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PowerShell If Not ...

Introduction to Windows PowerShell's If -Not Logic

Once you have mastered the basic 'If' statement, you just need to aquire the nack of extending the logic to embrace the PowerShell 'If not' syntax.

Topics for PowerShell PowerShell's If -Not Statement

• Construction of the 'If' Statement
• Example 1: Basic 'If' Statement
• Example 2: PowerShell If -Not Logic
• Example 3: PowerShell If -ne
• Example 4: PowerShell If -Or
• Summary of PowerShell's If Construction

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Construction of the PowerShell 'If' Statement

Let us get started by studying PowerShell's 'If' logic.  The secret is to identify the two parts of the construction: (test condition) and {block command}.

It helps to keep one eye on PowerShell's different types of bracket.  (The parenthesis style of brackets are used for the first part, namely the condition), while {braces denote the block command payload}.

Here is a different explanation of the same 'If' flow control:

Summary:  The PowerShell 'If' conditionally executes a block statement, providing the test expression is true.

Example 1: Basic 'If' Statement

Think of this script as a preamble which checks whether the Alerter service is installed on your machine, and introduces the basic 'If' statement.   There is no -not comparison here, that comes in Example 2.

Learning Points

Note 1:  The If (test) is simply this: can Get-Service find the $SrvName.  Try changing "Alerter" to "Print Spooler"

Note 2:  Avoid over-think; there is no 'Then' in a PowerShell 'If' statement. Furthermore, there is no endif in PowerShell as would be in VBScript.

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Example 2: PowerShell If -Not Logic

The purpose of this script is to check for the Alerter service, the reason being Windows 7 machines no longer install this service.

Observe how -not reverses the 'If' logic compared with Example 1.

Note 3:  Other examples of If logic benefit from chaning -not to -ne meaning not equal.

Example 3: PowerShell If -ne

Here is a variation which employs -ne (not equal) rather than -not.

Note 4:  This is a crude and forced example of -ne, a better example for 'not equal' would be testing numeric data.

Example 3a: PowerShell If -ne Numeric Data

If (Test numbers not equal) {Script block}

Note 5:  My biggest problem with not equal is wanting to write -neq, when I should be typing: -ne.  So often it's overthink that is my downfall!

Note 6:  While this a pretty crude example, it does plant the idea that you could use other comparators such as greater than -gt, or less than -lt.

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Example 4: PowerShell If -Or

Following PowerShell's If -Not or If -ne there are more variations on the logic, for example '-Or'.

Note 6:  Do check the logic of your (test1 -or test2) statement.

Production script:

In real life you may want to strip the code down, and append a command to actually start the spooler service.

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Researching Comparison Operators

For More information refer to the built-in About_IF file

Summary of PowerShell's If -Not Construction

When it comes to filtering output, one of the oldest and best statements is the 'If' clause.  As usual, the secret of understanding the syntax is to pay close attention to the style bracket.  If (parenthesis for the test) and {braces for the action}.  Once you have mastered the basic 'If' statement, then extend your capabilities by researching -Not, -ne, and also -or.

See more Windows PowerShell examples

• PowerShell Home  • PowerShell If Statement  • PowerShell ElseIf  • PowerShell If -Not

• PowerShell comparison operators  • PowerShell If -And  • PowerShell If -Or

• Where Filter   • Loops  • Brackets  • -Match  • Switch  • Conditional Operators

Please email me if you have a better example script. Also please report any factual mistakes, grammatical errors or broken links, I will be happy to correct the fault.

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Author: Guy Thomas Copyright © 1999-2012 Computer Performance LTD All rights reserved. Please report a broken link, or an error to: