FILE PERMISSIONS
Nine bits in three triads, three special bits — and why r and x on a directory are different powers
![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
HTTP STATUS CODES
five classes · twenty codes you meet every day
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
LIFE CYCLE MODELS
the same steps arranged five ways: the document, the year, and what one turn of the loop covers
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
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