Problem
You have a set of items (for example, error records, directory items, or .NET objects), and you want to display summary information about them in a table format.
Solution
To display summary information about a set of items, pass those items to the FormatTable cmdlet. This is the default type of formatting for sets of items in PowerShell and provides several useful features.
To use PowerShell’s default formatting, pipe the output of a cmdlet (such as the GetProcess cmdlet) to the FormatTable cmdlet:
GetProcess | FormatTable
To display specific properties (such as Name and WorkingSet,) in the table formatting, supply those property names as parameters to the FormatTable cmdlet:
GetProcess | FormatTable Name,WS
To instruct PowerShell to format the table in the most readable manner, supply the –Auto flag to the FormatTable cmdlet. PowerShell defines “WS” as an alias of the WorkingSet for processes:
GetProcess | FormatTable Name,WS Auto
To define a custom column definition (such as a process’s Working Set in megabytes), supply a custom formatting expression to the FormatTable cmdlet:
$fields = "Name",@{Label = "WS (MB)"; Expression = {$_.WS / 1mb}; Align = "Right"} GetProcess | FormatTable $fields Auto
Discussion
The FormatTable cmdlet is one of the three PowerShell formatting cmdlets. These cmdlets include FormatTable, FormatList, and FormatWide. The FormatTable cmdlet takes input and displays information about that input as a table. By default, PowerShell takes the list of properties to display from the *.format.ps1xml files in PowerShell’s installation directory. You can display all properties of the items if you type FormatTable *, although this is rarely a useful view.
The Auto parameter to FormatTable is a helpful way to automatically format the table to use screen space as efficiently as possible. It does come at a cost, however. To figure out the best table layout, PowerShell needs to examine each item in the incoming set of items. For small sets of items, this doesn’t make much difference, but for large sets (such as a recursive directory listing) it does. Without the Auto parameter, the FormatTable cmdlet can display items as soon as it receives them. With the Auto flag, the cmdlet can only display results after it receives all the input.
Perhaps the most interesting feature of the FormatTable cmdlet is illustrated by the last example—the ability to define completely custom table columns. You define a custom table column similarly to the way that you define a custom column list. Rather than specify an existing property of the items, you provide a hashtable. That hashtable includes up to three keys: the column’s label, a formatting expression, and alignment. The FormatTable cmdlet shows the label as the column header and uses your expression to generate data for that column. The label must be a string, the expression must be a script block, and the alignment must be either "Left", "Center",or "Right". In the expression script block, the $_ variable represents the current item being formatted.
The expression shown in the last example takes the working set of the current item and divides it by 1 megabyte (1 MB).
For more information about the FormatTable cmdlet, type GetHelp FormatTable.
