[Toybox] I hate the GNU design aesthetic.

[Rob Landley]

I just added sed --tarxform and taught tar --xform to use it, so a single
persistent instance of sed can speak a simple protocol allowing
call-and-response sed invocation across a pipe. (This didn't work before for
several reasons: a line that produced no output could block tar trying to read
the result, a sed invocation adding an extra \n or \0 to the output could get
tar out of sync, sed wouldn't produce output until it read the NEXT line of data
so it could do $ matching at EOF...) Anyway, wrapped in a protocol, works now.

I'm not pushing the commit publicly yet because I'm hopefully about to CHANGE
said protocol slightly, to add a type indicator because in
https://www.gnu.org/software/tar/manual/tar.html#transform we have this little
horror show:

  In addition, several transformation scope flags are supported, that control to
  what files transformations apply. These are:

  ‘r’ Apply transformation to regular archive members.
  ‘R’ Do not apply transformation to regular archive members.
  ‘s’ Apply transformation to symbolic link targets.
  ‘S’ Do not apply transformation to symbolic link targets.
  ‘h’ Apply transformation to hard link targets.
  ‘H’ Do not apply transformation to hard link targets.

  Default is ‘rsh’, which means to apply transformations to both archive members
  and targets of symbolic and hard links.

  Default scope flags can also be changed using ‘flags=’ statement in the
  transform expression. The flags set this way remain in force until next
  ‘flags=’ statement or end of expression, whichever occurs first. For example:

  --transform 'flags=S;s|^|/usr/local/|'

No, "flags=" is not how sed command syntax normally works, thanks for asking.

So now I'm starting at this going:

1) Is rsh only the default when there are no scope flags? As in if I tell it
scope s should that switch off r and h?

2) Does flags= interact with the block logic? If I do

  --transform '{flags=S;s/potato/blah/;};s/a/b/'

should the second transform apply to symlink type?

3) If how about jumps? If I b to a :label past a flags= statement does that
prevent the flag change from taking effect? (Is this a parse time attribute or a
runtime attribute?)

The sad part is I strongly suspect I'm putting more thought into this than the
tar developers did, but I kind of need to know the answers to do it RIGHT.

Sigh,

Rob