Powershell if changed Set-Content - powershell

Question

I have a PowerShell script that I use to change text in a number of files. The following script will work & changes the text as expected.
Get-ChildItem $FileFolder -Recurse |
select -ExpandProperty fullname |
foreach {
(Get-Content $_) |
ForEach-Object {$_ -replace $old $new } |
Set-Content $_
}
The problem is though, it changes every file that it opens, so everything has a timestamp of when the job was run even if nothing was changed.
I have tried something similar to what is here but it gives me an error:
The term 'if' is not recognized as the name of a cmdlet, function, etc...
Here is the code I am trying to run:
Get-ChildItem $FileFolder -Recurse |
select -ExpandProperty fullname |
foreach {
$b = ($a = Get-Content $_) |
ForEach-Object {$_ -replace $old $new } |
if (Compare $a $b -PassThru) {
$b | Set-Content $_
}
}
I know that the code isn't right, but if I move it inside the ForEach-Object, it won't run either.
What I want to do is to use the Set-Content statement only if the contents of the file have changed. Would appreciate any thoughts as to how best to do this.

Answer 1

What you can do is look for the string before getting and setting content. Something like:
Get-ChildItem $FileFolder -Recurse |
select -ExpandProperty fullname |
foreach {
If(Select-String -Path $_ -SimpleMatch $old -quiet){
(Get-Content $_) |
ForEach-Object {$_ -replace $old $new } |
Set-Content $_
}
}