How can I combine small CSV files that share the same headers?

Select the files explicitly rather than relying on similar filenames or a broad wildcard. Compare each file’s actual column names, in order, before combining its rows. Import-Csv uses the header row to name each row object’s properties, while Export-Csv writes a header and values to a CSV file. [S1] [S2]

Here is a small example. Replace the bracketed paths with your own. It assumes every input has at least one data row and that the files can be read with compatible CSV formatting.

$files = @(
    '[folder]\part-1.csv',
    '[folder]\part-2.csv'
)
$output = '[folder]\combined.csv'

$allRows = @()
$expectedHeaders = $null

foreach ($file in $files) {
    $rows = @(Import-Csv -LiteralPath $file)

    if ($rows.Count -eq 0) {
        throw "No data rows found in $file; check the file before combining."
    }

    $headers = @($rows[0].PSObject.Properties.Name)

    if ($null -eq $expectedHeaders) {
        $expectedHeaders = $headers
    } elseif ([string]::Join([char]0, $headers) -cne
               [string]::Join([char]0, $expectedHeaders)) {
        throw "Headers differ in $file; nothing was exported."
    }

    $allRows += $rows
}

$inputPaths = @($files | ForEach-Object {
    [System.IO.Path]::GetFullPath($_)
})
$outputPath = [System.IO.Path]::GetFullPath($output)
if ($inputPaths -contains $outputPath) {
    throw 'Choose an output path that is different from every input path.'
}

$allRows | Export-Csv -LiteralPath $output -NoTypeInformation

The output-path check helps prevent replacing a selected input. The header check is strict: both names and order must match. Export-Csv uses the first object’s properties for the output layout, so checking before export helps avoid mismatched properties producing nulls or being omitted. [S2]

A filename does not establish that two files have the same columns. The check reads the property names created from each CSV’s header row, then stops if a later file’s names or order differ. [S1] That matters because PowerShell’s export layout is based on the first object’s properties; later objects with mismatched properties can produce nulls or have properties omitted. [S2]

For example, name,city and city,name contain the same names but in a different order. This example rejects that difference rather than treating it as a match. Likewise, name,city and name,region should not be combined as though they have the same columns. Review or correct the inputs first, then run the check again.

It assumes each selected file has a header and at least one data row, and that the inputs can be read with compatible CSV formatting. The script gets header names from the first imported row, so a header-only file triggers the no-data check rather than being accepted. It also does not decide whether values from different files mean the same thing; matching column names alone cannot establish that.

The PowerShell documentation describes how Import-Csv and Export-Csv handle headers and objects. It does not establish that your files have compatible meanings or validate this complete multi-file workflow. [S1] [S2] Try the script on copies and inspect the resulting file before relying on it.

Use this before and after each combine:

1. List the exact input paths and confirm each file is one you intend to include.
2. Check that each file has a header and at least one data row for this example.
3. Compare header names and order; stop if any differ.
4. Choose an output path that is not one of the input paths.
5. Try the script on copies, then open the output and check its header and a few rows.

If a file has no data rows or the columns differ, review it separately rather than forcing it into the merge. The script does not validate the meaning or correctness of cell values.