Advanced Windows PowerShell Scripting Video Training

Advanced Windows PowerShell Scripting Video Training
Advanced Windows PowerShell Scripting Video Training

Tuesday, April 26, 2011

PowerShell Script to replace items in a text file

This script is a product of one my PowerShell classes in March 2011.  The problem was presented by a learner in the class.  His task was to take a large text file that needed to be parsed for question marks and have them replaced with spaces.  We expanded the script to make it more portable and useful in more situations.

As with all my PowerShell classes, I encourage the participants to have a project in mind when they arrive.  With a project in hand, the light bulb in the participants head turns on as they learn more and more skills to make their project a success.

<# ========================================================
Script: Replace.ps1
-----------------------------------------------------------
The input parameters are the input file, the new output
file.  We also needed to provide what we wanted to replace
with what.  Adding these extra parameters made the script
more portable.
-----------------------------------------------------------
#>
Param (
    $InFile = $(Read-Host 'Input File:
'),
    $OutFile = $(Read-Host 'Output File:
'),
    $ReplaceWhat = $(Read-Host 'Replace what:
'),
    $ReplaceWith = $(Read-Host 'Replace With:
')
    )
<#
After testing reviled that the question mark needed
an escape character, we added this switch statement
for some of the special characters used in Regular
Expressions.
#>
Switch ($ReplaceWhat){
    "^" {$ReplaceWhat = "\$ReplaceWhat"; Break
}
    "$" {$ReplaceWhat = "\$ReplaceWhat"; Break
}
    "*" {$ReplaceWhat = "\$ReplaceWhat"; Break
}
    "?" {$ReplaceWhat = "\$ReplaceWhat"; Break
}
    "\" {$ReplaceWhat = "\$ReplaceWhat"; Break
}
    "." {$ReplaceWhat = "\$ReplaceWhat"; Break
}
}
<#
The code below first grabs the content of the input file.
It then pipes that content to a ForEach loop that issues
a replace command between the contents of the $ReplaceWhat
with the $ReplaceWith variables.
#>

   
(Get-Content $InFile
) |
    ForEach {$_ -replace $ReplaceWhat, $ReplaceWith
} |
   Add-Content $OutFile

   
Write-Host
"Script: Replace.ps1 - Completed"

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