Fun with Bash – Making Robust Scripts
I was looking at the results of the overnight runs and realized that I really needed to work making the nightly runs far more robust by retrying the complete division run if there were errors in the processing. The trick was - How?
So I came up with the idea that the summary script that's gripping the log of the process, could, in fact, look at the log and determine if the run was a "success". Then, I could have it return a simple error code and the nightly run script could detect that and place the division into a retry queue if it failed.
Great idea, but getting the Bash scripts to do it was a little more work than I'd expected. Oh sure, the exit value from the summary script was easy, I just had to pick the right thing to test in that script, and after a few tries, I got what I needed. No… this was about the dealing with the string vs. integer nature of the bash variables.
For example, this is OK:
if [ $pass -gt 3 ]; then break fi
unless $pass is a string, and then you get an error and die. So it's possible to say:
if [[ $pass > 3 ]]; then break fi
but this seems to cause me grief:
if [[ $pass >= 3 ]]; then break fi
It's not easy to figure out all the edge cases until you've written more than a few bash scripts using a feature, but hey… that's the power and grief of using bash.
In the end, it was really much easier to force the type of variables and make sure they are OK, than it was to try and figure out why 'greater than' was OK, but 'greater than or equal to' wasn't. The goal was to have a couple of scripts tied together that allowed me to ensure that they nightly runs worked, and worked well, and I've got that now.
Problem solved.