That has nothing to do with Perl. That's PowerShell doing that. You can control the output as follows:

script | Out-File -Encoding UTF-8 file.out
[download]

The above outputs a BOM. The following doesn't, but requires PS6+

script | Out-File -Encoding UTF8NoBOM file.out
[download]

That said, -Encoding UTF8NoBOM is the default with PS6+, so all you need is the following if you're using PS6+:

script >file.out
[download]

So the issue is really that you are using an outdated PowerShell.

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References:

• Changing PowerShell's default output encoding to UTF-8.
• Using PowerShell to write a file in UTF-8 without the BOM.