HI Steve excellent article. As always, I try to avoid string parsing and use the object oriented cabilities of PowerShell and using XML files as input to obtain matches via XPath. But as we know when deailing with old native commands in Windows and Linux, you can’t avoid string parsing. So this is very helpful in that respect. Select-String uses the Pattern parameter to search each file for the string PowerShell. From the PowerShell command line, the $A variable contents are displayed. There's a line that contains two occurrences of the string PowerShell. The $A.Matches property lists the first occurrence of the pattern PowerShell on each line. In the first two examples, the script checks the string ends to see if it ends in a backslash. In the last two examples, the script check the string to see if it starts with one. The regex pattern being matched for the first two is $. What’s that mean?
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. One of my favourite alternative strategies is to use ‘Switch‘.
Topics for PowerShell’s If Statement
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’s worth tattooing into our memory that (parenthesis brackets are for the first part, namely the condition), while {braces are for the block command}.
Summary: In PowerShell, ‘If’ executes statements conditional on the truth of the test expression.
Example 1a: Plain ‘If’
Learning Points
Note 1: Trace the above construction, and separate the 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 in the above Example 1a.
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 be modified for a more constructive {outcome}.
Note 5: You could easily append an else statement to cater for a file not existing.Else {Write-Host 'File does not exist'}
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If Logic and Tactics
It’s rare that my first ‘If’ construction produces the desired results. The secret of success is to experiment with the If test, or alternatively start introducing one or more ‘ElseIf tests with their corresponding {outcome block}.
In this example I have introduced -Not into the logic:
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; incidentally, -Not 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’ in action. The idea is to ping 20 IP Addresses. The logic says If the StatusCode is 0, then display a label saying ‘ON NETWORK’.
Note 10: Once If statements get complicated it’s time to investigate PowerShell’s Switch parameter.
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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 ifyyyy Statement”).
Example 2b: Checking If a Service Has Been Installed
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Example 2c: PowerShell If -Not Logic
The purpose of this script is to employ -Not logic to check for the Alerter service. One 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 11: See more examples of PowerShell’s If -Not logic.
Example 2d: NetSh
The purpose of this example is to check the status of a firewall on a Windows client machine such as Windows 8.1 or Windows 7.
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; to check that we have the name of an actual file. Remember that the second (test statement) must be followed by a second {Block Script}.
Learning Points
Note 12: 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 13: 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.
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About_If
If you would another account of PowerShell’s If statement, then have a look at the built-in help file
This is Microsoft’s explanation:
Windows PowerShell evaluates the <test1> conditional expression as either true or false. Should the result be true, PowerShell obeys whatever is inside the {curly brackets}, whereupon PowerShell exits the If statement.
In the event of the first test being false PowerShell works its way through the ElseIf statements.
Powershell If File Contains String Do Action
Incidentally, the ‘Vehicle’ for our tests reveals a whole family of ‘about_zyx…’ files. My point is there is no command: ‘Get-Help if’, however, 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:
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 of 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’.
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See more Windows PowerShell flow control examples
• PowerShell Home • PowerShell If Statement • PowerShell ElseIf • Free Permissions Analyzer
• Conditional Operators • PowerShell -Match • PowerShell -Like • PowerShell -Contains
• PowerShell Comparison Operators • PowerShell Syntax • Where Filter • PowerShell Else
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.
Powershell Check If File Name Contains String
We can use the powershell’s like operator with wildcard character to check if a string contains a word or another string with case-sensitive and case-insensitive.
Note: You can not use the comparison operator contains to check the contains string, because it’s designed to tell you if a collection of objects includes (‘contains’) a particular object.
The following method is used to check if a string contains a word using like operator. By default like operator ignore the case-sensitive check.
To perform a Case-Sensitive comparison just prefix the word “c” with like operator (“clike”).
We can also use the built in .NET string extension function Contains to check whether a string contains a another string.
The .Contains() function is case sensitive. If you want to use the Contains() method for case-insensitive check, convert both strings to one case before compare.