Why does Add-Content translates the comma separator from .TotalSeconds into a dot separator?

When I use this:

$timer = (Get-Date)
$duration = (New-TimeSpan -Start $timer -End (Get-Date)).TotalSeconds
$time = [math]::Round($duration,2)
Add-Content $file $time

I get:

When I use this:

$timer = (Get-Date)
$duration = (New-TimeSpan -Start $timer -End (Get-Date)).TotalSeconds
$time = [math]::Round($duration,2)
Add-Content $file "some text;$time;some text"

I get:

How do I still get a comma separator when my $time variable is between other values?

I tried to put the variable between double qoutes:

$timer = (Get-Date)
$duration = (New-TimeSpan -Start $timer -End (Get-Date)).TotalSeconds
$time = [math]::Round($duration,2)
Add-Content $file "some text;""$time"";some text"

Anyone ideas?

Solution

Your problem is unrelated to Excel and boils down to the different ways culture-sensitive data types such as fractional numbers are stringified:

PowerShell's own string interpolation, via expandable strings (double-quoted, i.e. "..."), is culture-invariant by design, i.e. uses the invariant culture, which is based on, but distinct from, the US-English culture, in which . represents the decimal mark.
By contrast, passing a number (or any other non-string type whose string representation is culture-sensitive) directly to Add-Content saves a string representation that is formatted according to the rules of the current culture to the target file (applies equally to Set-Content and Out-File / >).
- That is - unlike inside an expandable PowerShell string - the resulting representation depends on the current culture in effect from .NET's perspective, as reflected by [cultureinfo]::CurrentCulture, Get-PSCulture, or $PSCulture.

Your symptom implies that your current culture is one where , (comma) serves as the decimal mark, such as fr-FR (French).

If you want to build a string involving culture-sensitive representations of numbers, instead of PowerShell's string interpolation you can use -f, the format operator, which is culture-sensitive:

Add-Content $file ('some text;{0};some text' -f $time)

Note that you can achieve the same culture-sensitive stringification for a single numeric variable by calling .ToString() on it (e.g., $time = 1.2; $time.ToString() yields 1,2 in cultures where , is the decimal mark).