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