${…}: 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

Built as a memo rather than a table: the thing worth hanging it up for reads across the room, with the full reference in smaller type below it.

Three sizes in one archive — from a sheet on the fridge to a poster on the wall.

Formats: A4 · A3 · A2
What you get: Print-ready PDFs, one per size, with every letterform converted to outlines — nothing to install, nothing to shift.
Subject: code · everyone · memo · study

Read from top to bottom: what each of the eight forms gives in the three states of the variable, what each of the four modifications does, and what the fine print costs. Every cell was printed by /bin/sh.

ONLY ONE FORM TELLS AN EMPTY VARIABLE FROM AN UNSET ONE

An empty variable is a declared variable, and the test “[ -z "$v" ]” cannot see that: it says “empty” both for the empty one and for the one that was never set. A run confirmed both.

Only the form without a colon tells them apart: “${v+W}” gives the word for the empty variable and nothing for the unset one. It is the only way to ask about the declaration itself.

On the sheet

Read from top to bottom: what each of the eight forms gives in the three states of the variable, what each of the four modifications does, and what the fine print costs. Every cell was printed by /bin/sh.
Colour carries meaning, but meaning never rests on colour alone — the sheet reads in black and white.
Nothing about how it was made: the sheet carries only what the reader needs.

Printing

Three sizes in the archive: A4 — 210×297 mm, A3 — 297×420 mm, A2 — 420×594 mm.
All text is converted to outlines. No fonts to install, and nothing shifts on another machine.
White background and sparing fills — it prints on a home printer without draining the cartridge.
Margins of at least 10 mm: a home printer cannot print to the edge.
No stroke thinner than 0.3 mm, so nothing disappears in print.

Why the numbers can be trusted. Every countable number here is computed from data rather than typed in, and the sheet must pass 10 independent checks before it is allowed to build — how many items there are, the order they come in, and the claim in the highlighted box itself. If one fails, there is no file.

${…}: FOUR MODIFICATIONS

ONLY ONE FORM TELLS AN EMPTY VARIABLE FROM AN UNSET ONE

On the sheet

Printing

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