How to split a date range into monthly subranges in PowerShell?

Question

In Powershell, assuming:

$rangeFrom = "2020-03-01" 
$rangeTo  =  "2020-05-13" 

How could I obtain:

$monthRange[0] = "2020-03-01","2020-03-31"
$monthRange[1] = "2020-04-01","2020-04-30"
$monthRange[2] = "2020-05-01","2020-05-13"

Dates will be used in a loop as strings (from/to) on commands that do not support more than one month in range, such as:

myCommand -From $rangeFrom -To $rangeTo # keep this in one month range

Answer 1

By using DateTime objects you can solve the most trouble, like calculating the last day of a month or iterating over dates. You can use the following code to solve your problem:

$rangeFrom = "2019-12-15" 
$rangeTo   = "2020-05-13"

$monthRange = @()

$dateFrom = Get-Date $rangeFrom
$dateTo = Get-Date $rangeTo
$dateCur = Get-Date $dateFrom -Day 1
while ($dateCur -lt $dateTo) {
    if (($dateCur.Year -eq $dateFrom.Year) -and ($dateCur.Month -eq $dateFrom.Month)) {
        $dateBegin = $dateFrom # First month exception
    } else {
        $dateBegin = $dateCur
    }
    if (($dateCur.Year -eq $dateTo.Year) -and ($dateCur.Month -eq $dateTo.Month)) {
        $dateEnd = $dateTo # Last month exception
    } else {
        $dateEnd = $dateCur.AddMonths(1).AddDays(-1)
    }
    $monthRange += [Tuple]::Create($dateBegin.toString('yyyy-MM-dd'), $dateEnd.toString('yyyy-MM-dd'))
    $dateCur = $dateCur.AddMonths(1)
}
$monthRange

Output:

Item1      Item2      Length
-----      -----      ------
2019-12-15 2019-12-31      2
2020-01-01 2020-01-31      2
2020-02-01 2020-02-29      2
2020-03-01 2020-03-31      2
2020-04-01 2020-04-30      2
2020-05-01 2020-05-13      2

You can access individual elements like this:

$monthRange[2].Item2

Output:

2020-02-29