diff --git a/docs/learning-powershell/working-with-powershell-objects.md b/docs/learning-powershell/working-with-powershell-objects.md new file mode 100644 index 0000000000..d747ec02f0 --- /dev/null +++ b/docs/learning-powershell/working-with-powershell-objects.md @@ -0,0 +1,124 @@ +Working with PowerShell Objects +==== +When cmdlets are executed in PowerShell, the output is an Object, as opposed to only returning text. +This provides the ability to store information as properties. +As a result, handling large amounts of data and getting only specific properties is a trivial task. + +As a simple example, the following function retrieves information about storage Devices on a Linux or MacOS operating system platform. +This is accomplished by parsing the output of an existing command, *parted -l* in administrative context, and creating an object from the raw text by using the *New-Object* cmdlet. + +```PowerShell +Function Get-DiskInfo { + $disks = sudo parted -l | Select-String "Disk /dev/sd*" -context 1,0 + $diskinfo = @() + foreach ($disk in $disks) { + $diskline1 = $disk.ToString().Split("`n")[0].ToString().Replace(' Model: ','') + $diskline2 = $disk.ToString().Split("`n")[1].ToString().Replace('> Disk ','') + $i = New-Object psobject -Property @{'Friendly Name' = $diskline1; Device=$diskline2.Split(': ')[0]; 'Total Size'=$diskline2.Split(':')[1]} + $diskinfo += $i + } + $diskinfo +} +``` + +Execute the function and store the results as a variable. +Now retrieve the value of the variable. +The results are formatted as a table with the default view. + +*Note: in this example, the disks are virtual disks in a Microsoft Azure virtual machine.* + +```PowerShell +PS /home/psuser> $d = Get-DiskInfo +[sudo] password for psuser: +PS /home/psuser> $d + +Friendly Name Total Size Device +------------- ---------- ------ +Msft Virtual Disk (scsi) 31.5GB /dev/sda +Msft Virtual Disk (scsi) 145GB /dev/sdb + +``` + +Passing the variable down the pipeline to *Get-Member* reveals available methods and properties. +This is because the value of *d$* is not just text output. +The value is actually an array of .Net objects with methods and properties. +The properties include Device, Friendly Name, and Total Size. + +```PowerShell +PS /home/psuser> $d | Get-Member + + + TypeName: System.Management.Automation.PSCustomObject + +Name MemberType Definition +---- ---------- ---------- +Equals Method bool Equals(System.Object obj) +GetHashCode Method int GetHashCode() +GetType Method type GetType() +ToString Method string ToString() +Device NoteProperty string Device=/dev/sda +Friendly Name NoteProperty string Friendly Name=Msft Virtual Disk (scsi) +Total Size NoteProperty string Total Size= 31.5GB +``` + +To confirm, we can call the GetType() method interactively from the console. + +```PowerShell +PS /home/psuser> $d.GetType() + +IsPublic IsSerial Name BaseType +-------- -------- ---- -------- +True True Object[] System.Array +``` + +To index in to the array and return only specific objects, use the square brackets. + +```PowerShell +PS /home/psuser> $d[0] + +Friendly Name Total Size Device +------------- ---------- ------ +Msft Virtual Disk (scsi) 31.5GB /dev/sda + +PS /home/psuser> $d[0].GetType() + +IsPublic IsSerial Name BaseType +-------- -------- ---- -------- +True False PSCustomObject System.Object +``` + +To return a specific property, the property name can be called interactively from the console. + +```PowerShell +PS /home/psuser> $d.Device +/dev/sda +/dev/sdb +``` + +To output a view of the information other than default, such as a view with only specific properties selected, pass the value to the *Select-Object* cmdlet. + +```PowerShell +PS /home/psuser> $d | Select-Object Device, 'Total Size' + +Device Total Size +------ ---------- +/dev/sda 31.5GB +/dev/sdb 145GB +``` + +Finally, the example below demonstrates use of the *ForEach-Object* cmdlet to iterate through the array and manipulate the value of a specific property of each object. +In this case the Total Size property, which was given in Gigabytes, is changed to Megabytes. +Alternatively, index in to a position in the array as shown below in the third example. + +```PowerShell +PS /home/psuser> $d | ForEach-Object 'Total Size' + 31.5GB + 145GB + +PS /home/psuser> $d | ForEach-Object {$_.'Total Size' / 1MB} +32256 +148480 + +PS /home/psuser> $d[1].'Total Size' / 1MB +148480 +``` \ No newline at end of file