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4.3 Manage Large Conditional Statements with Switches

Problem

You want to find an easier or more compact way to represent a large if … elseif … else conditional statement.

Solution

Use PowerShell’s switch statement to more easily represent a large if … elseif … else conditional statement.

For example:

$temperature = 20

switch($temperature)
{
   { $_ -lt 32 }   { "Below Freezing"; break }
   32              { "Exactly Freezing"; break }
   { $_ -le 50 }   { "Cold"; break }
   { $_ -le 70 }   { "Warm"; break }
   default         { "Hot" }
}

Discussion

PowerShell’s switch statement lets you easily test its input against a large number of comparisons. The switch statement supports several options that allow you to configure how PowerShell compares the input against the conditions—such as with a wildcard, regular expression, or even an arbitrary script block. Since scanning through the text in a file is such a common task, PowerShell’s switch statement supports that directly. These additions make PowerShell switch statements a great deal more powerful than those in C and C++.

As another example of the switch statement in action, consider how to determine the SKU of the current operating system. For example, is the script running on Windows 7 Ultimate? Windows Server Cluster Edition? The Get-CimInstance cmdlet lets you determine the operating system SKU, but unfortunately returns its result as a simple number. A switch statement lets you map these numbers to their English equivalents based on the official documentation:

##############################################################################
##
## Get-OperatingSystemSku
##
## From PowerShell Cookbook (O'Reilly)
## by Lee Holmes (http://www.leeholmes.com/guide)
##
##############################################################################

<#

.SYNOPSIS

Gets the sku information for the current operating system

.EXAMPLE

PS > Get-OperatingSystemSku
Professional with Media Center

#>

param($Sku =
    (Get-CimInstance Win32_OperatingSystem).OperatingSystemSku)

Set-StrictMode -Version 3

switch ($Sku)
{
    0   { "An unknown product"; break; }
    1   { "Ultimate"; break; }
    2   { "Home Basic"; break; }
    3   { "Home Premium"; break; }
    4   { "Enterprise"; break; }
    5   { "Home Basic N"; break; }
    6   { "Business"; break; }
    7   { "Server Standard"; break; }
    8   { "Server Datacenter (full installation)"; break; }
    9   { "Windows Small Business Server"; break; }
    10  { "Server Enterprise (full installation)"; break; }
    11  { "Starter"; break; }
    12  { "Server Datacenter (core installation)"; break; }
    13  { "Server Standard (core installation)"; break; }
    14  { "Server Enterprise (core installation)"; break; }
    15  { "Server Enterprise for Itanium-based Systems"; break; }
    16  { "Business N"; break; }
    17  { "Web Server (full installation)"; break; }
    18  { "HPC Edition"; break; }
    19  { "Windows Storage Server 2008 R2 Essentials"; break; }
    20  { "Storage Server Express"; break; }
    21  { "Storage Server Standard"; break; }
    22  { "Storage Server Workgroup"; break; }
    23  { "Storage Server Enterprise"; break; }
    24  { "Windows Server 2008 for Windows Essential Server Solutions"; break; }
    25  { "Small Business Server Premium"; break; }
    26  { "Home Premium N"; break; }
    27  { "Enterprise N"; break; }
    28  { "Ultimate N"; break; }
    29  { "Web Server (core installation)"; break; }
    30  { "Windows Essential Business Server Management Server"; break; }
    31  { "Windows Essential Business Server Security Server"; break; }
    32  { "Windows Essential Business Server Messaging Server"; break; }
    33  { "Server Foundation"; break; }
    34  { "Windows Home Server 2011"; break; }
    35  { "Windows Server 2008 without Hyper-V for Windows Essential Server"; break; }
    36  { "Server Standard without Hyper-V"; break; }
    37  { "Server Datacenter without Hyper-V (full installation)"; break; }
    38  { "Server Enterprise without Hyper-V (full installation)"; break; }
    39  { "Server Datacenter without Hyper-V (core installation)"; break; }
    40  { "Server Standard without Hyper-V (core installation)"; break; }
    41  { "Server Enterprise without Hyper-V (core installation)"; break; }
    42  { "Microsoft Hyper-V Server"; break; }
    43  { "Storage Server Express (core installation)"; break; }
    44  { "Storage Server Standard (core installation)"; break; }
    45  { "Storage Server Workgroup (core installation)"; break; }
    46  { "Storage Server Enterprise (core installation)"; break; }
    46  { "Storage Server Enterprise (core installation)"; break; }
    47  { "Starter N"; break; }
    48  { "Professional"; break; }
    49  { "Professional N"; break; }
    50  { "Windows Small Business Server 2011 Essentials"; break; }
    51  { "Server For SB Solutions"; break; }
    52  { "Server Solutions Premium"; break; }
    53  { "Server Solutions Premium (core installation)"; break; }
    54  { "Server For SB Solutions EM"; break; }
    55  { "Server For SB Solutions EM"; break; }
    56  { "Windows MultiPoint Server"; break; }
    59  { "Windows Essential Server Solution Management"; break; }
    60  { "Windows Essential Server Solution Additional"; break; }
    61  { "Windows Essential Server Solution Management SVC"; break; }
    62  { "Windows Essential Server Solution Additional SVC"; break; }
    63  { "Small Business Server Premium (core installation)"; break; }
    64  { "Server Hyper Core V"; break; }
    72  { "Server Enterprise (evaluation installation)"; break; }
    76  { "Windows MultiPoint Server Standard (full installation)"; break; }
    77  { "Windows MultiPoint Server Premium (full installation)"; break; }
    79  { "Server Standard (evaluation installation)"; break; }
    80  { "Server Datacenter (evaluation installation)"; break; }
    84  { "Enterprise N (evaluation installation)"; break; }
    95  { "Storage Server Workgroup (evaluation installation)"; break; }
    96  { "Storage Server Standard (evaluation installation)"; break; }
    98  { "Windows 8 N"; break; }
    99  { "Windows 8 China"; break; }
    100 { "Windows 8 Single Language"; break; }
    101 { "Windows 8"; break; }
    103 { "Professional with Media Center"; break; }

    default {"UNKNOWN: " + $SKU }
}

Although used as a way to express large conditional statements more cleanly, a switch statement operates much like a large sequence of if statements, as opposed to a large sequence of if … elseif … elseif … else statements. Given the input that you provide, PowerShell evaluates that input against each of the comparisons in the switch statement. If the comparison evaluates to true, PowerShell then executes the script block that follows it. Unless that script block contains a break statement, PowerShell continues to evaluate the following comparisons.

For more information about PowerShell’s switch statement, see “Conditional Statements” or type Get-Help about_Switch.

See Also

“Conditional Statements”