Powershell replace between start and end - powershell

Question

I need to replace everything between two points.
$import = Get-Content C:\bookmarks.html
$newbody = Get-Content C:\newbookmarks.html
$remove = '(?<=<DT><H3 ADD_DATE=""1544626193"" LAST_MODIFIED=""154649885"">Import-IE</H3>).*?(?=</DL>)'
$import | %{$_.replace($remove,"$newbody")}
My problem is to get all content between start:
<DT><H3 ADD_DATE=""1544626193"" LAST_MODIFIED=""154649885"">Import-IE</H3>
and the end:
</DL>
incl multiple lines
Example html:
<DT><H3 ADD_DATE="1544626193" LAST_MODIFIED="1546498855">Import-IE</H3>
<DL><p>
<DT>golem.de
<DT>heise online
</DL>
Regards

Answer 1

A couple of changes needed to make this work:
One big multiline string
Since you want to do a replace over multiple lines, we need to makes sure all the lines are contained in the same string, so let's start with that - we can use the -Raw parameter switch with Get-Content:
$import = Get-Content C:\bookmarks.html -Raw
Exact pattern matching in regex
Next up we have the regex pattern itself - there's a few discrepancies between that and the sample content you've shown:
LAST_MODIFIED=""154649885"" # pattern has nested double-quotes and only one 5 at the end
LAST_MODIFIED="1546498855" # input uses just one pair of double-quotes and value has two 5's at the end
So let's fix that, and make sure the input string we're looking for is properly escaped while we're at it:
$remove = "(?<=$([regex]::Escape('<DT><H3 ADD_DATE="1544626193" LAST_MODIFIED="1546498855">Import-IE</H3>'))).*?(?=</DL>)"
String.Replace doesn't support regex
Then, we'll have to abandon the String.Replace() method that you're currently using - because it doesn't actually support regex - so we'll use the -replace operator instead:
$import -replace $remove,"$newbody"
Use -replace in SingleLine mode
The only thing we need now, is to instruct the regex parser to treat the input in SingleLine mode - so that .*? will capture newlines as well. This is super easy though, we just add an options flag s at the start of the regex pattern:
$import -replace "(?s)$remove","$newbody"
And that's it :)
$import = Get-Content C:\bookmarks.html -Raw
$newbody = Get-Content C:\newbookmarks.html
$remove = "(?<=$([regex]::Escape('<DT><H3 ADD_DATE="1544626193" LAST_MODIFIED="1546498855">Import-IE</H3>'))).*?(?=</DL>)"
$import -replace "(?s)$remove","$newbody"