Regex is working on Regex101 but not inside Powershell - regex

Question

I have this Text file:
[Tabs]
MAILBOXSEND=1
MAILBOX=8
USERS=6
DOCUMENTS_Q=9
MED_WEBSERVCALLS_LOA=3
FCLMNA=1
INCZOOMFORM=1
USERSB=1
USERSB_ONE=1
DATAPRIV=1
MED_WEBSERVCALLS=2
TINVOICES=1
PORDERS=9
PORDERSTOTAL=1
LOGPART=1
LOGCOUNTERS=1
PARTMSG=1
[External Mail]
Send=Y
Hostname=Server
Domain=Domain
Myemail=My#email.com
MyName=My Test
Port=25
SSL=0
[Search]
SUPPLIERS=5,1
StartButton=1
Ignore Case=0
PART=6,1
I'm Trying to capture all the text between [External Mail] to the Next [] Brackets Group,
I have this Regex which do the job and tested in Regex101, after all the testing's I found it's not working inside powershell:
$Text = Get-Content c:\text.txt
$Text -match '(?s)(?<=\[External Mail\]).*?(?=\[.*?\])'
or:
$Text | Select-String '(?s)(?<=\[External Mail\]).*?(?=\[.*?\])'
Nothing Return
Do you have any idea what I'm missing?
Thanks

Answer 1

Looks like you are parsing an .INI file. Don't try to invent the wheel again, take leverage from existing code. This solution reads the .Ini file as nested hash tables that are easy to work with.
In case of link rot, here's the function from Scripting Guys archive:
function Get-IniContent ($filePath)
{
$ini = #{}
switch -regex -file $FilePath
{
"^\[(.+)\]" # Section
{
$section = $matches[1]
$ini[$section] = #{}
$CommentCount = 0
}
"^(;.*)$" # Comment
{
$value = $matches[1]
$CommentCount = $CommentCount + 1
$name = "Comment" + $CommentCount
$ini[$section][$name] = $value
}
"(.+?)\s*=(.*)" # Key
{
$name,$value = $matches[1..2]
$ini[$section][$name] = $value
}
}
return $ini
}
# Sample usage:
$i = Get-IniContent c:\temp\test.ini
$i["external mail"]
Name Value
---- -----
Domain Domain
SSL 0
Hostname Server
Send Y
MyName My Test
Port 25
Myemail My#email.com
$i["external mail"].hostname
Server

Answer 2

Since you are trying to get a multiline regex match you need to be working against a single multiline string. That is the difference between your two cases of regex101 and PowerShell. Get-Content will be returning a string array. Your regex was not matching anything as it was only doing the test on single lines within the file.
PowerShell 2.0
$Text = Get-Content c:\text.txt | Out-String
PowerShell 3.0 of higher
$Text = Get-Content c:\text.txt -Raw
As I said in my comments you don't really need regex, in this way, for this type of string extraction. There are scripts that already exist to parse INI content. If you intend to be replacing content you would have to find the partner cmdlet Out-INIContent assuming it exists but I am sure someone made it. vonPryz's answer contains more information on the cmdlet