Mastering Windows PowerShell Scripting - Third Edition

Contains and in

The -contains, -notcontains, -in, and -notin operators are used to test the content of arrays.

When using -contains or -notcontains, the array is expected to be on the left-hand side of the operator:

1, 2 -contains 2       # Returns true 
1, 2, 3 -contains 4    # Returns false 

When using -in or -notin, the array is expected to be on the right-hand side of the operator:

1 -in 1, 2, 3    # Returns true 
4 -in 1, 2, 3    # Returns false                   

Contains or in? When using comparison operators, I tend to write the subject on the left and the object on the right. Comparisons to null are an exception to this rule. The subject is the variable or property I am testing; the object is the thing I am testing against. For example, I might set the subject to ...