Updating File Programmatically

When working with text based files there might be a time to update the contents. PowerShell has a Get-Content Commandlet that gathers the content of a file and renders it to the console or saved in a variable. Once we get the content we can then manipulate it and save that back out.

So whats the goal?

To get the content of a file and update it with new information and save it, all without manually updating the file. This is helpful when replacing a lot of text within files.

Getting started

We will need a filepath, an old value, and a new value. We’ll get the contents of the file, and use the .replace() method from the string class.

In general our line would be:

The brown dog jumped over the fence

But lets replace fence with moon. So we’ll start by writing

"The brown dog jumped over the fence".replace("fence","moon")

and well see our console output

The brown dog jumped over the moon

Setting up the function

Writing our update file into a function allows us to reuse the command and ensure we keep things consistent.

Setting up our update command to get the file and replace a value:

(Get-Content dog.txt).replace("fence", "moon") | Set-Content dog.txt

This will get the content of dog.txt, find all references to fence and replace them with moon. Once done, the Set-Content method will write the new contents to the file.

Lets add this to a function so its more usable and understandable.

function UpdateFile{

    param(
    [Parameter(Position=1)]
    $filepath, 

    [Parameter(Position=2)]
    $oldvalue,
        
    [Parameter(Position=3)]
    $newvalue 

    )

    Write-Host "Updating $filepath. Changing $oldvalue to $newvalue"
    (Get-Content $filepath).replace($oldvalue, $newvalue) | Set-Content $filepath

}

Now we have our function made we can call it easily by doing

UpdateFile -filepath c:\dog.txt -oldvalue "fence" -newvalue "moon"

Wrap up

You can use the function anywhere you’d like to in your PS1 file then call it with the values needed.

Extra tip: to update a value and remove it, the -newvalue can be a set of double quotes to be blank "".