Powershell command returns null on success - powershell

Question

I am writing small utility scripts in Powershell. While trying to follow the principle of doing one job extremely well per script, I am running into an issue with one script that returns a null value on success. When I try to run the command, and pipe it through a command such as Send-MailMessage, I get an error when it should be successful. I am trying to get Send-MailMessage to only fire if there is output in the body (otherwise, there would be many emails coming in).
Currently, I'm trying to run this from the Powershell command line:
Send-MailMessage -From "powershell#example.com" -To "tech#example.com" -Subject "Disk usage on $($env:COMPUTERNAME)" -SmtpServer "192.168.0.1" -Body (.\diskUsage.ps1 | Out-String) -ErrorAction Continue
The error I'm receiving:
Send-MailMessage : Cannot validate argument on parameter 'Body'. The argument is null or empty. Provide an argument that is not null or empty, and then try the command again.
At line:1 char:156
+ ... SmtpServer "192.168.0.1" -Body (.\diskUsage.ps1 | Out-String) -ErrorA ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidData: (:) [Send-MailMessage], ParameterBindingValidationException
+ FullyQualifiedErrorId : ParameterArgumentValidationError,Microsoft.PowerShell.Commands.SendMailMessag
My goal is to run the command remotely to many computers, and only get email notifications when the disk usage is above a threshold. My script currently returns nothing if the disk space check is OK, and this is my expected behaviour. I need Send-MailMessage, on the command itself, to simply not run if there is nothing to put in the body, without an error appearing in the console that the body is empty.

Answer 1

If specified, the body parameter is going to be verified for not being null or empty. Here is the body part from the open source version of PowerShell:
/// <summary>
/// Specifies the body (content) of the message
/// </summary>
[Parameter(Position = 2)]
[ValidateNotNullOrEmpty]
public String Body
{
get { return _body; }
set
{
_body = value;
}
}
private String _body;
Notice that if no Body is assigned the default value is going to be used which is not defined but rather an implementation detail and in this example null (Send-MailMessage). Therefore not specifying the Body is what you would like to todo.
To ensure clean code you can use PowerShells splatting features or alternativly use simple branching using if statements.
Simple If
$diskUsage = (.\diskUsage.ps1 | Out-String)
If ($diskUsage){
# Disk usage was set
Send-MailMessage -From "powershell#example.com" -To "tech#example.com" -Subject "Disk usage on $($env:COMPUTERNAME)" -SmtpServer "192.168.0.1" -Body $diskUsage -ErrorAction Continue
} Else {
# Disk usage was not set notice that -body is omitted which is different from setting it to null or empty
Send-MailMessage -From "powershell#example.com" -To "tech#example.com" -Subject "Disk usage on $($env:COMPUTERNAME)" -SmtpServer "192.168.0.1" -ErrorAction Continue
}

Answer 2

First, emails are usuallly UTF8 to set the encoding of the body to UTF8 by using -Encoding UTF8
If you are trying to capture the output of diskUsage.ps1 it probably won't return a string like you think.
You can test it by running:
$output = & C:\path\to\diskUsage.ps1 | Out-String
if([String]::IsNullOrEmpty($output)) { echo 'no string is being returned' } else { echo 'String returned' }
If it says no string is being returned, then you should rethink this command into a script.
e.g. put the diskUsage.ps1 and this Send-MailMessage command into one script.