Welcome to Day 2 of my “A Month of PowerShell” series. This series will use the series landing page on this blog at //blog.waynesheffield.com/wayne/a-month-of-powershell/. Please refer to this page to see all of the posts in this series, and to quickly go to them.
Variables
As you start working with any scripting language, you inevitably end up needing to get some data and store it in a variable for use later on. In PowerShell, the syntax for a variable is the name of that variable preceded by a dollar sign ($). Values are assigned to the variable with the equals sign (=). (Note – don’t confuse the = assignment operator with the –EQ comparison operator!) When the variable is defined and a value is assigned to it, an appropriate .NET data type is created. For instance, $MyVariable = 123 creates the variable $MyVariable with a System.Int32 data type and assigns the value 123 to it.
String variables are assigned by using quotation marks. But does PowerShell use single or double quotation marks? The answer to that question is… Yes – you can use either single or double quotation marks. However, there is a difference in how they operate. Single quotation marks use the literal value inside the quotation marks as the string. Double quotation marks will perform string substitution of other variables in the string. Let’s look at a quick example:
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$i = 123 $s = 'Hello ' $s2 = "$s $i" $s2 |
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Hello 123 |
You can build a long string by concatenation:
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$q = "SELECT TOP (1000)" $q = $q + " [BusinessEntityId]," $q = $q + " [FirstName]," $q = $q + " [LastName]" $q = $q + " FROM [AdventureWorks2012].[dbo].[Person];" |
Or by the use of a “here-string”:
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$q = @" SELECT TOP (1000) [BusinessEntityId], [FirstName], [LastName] FROM [AdventureWorks2012].[dbo].[Person]; "@ $q |
When using a Here-String, the string starts with @” (or @’), and this must end the line that it is on. The string ends with “@ (or ‘@), which must be on a line by itself. What’s really neat about using a Here-String is that PowerShell respects all line breaks, quotation marks (single or double), and white space within the string and maintains that in the variable.
You can assign variables to specific .NET data types by preceding the variable declaration with the data type:
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[int]$A = 50 |
Special Variables
PowerShell has a few variables that are automatically created, as seen in the following table:
| Command | Description |
|---|---|
| Get-Help about_automatic_variables | Variables that store PowerShell state information. |
| Get-Help about_preference_variables | Variables that customize PowerShell behavior. |
| Get-Help about_environment_variables | Working with Windows environment variables within PowerShell. |
Arrays
Arrays are data structures designed to store a collection of items, which can be of the same type or of different types. Items can be assigned to arrays in a few different manners.
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$A = 5,3,4,2,1 #specific items $B = 6..10 #range, integers only $C = @("String1", "String2", "String3") #specific separate string items $D = @() #empty array [array] $E = "a;e;i;o;u;y" -split ";" #specific separate string items |
Hash Tables
A hash table is simply a Name-Value pair. The following example shows creating and adding to the hash table:
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$Z = @{"Colorado" = "Denver"; "Virginia" = "Richmond"; "North Carolina" = "Raleigh"} $Z.Add("Alaska", "Fairbanks") |
Operators
Yesterday we covered comparison operators. You can find out information on all of the operators that are available in PowerShell with the following (be sure to investigate any topics referenced in these):
| Get-Help about_Operators |
|---|
| Get-Help about_If |
| Get-Help about_For |
| Get-Help about_ForEach |
| Get-Help about_While |
| Get-Help about_Do |
| Get-Help about_Switch |
