Don't learn bash, learn Bourne shell (sh). You can always learn the Bash extensions later.
I'm tired of people coming for interview for jobs involving shell programming (we don't use bash) and not realising the difference!
They're the same people who almost invariably tell us that our "Up arrow is broken"* and the "Cursor keys aren't working in vi" (and also tend to pronounce vi as in vie instead of Vee Eye).
* - we aren't allowed to use any shell with a history due to security policy constraints.