+ and * are two of a set of characters known as quantifiers. Quantifiers are discussed in great detail later in this chapter.

The * character can be used to repeat the preceding character zero or more times, for example:

'aaabc' -match 'a*'# Returns true, matches 'aaa' 

However, zero or more means the character in question doesn't have to be present at all:

'bcd' -match 'a*'   # Returns true, matches nothing 

If a character must be present in a string, the + quantifier is more appropriate:

'aaabc' -match 'a+'# Returns true, matches 'aaa' 
'bcd' -match 'a+'   # Returns false 

Combining * or + with . produces two very simple expressions: .* and .+. These expressions may be used as follows:

'Anything' -match '.*'    # 0 or more. Returns true 
'' -match '.*'            # 0 or more. Returns true 
'Anything' -match '.+'# 1 or more. Returns true 

Attempting to use either * or + as a match without a preceding character will result in an error:

PS> '*' -match '*'
parsing "*" - Quantifier {x,y} following nothing.
At line:1 char:1
+ '*' -match '*'
+ ~~~~~~~~~~~~~~
    + CategoryInfo : OperationStopped: (:) [], ArgumentException
    + FullyQualifiedErrorId : System.ArgumentException