powershell month abbreviation to month number in a filename

$AbrevMonthNames = (Get-Culture).DateTimeFormat.AbbreviatedMonthNames

$InStuff = get-item *.csv
# grab 3rd from last & then 2nd item of each .Split()
$MonthAbr = $InStuff.name.Split('_')[-2].Split('-')[1]

# correct for off-by-one
$MonthNum = '{0:00}' -f ($AbrevMonthNames.IndexOf($MonthAbr) + 1)

# replace the abbreviated month with the month number
$outstuff = $instuff.name -replace $monthabr,$monthnum

# rename the original file with the new name
rename-item $instuff $outstuff