PowerShell: Format-Table Breaks the Next Command

Get-Service | Format-Table | Export-Csv services.csv produces a CSV full of garbage, or an error about formatting records, depending on the version and the next command. Format-Table did what it is for. It turned service objects into instructions for the console. Export-Csv then serialized those instructions. The file is not a list of services.

Format cmdlets are the end of the object pipeline. They belong in the last position, when a person is looking at the screen. They do not belong in the middle of a script.

What to use instead

You wanted	Write this
A table on screen, and then stop	Get-Service | Format-Table -AutoSize as the last line
A CSV of real properties	Get-Service | Select-Object Name, Status, StartType | Export-Csv services.csv -NoTypeInformation
Only some columns, still objects	Select-Object. Never Format-Table
A string for a log line	"$($_.Name) is $($_.Status)" or -join. Not Out-String on the whole table unless you mean to log the rendering

Select-Object chooses properties and emits objects. Format-Table chooses columns and emits format data. The names sound similar. The next command can tell them apart, and only one of them is still data.

The bug in the middle of a function

function Get-RunningServices {
    Get-Service |
        Where-Object Status -eq Running |
        Format-Table Name, Status
}

Callers who do $svc = Get-RunningServices; $svc.Name get nothing useful. The function displayed a table and returned formatting objects. Return the objects. Let the caller format.

function Get-RunningServices {
    Get-Service | Where-Object Status -eq Running | Select-Object Name, Status, StartType
}

If the function is interactive and you want a table when someone runs it at the prompt, that already happens. PowerShell formats objects for the host when they reach the end of the pipeline. You do not have to call Format-Table to get a table. You call it when you need widths, a custom column, or to force the view. Do that in the script the human runs, not in the function other scripts call.

Out-String and Format-List have the same rule

Out-String collapses the stream into one string. A later Where-Object filters lines of text, badly, because a wrapped line is not a row. Format-List is the vertical version of Format-Table and is just as final.

The check is mechanical. Search scripts for Format-Table, Format-List, and Out-String. If the next pipe is anything other than Out-Host, Out-File of a report you intend to be text, or the end of the script, delete the format cmdlet and project with Select-Object. The CSV, the JSON, and the next function will start receiving the objects you thought you were sending all along.