Windows 7 / Getting Started

Collections

A collection is a type of an array used to hold information on objects.

Imagine that you have a bucket, and you've placed 10 marbles in the bucket. These marbles are objects and very likely they are different. Some may be clear and others cloudy, some steel and others glass, some small and others large. You get the idea. Each of these marbles has specific properties that can be used to describe it.

Now if you created a spreadsheet, you could list each of the marbles and their associated properties. Later, if you wanted information on a specific marble, you could access the spreadsheet and retrieve the information. In this context, the data in the spreadsheet is the collection that represents the actual objects.

Similarly, with PowerShell you can create a collection of information on objects. You can then use code to loop through the collection.

As an example, consider this code:

$colLog = get-EventLog -list

The Get-EventLog -list will list information on the EventLogs on a system in five columns: Max(K), Retain, OverflowAction, Entries, and Log. The $colLog = will store the result of the command in the variable named $colLog. While the get-EventLog command will retrieve many logs, imagine there are only five. The collection would look like Table below.

A Collection of Logs

Max(K)RetainOverFlowActionEntriesLog
20,4800OverwriteAsNeeded46,266Application
20,4800OverwriteAsNeeded53,635System
20,4807OverwriteOlder2,345Security
15,3600OverwriteAsNeeded1,206Session
15,3600OverwriteAsNeeded453Windows PowerShell

Data stored in the collection can be accessed and retrieved, and it is commonly done so using a ForEach command. As an example, the following script will store the data in a collection and then loop through the collection to retrieve it:

$colLog = get-EventLog -list
ForEach ($Item in $colLog) {
Write-0utput $Item
}

This is actually no different than just executing the Get-EventLog -List command. However, the real strength of the collection is that you can manipulate it. If you were interested in only some of the columns, you could pick and choose what is displayed.

Imagine that all you really want to know is the log name and its size. These two columns have headers of Log and Max(K) (though Max(K) is identified as MaximumKilobytes). Each item in the collection can be identified using these names. Because the script uses $Item as the variable name to hold the collection, the columns would be identified as $Item.Property. In other words, $Item.Log retrieves the log name and $Item.

MaximumKilobytes retrieves the Max(K) value.
$colLog = get-EventLog -list
ForEach ($Item in $ColLog) {
Write-Output $Item.Log, $Item.MaximumKilobytes
}

However, this is pretty messy. Instead of outputting the data as a table, it sends each item on a single line. You'll see later in the tutorial how this can be cleaned up using the -f formatting switch.

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In this tutorial:

  1. Working with the Command Prompt
  2. Starting and Ending a Command Prompt Session
  3. Easy ways to invoke administrator Command Prompt sessions
  4. Starting Command Prompt at a Particular Folder
  5. Strings with Spaces Need Quotes
  6. Cmd.exe vs. Command.com
  7. Commands Are Not Case Sensitive
  8. Starting Command Prompt and Running a Command
  9. Cmd.exe and Other Command Prompts
  10. Using AutoRun to Execute Commands When Command Prompt Starts
  11. Using Cmds Command-Line Syntax
  12. Using Commands
  13. Type /? for help
  14. Starting Programs
  15. Open Windows Explorer at the current Command Prompt folder
  16. Using File-Name and Folder-Name Completion
  17. Use a different completion character
  18. Using Wildcards
  19. Editing the Command Line
  20. Using Command Symbols
  21. The Redirection Symbols
  22. The Pipe Symbol
  23. The Command Combination Symbols
  24. Pausing or Canceling Commands
  25. Simplifying Command Entry with Doskey Macros
  26. DOSKEY Saves Typing
  27. System Variables Identify the Environment
  28. Viewing Environment Variables
  29. Modifying Environment Variables
  30. Predefined Environment Variables
  31. Customizing Command Prompt Windows
  32. Setting the Window Size and Position
  33. Setting the Window Size and Position Visually
  34. Selecting a Font
  35. Setting Colors
  36. Setting Other Options
  37. Copy and paste in the command prompt window
  38. Navigating from the command prompt
  39. Printing a list of filenames
  40. Commands Use Paths
  41. Identifying Executables
  42. Modifying the Path to Executables
  43. Modifying the Path with the GUI
  44. Changing the Current Path with CD
  45. Changing the Current Path with Windows Explorer
  46. Capturing the Output
  47. A Sampling of Commands
  48. Dir
  49. Copy
  50. XCopy
  51. SET
  52. NET USE
  53. SystemInfo
  54. DriverQuery
  55. Echo
  56. Advanced Shell Commands
  57. Creating a Batch File
  58. Scheduling a Batch File
  59. Creating Scheduled Tasks with a Script
  60. Using Windows PowerShell and the PowerShell ISE
  61. Windows PowerShell ISE
  62. PowerShell Commands
  63. Verbs and Nouns
  64. Sending Output to a Text File
  65. PowerShell Syntax
  66. Variables Created with a $ Symbol
  67. Comparison Operators
  68. Parentheses, Brackets, and Braces
  69. Running PowerShell Scripts
  70. PowerShell Execution Policy
  71. Changing the Execution Policy
  72. Looping
  73. Collections
  74. Creating a PowerShell Script
  75. Documenting Scripts
  76. Using PowerShell Commands
  77. Getting Help on PowerShell
  78. Using WMI_Cmdlets
  79. Getting Details on an Object
  80. Querying Information on Specific Objects
  81. Terminate Applications with Win32_process
  82. Formatting Output with the -f Format Operator
  83. Filtering the Output with the Where-Object Command
  84. Using the IF statement
  85. Using the Switch Statement
  86. Script Reusability