How can I split a binary file into chunks with certain size with batch script without external software?

Question

There are many reasons to want to split file into chunks - mainly for network transfer (e.g. e-mail attachments) but I'm sure there are scenarios that could require such thing I cannot imagine. So how can a file be split into chunks that can be easily assembled back to original file (including non-windows systems) ?

What are possibilities:

1. MAKECAB - the built-in Windows archiver - it can compress file and split it , but will be difficult to assemble the file on non-Windows machine.
2. WSH/Jscript/VBscript - binary files can be easy processed with ADODB Streams.And according to me JScript is preferable.
3. .NET/JScript.net/VB/C# - As .NET comes with command line compilers it also can be used for this purpose . .NET binary streams probably are the best in this case that it can offer .
4. CERTUTIL - as it can convert a binary file to HEX and back it's possible to process the HEX data with batch file and split the file to chunks.

Probably GZipStreams can be used also as they allows reading bytes (and offer portable compression !).I promise an upvote If anyone succeed with this (or offer any other method) :-)

Answer 1

Some time ago I wrote a Batch-JScript hybrid script called BinToBat.bat with this purpose. This is its help screen:

Create an installer Batch program for data files of any type

BINTOBAT [/T:.ext1.ext2...] [/L:lineSize] [/F[:fileSize]] filename ...

  /T:.ext1.ext2    Specify the extensions of text type files that will not be
                   encoded as hexadecimal digits, but preserved as text.
  /L:lineSize      Specify the size of output lines (default: 78).
  /F[:fileSize]    /F switch specify to generate a Full installer file.
                   The optional fileSize specify the maximum output file size.

BinToBat encode the given data files as hexadecimal digits (or preserve they
as compressed text) and insert they into InstallFiles.bat program; when this
program run, it generates the original data files.

You may rename the InstallFiles.bat program as you wish, but preserving the
"Install" prefix is suggested.

You may use wild-cards in the filename list.

If the /F switch is not given, a Partial installer is created:
- You may insert a short description for each file.
- You may insert divisions in the file listing via a dash in the parameters.
- The installer allows to select which files will be downloaded and ask
  before overwrite existent files.

If the /F switch is given, a Full installer is created:
- The installer always download all files.
- You may specify commands that will be executed after the files were copied.
- You may specify the maximum size of the output file via /F:fileFize, so in
  this case the output file will be divided in parts with a numeric postfix.

  If you use /F switch you can NOT rename the InstallFiles??.bat files; the
  first one is the installer and the rest just contain data.

You may download BinToBat.bat program from this site.

Answer 2

With all scripts syntax is the same - the file to split and the size in bytes.

1) MAKECAB - the main limitation is the usage on Unix/Mac machines.For unix eventually cabextract or 7zip could be used , but I'm not sure if it can handle split CAB file .Even on windows the EXPAND command cant do it and EXTRAC32 (command is given in the help message) should be used (or Shell.Application )

;@echo off

;;;;; rem start of the batch part  ;;;;;
;; 
;; 
;; rem the first parameter is the file you want to split  the second is the size in bytes.
;; rem size is not guaranteed but will be not overflown 
;; 
; if "%~2" equ "" (
; call :helpmessage
; exit /b 1 
;)
;if not exist "%~dpnx1" (
; call :helpmessage
; exit /b 2
;)
;if exist  "%~dpnx1\" (
; call :helpmessage
; exit /b 3
;)
; rem remove leading zeroes
; cmd /c exit /b %~2
; set /a size=%errorlevel%
; if %size% equ 0 (
; echo size must be greater than 0
; exit /b 4
;)
; rem MaxDiskSize must be multiple of 512 and closest possible to desired size.
;if %~2 LSS 512 set diskSize=512 else (
; set /a part=%~2%%512
; set /a diskSize=%~2-part
;)
;makecab /d the_file="%~1" /d diskSize=%diskSize% /d the_size="%~2" /F "%~dpfnxs0"
;exit /b %errorlevel%
;:helpmessage
; echo no existing file has been passed
; echo usage [split a file to cab parts with given size]:
; echo %~nx0 file size
; echo(
; echo size must be greater than 0
; echo (
; echo for extraction use :
; echo extrac32 /a /e file.ext_part1.cab /l .
; exit /b 0

;;
;;;; rem end of the batch part ;;;;;

;;;; directives part ;;;;;
;;
.New Cabinet
.set GenerateInf=OFF
.Set Cabinet=on
.Set Compress=on
.Set MaxDiskSize=%diskSize%;
.Set MaxCabinetSize=%the_size%
.set CabinetFileCountThreshold=1
.set CompressedFileExtensionChar=_
.Set CabinetNameTemplate=%the_file%_part*.cab
.set DestinationDir=.
.Set DiskDirectoryTemplate=; 

