Collections, comparisons, and null

The idea

A command may emit zero, one, or many results, and assignment can therefore produce different shapes. The array subexpression operator @() collects results into an array, making Count and iteration easier to reason about when one consistent collection shape is required. Do not infer a collection’s cardinality from how a single value happens to display in the console.

Comparison operators also depend on the left operand. Comparing a scalar usually produces a boolean; comparing a collection with -eq returns matching elements. This can surprise code that expects a single truth value. For a null test, place $null on the left when checking whether a variable itself is null. PowerShell string comparisons are case-insensitive by default; use explicit case-sensitive variants when the contract requires them.

$values = @(1, 2, 2, 3)
$matches = @($values -eq 2)
$matches.Count
("a" -ceq "A")

2
False

Collection comparison returns both matching twos, so the collected result contains two elements. The case-sensitive comparison distinguishes the two letters.