tool_dependencies.xml

<?xml version="1.0"?>
 <tool_dependency>
    <package name="expat" version="2.1.0">
        <install version="1.0">
            <actions>
                <!-- first action is always downloading -->
                <action type="download_by_url" sha256sum="823705472f816df21c8f6aa026dd162b280806838bb55b3432b0fb1fcca7eb86">https://depot.galaxyproject.org/software/expat/expat_2.1.0_src_all.tar.gz</action>
                <action type="autoconf" />

                <action type="set_environment">
                    <environment_variable name="PATH" action="prepend_to">$INSTALL_DIR/bin</environment_variable>
                    <environment_variable name="LD_LIBRARY_PATH" action="prepend_to">$INSTALL_DIR/lib</environment_variable>
                    <environment_variable name="C_INCLUDE_PATH" action="prepend_to">$INSTALL_DIR/include</environment_variable>
                    <environment_variable name="EXPAT_ROOT_DIR" action="set_to">$INSTALL_DIR</environment_variable>
                </action>
            </actions>
        </install>
        <readme>Compiling expat requires make and a C compiler. You can access expat with $EXPAT_ROOT_DIR. http://expat.sourceforge.net/</readme>
    </package>
</tool_dependency>