Linux Classroom Series – 20/Jul/2020

Environment

• Shell maintains lot of information during our shell session called the environment
• Programs/applications can use the data stored in this environment to determine info about system’s configuration.
• In this series
  • printenv
  • set
  • export
  • alias

What gets stored in Environment?

• Two types of data gets stored in the environment
  • environment variables
  • shell variables
• In addition to above mentioned variables shell stores
  • aliases
  • shell functions

Examine the Environment

• Execute the following command

printenv|less
printenv USER
printenv PATH

• Now lets execute one more comand

set | less
echo $HOME

• printenv command shows only environmental variables where set command displays both environment and shell variables
• we can print variables by adding $ to the varaible name
• Neither printenv nor set commands show aliases for that we need use command alias

Some Interesting Variables

• SHELL: The name of your shell program
• HOME: The path of your home directory
• LANG: Defines the character set
• OLDPWD: Previous working directory
• PATH: A colon-separated list of directories that are searched when you enter the name of a executable program
• USER: Your username

How is this Environment established

• When we login into linux system, bash program starts and reads series of configuration scripts called as start up files
• The exact sequence of files depends on type of shell you have started. There are two types
  • Login shell session: This is the one in which we are prompted for username & password (ssh)
  • A non-login shell: This generally occurs when we launch a terminal in GUI.