How to read a line to a specific point and then add a new line

Question

I am attempting to make a file parser that will take a raw input file and then create a new file that has all the elements in the correct order and with proper new lines so another parser can read it.

So my file is a PGN (Portable Games Notation). These files are used in chess to record games people play on the computer.

They look like:

--------------------------------------
[Event "Computer chess game"]
[Date "2015.10.28"]
[Round "?"]
[White "White Player"]
[Black "Black Player"]
[Result "1-0"]
[BlackElo "2400"]
[ECO "A25"]
[Opening "English"]
[Time "10:39:20"]
[Variation "Closed"]
[WhiteElo "2400"]
[Termination "normal"]
[PlyCount "63"]
[WhiteType "human"]
[BlackType "human"]
1. f3 e6 2. g4 Qh4# 1-0
-------------------------------

On Reddit's /r/chess, they have it to where you can surround your games with [pgn][/pgn] and it will then create a playable board that you or others can step through your game and offer you advice, etc.

The problem is the site I play on, the PGN comes out as above. The /r/chess parser doesn't like it.

It prefers each move to be on a seperate line:

1. f3 e6 
2. g4 Qh4# 1-0

Since I am trying to learn Powershell, I wanted to create a script that would open the raw PGN, and then reformat it to look like the above and maybe pull out Event, Date, White Player, Black Player, and the Result. Then format it so that after each move a new line is inserted. Then output a new file surrounded with [pgn][/pgn].

I am kind of lost on how to do this. Do I need to use a regular expression? I know that once I read a file into Powershell I can treat it like an array too.

The output file should look like this:

[pgn][Event "Computer chess game"]
[Date "2015.10.28"]
[White "White Player"]
[Black "Black Player"]
[Result "1-0"]
1. f3 e6 
2. g4 Qh4# 1-0 [/pgn]

Any and all help is appreciated!

beatcracker · Accepted Answer

Here is the function, that will convert your PGNs to Reddit-compatible format. Please note, that currently it doesn't support PGNs with multiple games per file.

With this function, you can:

Choose what "headers" to keep. By default in keeps only Event, Date, White, Black, and the Result
Save new PGN to file or output to the pipeline

Function accepts following arguments:

Path: Path to original PNG file
OutFile: Path to the converted PGN file
KeepHeaders: List of "headers" to keep

Usage examples:

Convert file, output to screen

ConvertPgn-ForReddit -Path .\Foo.pgn

[pgn]
[Event "Computer chess game"]
[Date "2015.10.28"]
[White "White Player"]
[Black "Black Player"]
[Result "1-0"]
1. f3 e6 
2. g4 Qh4# 1-0
[/pgn]

Convert file, output to file

ConvertPgn-ForReddit -Path .\Foo.pgn -OutFile .\Bar.pgn

Convert file, output to screen, keep only BlackElo and Time headers

ConvertPgn-ForReddit -Path .\Foo.pgn -KeepHeaders BlackElo, Time

[pgn]
[BlackElo "2400"]
[Time "10:39:20"]
1. f3 e6 
2. g4 Qh4# 1-0
[/pgn]

Code:

function ConvertPgn-ForReddit
{
    [CmdletBinding()]
    Param
    (
        [Parameter(Mandatory = $true, ValueFromPipeline = $true)]
        [ValidateScript({
            Test-Path $_
        })]
        [ValidateNotNullOrEmpty()]
        [string]$Path,

        [Parameter(ValueFromPipelineByPropertyName = $true)]
        [string]$OutFile,

        [Parameter(ValueFromPipelineByPropertyName = $true)]
        [string[]]$KeepHeaders = @('Event', 'Date', 'White', 'Black', 'Result')
    )

    Process
    {
        # Get file contents as array of strings
        $PgnFile = Get-Content -Path $Path 

        # Get all "headers", e.g. [Event "Computer chess game"]
        $Headers = $PgnFile | Where-Object {$_ -match '$$.*$$'}

        # Filter "headers", so they contain only the ones we want
        $FilteredHeaders = $KeepHeaders | ForEach-Object {
            $currHeader = $_
            $Headers | Where-Object {$_ -match  "$$$currHeader\s+.*$$"}
        }

        # Get chess moves
        $Moves = $PgnFile | Where-Object {$_ -match '^\d+\.'}
        # Split them, remove empty lines if any
        $SplittedMoves = $Moves | ForEach-Object {$_ -split '(\d+\.)'} | Where-Object {$_}
        # Join splitted chess moves: delimeter + actual move. E.g. "1." +  "f3 e6 "
        $JoinedMoves = 0..($SplittedMoves.Count - 1) | ForEach-Object {
            if([bool]!($_ % 2))
            {
                '{0} {1}' -f $SplittedMoves[$_], $SplittedMoves[$_+1]
            }
        }

        # Create PGN in Reddit-compatible format
        $RedditPgn = '[pgn]', $FilteredHeaders, $JoinedMoves, '[/pgn]'

        if($OutFile)
        {
            # If OutFile is specified, save it
            $RedditPgn | Set-Content -Path $OutFile
        }
        else
        {
            # If not - just output to the pipeline
            $RedditPgn
        }
    }
}

How to read a line to a specific point and then add a new line

Answers (2)

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