Delete a part in a file without ruining the encoding and extension

Question

I have a fairly large database of files. The files have very different extensions (.txt, .doc, .ppt etc), but every one of them has a certain phrase at the start of the file which has to be removed.

So, let's say I have a file randomtext.doc. Looking at the file in a simple text editor, the file would normally begin with:

\D0\CFࡱ\E1\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00>\00\00\FE\FF                           \00\00\00\00\00\00\00\00\00\00\00\00\00\00\00K\00\00\00\00\00\00\00\00\00\00M\00\00\00\00\00\00\FE\FF\FF\FF\00\00\00\00J\00\00\00\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\

But my file begins with:

MYPHRASE \D0\CFࡱ\E1\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00>\00\00\FE\FF  \00\00\00\00\00\00\00\00\00\00\00\00\00\00\00K\00\00\00\00\00\00\00\00\00\00M\00\00\00\00\00\00\FE\FF\FF\FF\00\00\00\00J\00\00\00\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\FF\

Deleting the phrase in a regular text editor ruins the file (for example, this file, which would normally be a .doc file, wouldn't be able to be viewed by Microsoft Word). I need to be able to delete the phrase, but keep the file extension etc.

Answer 1

This can be accomplished in multiple ways. For example, a search and replace utility that support binary files can be used to replace "MYPHRASE " with an empty string. There are also hex editors available that can be scripted to do this.

I would recommend using dd for Windows though (be sure to download the latest version i.e. dd-0.6beta3.zip).

The following command can be used to delete 9 bytes ("MYPHRASE ") from the beginning of a file:

dd bs=9 skip=1 if="Drive:\Path\to\infile.ext" of="Drive:\Path\to\outfile.ext"

If you want to do this with lots of files, place them all in a single directory and run the following batch file after editing the delbytes and rootfolder variables as per your requirements:

@echo off
cls
set delbytes=9
set rootfolder="C:\My Files"
for /r %rootfolder% %%a in (*.*) do (
    echo Truncating first %delbytes% bytes of "%%a"
    dd bs=%delbytes% skip=1 if="%%a" of="%%~dpna (Truncated)%%~xa"
    echo.
)