PowerShell and the -contains operator

You can use like:

"12-18" -like "*-*"

Or split for contains:

"12-18" -split "" -contains "-"

The -Contains operator doesn't do substring comparisons and the match must be on a complete string and is used to search collections.

From the documentation you linked to:

-Contains Description: Containment operator. Tells whether a collection of reference values includes a single test value.

In the example you provided you're working with a collection containing just one string item.

If you read the documentation you linked to you'll see an example that demonstrates this behaviour:

Examples:

PS C:\> "abc", "def" -Contains "def"
True

PS C:\> "Windows", "PowerShell" -Contains "Shell"
False  #Not an exact match

I think what you want is the -Match operator:

"12-18" -Match "-"

Which returns True.

Important: As pointed out in the comments and in the linked documentation, it should be noted that the -Match operator uses regular expressions to perform text matching.

-Contains is actually a collection operator. It is true if the collection contains the object. It is not limited to strings.

-match and -imatch are regular expression string matchers, and set automatic variables to use with captures.

-like, -ilike are SQL-like matchers.