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Windows PowerShell -Replace (Search and Replace)

Introduction to Windows PowerShell -Replace Parameter

The first point to note with -Replace is that it is a parameter or a switch, therefore it needs input from another PowerShell cmdlet.  One way of preparing a text string for such a search and replace operation is by using Get-Content.

Introduction to: Select-String  -Replace

Before you call for the -replace parameter, first you need to obtain stream of text.  Once you connect to the input stream, then define the pattern that you are seeking.  As you are reading this I expect you are thinking of possible applications for this technique.  Perhaps you wish to find which documents contain a particular string, alternatively, you may be trying a more complex search and replace operation.  My point is -replace maybe a bit-part in a bigger drama.

Topics for PowerShell -Replace String

• Example 1 Select-String -path -pattern
• Example 1a Select-String using variable $Location
• Example 2 PowerShell -Replace (The Main Event)
• Summary of -Replace

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Example 1 Select-String -path -pattern

Let us build up slowly, before we use the -replace parameter, let us have a refresher on Select-String and Get-Content.  The key to understanding Select-String is studying the two main switches -path and -pattern.  They say to me 'Where is the input?' and 'What pattern do you want to match?'.

To ensure that my examples work, we need to agree on the file location and the pattern to search.  Thus for 'our' script to work you need to embrace one of two tactics, either mimic my folder structure and patterns, or amend the script to fit in with your environment.  My folder happens to be called : D: \powershell\stuff. 

Here are two simple Select-String scripts which produce the same result using slightly different methods.  By studying both you will gain both perspective and ideas for the best method for your scripts.

Assumptions:
You have a file called gopher.txt. 
In gopher.txt is the the word Guido.

Example 1a Select-String Using Variable $Location

Remember we are building up to replace string gradually.

Expected outcome:
D:\powershell\stuff\gopher.txt:3:Guido is king

:3:  Means line number 3
:Guido is king  Refers to the line where the Pattern "Guido" occurs.

Example of Select-String (Pure no extra commands)

See more about PowerShell Parameters

Example 2 PowerShell -Replace (The Main Event)

My idea in Example 1b is to build on Select-String, now, at last, we are ready to replace one string with another.  Here is a common problem a repeated word "the the".  What I want to do is replace the double word with a single instance.

Replace Rationale

1. Get-ChildItem locates all files beginning with 'g'.  Note the path.
2. Get-Content reads the files
3. A second foreach construction deals with the -replace "the the" operation.

Note 1: The purpose of `n is to force a carriage return.

Note 2: Troubleshooting.  Remember this is an example, you need to create your own file, and you probably need to change the value of $file to suit your computer.

Note 3: See more about the Set-Content cmdlet.

Note 4: See more about the Remove-Item cmdlet.

Researching PowerShell's -Replace Parameter

Much to my surprise the only cmdlet to feature -replace is Update-List.

-Replace <Object[]>
Specifies a new collection. This parameter replaces all items in the original collection with the items specified by this parameter.

Summary of PowerShell -Replace String

This is a classic example of building a script gradually.  Master the basics of Select-String, and only then focus on the -replace parameter.  Remember that firstly first you need to obtain stream of text.  Once you connect to the input stream, then define the pattern that you are seeking. 

See more PowerShell examples for syntax advice

• PowerShell Tutorials  • Syntax  • PowerShell functions  • Plist  • RegEx  • -Com

• PowerShell -confirm  • WhatIf  • -Match  • -Online  • Where  • -ErrorAction  • -Replace

Please write in 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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