Splitting text in PowerShell using content delimiter as filename - regex

Question

I am trying to split a txt transcription into single files, one for each folio.
The file is marked as [c. 1r],[c. 1v] ... [c. 7v] and so on.
Using this example I was able to create a PowerShell script that does the magic with a regex that match each page delimiter , but I seem totally unable to use the regex in order to give proper names to the pages. With this code
$InputFile = "input.txt"
$Reader = New-Object System.IO.StreamReader($InputFile)
$a = 1
while (($Line = $Reader.ReadLine()) -ne $null) {
if ($Line -match "\[c\. .*?\]") {
$OutputFile = "MySplittedFileNumber$a$Matches.txt"
$a++
}
Add-Content $OutputFile $Line
}
all the files are named with MySplittedFileNumber1System.Collections.Hashtable.txt instead of the match, with "$Matches[0]" I'm told that the variable does not exist or has been filtered by -Exclude.
All my attempts of setting the $regex before executing seems to go nowhere, can someone point me on how to get the result filenames formatted as MySplittedFileNumber[c. 1r].txt.
Using just a partial match as \[(c\. .*?)\] would be even better, but once I know how to retrieve the match, I bet I can find the solution.
I can do the variable 1r 1v setting in $a, somehow, but I'd rather use the one inside the txt file, since some folio may have been misnumbered in the manuscript and I need to retain this.
Content of original input.txt:
> [c. 1r]
Text paragraph
text paragraph
...
Text paragraph
[c. 1v]
Text paragraph
text paragraph
...
Text paragraph
[c. 2r]
Text paragraph
text paragraph
...
Text paragraph
Desired result:
Content of MySplittedFileNumber[c. 1r].txt:
> [c. 1r]
Text paragraph
text paragraph
...
Text paragraph
Content of MySplittedFileNumber[c. 1v].txt:
> [c. 1v]
Text paragraph
text paragraph
...
Text paragraph
Content of MySplittedFileNumber[c. 2r].txt:
> [c. 2r]
Text paragraph
text paragraph
...
Text paragraph

Answer 1

I tried to reproduce it and with a little change it worked:
$InputFile = "input.txt"
$Reader = New-Object System.IO.StreamReader($InputFile)
$a = 1
While (($Line = $Reader.ReadLine()) -ne $null) {
If ($Line -match "\[c\. .*?\]") {
$OutputFile = "MySplittedFileNumber$a$($Matches[0]).txt"
$a++
}
Out-File -LiteralPath "<yourFolder>\$OutputFile" -InputObject $Line -Append
}
To call a position of an array while in "" you have to format the variable like this $($array[number])
To write to the file, you should give the Fullpath and not just the Filename.

Answer 2

From Version 3 on PowerShells Get-Content cmdlet has the -Raw parameter which allows to read a file as a whole into a string you can then split into chunks with a regular exression (using a positive look ahead ).
The very same RegEx can be use to grep the section name and insert into the destination file name.
## Q:\Test\2018\07\19\SO_51421567.ps1
##
$RE = [RegEx]'(?=(\[c\. \d+[rv]\]))'
$Sections = (Get-Content '.\input.txt' -raw) -split $RE -ne ''
ForEach ($Section in $Sections){
If ($Section -Match $RE){
$Section | Out-File -LiteralPath ("MySplittedFileNumber{0}.txt" -f $Matches[1])
}
}