Typically, users will see this error when installing the smarty package with composer and svn has not been installed yet.
ubuntu@precise64:~$ composer5.4-sp install
Loading composer repositories with package information
...
[RuntimeException]
Package could not be downloaded, sh: 1: svn: not found
The solution is to install the subversion package as root.
sudo apt-get install subversion
For more information, see How to Use the PHP CLI and No command 'composer' found.