Why does the following PowerShell 5.1 statement produce output on 2 lines
Write-Output ($results | Measure-Object).Count ' rows returned'
Output
11
rows returned
More context:
$results = Get-Service -ComputerName $computers -DisplayName *Transportation* | Where-Object {$_.Status -eq "Running"}
$results | Format-Table -AutoSize
Write-Output ($results | Measure-Object).Count ' rows returned'
Given PowerShell's implicit output behavior, there's rarely a good reason to use Write-Output - see the bottom section of this answer for background information.
Thus, combined with the fact that you don't need Measure-Object to get the count of objects, you can simplify to one of the following, both of which implicitly output the resulting string, which by default prints to the display:
# Expression
[string] $results.Count + ' rows returned'
# Expandable string.
"$($results.Count) rows returned.
As for what you tried:
Write-Output accepts an open-ended number of arguments, which it outputs one by one, as-is - whatever data type they are.
Therefore, what ($results | Measure-Object).Count evaluates to becomes the first output object - of type [int] - followed by [string] ' rows returned', and they print separately, on their own lines.
By contrast, Write-Host would have given you the desired display output (save for an extra space), as it stringifies all its arguments and prints on the same line, separated with spaces:
# Prints '42 and a half' to the display - does NOT produce *data output*
Write-Host (40 + 2) 'and a half'
However, note that Write-Host is typically the wrong tool to use, unless the intent is to write to the display only, bypassing the success output stream and with it the ability to send output to other commands, capture it in a variable, or redirect it to a file.
See this answer for a juxtaposition of Write-Host and Write-Output.
Write-Outputwhen this is already implicit for PowerShell. The reason you see them in new lines is becauseInputObjectis decorated withValueFromRemainingArgumentsso you're actually passing an array to the cmdlet and the cmdlet is outputting exactly that"$(($results | Measure-Object).Count) rows returned"