It is often useful to read input from the user but restrict it to a list of choices that you specify. The following script lets you access PowerShell’s prompting functionality in a manner that is friendlier than what PowerShell exposes by default. It returns a number that represents the position of their choice from the list of options you provide.
PowerShell's prompting requires that you include an accelerator key (the & before a letter in the option description) to define the keypress that represents that option. Since you don't always control the list of options (for example, a list of possible directories), Example 121 automatically generates sensible accelerator characters for any descriptions that lack them.
Example 121. ReadHostWithPrompt.ps1
############################################################################## ## ## ReadHostWithPrompt.ps1 ## ## Read user input, with choices restricted to the list of options you ## provide. ## ## ie: ## ## PS >$caption = "Please specify a task" ## PS >$message = "Specify a task to run" ## PS >$option = "&Clean Temporary Files","&Defragment Hard Drive" ## PS >$helptext = "Clean the temporary files from the computer", ## >> "Run the defragment task" ## >> ## PS >$default = 1 ## PS >ReadHostWithPrompt $caption $message $option $helptext $default ##
Example 121. ReadHostWithPrompt.ps1 (continued)
## Please specify a task ## Specify a task to run ## [C] Clean Temporary Files [D] Defragment Hard Drive [?] Help ## (default is "D"):? ## C Clean the temporary files from the computer ## D Run the defragment task ## [C] Clean Temporary Files [D] Defragment Hard Drive [?] Help ## (default is "D"):C ## 0 ## ##############################################################################
param( $caption = $null, $message = $null, $option = $(throw "Please specify some options."), $helpText = $null, $default = 0 )
## Create the list of choices [Management.Automation.Host.ChoiceDescription[]] $choices = @()
## Create a list of possible key accelerators for their options $accelerators = NewObject System.Collections.ArrayList
## First, add a the list of numbers as possible choices $startNumber = [int][char] '0' $endNumber = [int][char] '9' foreach($number in $startNumber..$endNumber) {
[void] $accelerators.Add([char] $number) }
## Then, a list of characters as possible choices $startLetter = [int][char] 'A' $endLetter = [int][char] 'Z' foreach($letter in $startLetter .. $endLetter) {
[void] $accelerators.Add([char] $letter) }
## Go through each of the options, and add them to the choice collection for($counter = 0; $counter lt $option.Length; $counter++) {
$optionText = $option[$counter]
## If they didn't provide an accelerator, generate new option ## text for them if($optionText notmatch '&') {
$optionText = "&{0} {1}" f $accelerators[0],$optionText }
Example 121. ReadHostWithPrompt.ps1 (continued)
## Now, remove their option character from the list of possibilities $acceleratorIndex = $optionText.IndexOf('&') $optionCharacter = $optionText[$acceleratorIndex + 1] $accelerators.Remove($optionCharacter)
## Create the choice $choice = NewObject Management.Automation.Host.ChoiceDescription $optionText if($helpText and $helpText[$counter]) {
$choice.HelpMessage = $helpText[$counter] }
## Add the choice to the list of possible choices $choices += $choice }
## Prompt for the choice, returning the item the user selected $host.UI.PromptForChoice($caption, $message, $choices, $default)
