CentOS6
yum update bash
--Version
bash-4.1.2-15.el6_5.2.x86_64
CentOS5 x86-64
wget http://mirrors.aliyun.com/centos/5/updates/x86_64/RPMS/bash-3.2-33.el5_10.4.x86_64.rpm && rpm -Uvh bash-3.2-33.el5_10.4.x86_64.rpm
--version
bash-3.2-33.el5_10.4.x86_64.rpm
Ubuntu
sudo apt-get install bash