Run a Command Until it Stops Failing

I want to run a command until it completes sucessfully, then stop. I know I can set up a bash loop to do this, but I'm curious if there are any portable ways to do this similar to watch -n5 that would do what I'm looking for.

The use case: I'm trying to connect via SSH to a server that may not be up yet.

Just wrap said bash loop in a script, using $1 to specify the actual command to be executed and $2 for an arbitrary sleep value. Doing this, you'd be able to run the command like:

$ reallyrunit "ls" 5

# xxx.xxx.xxx.xxx = ipaddr ssh host
until [ `nmap --open -p 22 xxx.xxx.xxx.xxx |grep -c "ssh"` -eq 1 ]
do 
sleep 4
done 

# ssh stuff here

I'm not aware of a builtin to so this, but the bash to use is something like:

RET=1;until [[ $RET = 0 ]];do echo "$(date): About to make an attempt to connect"; ssh 192.168.33.12; RET="$?";sleep 1;done

EDIT: Added date and comment so you can track how long it has been failing for.