.set RptFileName=nul
.set UniqueFiles=ON
;.set DoNotCopyFiles=ON
;.set MaxDiskFileCount=1
.set MaxErrors=1
.set GenerateInf=OFF
%the_file% /inf=no
;;
;;;; end of directives part ;;;;;

--All other methods are direct splitting and files can be assembled with appending them to each other in correct order --

2) JScript - a hybrid file that must be saved with .bat extension

     @if (@x)==(@y) @end /***** jscript comment ******
         @echo off
         cscript //E:JScript //nologo "%~f0" "%~nx0" %* 
         exit /b %errorlevel%

     @if (@x)==(@y) @end ******  end comment *********/

     //https://github.com/npocmaka/batch.scripts/blob/master/hybrids/jscript/zipjs.bat

    var FileSystemObj = new ActiveXObject("Scripting.FileSystemObject");
    var AdoDBObj = new ActiveXObject("ADODB.Stream");

    var ARGS = WScript.Arguments;
    var scriptName=ARGS.Item(0);

    if (ARGS.length <3) {
        WScript.Echo("Wrong arguments");
        WScript.Echo("usage:");
        WScript.Echo(scriptName +"file_to_split size_in_bytes");
        WScript.Quit(1);
    }
    var file=ARGS.Item(1);
    var max_size=parseInt(ARGS.Item(2));

    function getSize(file){
        return FileSystemObj.getFile(file).size;
    }

    function isExist(file){
        return FileSystemObj.FileExists(file);
    }

    function writeFile(fileName,data ){
        AdoDBObj.Type = 1;       
        AdoDBObj.Open();
        AdoDBObj.Position=0;
        AdoDBObj.Write(data);
        AdoDBObj.SaveToFile(fileName,2);
        AdoDBObj.Close();   
    }

    function readFile(fileName,size,position){
        AdoDBObj.Type = 1; 
        AdoDBObj.Open();
        AdoDBObj.LoadFromFile(fileName);
        AdoDBObj.Position=position;
        fileBytes=AdoDBObj.Read(size);
        AdoDBObj.Close();
        return fileBytes;


    }

    function chunker(file,size){
        var part=0;
        var position=0;
        var buffer=readFile(file,size,0);
        file_size=getSize(file);
        while (buffer !== null ) {
            part++;
            WScript.Echo("Creating: "+file+".part."+part);
            writeFile(file+".part."+part,buffer);
            if (size*part <= file_size) {
                position=size*part;
            } else {
                position=file_size;
            }
            buffer=readFile(file,size,position);
        }
    }

    if (!isExist(file)){
        WScript.Echo(file+" does not exist");
        WScript.Quit(2);
    }

    if(max_size<=0){
        WScript.Echo("Size must be bigger than 0.")
        WScript.Quit(3);
    }

    chunker(file,max_size);

3) JScript.net - self compiled hybrid that must be saved with .bat extension.

@if (@X)==(@Y) @end /* JScript comment
@echo off
setlocal

for /f "tokens=* delims=" %%v in ('dir /b /s /a:-d  /o:-n "%SystemRoot%\Microsoft.NET\Framework\*jsc.exe"') do (
   set "jsc=%%v"
)

::if not exist "%~n0.exe" (
    "%jsc%" /nologo /out:"%~n0.exe" "%~dpsfnx0"
::)

 %~n0.exe  %*

endlocal & exit /b %errorlevel%

*/

import System;
import System.IO;

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

if (arguments.length<3){
    Console.WriteLine("Wrong arguments");
    Console.WriteLine("usage:");
    Console.WriteLine(arguments[0]+"file_to_split size_in_bytes");
    Environment.Exit(1);
}

var file=arguments[1];
var max_size=parseInt(arguments[2]);

if (max_size<=0){
    Console.WriteLine("size must be bigger than zero");
    Environment.Exit(2);
}

if (!File.Exists(file)){
    Console.WriteLine("file"+file+" does not exist");
    Environment.Exit(3);
}

function writeData(file,data:byte[]){
    Console.WriteLine(data.Length);
    var writer = new BinaryWriter(File.Open(file, FileMode.Create));
    writer.Write(data);
    writer.Close();
}

function  chunker(inputFile, chunkSize){

    var part=0;
    var reader= new BinaryReader(File.Open(inputFile, FileMode.Open));
    var data:byte[]=reader.ReadBytes(chunkSize);

    while(reader.BaseStream.Position !== reader.BaseStream.Length) {
        part++;
        Console.WriteLine("Processing part " + part);
        writeData(inputFile+".part."+part,data);
        data=reader.ReadBytes(chunkSize);

    }
    if (data.Length !== 0) {
        part++;
        Console.WriteLine("Processing part " + part)
        writeData(inputFile+".part."+part,data);    
    }
    reader.Close();
}

chunker(file,max_size);

