# USE1.4.1-B Overview
# Background

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.

# Aim
  * To describe the principles of a package manager and how it interfaces with the shell.

# Outcomes
  * 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.

# Subskills