When I try to install php 5.3 stable from source on Ubuntu (downloading compressed installation file from http://www.php.net/downloads.php) and I run ./configure I get this error:
configure: error: xml2-config not found. Please check your libxml2 installation.
All you need to do instal install package libxml2-dev for example:
sudo apt-get install libxml2-dev
On CentOS/RHEL:
sudo yum install libxml2-devel
For the latest versions it is needed to install libxml++2.6-dev like that:
apt-get install libxml++2.6-dev
I had the same issue when I used a DockerFile. My Docker is based on the php:5.5-apache image.
I got that error when executing the command "RUN docker-php-ext-install soap"
I have solved it by adding the following command to my DockerFile
"RUN apt-get update && apt-get install -y libxml2-dev"
来源：https://stackoverflow.com/questions/19904083/how-to-fix-error-with-xml2-config-not-found-when-installing-php-from-sources