functions/Find-DbaBackup.ps1

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#ValidationTags#Messaging,FlowControl,Pipeline,CodeStyle#
function Find-DbaBackup {
    <#
        .SYNOPSIS
            Finds SQL Server backups on disk.
 
        .DESCRIPTION
            Provides all of the same functionality for finding SQL backups to remove from disk as a standard maintenance plan would.
 
            As an addition you have the ability to check the Archive bit on files before deletion. This will allow you to ensure backups have been archived to your archive location before removal.
 
        .PARAMETER Path
            Specifies the name of the base level folder to search for backup files.
 
        .PARAMETER BackupFileExtension
            Specifies the filename extension of the backup files you wish to find (typically 'bak', 'trn' or 'log'). Do not include the period.
 
        .PARAMETER RetentionPeriod
            Specifies the retention period for backup files. Correct format is ##U.
 
            ## is the retention value and must be an integer value
            U signifies the units where the valid units are:
            h = hours
            d = days
            w = weeks
            m = months
 
            Formatting Examples:
            '48h' = 48 hours
            '7d' = 7 days
            '4w' = 4 weeks
            '1m' = 1 month
 
        .PARAMETER CheckArchiveBit
            If this switch is enabled, the filesystem Archive bit is checked.
            If this bit is set (which translates to "it has not been backed up to another location yet"), the file won't be included.
 
        .PARAMETER EnableException
            By default, when something goes wrong we try to catch it, interpret it and give you a friendly warning message.
            This avoids overwhelming you with "sea of red" exceptions, but is inconvenient because it basically disables advanced scripting.
            Using this switch turns this "nice by default" feature off and enables you to catch exceptions with your own try/catch.
 
        .NOTES
            Tags: Storage, DisasterRecovery, Backup
            Author: Chris Sommer, @cjsommer, www.cjsommer.com
 
            dbatools PowerShell module (https://dbatools.io, clemaire@gmail.com)
            Copyright (C) 2016 Chrissy LeMaire
            License: MIT https://opensource.org/licenses/MIT
 
        .LINK
            https://dbatools.io/Find-DbaBackup
 
        .EXAMPLE
            Find-DbaBackup -Path 'C:\MSSQL\SQL Backup\' -BackupFileExtension trn -RetentionPeriod 48h
 
            '*.trn' files in 'C:\MSSQL\SQL Backup\' and all subdirectories that are more than 48 hours old will be included.
 
        .EXAMPLE
            Find-DbaBackup -Path 'C:\MSSQL\Backup\' -BackupFileExtension bak -RetentionPeriod 7d -CheckArchiveBit
 
            '*.bak' files in 'C:\MSSQL\Backup\' and all subdirectories that are more than 7 days old will be included, but only if the files have been backed up to another location as verified by checking the Archive bit.
 
    #>

    [CmdletBinding()]
    param (
        [parameter(Mandatory = $true, HelpMessage = "Full path to the root level backup folder (ex. 'C:\SQL\Backups'")]
        [Alias("BackupFolder")]
        [string]$Path,
        [parameter(Mandatory = $true, HelpMessage = "Backup File extension to remove (ex. bak, trn, dif)")]
        [string]$BackupFileExtension ,
        [parameter(Mandatory = $true, HelpMessage = "Backup retention period. (ex. 24h, 7d, 4w, 6m)")]
        [string]$RetentionPeriod ,
        [parameter(Mandatory = $false)]
        [switch]$CheckArchiveBit = $false ,
        [switch][Alias('Silent')]$EnableException
    )

    begin {
        ### Local Functions
        function Convert-UserFriendlyRetentionToDatetime {
            [cmdletbinding()]
            param (
                [string]$UserFriendlyRetention
            )

            <#
            Convert a user friendly retention value into a datetime.
            The last character of the string will indicate units (validated)
            Valid units are: (h = hours, d = days, w = weeks, m = months)
 
            The preceeding characters are the value and must be an integer (validated)
 
            Examples:
                '48h' = 48 hours
                '7d' = 7 days
                '4w' = 4 weeks
                '1m' = 1 month
            #>


            [int]$Length = ($UserFriendlyRetention).Length
            $Value = ($UserFriendlyRetention).Substring(0, $Length - 1)
            $Units = ($UserFriendlyRetention).Substring($Length - 1, 1)

            # Validate that $Units is an accepted unit of measure
            if ( $Units -notin @('h', 'd', 'w', 'm') ) {
                throw "RetentionPeriod '$UserFriendlyRetention' units invalid! See Get-Help for correct formatting and examples."
            }

            # Validate that $Value is an INT
            if ( ![int]::TryParse($Value, [ref]"") ) {
                throw "RetentionPeriod '$UserFriendlyRetention' format invalid! See Get-Help for correct formatting and examples."
            }

            switch ($Units) {
                'h' { $UnitString = 'Hours'; [datetime]$ReturnDatetime = (Get-Date).AddHours( - $Value)  }
                'd' { $UnitString = 'Days'; [datetime]$ReturnDatetime = (Get-Date).AddDays( - $Value)   }
                'w' { $UnitString = 'Weeks'; [datetime]$ReturnDatetime = (Get-Date).AddDays( - $Value * 7) }
                'm' { $UnitString = 'Months'; [datetime]$ReturnDatetime = (Get-Date).AddMonths( - $Value) }
            }
            $ReturnDatetime
        }

        # Validations
        # Ensure BackupFileExtension does not begin with a .
        if ($BackupFileExtension -match "^[.]") {
            Write-Message -Level Warning -Message "Parameter -BackupFileExtension begins with a period '$BackupFileExtension'. A period is automatically prepended to -BackupFileExtension and need not be passed in."
        }
        # Ensure Path is a proper path
        if (!(Test-Path $Path -PathType 'Container')) {
            Stop-Function -Message "$Path not found"
        }

    }
    process {
        if (Test-FunctionInterrupt) { return }
        # Process stuff
        Write-Message -Message "Finding backups on $Path" -Level Verbose
        # Convert Retention Value to an actual DateTime
        try {
            $RetentionDate = Convert-UserFriendlyRetentionToDatetime -UserFriendlyRetention $RetentionPeriod
            Write-Message -Message "Backup Retention Date set to $RetentionDate" -Level Verbose
        }
        catch {
            Stop-Function -Message "Failed to interpret retention time!" -ErrorRecord $_
        }

        # Filter out unarchived files if -CheckArchiveBit parameter is used
        if ($CheckArchiveBit) {
            Write-Message -Message "Removing only archived files." -Level Verbose
            filter DbaArchiveBitFilter {
                if ($_.Attributes -notmatch "Archive") {
                    $_
                }
            }
        }
        else {
            filter DbaArchiveBitFilter {
                $_
            }
        }
        # Enumeration may take a while. Without resorting to "esoteric" file listing facilities
        # and given we need to fetch at least the LastWriteTime, let's just use "streaming" processing
        # here to avoid issues like described in #970
        Get-ChildItem $Path -Filter "*.$BackupFileExtension" -File -Recurse -ErrorAction SilentlyContinue -ErrorVariable EnumErrors |
            Where-Object LastWriteTime -lt $RetentionDate | DbaArchiveBitFilter
        if ($EnumErrors) {
            Write-Message "Errors encountered enumerating files." -Level Warning -ErrorRecord $EnumErrors
        }
    }
}