When building an interactive script capturing a single key press might be necessary. This can be done by using the $host variable, specifically the ReadKey method. It is important to note that this method is only available in the PowerShell console this does not work in the PowerShell Integrated Scripting Environment (ISE).
A simple example: You might require your script to ask for Yes / No, using the Read-Host would allow the user to type in more than one character and the enter key would have to be pressed. In this scenario the ReadKey method is can be preferably, because it registers a single key press:
$KeyPress = $host.UI.RawUI.ReadKey("NoEcho,IncludeKeyDown") |
Now if we were to display the contents of the $KeyPress variable, we can see the following information:
PS> $KeyPress VirtualKeyCode Character ControlKeyState KeyDown -------------- --------- --------------- ------- 89 y NumLockOn True |
So the information contained that is captured by this method not only contains the character, but also the type of key press as well as which additional ‘Control Keys’ were pressed. Control keys for example are the Numlock and Capslock status on your keyboard as well as Alt, Win and Ctrl keys. The control keys are part of the ControlKeyStates enumeration which can be enumerated using the [Enum] Class as shown in the following example:
PS> [Enum]::GetNames([System.Management.Automation.Host.ControlKeyStates]) RightAltPressed LeftAltPressed RightCtrlPressed LeftCtrlPressed ShiftPressed NumLockOn ScrollLockOn CapsLockOn EnhancedKey |
For more information about using the GetNames method of the [System.Enum] class, please refer to my previous article: QuickTip: Enumerate objects with [System.Enum] class.
For example, if the goal is to construct a simple Y/N question using what we’ve learned so far can be placed in a while-loop:
$KeyOption = 'Y','N' while ($KeyOption -notcontains $KeyPress.Character) { $KeyPress = $host.UI.RawUI.ReadKey("NoEcho,IncludeKeyDown") } |
And that how a single key press can be caught in a variable, adding in a switch or if-elseif-else statement will allow for action based on the key that has been pressed. Next week I will discuss an alternative to using the $host object for this purpose, stay tuned!
