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Make Export-Csv -Append and -NoHeader mutually exclusive #26472

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Merged
iSazonov merged 6 commits into from
Nov 22, 2025
Merged

Make Export-Csv -Append and -NoHeader mutually exclusive #26472

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f5b52bb
Fix #25820: Make Export-Csv -Append and -NoHeader mutually exclusive
yotsuda Oct 24, 2025
da2b218
Add newline at end of file
yotsuda Nov 18, 2025
81d842e
Update src/Microsoft.PowerShell.Commands.Utility/commands/utility/Csv…
yotsuda Nov 18, 2025
5365418
Update test to use consistent error ID
yotsuda Nov 19, 2025
8a1a1b0
Update src/Microsoft.PowerShell.Commands.Utility/resources/CsvCommand…
yotsuda Nov 21, 2025
061a6fc
Address PR feedback: simplify condition and use InvalidData for consi…
yotsuda Nov 21, 2025
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8 changes: 8 additions & 0 deletions src/Microsoft.PowerShell.Commands.Utility/commands/utility/CsvCommands.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -270,6 +270,14 @@ protected override void BeginProcessing()
this.ThrowTerminatingError(errorRecord);
}

// Validate that Append and NoHeader are not specified together.
if (Append && NoHeader)
{
InvalidOperationException exception = new(CsvCommandStrings.CannotSpecifyAppendAndNoHeader);
ErrorRecord errorRecord = new(exception, "CannotSpecifyBothAppendAndNoHeader", ErrorCategory.InvalidData, null);
this.ThrowTerminatingError(errorRecord);
}

_shouldProcess = ShouldProcess(Path);
if (!_shouldProcess)
{
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3 changes: 3 additions & 0 deletions src/Microsoft.PowerShell.Commands.Utility/resources/CsvCommandStrings.resx
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Expand Up @@ -157,4 +157,7 @@
<data name="EOFIsReached" xml:space="preserve">
<value>EOF is reached.</value>
</data>
<data name="CannotSpecifyAppendAndNoHeader" xml:space="preserve">
<value>You must specify either the -Append or -NoHeader parameters, but not both.</value>
</data>
</root>
4 changes: 4 additions & 0 deletions test/powershell/Modules/Microsoft.PowerShell.Utility/Export-Csv.Tests.ps1
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Expand Up @@ -187,6 +187,10 @@ Describe "Export-Csv" -Tags "CI" {
$results[1].PSObject.properties.Name | Should -Not -Contain 'third'
}

It "Should throw when -Append and -NoHeader are specified together" {
{ $P1 | Export-Csv -Path $testCsv -Append -NoHeader -ErrorAction Stop } | Should -Throw -ErrorId "CannotSpecifyBothAppendAndNoHeader,Microsoft.PowerShell.Commands.ExportCsvCommand"
}

It "First line should be #TYPE if -IncludeTypeInformation used and pstypenames object property is empty" {
$object = [PSCustomObject]@{first = 1}
$pstypenames = $object.pstypenames | ForEach-Object -Process {$_}
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