Let's say you want to trim your audit log in your SharePoint production site. Here are the list of PowerShell commands to trim audit logs for all the sites with in a site collection.
$user = "<domain\user>"
foreach ($site in get-spsite -Limit ALL)
{
if (($site.Owner.UserLogin -eq $user))
{
$i = -350
do {
$site.audit.deleteentries([System.DateTime]::Now.ToLocalTime().AddDays($i))
$site.audit.update()
$i++
}
while ($i -le 1)
}
}
Please ensure that you are the site Collection Admin while execution.