Comparison-operators-with-collections

Comparison operators work differently with scalars and collections

See

help about_Comparison_Operators

   When the input to an operator is a scalar value, comparison operators
   return a Boolean value. When the input is a collection of values, the
   comparison operators return any matching values. If there are no matches
   in a collection, comparison operators do not return anything.

   The exceptions are the containment operators (-Contains, -NotContains),
   the In operators (-In, -NotIn), and the type operators (-Is, -IsNot),
   which always return a Boolean value.

Comparison operators applied to collections is a very useful feature when used properly. But how this actually works is not always obvious. It may be a trap.

For example, the comparison like this

    $object -eq $value

is not a safe way to test that $object is equal to $value if an object may be a collection as well. See the tests.

Scripts

• looks-like-object-is-null.ps1 shows how -eq $null may look like true for a not null object.
• object-is-eq-and-ne-to-1.ps1 shows how -eq 1 and -ne 1 may look like true for the same object.

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• Stack Overflow Match operator returns true but $matches is null