Run your shell scripts against any version of Bash back to version 2.02 all the way through the most current releases. This also includes Apple's version of Bash, which are given an arbitrary number (possibly a build number). Symbolic links are created so bash-4.3 runs against the latest bash-4.3.x version, and likewise if you only use a major number, such as bash-4.
# See all of the shells $ ls /usr/local/bin
Shells that are included: