Implementing FileSeek

[Queue]

What I want to accomplish:

Reading from the end of a log file that constantly gets data appended. This log file is too big for the standard methods of just loading it in its entirety into memory, doing a line count and then using FileReadLine, etc. AutoIt constantly checks the file's size and should only read in new data when the file size increases (if it decreases, it simply sets its last known size to whatever the new smaller size is).

What I'm looking for help with:

Is there a way to shift AutoIt's file pointer for the currently opened file to a given offset (so it thinks the beginning of the file is actually X bytes in)? Even if it's a fairly dirty hack (modifying AutoIt's own memory after a FileOpen command to shift the file pointer), it would be acceptable.

Something I've tried that doesn't work:

FileReadLine($file_handle, -2)

Or -3, etc. Only -1 works and that most recent line is often not enough (sometimes multiple lines get appended at once).

Queue

Edited January 30, 2010 by Queue

[ProgAndy]

In the current AutoIt-Version there is a function called FileSetPos

To read the new contents, you could just do this. Then, AutoIt reads everything that was added since the last FileRead-command:

$hFile = FileOpen($file, 0) ; open for reading
FileSetPos($hFile, 0, 2) ; move to end
OnAutoItExitRegister("_Close") ; close on Exit

While 1
    Sleep(500)
    $sNewLines = FileRead($hFile) ; read everything from current position to end
    If Not @error Then ; when something was read
        MsgBox(0, 'New Text', $sNewLines)
    EndIf
WEnd

Func _Close()
    FileClose($hFile)
EndFunc

Edited January 30, 2010 by ProgAndy

[Queue]

In the current AutoIt-Version there is a function called FileSetPos

Crud, that figures. I can't use versions beyond 3.2.12.X due to Win9x support being dropped. For any NT projects though, this information will be quite handy. Thank you.

Also, it looks like the _WinAPI_SetFilePointer, ReadFile, etc. calls will be acceptable. Funny how you only manage to find an answer AFTER you ask the question out loud.

Queue

Edited January 30, 2010 by Queue

[ProgAndy]

You could try to use KernelEx on your Win98-machines.

Or try to use the append-mode to open a file. Then the filepointer is at the end of the file, and when another app adds something, you should be able to read it.

$hFile = FileOpen($file, 1) ; open for append

While 1
    Sleep(500)
    $sNewLines = FileRead($hFile) ; read everything from current position to end
    If Not @error Then ; when something was read
        MsgBox(0, 'New Text', $sNewLines)
    EndIf
WEnd

Func OnAutoItExit()
    FileClose($hFile)
EndFunc

Edited January 30, 2010 by ProgAndy

[Queue]

I actually know of (and use) KernelEx, but I can't guarantee it will be available on each machine I intend this script for (nor have I personally tested a newer AutoIt on machines with KernelEx since doing so is pointless when I can't guarantee it will be on all mach... you get the point).

Thanks for the idea with append, also good to know that affects the file pointer.

Queue