# USE1.5 Overview: Software Environment

HPC systems have generally installed multiple versions of several essential software tools and software environments.
Package management tools provide access to this wide variety of software.
A user has to load the software for the current shell session to make commands available.

The widely available software tools are:
  * Environment modules
  * Spack

## Learning objectives
  * Understand shell variables relevant for executing and building software.
  * Query available software using the package manager.
  * Select the appropriate versions for deployment in the session environment.
  * 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
  * [[skill-tree:use:1:5:1:b]]
  * [[skill-tree:use:1:5:2:b]]
  * [[skill-tree:use:1:5:3:b]]