bash - restart program if it outputs some string -

i want loop process in bash script, process should run forever fails.

when fails, outputs >>747;3r last line, keeps running.

i tried (just testing)

while [ 1 ]   mono program.exe   last_pid=$!   sleep 3000   kill $last_pid done 

but doesn't work @ all, process mono program.exe runs forever (until crashes, script nothing.)

$! expands pid of last process started in background. can seen with:

cat test sleep 2 lastpid=$! echo $lastpid  ~$ bash -x test + sleep 2 + lastpid= + echo 

vs

~$ cat test sleep 2 & lastpid=$! echo $lastpid  :~$ bash -x test + lastpid=25779 + sleep 2 + echo 25779 

the fixed version of script read:

while true;   mono program.exe &   last_pid=$!   sleep 3000   kill $last_pid done 

your version running mono program.exe , sitting there. didn't make next line waiting process finish. kill command didn't work $! never populated (wasn't background process).