Delete content between 2 lines - powershell

Question

I have a pacfile which I am trying to update and need to remove content between two strings; the strings themselves should be kept:
// OFFICE 365 DIRECT ACCESS
and
// END OFFICE 365 DIRECT ACCESS
example:
// OFFICE 365 DIRECT ACCESS
if (isInNet(hostip, "23.103.132.0","255.255.252.0") || //EOP
isInNet(hostip, "23.103.136.0","255.255.248.0") || //EOP
isInNet(hostip, "23.103.144.0","255.255.240.0") || //EOP
isInNet(hostip, "23.103.191.0","255.255.255.0") || //EOP
// END OFFICE 365 DIRECT ACCESS
I want to remove the lines between the top and bottom lines
$Pacfile = Get-ChildItem .\o365.pac | Get-Content -Raw
$startstring= " \/\/ OFFICE 365 DIRECT ACCESS(.*? )\/\/END OFFICE 365 DIRECT ACCESS"
$NewPacfile = [regex]::match($Pacfile, $startstring).Groups[1].value
$NewPacfile

Answer 1

$regex=#'
(?ms)^(\s*// OFFICE 365 DIRECT ACCESS\s*?\r?\n).*?\r?\n(\s*// END OFFICE 365 DIRECT ACCESS\s*)
'#
(Get-Content -Raw .\o365.pac) -replace $regex, '$1$2'
-replace $regex, '$1$2' replaces what the regex matched with what the 1st ($1) and 2nd capture groups ($2) (parenthesized subexpression, (...)) inside of it matched.
Here, these capture groups capture the strings enclosing the range of interest.
(?ms) sets both the multi-line and the single-line option for the regex:
m means that ^ and $ should match the start and end of each line rather than the input string as a whole.
s means that metacharacter . should match \n characters too, so that an expression such as .* can be used to match across lines.
\r?\n matches a single line break, both the CRLF and the LF variety.
.*? matches the part to remove; note the non-greedy modifier (?) following .*, which ensures that the next occurrence of the end string is matched.