Seek method not working in Powershell script

Question

I´m trying to use the .net API to seek in a large data file. For some reason I am unable to make it work. Here is my code:

function check_logs{
  $pos = 8192
  $count = 1
  $path = 'C:\Program Files\Microsoft SQL Server\MSSQL10.MSSQLSERVER\MSSQL\Log\ERRORLOG.2'
  $br = 0
  $reader = [System.IO.File]::OpenText($path)
  $reader.DiscardBufferedData()
  $reader.BaseStream.Seek(0, [System.IO.SeekOrigin]::Begin)
    for(;;){
    $line = $reader.ReadLine()
    if($line -ne $null){$br = $br + [System.Text.Encoding]::UTF8.GetByteCount($line)}
    if($line -eq $null -and $count -eq 0){break}
    if($line -eq $null){$count = 0}
    elseif($line.Contains('  Error:')){
        Write-Host "$line  $br"
    }
}

}

If I use 0 as a parameter for the seek method it seeks from the beginning as expected but it also writes 0 out to the console before it writes the lines read. Example:

 0
 2011-08-31 09:26:36.31 Logon       Error: 17187, Severity: 16, State: 1.  4101
 2011-08-31 09:26:36.32 Logon       Error: 17187, Severity: 16, State: 1.  4489
 2011-08-31 09:26:38.25 Logon       Error: 17187, Severity: 16, State: 1.  4929
 2011-08-31 09:26:38.25 Logon       Error: 17187, Severity: 16, State: 1.  5304
 2011-08-31 09:26:43.75 Logon       Error: 17187, Severity: 16, State: 1.  6120

If I try to seek using 4096 instead of 0 it only writes out:

4096

I would have thought it would write out the same lines as the first one did apart from the first two.

Can someone see the problem? I had another question that got me to this. For further background see this

EDIT: Still trying to figure this out. Does anyone know where else I could try to find information regarding this problem? Is it possible to send questions to the Microsoft scripting guy?

Best regards

Gísli

Answer 1

The Seek method returns the new position within the stream, which is why you are having a number printed out.

As to why you are not getting an output:

1. Confirm the file is greater than 4K in size.
2. Try printing out all lines, rather than just lines with the word "Error" in them. That might give you a clue
3. StreamReader is a buffered wrapper around the base stream, so Seek and Position may not work quite like you expect. Consider http://geekninja.blogspot.com/2007/07/streamreader-annoying-design-decisions.html. Try adding in a call to $reader.DiscardBufferedData() before the seek.