Trouble reading last line of CSV - powershell

Question

I am getting CSV files (with no header) from another system. The last line ends the file, (there is not a newline after the last line of data). When I try Import-CSV, it will not read the last line of the file.
I do not have the ability to have the input file changed to include the newline.
I have noticed that the Get-Content doesn't have a problem reading the entire file, but then it isn't a CSV and I'm unable to reference the fields in the file.
Currently I'm doing:
$w = Import-CSV -path c:\temp\input.txt -header 'head1', 'head2', 'head3'
This will not read the last line of the file
This reads the entire file:
$w = Get-Content -path c:\temp\input.txt
But the data doesn't have the ability to reference the fields like: $w.head1
Is there a way to get Import-CSV to read the file including the last line?
OR Is there a way to read in the data using Get-Content, adding a header to it and then converting it back to a CSV?
I've tried use ConvertTo-CSV but have not had success:
$w = Get-Content -path c:\temp\input.txt
$csvdata = $w | ConvertTo-CSV # No header option for this function
I'd rather not create an intermediate file unless absolutely necessary.

Answer 1

You're very close! What you're after is not ConvertTo-Csv, you already have the file contents in CSV-format after all. So change that to ConvertFrom-Csv instead, which incidentally does support the -Headers parameter. So something like this:
$w = Get-Content -path c:\temp\input.txt
$csvdata = $w | ConvertFrom-Csv -Header 'head1', 'head2', 'head3'

Answer 2

If I understand correctly, you know the number of columns in the file and all it is missing is a header line. Since in your code you do not specify a -Delimiter parameter I'm assuming the delimiter character used in the file is a comma.
Best thing to do IMHO is to create a new output file and always keep the original.
$fileIn = 'c:\temp\input.txt'
$fileOut = 'c:\temp\input.csv'
# write the header line to a new file
Set-Content -Path $fileOut -Value 'head1,head2,head3'
# read the original file and append it to the one you have just created
Get-Content -Path $fileIn -Raw | Add-Content -Path $fileOut
If your file is really large, below a faster alternative:
$fileIn = 'c:\temp\input.txt'
$fileOut = 'c:\temp\input.csv'
# write the header line to a new file
Set-Content -Path $fileOut -Value 'head1,head2,head3'
# read the original file and append it to the one you have just created
[System.IO.File]::AppendAllText($fileOut, ([System.IO.File]::ReadAllText($fileIn)))
If you really do want to take the risk and overwrite the original file, you can do this:
$file = 'c:\temp\input.txt'
$content = Get-Content -Path $fileIn -Raw
# write the header line to a the file destroying what was in there
Set-Content -Path $file -Value 'head1,head2,head3'
# append the original content to it
$content | Add-Content -Path $file