How to use a $_. variable in a herestring? - powershell

Question

I can't seem to figure out how to use a variable in a herestring, and for the variable to be expanded at a later time in a piped command. I have experimented with single ' and double " quotes, and escape ` characters.
I am trying to use the herestring for a list (e.g. like an array) of Exchange groups, and a corresponding list of conditions to apply to those groups. Here is a simplified example which fails to use the $Conditions variable correctly (it does not expand the $_.customattribute2 variable):
# List of groups and conditions (tab delimitered)
$records = #"
Group1 {$_.customattribute2 -Like '*Sales*'}
Group2 {$_.customattribute2 -Like '*Marketing*' -OR $_.customattribute2 -Eq 'CEO'}
"#
# Loop through each line in $records and find mailboxes that match $conditions
foreach ($record in $records -split "`n") {
($DGroup,$Conditions) = $record -split "`t"
$MailboxList = Get-Mailbox -ResultSize Unlimited
$MailboxList | where $Conditions
}

Answer 1

No, no that's not going to work. The whole good bit about PowerShell is not having to make everything a string and then drag it to the moon and back trying to get the important stuff back out of the string. {$_.x -eq "y"} is a scriptblock. It's a thing by itself, you don't need to put it in a string.
#Array of arrays. Pairs of groups and conditions
[Array]$records = #(
('Group1', {$_.customattribute2 -Like '*Sales*'}),
('Group2', {$_.customattribute2 -Like '*Marketing*' -OR $_.customattribute2 -Eq 'CEO'})
)
#Loop through each line in $records and find mailboxes that match $conditions
foreach ($pair in $records) {
$DGroup, $Condition = $pair
$MailboxList = Get-Mailbox -ResultSize Unlimited
$MailboxList | where $Condition
}

Answer 2

TessellatingHeckler's explanation is right. However, if you insist on herestring, it's possible as well. See the following example (created merely for demonstration):
$records=#'
Group1 {$_.Extension -Like "*x*" -and $_.Name -Like "m*"}
Group2 {$_.Extension -Like "*p*" -and $_.Name -Like "t*"}
'#
foreach ($record in $records -split "`n") {
($DGroup,$Conditions) = $record -split "`t"
"`r`n{0}={1}" -f $DGroup,$Conditions
(Get-ChildItem |
Where-Object { . (Invoke-Expression $Conditions) }).Name
}
Output:
PS D:\PShell> D:\PShell\SO\47108347.ps1
Group1={$_.Extension -Like "*x*" -and $_.Name -Like "m*"}
myfiles.txt
Group2={$_.Extension -Like "*p*" -and $_.Name -Like "t*"}
Tabulka stupnic.pdf
ttc.ps1
PS D:\PShell>
Caution: some text/code editors could convert tabulators to space sequences!