Understanding the general principles of a package manager is the foundation to utilize them. The package manager provides a repository of software stored in a dedicated file system location – even for different versions. Specific software and version may depend on other software or libraries forming a tree of dependencies. The software might be incompatible with another software, too.

The user can query available software via commands and load software using a program of the package manager via the shell command-line interface. A package manager then makes it available by manipulating shell variables. Understanding these variables is crucial to understand the system behavior and to debug issues.

• To describe the principles of a package manager and how it interfaces with the shell.

• Describe the general dependency structure of software.
• Describe how a package manager makes software available.
• Use the export command to print shell variables.
• Understand shell variables relevant for executing and building software:
  • PATH for executables
  • LD_LIBRARY_PATH for libraries
  • MANPATH for manual pages (man command)
  • PKG_CONFIG_PATH for pkg-config
• Manipulate shell variables to include additional software:
  • Setting shell variables for a single program by prefixing or by using export.