Update README.md

README.md

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 # Building RPMs for Pmodules
 
-With the spec files in this repository you can build RPMs for Pmodules. 
+## The spec files
+With the spec files in this repository can be used to build RPMs for Pmodules. 
+
+**Pmodules.spec**
+The spec file to build the Pmodules RPM. 
+
+**Pmodules_modules.spec**
+Pmodules is a wrapper around the C implementation of Environment Modules 3.2.10 with some patches (e.g.: except `%#Pmodules` as shebang). This RPM is set as 'required' in the Pmodules RPM.
+
+**Pmodules_bash.spec**
+The Pmodules wrapper is written in Bash and uses feature only available in Bash version 5 and newer. On most current Linux distributions only Bash 4 is available. This RPM is set as 'required' in the Pmodules RPM.
+
+## Building the RPMs
+
+**Requirements (on RHEL8/9)**\
+The RPMs `rpm-build` and `rpmdevtools` must be installed.
+
+**Setup the directories for `rpmbuild` (if not already done)**
+```
+mkdir -p ~/rpmbuild/{BUILD,RPMS,SOURCES,SPECS,SRPMS}
+echo '%_topdir %(echo $HOME)/rpmbuild' > ~/.rpmmacros
+```
+
+**Download the required sources**
+```
+cd ~/rpmbuild/SPECS
+for f in Pmodules.spec Pmodules_bash.spec Pmodules_modules.spec; do
+    spectool "$f"
+fone
+```
+
+**Build the RPMs**
+```
+for f in Pmodules.spec Pmodules_bash.spec Pmodules_modules.spec; do
+    rpmbuild -bb "$f"
+fone
+```
+
+