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 ci...@xenosoft.com
