Powershell - adding a string to each row - powershell

Question

I have a csv with over 1,000 rows.
In powershell how do I add a fixed string (e.g. "File1")to each row of the csv file.
For example:
Cat,dog,mouse should become file1,cat,dog,mouse.
Hopefully this is clear. Thanks for assistance.

Answer 1

Try like this:
Import-Csv "CSV FILE Path" |
Select-Object #{n='YOUR NEW COLUMN HEADER NAME';e={"file1"}},* |
Export-Csv "CSV FILE Path"

Answer 2

Looking at your latest comment, I think the fastest way here is to read the file line-by-line and output that same line with the wanted prefix attached.
Something like:
$prefix = 'File1'
$result = switch -File 'D:\Test\TheInputFile.csv' {
default { "$prefix,$_" }
}
$result | Set-Content -Path 'D:\Test\TheOutputFile.csv'
If the input file is a csv with headers, you'll need to supply a new column header for the inserted field:
$prefix = 'File1'
$header = 'Path' # or some other not already used column name
$firstLine = $true
$result = switch -File 'D:\Test\TheInputFile.csv' {
default {
if ($firstLine) { "$header,$_"; $firstLine = $false }
else { "$prefix,$_" }
}
}
$result | Set-Content -Path 'D:\Test\TheOutputFile.csv'
A CSV file is a text file. The difference is that in a csv, data is presented in a structured way. Ideally it starts with a header line, defining the field names for the rest of the lines which contain the actual data.
Each field is separated from the next by a specific character, usually a comma or semi-colon or tab.
To make sure a field can also include such a character, these fields must be enclosed in double-quotes.
See here