Variable in string that's evaluated upon usage - string

Question

I'm setting up a Powershell script to provide some user notifications. The notification is legal in nature and may be updated/changed from time to time so it must be fairly easy to locate. It also has a few 'fill in the blank' variables that depend on the person receiving the notification.
I wanted to have a secondary Powershell file that contained the copy (text) to be used, so something like...
$body = "By accessing this system, you agree that your name ($currentUserName) and IP address ($currentUserIPAddr) will be recorded and stored for up to ($currentUserRetentionPeriod)."
The file could be updated as needed without actually opening the script, finding the line to edit, and potentially messing up other items/just being difficult. However, I'm looping through several thousand users in a single execution, so all the $currentUser... variables will be re-used frequently. This poses a problem because $body tries to get the variables immediately and acts as a static string instead of evaluating the variable contents each time it's invoked.
Is there a clever way for me to define $body a single time (i.e. not inside a loop) but still allow for redefinition of internal variables? I'd also rather not split the string up into multiple parts so it became $part1 + $var1 + part2 + var2....n+1 times.

Answer 1

A simple approach would be to just dot-source the script containing the copy whenever you need the variable "re-compiled":
BodyDef.ps1:
$body = "By accessing this system, you agree that your name ($currentUserName) and IP address ($currentUserIPAddr) will be recorded and stored for up to ($currentUserRetentionPeriod)."
Send-Notification.ps1
$bodyDefPath = (Join-Path $PSScriptRoot BodyDef.ps1)
foreach($user in Get-Users){
$currentUserName = $user.UserName
$currentUserIPAddr = $user.IPAddress
$currentUserRetentionPeriod = $user.RententionPeriod
. $bodyDefPath
Send-MailMessage -Body $body
}
The above would work just fine, but it's not very powershell-idiomatic, and kind of silly, reading the file over and over again.
As suggested in the comments, you should define a second function (or just a scriptblock) if you want to reuse the same template with different values:
Send-Notification.ps1
# You could as well define this as a function, doesn't make much difference
$NotificationSender = {
param($User)
$body = "By accessing this system, you agree that your name ($($user.UserName)) and IP address ($($user.IPAddress)) will be recorded and stored for up to $($user.RetentionPeriod)."
Send-MailMessage -Body $body
}
foreach($user in Get-Users){
& $NotificationSender -user $user
}