FileWrite Challenge

[TheDcoder]

Hello :), I wanna insert a backspace in a file (Sorry, I don't know what to say formally)

I tried this:

#include <Array.au3>

Func FileBackspace($sFile, $iLine, $iCount) ; Pretty straight forward name, isn't it?
    $hFile = FileOpen($sFile, 2) ; Open file in over-write mode
    $aFile = FileReadToArray($hFile) ; File to array
    $aFile[$iLine] = StringTrimRight($aFile[$iLine], $iCount) ; Trim the line (NOTE: Backspace means trim starting from right)
    $sFile = _ArrayToString($aFile, @CRLF) ; Store new modifed file in a variable
    FileWrite($hFile, $hFile) ; Hmmmm... What would FileWrite do?
EndFunc

This is not the best way to do this. This will be OK for small files but for files with size of 1 GB!!! I tried hard but I failed to insert backspace without storing the entire file in the RAM

I want a function which does this but without storing the entire file

 

Thanks in advance, TD

[water]

So you want to remove the last n characters from every line?
You could process the file line by line using FileReadLine and FileWriteLine.
Or process the file in blocks of e.g. 1MB by using FileRead/FileWrite.

Edited May 1, 2015 by water

[TheDcoder]

So you want to remove the last n characters from every line?

​Only specified line

[water]

If all lines in the file have the same length then you could calculate the position of this line, read all the data before this line and write it to the output file, read and process the line and write it to the output file, then the rest of the file.

[TheDcoder]

#include <Array.au3>
#include <File.au3>

Func FileBackspace($sFile, $iLine, $iCount) ; Pretty straight forward name, isn't it?
    $hFile = FileOpen($sFile) ; Open file in read only mode
    $sTempFile = _TempFile() ; Create a temp file
    $hTempFile = FileOpen($sTempFile) ; Open the temp file
    ; Copy contents of original file to temp file until the line to insert backspace is reached
    For $i = 1 To $iLine - 1
        FileWrite($hTempFile, FileReadLine($hFile, $i) & @CRLF)
    Next
    FileWrite($hTempFile, StringTrimRight(FileReadLine($hFile, $iLine), $iCount)) ; Write the modified line
    ; Copy the remaining contents
    For $i = $iLine + 1 To _FileCountLines($sFile)
        FileWrite($hTempFile, FileReadLine($hFile, $i) & @CRLF)
    Next
    FileMove($sTempFile, $sFile, 1) ; Overwite the original file
EndFunc

Like this?

[TheDcoder]

Whoa! What happen to the source?

[water]

From the help file:

"From a performance standpoint it is a bad idea to read line by line specifying "line" parameter whose value is incrementing by one. This forces AutoIt to reread the file from the beginning until it reach the specified line."

So use

#include <Array.au3>
#include <File.au3>

Func FileBackspace($sFile, $iLine, $iCount) ; Pretty straight forward name, isn't it?
    $hFile = FileOpen($sFile) ; Open file in read only mode
    $sTempFile = _TempFile() ; Create a temp file
    $hTempFile = FileOpen($sTempFile) ; Open the temp file
    ; Copy contents of original file to temp file until the line to insert backspace is reached
    For $i = 1 To $iLine - 1
        FileWriteLine($hTempFile, FileReadLine($hFile))
    Next
    FileWriteLine($hTempFile, StringTrimRight(FileReadLine($hFile), $iCount)) ; Write the modified line
    ; Copy the remaining contents
    While True
        $sTemp = FileReadLine($hFile)
        If @error Then ExitLoop    
        FileWriteLine($hTempFile, $sTemp)
    Next
    FileClose($hTempFile)
    FileMove($sTempFile, $sFile, 1) ; Overwite the original file
EndFunc

 

Edited May 1, 2015 by water

[TheDcoder]

Why use file close?

[nitekram]

The file is left open (FileOpen), after you use it or update it, a good practice is to close it.

Edited May 2, 2015 by nitekram

[water]

Why use file close?

​Because FileMove won't work if the file to be moved is still open (in use) by another application.