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How to Search Strings with [ and ] in Them

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One of the more difficult aspects of teaching PowerShell is the PowerShell pipeline. After delivering over 70 PowerShell classes, I know this is the part to really slow down and take our time with.  I’ve been working on some code to help answer the question “What can you pipe to what without plowing through the objects and help files.”  Since this is a repetitive task for anybody who codes in PowerShell, I thought it would be fun to automate the process.

While doing my R&D on this project, I discovered that to search for strings with ‘[‘ or ‘]’ cannot be done with the –Like comparison operator.  Take a look below.

PS C:\> $String = "ABC[CDE]"

PS C:\> $Sting -like "*[*"
The specified wildcard character pattern is not valid: *[*
At line:1 char:1
+ $Sting -like "*[*"
+ ~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], WildcardPatternException
    + FullyQualifiedErrorId : RuntimeException



It turns out the characters ‘[‘ and ‘]’ are actually part of our wildcard characters.  That is why we get a pattern error. Take a look at this MSDN article: Supporting Wildcard Characters in Cmdlet Parameters.


The below image is from that MSDN article.

The last usage is the key to our success.  We actually need to encapsulate our query for a ‘[‘ or ‘]’ inside of square braces.

PS C:\> $String = "ABC[CDE]"

PS C:\> $String -like "*[[]*"
True

In this case, we are only looking for a pattern of anything with a ‘[‘ somewhere in it.

PS C:\> $String = "String[]"

PS C:\> $String -like "*[[]]"
True

In the above example, we are looking for a string that ends with ‘[]’.

Pattern matching is an extremely valuable tool to have in your PowerShell arsenal.  This little trick is helping me produce the code that I need to help make learning PowerShell even easier.


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