9 Apr
2010
9 Apr
'10
4:11 a.m.
On Thu, 8 Apr 2010, Norman Wilson wrote:
Bob Eager:
The 'ar' format of that vintage is trivial, and documentation easily
found. I wrote programs to read it back in 1976!
======
That's nothing. Either Ken or Dennis wrote such a program
years before that!
Warren even has a binary somewhere to prove it!
Seriously, it's a binary format, so I don't know that
it would be easy to process in awk. (At least not in
awk-classic; stuff that works only in ghootandwaveawk
is not all that interesting to me.) But the format is
simple, and any language new or old that can handle
binary data without tears should do.
I can't see how to do it in awk either.
If I didn't have an overfull plate already (and
a
visit to the Auto-Electrocution Consultant tomorrow,
and one to the Canal Rooting Clinic Monday--proving
that one should follow Father's advice and Stay Away
Well I found the ar specification (in ar.5 not ar.1).
struct ar_hdr {
char ar_name[14];
long ar_date;
char ar_uid;
char ar_gid;
int ar_mode;
long ar_size;
};
This is same as the old ar.c source.
(plus more in the manual page.)
Now my problem is I don't know what "long" or "int" is on the old
PDP-11
/ system 5 this was made on.
And I read about PDP-11 "middle endianess" (first time I heard of
"middle").
So I had (wrong but gets ar_name and ar_size correct for my few tests
for the first header but chops two characters into the data section).
struct {
char ar_name[14];
int32_t ar_date;
char ar_uid;
char ar_gid;
uint16_t ar_mode;
uint16_t ar_size;
} ar_buf;
Well I know above is wrong because ar_size and ar_date should be the
same. But I get ar_size correct each time. But it also loses the next
two bytes from the data. So I am guessing I have some endian issue where
I am getting some things reversed.
Any ideas?
Note I am not using any system 5 or PDP-11 system. I am using a modern
little endian (amd64) system to extract the files that were created in
1970s.
Once I figure out the structure and endianness (if applicable) I will
share back my code so others can extract ...
>From The Canal, Neddie) it would be
interesting to
collect the different specifications for ar headers
over the years, and write a small suite of programs
to read them. Perhaps in Python, just to be difficult.
(Why isn't there a language called Goon, Warren?)