[RuntimeException] Package could not be downloaded, sh:1 svn: not found

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
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.