1 Feb
2023
1 Feb
'23
7:38 p.m.
>>
FILE1.ZIP+FILE2.ZIP+FILE3.ZIP+FILE4.ZIP+FILE5.ZIP COMBINED.ZIP
> THAT will give you a corrupted file!
> Concatenated copy (COPY with '+') has a behavior that you need to take into
account.
> PC/MS-DOS 1.00 kept track of the file size with a course granularity. (logical
sectors, not bytes) Therefore, PC/MS-DOS supported CTRL-Z as an end of file character!
> (A legacy of CP/M)
> When you copy a file, it copies the whole thing. Any extraneous
> content after EOF won't matter.
> BUT! When you concatenate files,
> COPY FILE1.ZIP + FILE2.ZIP COMBINED.ZIP
> COPY will terminate FILE1.ZIP at the first CTRL-Z that it encounters!
> When copying text files, Concatenated COPY will trim off all content after EOF!
> It is called "text mode".
> You need to change your command to
> COPY /B FILE1.ZIP+FILE2.ZIP+FILE3.ZIP+FILE4.ZIP+FILE5.ZIP COMBINED.ZIP
> to get "binary mode", so that it will copy ALL of each file, rather than
just to the "end of file character" of each!
> Compare the final resulting file size of COPY and COPY /B
On Wed, 1 Feb 2023, Zane Healy wrote:
I’m running the version of DOS that comes with
DOSBOX-X (I think
it’s FreeDOS?). Checking COPY, and I’m not sure it supports /B, but
it also doesn’t complain, the resulting combined ZIP is the same in
both cases. Turns out that I have three corrupted files in the fixed
Zip, before fixing it there are a lot more. That’s based on telling
PKZIP to check the ZIP integrity.
If you get a convenient chance, try COPY /A ...+...+... ...
/A ("ASCII" or text mode) is the default in PC/MS-DOS, where CTRL-Z, and
any padding/junk after the EOF (CTRL-Z) character in the files in the
middle is truncated. That is so that when you concatenate text files, you
don't leave EOFs and sector/record padding in the middle.
If /A gives the same as /B and the same as no switch, then either your
version does not have that "feature", OR there are no CTRL-Z's (1Ah)
anywhere in the middle files!
If /A gives a shorter result, stay away from it, but that would mean that
/B is the default in your version.
--
Grumpy Ol' Fred cisin(a)xenosoft.com