Windows PowerShell -Replace (Search and Replace)

Introduction to Windows PowerShell -Replace Operator

The first point to note with -Replace is we are discussing a PowerShell operator, it works in a similar fashion to its cousin -Match.  Secondly, these comparison operators need input from a cmdlet such as Get-Content.

Introduction to -Replace

Before you call for the -Replace operator, you need to obtain stream of text, only then can you define the pattern to search for, and the pattern to replace.  For example, you have a document where you wish to update a string of characters - say Code2013, with new values  - say Code2014.  Alternatively, you may be trying a more complex search and replace operation.  My point is PowerShell's -Replace is a bit-Part in a bigger script drama.

Topics for PowerShell -Replace String

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Example 1: Select-String Then -Replace

Let us build up slowly; before we use the -Replace operator, let us have a refresher on Select-String.  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?'.

Example 1a: Select-String, ForEach-Object and -Replace
Remember we are building up gradually; I have not forgotten our goal, which is replacing "Guido" with "Guy".

Assumptions:
We have a file called gopher.txt. 
Within this text file is the word "Guido".

# Stage 1: Preparation - just finding the text
Select-String -Path "C:\Change\gopher.txt" -Pattern "Guido"

# Expected result:
C:\Change\gopher.txt:3:Guido is king

Note 1: :3:  Means line number 3
:Guido is king  Refers to the line where the Pattern "Guido" occurs.

Example 1b:  Conditional Operator -Replace into Action

# Stage 2: -Replace actually makes a change
Select-String -Path "C:\Change\gopher.txt" -Pattern "Guido" |
ForEach-Object {$_ -Replace "Guido", "Guy"}

# Expected result after -Replace:
C:\Change\gopher.txt:3:Guy is king

Note 2: Observe the important role played by ForEach-Object, it supplies a stream of text, and passes it to the {Block Statement containing -Replace}.

Note 3: The placeholder is just $_  no dot or property is required.

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Example 2: PowerShell -Replace with Get-Content

My idea in Example 2 is to choose a different cmdlet to provide the text stream.  Our task is to correct a common problem, namely finding a repeated word such as "the the", and replacing with a single instance of "the".

Tasks for the -Replace Operator

  1. Get-Content reads the file then | pipes a stream of data.
  2. ForEach-Object provides a loop construction to process each item.
  3.  -Replace takes "the the" and substitutes a single "the".
  4. Set-Content writes the result back to the original file.

# Example of PowerShell replacing text
Clear-host
$Location = "C:\Change\report.txt"
$Change = Get-Content $Location
$Change | ForEach-Object {$_ -Replace "the the", "the"} | Set-Content $Location
# Below are two optional items for testing
# $Change | ForEach-Object {$_ -Replace "the", "the the"} | Set-Content $Location
# Invoke-Item $Location

Note 4: Because -Replace is an operator, here it needs the {block} supplied by ForEach-Object. 

An Example of even simpler syntax for -Replace:

Clear-host
"Humour my Neighbour's favourite colour!" -Replace "our", "or"

Humor my Neighbor's favorite color!

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Example 3: PowerShell's -Replace with Special Characters

The task here is to replace special characters such as brackets in filenames.  We will be using Get-ChildItem as the vehicle.  Here is a break-down of the three tasks.

  1. Create the files with Set-Content (Optional).
  2. Employ the Rename-Item cmdlet.
  3. Replace the brackets, using the escape character "\".

3a) Preparation: Create a series of files starting with Bracket(0)

# The only purpose of this script is to create files for testing.
Clear-Host
$Brackety = "C:\Change"
For($i=0;$i -le 6; ++$i) {
Set-Content -Path $("$Brackety\Stuff($i).txt") -value $i
}

Note 5: You may wish to change the value of $Brackety.

Note 6: If you experience formatting problems add -f $i, thus:
("$Brackety\Stuff($i).txt" -f $i)

3b) Replace in Action: Removing (brackets)

$Brackety = "C:\Change"
Get-ChildItem $Brackety | Rename-Item -NewName { $_.name -Replace "\(","" }
#Get-ChildItem $Brackety | Rename-Item -NewName { $_.name -Replace "\)","" }
Invoke-item $Brackety

Note 6: To remove the closing bracket cut the # (hash) at the start of line 3, and paste this # at the start of line 2.

Note 7: Observe how the "\"  escapes the bracket to make PowerShell treat the next character as pure text rather than part of the command's syntax.

Research PowerShell's -Replace Operator

For learning more about operators such as -Replace try PowerShell's built-in Get-Help about_

Clear-Host
Get-Help about_Operators

Another source of ideas is to study similar PowerShell operators, for example:

Summary of PowerShell -Replace

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

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See more examples of PowerShell syntax

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

PowerShell -confirm  • WhatIf  • -Match  • -Like  • -Online  • Where  • Free WMI Monitor

-ErrorAction  • -Replace  • Windows PowerShell  • PowerShell module directory

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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