Just following the steps described in this neat summary.

For information on how to install MacPorts see here and here.

export PATH="/opt/local/bin:/opt/local/sbin:/opt/local/lib:/opt/local/include:/opt/local/man:/usr/bin:/bin:/usr/sbin:/sbin"
export IFS=$' \t\n'


1.
/opt/local/bin/port info bash
/usr/bin/sudo /opt/local/bin/port -c install bash

2.
# add '/opt/local/bin/bash' to /private/etc/shells
/usr/bin/sudo /usr/bin/nano /private/etc/shells

3. 
# enable UTF-8 support by adding to your ~/.bash_login (or alternatives):
# /usr/bin/locale -a
export LC_ALL=en_US.UTF-8
export LANG=en_US.UTF-8

4.
man chsh
# run chsh and change the path of the shell to /opt/local/bin/bash
chsh

5.
# set encoding of Terminal.app to UTF-8
/usr/bin/defaults read com.apple.Terminal StringEncoding
/usr/bin/defaults write com.apple.Terminal StringEncoding -int 4

/usr/bin/defaults read com.apple.Terminal DoubleWideChars
/usr/bin/defaults write com.apple.Terminal DoubleWideChars -bool YES

kill -HUP $$
#killall -HUP Terminal


6.
# [cmd-,]
Terminal -> Preferences... -> select: Execute this command (specify complete path): /opt/local/bin/bash


#---------------------------------------------------------------------------


# Bash 3.0 Announcement
# http://groups.google.com/group/gnu.announce/msg/e05c4cbeecdb24c7
# http://en.opensuse.org/Bash

bash --version
which bash

dscl . read /Users/$(/usr/bin/logname) UserShell

man 7 re_format     # POSIX 1003.2 regular expressions
man /opt/local/share/man/man1/bash.1.gz 2>/dev/null | less -p '=~'
man /opt/local/share/man/man1/bash.1.gz 2>/dev/null | less -p regex

# new feature of Bash 3.0 ff.: in-process regular expression matching
str='abc def'
if [[ "${str}" =~ 'c d' ]]; then printf "%s\n" "${BASH_REMATCH[0]}"; fi

printf "%s\n" "${BASH_REMATCH[0]}"
printf "%s\n" "${#BASH_REMATCH[*]}"
printf "%s\n" "${#BASH_REMATCH[@]}"