Steps to install the SOLR PHP extension on RHEL. Installation is a little trickery because of how curl is built into PHP as a shared library and not statically compiled.

solr-extension-php-rhel.sh

# install dependencies
sudo yum install curl-devel
sudo yum install libxml2-devel

# install extension for solr -- note use pear instead of pecl install
sudo pear install pecl/solr

# when it asks for libcURL path if you are on a 64bit machine
# change:
libcURL install prefix [/usr] : /usr/lib64

sudo chmod 755 /usr/lib64/php/modules/solr.so

sudo vi /etc/php.d/solr.ini
# add:
extension=solr.so

# restart apache
sudo service httpd restart

Note you might need to change the tmp dir of pear/pecl before running the pear install:

mkdir /root/tmp 
pecl config-set temp_dir /root/tmp
pear config-set temp_dir /root/tmp

pecl config-set temp_dir /root/tmp
or:
pear config-set temp_dir /root/tmp