five arguments that name opposite things — and why umask 022 is not chmod 755
UML DIAGRAMS
the fourteen kinds, and the notation a class diagram is made of
THE UNICODE SPACE
1 114 112 code points in 17 planes: 159 866 characters, 137 468 private, 814 730 free
PERCENT-ENCODING IN URIs
128 ASCII positions: 66 unreserved, 18 delimiters, 43 that must always be encoded — and the "%" itself
THE UTF-8 ENCODING
how a Unicode code point falls into one, two, three or four bytes — and which bytes never appear
UUID
thirty-six characters: where the version sits, where the variant sits, and what each of the eight versions is made of
VIDEO CARRIERS
nine formats at true scale — and the frame that kept growing after the carrier stopped
VIDEO FORMATS
who published each standard, when, the names it goes by, and what has to be squeezed
VIM COMMANDS
modes, motions and editing per the Vim 9.1 help — and the grammar that composes them into commands
WORD EXPANSION
Four steps in a fixed order — and only two of them can change how many fields reach the command
BEER STYLES
colour, bitterness and strength of 15 styles from the BJCP 2021 guidelines
COCKTAIL FORMULAS
five templates by ratio, not fixed recipes — millilitres straight from the official IBA recipes
NINE DRINKS
the same coffee, different proportions
HOW MUCH COFFEE TO WATER
six methods · weight, grind, time
ARABICA AND ROBUSTA
two species, six varieties, one difference
POST-FERMENTED TEAS
six teas changed by microbes rather than oxygen
ESPRESSO
the nine requirements of a certified Italian espresso, with their tolerances