安装PHP PEAR ubuntu 12.04时出错

I have installed PHP PEAR in ubuntu using

sudo apt-get install php-pear

After successfull installation first time.When I try to run it in terminal, it shows error:

The program 'pear' is currently not installed.  You can install it by typing:
sudo apt-get install php-pear

I again tried to install it. Then it shows that

php-pear is already the newest version.

I have checked many questions on SO. In every question it is mentioned to locate pear etc. But above mentioned error is not solved.

I even tried installing pear many times with sudo and running it. It gives same error.

Please help to sort it out.