select-arg-keyhandler.ps1

Set-PSReadLineKeyHandler -Key 'Alt+a' -ScriptBlock {
  param($key, $arg)

  $line = $null
  $cursor = $null
  [Microsoft.PowerShell.PSConsoleReadLine]::GetBufferState([ref]$line, [ref]$cursor)

  $tokens = $null
  $ast = $null
  $parseErrors = $null
  [Microsoft.PowerShell.PSConsoleReadLine]::GetBufferState([ref]$ast, [ref]$tokens, [ref]$parseErrors, [ref]$null)

  $asts = $ast.FindAll( {
      $args[0] -is [System.Management.Automation.Language.StringConstantExpressionAst] -and
      $args[0].Parent -is [System.Management.Automation.Language.CommandAst] -and
      $args[0].Extent.StartOffset -ne $args[0].Parent.Extent.StartOffset
    }, $true)

  if ($null -ne $arg) {
    $nextAst = $asts[$arg - 1]
  }
  else {
    foreach ($ast in $asts) {
      if ($ast.Extent.StartOffset -ge $cursor) {
        $nextAst = $ast
        break
      }
    } 
  
    if ($null -eq $nextAst) {
      $nextAst = $asts[0]
    }
  }
  
  if ($nextAst.StringConstantType -ne [System.Management.Automation.Language.StringConstantType]::BareWord) {
    $startOffsetAdjustment = 1
    $endOffsetAdjustment = 2
  }
  else {
    $startOffsetAdjustment = 0
    $endOffsetAdjustment = 0
  }

  [Microsoft.PowerShell.PSConsoleReadLine]::SetCursorPosition($nextAst.Extent.StartOffset + $startOffsetAdjustment)
  [Microsoft.PowerShell.PSConsoleReadLine]::SetMark($null, $null)
  [Microsoft.PowerShell.PSConsoleReadLine]::SelectForwardChar($null, ($nextAst.Extent.EndOffset - $nextAst.Extent.StartOffset) - $endOffsetAdjustment)
}