Replacing IF statements with a SWITCH statement

[kvprasoon]

Hi,

I’ve created the below script as part of a training exercise to improve my PowerShell skills. It works as expected but could do with some advice on how to replace the IF statements with a switch statement.

PowerShell

Function Get-LocalProcesses { # Default to SortByName [CmdletBinding(DefaultParameterSetName = 'SortByName')] Param ( [Parameter(ParameterSetName = 'SortByCPU')] [switch]$SortByCPU, [Parameter(ParameterSetName = 'SortByRAM')] [switch]$SortByRAM, [Parameter(ParameterSetName = 'SortByName')] [switch]$SortByName, [int]$ShowFirst = '5' ) # Outputs which parameter is being used with the command $PSCmdlet.ParameterSetName # Set sort variable depending on switch used If ($SortByCPU) { $SortChoice = 'cpu' } If ($SortByRAM) { $SortChoice = 'ws' } If ($SortByName) { $SortChoice = 'name' } # Get local processes using chosen switch in sort cmdlet Get-Process | Sort-Object $SortChoice | Select-Object Id, Handles, @{Label = 'WS(k)'; Expression = { ($_.ws / 1024) } }, @{Label = 'CPU(m)'; Expression = { ($_.cpu).tostring("#.##") } }, @{Label = 'Priority'; Expression = { ($_.Priorityclass) } }, Name, Description -First $ShowFirst | FT -AutoSize } Get-LocalProcesses -SortByRAM

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Function Get-LocalProcesses {     # Default to SortByName     [CmdletBinding(DefaultParameterSetName = 'SortByName')]     Param (         [Parameter(ParameterSetName = 'SortByCPU')]         [switch]$SortByCPU,           [Parameter(ParameterSetName = 'SortByRAM')]         [switch]$SortByRAM,           [Parameter(ParameterSetName = 'SortByName')]         [switch]$SortByName,           [int]$ShowFirst = '5'     )     # Outputs which parameter is being used with the command     $PSCmdlet.ParameterSetName       # Set sort variable depending on switch used     If ($SortByCPU) {         $SortChoice = 'cpu'     }     If ($SortByRAM) {         $SortChoice = 'ws'     }     If ($SortByName) {         $SortChoice = 'name'     }       # Get local processes using chosen switch in sort cmdlet     Get-Process | Sort-Object $SortChoice | Select-Object Id, Handles, @{Label = 'WS(k)'; Expression = { ($_.ws / 1024) } }, @{Label = 'CPU(m)'; Expression = { ($_.cpu).tostring("#.##") } }, @{Label = 'Priority'; Expression = { ($_.Priorityclass) } }, Name, Description -First $ShowFirst | FT -AutoSize }   Get-LocalProcesses -SortByRAM

Any advice would be very much appreciated.

Cheers

Jamie

• This topic was modified 2 weeks ago by kvprasoon. Reason: code formatting

[Rob Simmers Participant Topics: 15 Replies: 1775 Points: 3,214Rank: Community Hero]

As you use Powershell cmdlets, pay attention to how they are named and the parameter names and how they are used.

• Singular – Notice how cmdlets are named singular (e.g Get-User, Get-Service, Get-Process), not Get-Processes
• Function Purpose – For what you are doing, the function should just return data. Get-Data | Sort-Data. If you look at other cmdlets, they don’t have sort capabilities because the goal of the function should be just to get the data, so you would normally have filter capabilities in a GET cmdlet\function.
• Switch – In your case, a switch statement isn’t applicable. Typically a switch compares the same variable and executes a code block based on different values. If we wanted to check $Name and if it’s John, Sue or Sam then do something. In this case, you have three separate variables.
• Parameter Names – Leveraging Select-Object with a First param, try to follow the same naming schema (i.e. First vs. ShowFirst) so that it’s consisten. Anyone that has used First will know what the purpose of the switch is. If you still want to use ShowFirst, then you should set the variable to First and use an Alias for Show First.

A better approach would be to use a validateset to show the possible sort options:

PowerShell

Function Get-LocalProcess { [CmdletBinding()] param ( [Parameter(Mandatory=$false)] [ValidateSet('CPU','RAM','Name')] [string]$SortBy = 'Name', [Parameter(Mandatory=$true)] [Alias('ShowFirst')] [int]$First = '5' ) Write-Verbose -Message ('Sorting on {0}' -f $SortBy) Get-Process | Sort-Object $SortBy | Select-Object -First $First } Get-LocalProcess -ShowFirst 3 -SortBy RAM -Verbose

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Function Get-LocalProcess {     [CmdletBinding()]     param (         [Parameter(Mandatory=$false)]         [ValidateSet('CPU','RAM','Name')]         [string]$SortBy = 'Name',         [Parameter(Mandatory=$true)]         [Alias('ShowFirst')]         [int]$First = '5'     )       Write-Verbose -Message ('Sorting on {0}' -f $SortBy)     Get-Process |     Sort-Object $SortBy |     Select-Object -First $First }   Get-LocalProcess -ShowFirst 3 -SortBy RAM -Verbose

[AdminOfThings45 Participant Topics: 0 Replies: 81 Points: 362Rank: Contributor]

You can turn your if statement block into switch statements using your parameter sets.

PowerShell

switch ($PSCmdlet.ParameterSetName) { 'SortByCPU' { $sortchoice = 'cpu' } 'SortByRam' { $sortchoice = 'ws' } default { $sortchoice = 'name' } }

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switch ($PSCmdlet.ParameterSetName) {     'SortByCPU' { $sortchoice = 'cpu' }     'SortByRam' { $sortchoice = 'ws' }     default { $sortchoice = 'name' } }

[jshizzle14]

Sorted it (Pardon the pun)…..

PowerShell

switch ($PSCmdlet.ParameterSetName) {` 'SortByCPU' { $SortChoice = @{expression = 'cpu';descending = $true} } 'SortByRam' { $SortChoice = @{expression = 'ws';descending = $true} } default { $SortChoice = @{expression = 'name';descending = $false} }

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switch ($PSCmdlet.ParameterSetName) {` 'SortByCPU' { $SortChoice = @{expression = 'cpu';descending = $true} } 'SortByRam' { $SortChoice = @{expression = 'ws';descending = $true} } default { $SortChoice = @{expression = 'name';descending = $false} }

Thanks for the help with all the other bits.

Cheers
Jamie

PowerShell

1

• This reply was modified 1 week, 4 days ago by jshizzle14.
• This reply was modified 1 week, 4 days ago by jshizzle14.

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