SPRING AND NEAP TIDES
the Earth–moon–sun geometry that makes the tides swing — after NOAA
CPR AND CHOKING
the 2025 American Heart Association algorithms, step by step — bystander, trained rescuer, and choking at three ages
THREE HAND STITCHES
backstitch · running stitch · whipstitch — what shows on the face and what the thread does underneath
HANDWASHING
five steps, and the 20 seconds that actually matter
STAIN REMOVAL
five stain classes and the method for each — per publication H.E. 2-840 of the University of Kentucky Cooperative Extension
BINARY COUNTING
five doubling cards build every number from 0 to 31 — exactly the way every computer counts
THE EXIT STATUS
One byte from a command to the shell: what the standard assigns in it, what it leaves to the system — and why “128 + signal number” is nowhere in the standard
FILE DESCRIPTORS
Three levels between a number and a file: what two numbers of one description share, what two descriptions do not — and where the offset lives
FILE LOCKS
A lock lies on a range of bytes, it has two different kinds of owner, and it guards no byte at all
FILE PERMISSIONS
Nine bits in three triads, three special bits — and why r and x on a directory are different powers
CSS FLEXBOX
main axis and cross axis · which property belongs to which
GIT WORKING AREAS
four areas · the command that moves code between them
![FILENAME EXPANSION: *, ?, […]](/api/img/cmsp2eg3h001q2dpdnyxkt8mu)
FILENAME EXPANSION: *, ?, […]
A leading dot and a slash disappear only in filename expansion: the same pattern “*” is seen by case, but not by expansion itself
HERE-DOCUMENTS
The body reaches the command as a single word, and one quote in the delimiter decides whether it arrives as typed
IFS AND FIELD SPLITTING
Two kinds of delimiter: white ones merge into one, non-white ones each cut on their own — and the same value gives one field or four
LOGIC GATES
Seven digital-logic symbols — and how to build six of them from a single element, NAND
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
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
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