[RndTbl] Shell exec(2) help?

[Adam Thompson]

I've written a shell script that redownloads itself and re-executes 
itself, but I'm not quite seeing the behaviour I'd expect out of "exec 
sh".  Instead of one process, I get an infinite progression of shells 
that finally blows up when I hit ulimits.

The script:

===BOF===
curl -s $URL/targets \
| while read TGTNAME TGTIP ; do
     (
         echo -n "."

         mtr \
             --interval 0.1 \
             --gracetime 1 \
             --timeout 1 \
             --report-wide \
             --report-cycles 600 \
             --show-ips \
             --aslookup \
             --no-dns \
             ${TGTIP} \
         | awk -f parse.awk -v TGT=${TGTNAME}  \
         | psql -q -b -h $PGHOST -U $PGUSER $PGDB
     ) &
    wait &
done

# start all over again
sleep 60 &
wait
curl -s $URL/go.sh | exec sh
===EOF===

The key items are the backgrounding of mtr/awk/psql, which appears to 
work properly - there's 12 lines in "targets" and I only see 12 
mtr/awk/psql process groups at a time - the sleeping + waiting (which 
theoretically reaps all children and grandchildren, I think) and the 
final "exec".

Except instead of exec'ing, I run an infinite sequence of shells, each 
one a child of the previous.  E.g. from pstree(1):

# pstree -lp 1628
screen(1628)─┬─bash(1629)───sh(12707)───sh(12854)───sh(12986)───sh(13154)───sh(13309)───sh(13444)───sh(13579)───sh(13709)───sh(13842)───sh(13979)───sh(14101)───sh(14242)───sh(14396)───sh(14530)───sh(14655)───sh(14795)───sh(14935)───sh(15076)───sh(15203)───sh(15353)───sh(15490)───sh(15624)───sh(15753)───sh(15891)───sh(16023)───sh(16154)───sh(16282)───sh(16418)───sh(16551)───sh(16696)───sh(16842)───sh(16975)───sh(17112)───sh(17241)───sh(17388)───sh(17522)───sh(17664)───sh(17824)───sh(17956)───sh(18096)───sh(18233)───sleep(18279)

I think the problem has something to do with the fact the final exec is 
on the RHS of a pipe, and thus is executing inside a subshell, but how 
do I fix this?

Thanks,
-Adam