4) CERTUTIL - rather an experimental stuff - it's slower as the buffers are limited to the max length that can string have 8,1** characters and is rather text processing:

@echo off

setlocal enableExtensions
rem :-----------------------------------------
rem : check if should prompt the help message
rem :-----------------------------------------
if "%~2" equ "" goto :help
for %%H in (/h -h /help -help) do (
    if /I "%~1" equ "%%H" goto :help
)
if not exist "%~1" echo file does not exist & exit /b 1


rem :-----------------------------------------
rem : validate input
rem :-----------------------------------------
set /a size=%~2
if not defined size echo something wrong with size parameter & exit /b 2
if %size%0 LSS 00 echo not a valid number passed as a parameter & exit /b 3

rem : -- two hex symbols and an empty space are 1 byte
rem : -- so the sum of all hex symbols
rem : -- per part should be doubled
set /a len=%size%*2
set "file=%~dfn1"

for %%F in ("%file%") do set fn=%%~nxF

rem : -- clear temp data
del /F /Q "%temp%\file" >nul 2>&1
del /F /Q  "%temp%\fn.p.*" >nul 2>&1
certutil -encodehex -f "%file%" "%temp%\file" >nul
set "part=1"

setlocal enableDelayedExpansion
        set "hex_str="
        set hex_len=0
        break>%temp%\fn.p.!part!

rem : -- reads the hex encoded file
rem : -- and make it on a parts that will
rem : -- decoded with certutil

rem :-- the delimitier is <tab> wich separates
rem :-- line number from the rest of the information
rem :-- in the hex file
rem :---------------------------- v <tab>
for /f "usebackq tokens=2 delims=   " %%A in ("%temp%\file") do (
        set "line=%%A"
        rem : -- there's a double space in the middle of the line
        rem :-- so here the line is get
        set hex_str=!hex_str!!line:~0,48!
        rem echo hex_str !hex_str!
        rem :-- empty spaces are cleared
        set hex_str=!hex_str: =!
        rem echo hex_str !hex_str! 
        rem :-- the length of the hex line 32
        set /a hex_len=hex_len+32

        rem : -- len/size is reached
        rem : -- and the content is printed to a hex file
        if !hex_len! GEQ !len! (
            echo  !hex_len! GEQ !len!
                set /a rest=hex_len-len
                for %%A in (!rest!) do (
                        (echo(!hex_str:~0,-%%A!)>>%temp%\fn.p.!part!
                        rem : -- the rest of the content of the line is saved
                        set hex_str=!hex_str:~-%%A!
                        set /a hex_len=rest
                        echo !hex_len!
                )
                certutil -decodehex -f %temp%\fn.p.!part! %fn%.part.!part! >nul
                echo -- !part!th part created --
                rem :-- preprarin next hex file
                set /a part=part+1
                break>%temp%\fn.p.!part!
                rem :-- reinitilization of the len/size of the file part
                set /a len=%size%*2
        )
        rem : -- a buffer that not allows to
        rem : -- to enter too long commmands
        rem : -- used to reduce disk operations
        if !hex_len! GEQ 7800 (
                (echo(!hex_str!)>>%temp%\fn.p.!part!
                set "hex_str="
                set hex_len=0
                rem :-- the size that need to be reached is reduces
                rem :-- as there's alredy part of the part of the file
                rem :-- added to the hex file
        set /a len=!len!-7800
                if !len! LSS 0 set len=0

        )

)
rem : -- adding the rest of the file
echo !hex_str!>>%temp%\fn.p.!part!
certutil -decodehex -f %temp%\fn.p.!part! %fn%.part.!part! >nul
echo -- !part!th part created --

rem : -- clear created temp data
rem del /F /Q  %temp%\fn.p.* >nul 2>&1
rem del /F /Q  %temp%\file >nul 2>&1
endlocal
endlocal

goto :eof
rem :-----------------------------------------
rem : help message
rem :-----------------------------------------

:help
echo\
echo Splits a file on parts by given size in bytes in 'pure' batch.
echo\
echo\
echo    %0 file size
echo\
echo\

here's a script that can assemble files split with the last three methods:

@echo off
if "%~1" EQU "" echo parameter not entered & exit /b 1
set "parts=%~1.part"

setlocal enableDelayedExpansion
set numb=0
for /f "delims=." %%P in ('dir /b %parts%*') do (
    set /a numb=numb+1
)
rem echo !numb!


setlocal enableDelayedExpansion
set "string=%~1.part.1"
for /l %%n in (2;1;!numb!) do (
    set "string=!string!+!parts!.%%n"
)
rem echo !string!
copy /y /b !string! %~1%~x1
endlocal