Powershell hashtable does not write to file as expected - receive only "System.Collections" rows

Question

Can someone please explain Why my first examples don't work, and why adding in a ForEach-Object solves the problem? Thanks in advance!


I parsed the return from a command into a hashtable (sample at end of post) and want to log the information to a file as part of my processing. I know that $ht.GetEnumerator() | Sort-Object Name will return the full hash to screen, sorted. However, once I try sending things to file, it breaks.

$ht | Add-Content log.txt

only logs a single row of System.Collections.Hashtable. So, I've also tried

$ht.GetEnumerator() | Sort-Object Name | Add-Content log.txt 

and end up with rows of

System.Collections.DictionaryEntry
System.Collections.DictionaryEntry
System.Collections.DictionaryEntry

So then I tried to loop through and handle each individually with

foreach ($key in $ht.keys) {
Add-Content log.txt "$key : $ht.$key" }

and end up with

Server address : System.Collections.Hashtable.Server address
Client address : System.Collections.Hashtable.Client address
User name : System.Collections.Hashtable.User name

Solved with:

$ht.GetEnumerator() | Sort-Object Name |
ForEach-Object {"{0} : {1}" -f $_.Name,$_.Value} |
Add-Content log.txt 

For reference, the hashtable sample:

$ht = @{
    "Server address" = "server.net";
    "Client address" = "10.20.121.153";
    "User name" = "myuser"
}
Solution

Answering the why part, you obviously have a solution :)

In your first example

$ht | Add-Content log.txt

PowerShell takes $ht and tries to somehow convert it to a string so that it can be stored via Add-Content. Because there is no conversion defined for the hashtable, only the type name is returned from the conversion. Same as for example new-Object Random|Add-Content d:\log.txt. Again, only type name is written.

Next

$ht.GetEnumerator() | Sort-Object Name | Add-Content log.txt 

is similar. GetEnumerator returns object that is used for iteration; objects of type System.Collections.DictionaryEntry are returned. Again, there is no conversion to string, so type names are returned.

Personally, I think PowerShell should be smart enough and help here. The question is "how?". Designers probably didn't want to hardcode the output. It might be "{key}: {value}" or "{key} = {value}", or "{key}/{value}", or ... The format is not clear, so they left it for us to decide and format as you did it with the foreach statement.