Various bits of what is known about busybox shells, in no particular order.

2007-05-03
hush: update on "sleep 1 | exit 3; echo $?" bug.
parse_stream_outer() repeatedly calls parse_stream().
parse_stream() is now fixed to stop on ';' in this example,
fixing it (parse_stream_outer() will call parse_stream() 1st time,
execute the parse tree, call parse_stream() 2nd time and execute the tree).
But it's not the end of story.
In more complex situations we _must_ parse way farther before executing.
Example #2: "{ sleep 1 | exit 3; echo $?; ...few_lines... } >file".
Because of redirection, we cannot execute 1st pipe before we parse it all.
We probably need to learn to store $var expressions in parse tree.
Debug printing of parse tree would be nice too.

2007-04-28
hush: Ctrl-C and Ctrl-Z for single NOFORK commands are working.
Memory and other resource leaks (opendir) are not addressed
(testcase is "rm -i" interrupted by ctrl-c).

2007-04-21
hush: "sleep 5 | sleep 6" + Ctrl-Z + fg seems to work.
"rm -i" + Ctrl-C, "sleep 5" + Ctrl-Z still doesn't work
for SH_STANDALONE case :(

2007-04-21
hush: fixed non-backgrounding of "sleep 1 &" and totally broken
"sleep 1 | sleep 2 &". Noticed a bug where successive jobs
get numbers 1,2,3 even when job #1 has exited before job# 2 is started.
(bash reuses #1 in this case)

2007-04-21
hush: "sleep 1 | exit 3; echo $?" prints 0 because $? is substituted
_before_ pipe gets executed!! run_list_real() already has "pipe;echo"
parsed and handed to it for execution, so it sees "pipe"; "echo 0".

2007-04-21
hush: removed setsid() and made job control sort-of-sometimes-work.
Ctrl-C in "rm -i" works now except for SH_STANDALONE case.
"sleep 1 | exit 3" + "echo $?" works, "sleep 1 | exit 3; echo $?"
shows exitcode 0 (should be 3). "sleep 1 | sleep 2 &" fails horribly.

2007-04-14
lash, hush: both do setsid() and as a result don't have ctty!
Ctrl-C doesn't work for any child (try rm -i), etc...
lash: bare ">file" doesn't create a file (hush works)