Attributes

R Read-only

A Archive

S System

H Hidden

attrib +R <file>	Add read-only attribute
attrib -H <file>	Remove hidden attribute
attrib +H +S <file>	Set as Hidden and System attributes
attrib +h *.txt	Hide all .txt files

Add read-only:

Set-ItemProperty <file> -Name Attributes -Value ([System.IO.FileAttributes]::ReadOnly)

Remove read-only:

$attributes = (Get-Item <Path\FileName>).Attributes -band (-bnot [System.IO.FileAttributes]::ReadOnly)

Set-ItemProperty <Path\FileName> -Name Attributes -Value $attributes

Add multple attributes:

$attributes = (Get-Item <Path\FileName>).Attributes -bor [System.IO.FileAttributes]::Hidden -bor [System.IO.FileAttributes]::System

Set-ItemProperty <Path\FileName> -Name Attributes -Value $attributes