Not Bash, not Excel, not any special-purpose tool because the motto of those is "you can't get there from here". Maybe you can get 80% of the way there, which is really seductive, but that last 20% is like going to the moon. Specifically, real programming languages have the tools to format dates correctly with a few lines of code you can wrap into a function, fake programming languages don't. Mapping codes is straightforward, etc.