Prerequisites

• Write a descriptive title.
• Make sure you are able to repro it on the latest released version
• Search the existing issues.
• Refer to the FAQ.
• Refer to Differences between Windows PowerShell 5.1 and PowerShell.

Steps to reproduce

• -NoHeader is invariably implied when using -Append, assuming that the target file exists and contains data, which only succeeds if the existing data starts with a header row.

• However, if the target file doesn't exist yet or is an empty file, -Append -NoHeader creates the file without a header row, and that causes subsequent calls targeting the same with the same switches to fail.

$tempFile = New-TemporaryFile

@(
[pscustomobject] @{ prop = 'A' },
[pscustomobject] @{ prop = 'B' }
) | 
  ForEach-Object {
    $_ | Export-Csv -Append -NoHeader $tempFile
  } 

$tempFile | Remove-Item

Expected behavior

A parameter-binding error that indicates that -Append and -NoHeader are mutually exclusive.

Actual behavior

Cannot append CSV content to the following file: <file>. 
The appended object does not have a property that corresponds to the following column: A.
To continue with mismatched properties, add the -Force parameter, and then retry the command.

That is, the combination of -Append and -NoHeader was accepted, and created a no-header CSV file in the first call, causing the second one to predictably fail.

If backward compatibility is a concern, the alternative is to selectively and quietly ignore -NoHeader if combined with -Append, in case the target file happens to either not yet exist or happens to be empty (0 bytes).

Error details

Environment data

PowerShell 7.6.0-preview.4

Visuals

No response