Remove character from file in-place with native Windows tools

Question

I'd like to remove the last character off a large file. The restrictions are that:

• the file has to be modified in-situ, without using the disk space required for a similar second file
• it's a windows machine
• I cannot copy any compiled code onto the machine so I cannot create a small c# program of c++ program to manipulate the file
• this also means any non-native scripting is not available, like python.

As far as I know, this limits me to bat, VB (or JScript) but it does not look like there is a viable option in these. VB requires a TextStream to be created from a systemfile object, but then this stream I believe must be saved elsewhere, using diskspace.

Is there a way to do this simply?

Answer 1

Following the idea from Noodles (of course you need to have some .net framework version installed), you can try this

(save as trim.cmd and call as trim.cmd "fileToTrim.dat")

@if (@this==@isBatch) @then
@echo off
    setlocal enableextensions disabledelayedexpansion

    rem check arguments
    set "fileToTrim=%~1"
    if not exist "%fileToTrim%" goto :eof

    rem search for a valid framework version
    set "frameworks=%SystemRoot%\Microsoft.NET\Framework"
    set "jsc="
    for /f "tokens=* delims=" %%a in (
        'dir /b /a:d  /o:-n "%frameworks%\v*"'
    ) do if not defined jsc if exist "%frameworks%\%%a\jsc.exe" set "jsc=%frameworks%\%%a\jsc.exe"

    if not defined jsc goto :eof

    set "executable=%~dpn0.%random%.exe"
    %jsc% /nologo /out:"%executable%" "%~f0"
    if exist "%executable%" (
        "%executable%" "%fileToTrim%"
        del "%executable%" >nul 2>nul 
    )
    endlocal
    exit /b 0
@end
import System;
import System.IO;

var arguments:String[] = Environment.GetCommandLineArgs();

    if (arguments.length > 1) {
        var fi:FileInfo = new FileInfo(arguments[1]);
        var fs:FileStream = fi.Open(FileMode.Open);
        fs.SetLength (
            Math.max(0, fi.Length - 1)
        );
        fs.Close();
    };

This is far from efficient, the jscript code is compiled each time. Better directly write the program, compile and use. But just as an example ...