(PowerShell) Read-InputLine

Read-InputLine.ps1

# Like Read-Line but can be exited from via a configured key press
# 
# Returns the entered string or $false if CancelKeyCode (default is Esc) pressed
# Input truncated in display to fit one line
function Read-InputLine {
  param (
    [Parameter(Mandatory = $false, Position = 0)]
    [string]$Prompt = "",

    [Parameter(Mandatory = $false, Position = 1)]
    [int]$CancelKeyCode = 27 # 27 = Escape
  )
  Try {
    $Host.UI.RawUI.FlushInputBuffer()
  }
  Catch {
    
  }

  # display initial prompt
  if ($Prompt.Length -gt 0) {
    Write-Host "`r$Prompt" -NoNewLine
  }

  # accept and display input until enter or esc is pressed
  $cancelled = $false
  $inputLine = "";
  $inputLineDisplay = ""
  do {
    # Test to see if escape was pressed within the loop
    $key = $Host.UI.RawUI.ReadKey("IncludeKeyUp,NoEcho")

    # exit if enter or esc pressed
    # 13 = Enter
    $exit = $key.VirtualKeyCode -eq 13 -or $key.VirtualKeyCode -eq $CancelKeyCode

    # add char to input line
    if (!$exit -and $key.Character) {
      $inputLine += $key.Character
    }
    elseif ($key.VirtualKeyCode -eq $CancelKeyCode) {
      $cancelled = $true
    }

    $maxWidth = $Host.Ui.RawUI.WindowSize.Width

    # 8 = Backspace
    if ($key.VirtualKeyCode -eq 8) {
      # remove last character from input line
      $newLength = $inputLine.Length - 2;
      if ($newLength -lt 0) {
        $newLength = 0
      }
      $inputLine = $inputLine.Substring(0, $newLength)
    }

    # update display line (truncate if console edge reached)
    $startIndex = 0
    $totalLength = $prompt.Length + $inputLine.Length
    $inputLineDisplay = if ($totalLength -le $maxWidth - 1) {
      $inputLine
    }
    else {
      $startIndex = $totalLength - $maxWidth
      $inputLine.SubString($startIndex, ($inputLine.Length - $startIndex))
    }

    # replace line with blank space
    if ($totalLength -le $maxWidth - 1) {
      $blank = ""
      $lineLength = $prompt.length + $inputLine.Length
      if ($lineLength -gt $maxWidth) {
        $lineLength = $maxWidth
      }
      for ($l = 0; $l -le $lineLength; $l++) {
        $blank = $blank + " "
      }
      Write-Host "`r$blank" -NoNewline
    }

    # replace line with new input line
    if (!$exit) {
      Write-Host "`r$prompt$inputLineDisplay" -NoNewline
    }
  } while (!$exit)

  # replace line with blank space
  $blank = ""
  $lineLength = $prompt.length + $inputLine.Length
  if ($lineLength -gt $maxWidth) {
    $lineLength = $maxWidth
  }
  for ($l = 0; $l -le $lineLength; $l++) {
    $blank = $blank + " "
  }
  Write-Host "`r$blank" -NoNewline

  # empty input line if esc pressed
  if ($cancelled) {
    $inputLine = $false
  }

  # start console at beginning of line
  Write-Host "`r" -NoNewline
  $inputLine
}