[Toybox] [PATCH] tar: add -I (--use-compress-program) support.

[Rob Landley]

On 8/24/20 12:15 PM, enh via Toybox wrote:
> unfortunately, -I was just the easy request... they also want --transform.
> 
> this is the specific command:
> 
> tar -I $(KGZIP) -c $(RCS_TAR_IGNORE) -f $(2).tar.gz \
>     --transform 's:^:$(2)/:S' $(TAR_CONTENT) $(3); \
> 
> https://android.googlesource.com/kernel/common/+/refs/heads/android-mainline/scripts/Makefile.package#49

Eh, this is just some variant of:

int fds[2] = {-1, -1}, len;
pid_t pid = xpopen_both((char *[]){"sed", "-e", arg, 0}, fds);

if (pid<0) sadness();
for (;;) {
  char *line = 0;

  len = 0
  dprintf(*fds, "%s\n", filename);
  len = readline(&line, *len);
}

> it's not clear to me just how complete that "sed expression" is. oh, looks like
> it's just 's': https://www.gnu.org/software/tar/manual/tar.html#SEC115 (but with
> some weird extra flags rRsShH)

Except for that bit, where it's using flags not explained in the manual. I don't
have "info" installed, is this available on the web somewhere?

https://www.gnu.org/software/sed/manual/sed.html#The-_0022s_0022-Command

Does not mention s///S because of course not.

sed s///H is multi-line mode? Is there any way I can continue to _not_ care
about that for a little while longer? Hmmm... \S is a regex extension to match
non-whitespace chars but there's no \ here...

  $ echo hello | sed -e 's/x/y/S'
  sed: -e expression #1, char 7: unknown option to `s'

And the gnu/dammit sed in debian doesn't understand trailing S either. Huh. Is
it a tar --transform thing? Nothing in the man page about that...

Ok, it IS a tar thing (not a sed thing) which is NOT described in the tar man
page but IS described in the tar online manual but NOT in the part about
--transform but instead in the "modifying file and member names" part and then
hit page down 4 times.

Wheee.

Do I police that the sed pattern is s/x/x/ or just let them pass in y/x/z and
friends if they really want to? (Hmmm, probably police it given they can w to
create new files otherwise. So start with s%c and then require the %c twice more
and no ; after the last %c. No ispunct at all, really...

ok, gix#rRsShH are the supported flags. Currently gi# are normal sed commands
(along with iI). We don't yet support x and that seems like basic sed should
have that but it's not in the sed manual. (I can feed -E to sed when we see x
but controlling that for a given s/// search pattern seems kinda useful. Oh well...

rRsShH are just "apply to regular, symlink, or hardlink" target filters. Easy
enough to put in the

Anyway, yeah should be doable.

Rob