Apple - Is it safe to upgrade Bash via Homebrew?

Binaries in /{,usr/}{,s}bin/ should not usually be replaced with other files. Other programs expect them to be the versions that came with OS X, and they are replaced by OS upgrades.

After running brew install bash, you can change the default shell safely by:

• Adding /usr/local/bin/bash to /etc/shells
• Running chsh -s /usr/local/bin/bash.

Settings in Terminal or iTerm 2 don't normally have to be changed. Both of them default to opening new windows with a login shell of the default shell.

The default shell can also be changed from System Preferences or with dscl, but all three options just modify /var/db/dslocal/nodes/Default/users/$USER.plist.

I could be wrong here, but as far as I know brew would install it's own instance of bash, since brew works under /usr/local/bin while the system defaults works under /bin (and /usr/bin).

About Terminal, you can make shells open with your own, custom command. Go to Preferences > Startup and select Shells open with: Command (complete path). Simply type the path to your new bash and vuala!

Hope it helps!

BTW: Backup! Best advice in this situations!