how to replace one line with two lines in txt file - powershell

Question

I want some .cs model file to append annotation. If script finds specific property it will put above that property annotation.
Here is the script:
$annotation = "[DatabaseGenerated(DatabaseGeneratedOption.Computed)]"
Get-ChildItem -Filter *.cs | % {
(Get-Content $_.FullName) | ForEach-Object {
if ($_ -match "StartDateTime") {
$_ -replace $_ , "`n`t`t$annotation`n$_"
}
} | Set-Content $_.FullName
}
It works with replacing, but at the end I get a blank file with only two lines (annotation and custom property). I realize that the last pipeline Set-Content $_.FullName is messed up.
If I remove Set-Content, nothing happens with my file (it's not updated)?

Answer 1

This should work better for you:
$filePath = '<YOUR PATH HERE>'
$annotation = "[DatabaseGenerated(DatabaseGeneratedOption.Computed)]"
Get-ChildItem -Path $filePath -Filter *.cs | ForEach-Object {
$file = $_.FullName
(Get-Content $file) | ForEach-Object {
# test all strings in $file
if ($_ -match "StartDateTime") {
# emit the annotation followed by the string itself
"`r`n`t`t$annotation`r`n" + $_
}
else {
# just output the line as-is
$_
}
} | Set-Content -Path $file -Force
}
Within the Foreach-Object I'm capturing the $_.FullName for later use and also to not confuse it with the $_ you use later on as line in the file.
Then, if the line does match the if, output the replaced line, but if it does not (in the else) you should output the line unchanged.
Then, the Set-Content always outputs each line, replaced or not.
Since you actually are not replacing anything inside the string, but rather prefixing it with an annotation, this can be simplified a bit like so:
$annotation = "[DatabaseGenerated(DatabaseGeneratedOption.Computed)]"
Get-ChildItem -Path 'D:\' -Filter *.cs | ForEach-Object {
$file = $_.FullName
(Get-Content $file) | ForEach-Object {
# test all strings in $file
if ($_ -match "StartDateTime") {
# emit the annotation
"`r`n`t`t$annotation"
}
# output the line as-is
$_
} | Set-Content -Path $file -Force
}