An object type classifies the data held by a PowerShell object and determines which members and operations are available. Check a value with Get-Member (gm) before deciding what a later pipeline command can do. section 8.9
Use explicit types when a variable must hold predictable data:
- [int] stores integer numbers; [single] and [double] store decimal numbers; [string] stores characters; [char] stores one character; and [xml] validates XML markup. section 16.6
- Declare [int]$number before reading input to convert valid input into an integer, so multiplication produces numeric results instead of string repetition. section 16.6
- PowerShell rejects input that cannot be converted and continues enforcing the declared type until the variable is explicitly retyped. section 16.6
Inspect and constrain a variable
Read input as an integer, then verify its type and value: [int]$number = Read-Host "Enter a number"; $number | Get-Member; $number = $number * 10; $number. Entering 100 reports System.Int32 and produces 1000. Entering Hello raises a conversion error.
PS /Users/jamesp/> Get-Process; Get-History
NPM(K) PM(M) WS(M) CPU(s) Id SI ProcessName
------ ----- ----- ------ -- -- -----------
...
0 0.00 1.74 0.25 1244 1 UsageTrackingAg
0 0.00 0.68 0.19 710 1 USBAgent
0 0.00 4.12 6.37 544 1 useractivityd
0 0.00 5.44 8.00 407 1 UserEventAgent
0 0.00 7.50 3.43 428 1 usernoted
0 0.00 3.44 8.71 506 1 ViewBridgeAuxil
0 0.00 5.91 0.08 27019 ...19 VTDecoderXPCSer
0 0.00 5.92 0.07 89048 ...48 VTDecoderXPCSer
0 0.00 10.79 50.02 434 1 WiFiAgent
0 0.00 1.11 0.20 1242 1 WiFiVelocityAge
0 0.00 10.28 4.30 20921 ...21 XprotectService
Id : 1
CommandLine : Update-TypeData -Path /tmp/Uri.Types.ps1xml
ExecutionStatus : Completed
StartExecutionTime : 9/21/2019 12:20:03 PM
EndExecutionTime : 9/21/2019 12:20:03 PM
Duration : 00:00:00.0688690
Id : 2
CommandLine : Update-TypeData -Path /tmp/Uri.Types.ps1xml
ExecutionStatus : Completed
StartExecutionTime : 9/21/2019 12:21:07 PM
EndExecutionTime : 9/21/2019 12:21:07 PM
Duration : 00:00:00.0125330eyp
Compare the formatting result when process objects and history objects share a pipeline: the display begins as a process table and then falls back to a list. section 11.9.2
