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Windows PowerShell's If Statement

Introduction to The Windows PowerShell If Statement

PowerShell's 'If' statement comes under the umbrella of flow control.  Once you master the basic construction then you can increase its usefulness by appending, 'Else' and 'ElseIf' statements.  Another alternative would be to use 'Switch'.

Topics for PowerShell's If Statement

• Construction of the 'If' Statement
• Example 1: Plain If
• Example 2: If ... Else
• Example 3: PowerShell ElseIf
• PowerShell If -Not
• PowerShell If -Or
• Summary of PowerShell's If Construction

 ♣

Construction of the PowerShell 'If' Statement

As with so many PowerShell constructions, the type of bracket signifies how to break the script into sections.  It is worth emphasising that (parenthesis are for the first part, namely the condition), while {braces are for the block command}.

Summary:  The PowerShell 'If' conditionally executes a statements, depending on the truth of the test expression.

Example 1a Plain 'If'

Learning Points

Note 1:  Trace the construction, and separate into two components: if (test) and {what to do}.

Note 2:  Avoid over-think; there is no 'Then' in a PowerShell 'If' statement.  My advice is that instead of worrying about 'If Then', pay close attention to the two types of bracket.  Furthermore, there is no endif in PowerShell as there is in VBScript.

Note 3:  To double check your understanding, try amending, "Bigger than Zero" to a different text string, such as:  "Less than nought".  Once you have done that, set $Number to -1.

Example 1b PowerShell Script to Checks If a File Exists

Note 4: You probably want to change the file referenced by $ChkFile.  Indeed, the script cries out to modified for a more constructive {outcome}.

Note 5: You could easily append an else statement to cater for file not exist.
Else {Write-Host "File not exist"}

See more on PowerShell's Test-Path

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Example 1b PowerShell If -Not Statement to Check for a Service

Note 6: This script uses the Display Name property of the service.  Remember in PowerShell 'If Then' does not exist.  Observe it's plain 'If'.

Note 7: Observe in passing the If -not construction, which is sometimes abbreviated to an exclamation mark ! in PowerShell.

Note 8: This script cries out for an Else statement.  We need to know if the named service has been installed.

Note 9: See more on -ErrorAction SilentlyContinue

Example 1c PowerShell If Statement To Check IP Addresses

Here is another real-life example of the 'If statement'.  The idea is to ping 20 IP Addresses.  The logic says If the StatusCode is 0, then display a label saying 'ON NETWORK'.

Example 1d File Content Example of Plain 'If'

PowerShell has a batch of help files.  One of these files contains help about the 'if' statement.   In the example below, $File references that file.  $Content is set to the content of the file.  The third line attempts to match a string to the contents of the file.

Learning Points

The above example is concerned with matching a string "The if Statement" to the contents of the built in help file.

Example 2a 'If' With 'Else'

This example deal with plain 'Else'.  This is a simple command, unlike ElseIf there is no second test construction, Else just follows on to reflect what to do if the If statement is false.

Learning Points

The best way to see how 'else' operates is to amend line 3 thus:
($File -match "The ifzz Statement").

Example 2b Checking If a Service Has Been Installed

Example 2c PowerShell If -Not Logic

The purpose of this script is to employ -not logic to check for the Alerter service.  Once scenario is you are working with Windows 7 machines, and they no longer install this service.

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

Note 10:  See more examples of PowerShell's If -not logic.

Example 2d NetSh

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Researching If, Else and ElseIf

• For More information refer to the built-in About_IF file
• See how to disable Windows 8 firewalls with a Group Policy.

Example 3 ElseIf

This example has a real task, and that is to check that we have the name of an actual file.  Remember the second (test statement) followed by a second {Block Script}.

See more on the PowerShell ElseIf construction.

Learning Points

Note 1:  The advantage of ElseIf over plain Else, is that we can introduce a new test.  In the above example we use ElseIf to check if the length of the file is less than 1.  To activate the 'ElseIf' block, set $File to a non-existent file for example
$File = Get-Help about_ifxx.

Note 2: To trigger the final 'Else', try changing:
$File = Get-Help about_if
to
$File = Get-Help about_scope

If you have time, you could add more 'ElseIf' statements to cater for other eventualities.  Alternatively, if the ElseIf construction is getting unwieldy, then try the superior switch command.

Summary of PowerShell's If 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 'Else' and 'ElseIf'.

Incidentally, the 'Vehicle' for our tests reveals a whole family of about_zyx files.  My point is there is no command : 'Get-help if', but there is a help file called, 'about_if'.  Furthermore, if you look in the PowerShell directory then you will see 'About' files to assist with commands such as 'If' and 'ElseIf'.  You can list these 'About' files with the command:

Get-help about*

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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