replace content of multiple Files with PowerShell - powershell

Question

I'm trying to replace a certain Line in multiple logonscripts (>2000 Scripts).
The script works in the current form, but it writes every file to the disk, even when no changes are made, but I don't want this behaviour. It only should write to the disk, if changes are made.
This is what I already have:
$varFiles = Get-ChildItem $varPath*.$VarEnding
foreach ($file in $varFiles)
{
(Get-Content $file) |
Foreach-Object { $_ -replace [regex]::Escape("$varFind"), "$varReplace" } |
Set-Content $file
}
And this is what I already tried, but it seems, that it is not possible to use if in piped commands:
$varFiles = Get-ChildItem $varPath*.$VarEnding
foreach ($file in $varFiles)
{
$control = $file
(Get-Content $file) |
Foreach-Object { $_ -replace [regex]::Escape("$varFind"), "$varReplace" } |
If($control -ne $file){Set-Content $file}
}
The variables $varPath, $varEnding, $varFind and $varReplace are defined by a few Read-Host commands at the start of the script.
I hope you guys can help me :)

Answer 1

For simplicity and speed - although at the expense of memory use - I'd simply cache and operate on whole input files (requires PowerShell v3+, due to use of -Raw[1]); since logon scripts are generally small, this should be acceptable:
$varFindEscaped = [regex]::Escape($varFind)
$varReplaceEscaped = $varReplace -replace '\$', '$$$$'
foreach ($file in Get-ChildItem $varPath*$varEnding) {
$contentBefore = Get-Content -Raw $file
$contentAfter = $contentBefore -replace $varFindEscaped, $varReplaceEscaped
if ($contentBefore -ne $contentAfter) {
Set-Content $file $contentAfter
}
}
To improve performance I've moved escaping of the -regex operands outside the loop.
Note that I'm also escaping $ instances in the replacement value to prevent their interpretation as references to what was matched, such as $& to refer to the entire match.
Note that Set-Content by default uses the system's default code page rather than UTF-8 encoding.
[1]
In PS v2, you may omit -Raw, which turns $contentBefore into an array of strings (lines) on whose elements -replace then operates individually (as in the OP's approach). While probably slightly slower, it does have the advantage of performing the substitution on individual lines only rather than potentially across multiple lines.