.contains() vs -contains, one returns true, other returns false

Question

I have a Hash Table like this:

$Path = @{
    "BM"    = "\\srv\xy"
    "BB4-L" = "\\srv\xy"
    "BB4-R" = "\\srv\xy"
    "HSB"   = "\\srv\xy"
    "IB"    = "\\srv\xy"
    "LM1"   = "\\srv\xy"
    "LM2"   = "\\srv\xy"
    "sis"   = "\\srv\xy"
}

my $env:username is sis. Why does .contains() and -contains something different?

PS Z:\Powershell-Scripts\Functions> $Path -contains $env:username
False

PS Z:\Powershell-Scripts\Functions> $Path.contains($env:username)
True

I always like to go with the PowerShell Syntax if possible, but I can't in this case, since -contains would return false.

How are .contains() and -contains different?

Possible duplicate of [PowerShell and the -contains operator](https://stackoverflow.com/questions/18877580/powershell-and-the-contains-operator) — TessellatingHeckler, Sep 05 '18 at 07:33

score 2 · Answer 1 · answered Sep 05 '18 at 07:15

$Path is a System.Collections.Hashtable. You can also read in documentation that:

When the test value is a collection, the Contains operator uses reference equality. It returns TRUE only when one of the reference values is the same instance of the test value object.

Each item in hashtable is System.Collections.DictionaryEntry. You are comparing it to string. Since types do not match, references do not match as well. Contains(System.Object key) and ContainsKey(System.Object key) use keys to test. To be consistent in comparisons you should write:

$Path.Keys -contains $env:username

score 1 · Accepted Answer · answered Sep 05 '18 at 06:59

From MS documentation:

-Contains
      Description: Containment operator. Tells whether a collection of reference
      values includes a single test value. Always returns a Boolean value. Returns TRUE
      only when the test value exactly matches at least one of the reference values.

.Contains() Method is one of the methods of a String object that supports substring hence why you get True when you run $Path.Contains($env:username)

score 0 · Answer 3 · answered Mar 06 '20 at 13:33

I got the code to work by changing from hashtable.containskey to -contains. In the following code snippit, i commented our the line containing .containsKey($UserIDFromAD) and added the line containing $UserIDsFromFile.keys -contains $UserIDFromAD. The code now works as expected.

So, whats the difference between .containskey and -contains?

#if ($UserIDsFromFile.containsKey($UserIDFromAD)){ #If the UserID is in Yesterdays list ignore it.
if ($UserIDsFromFile.keys -contains $UserIDFromAD){ #If the UserID is in Yesterdays list ignore it.

.contains() vs -contains, one returns true, other returns false

3 Answers3