Shell Programming and Scripting

Hello,
I have a script that runs a series of commands. Halfway through the script, I want it to check whether everything is going alright: if it is, to proceed with the script, if it isn't to repeat the last step until it gets it right.
My code so far looks like this, simplified a bit:

Code:

#!/bin/bash

command -i Input1.in -o Output1.out
command -i Input2.in -o Output2.out
command -i Input3.in -o Output3.out
if grep -q NaN Output3.out
then command -i Input3.in -o Output3.out
fi
command -i Input4.in -o Output4.out
command -i Input5.in -o Output5.out

If it finds NaN, it means that the command has failed.
This script, however, just repeats the third step once. How can I get it to do the third step, check for NaN, repeat if found, check again and keep doing it until the command works?
Thank you in advance.

Code:

while grep -q NaN Output3.out
do
    command
done

---------- Post updated at 09:33 AM ---------- Previous update was at 09:31 AM ----------

that's asking for an infinite loop though. usually put a limit on such things.

Code:

while grep ... && ((fail++ < 10)); do
    command ...
done

for example to kill loop. or maybe exit

Code:

while grep -q ...; do
  if ((fail++ > 100)); then
    echo "this really just isn't going to work. i give up" >&2
    exit 1
  fi
 
  command ...
done

And please, "if" is not a loop. Its a conditional "statement".

Once the command within the do-done loop is successful, issue a Shell break command to get out of the do-done loop and the script will continue with the next statement after the done.