This sounds as if your installation of the "pear" utility script refers to a nonexistent php binary.
Depending on your system configuration, the php interpreter might be in /usr/bin, /usr/local/bin, some other place in the filesystem, or nowhere at all.
Type
which pear
to find the location of the pear script.
Then type
which php
to find the location of the php binary.
View the first line of the pear script and compare the path to PHP with the actual location on your system.
If you don't have a php binary, reinstall. If you do, a symbolic link will cure the problem.
