Environment Variables in Linux
Linux environment variables are backbone of Linux operating system. A variable stores a value and gives you flexibility to call the variable in any shell script. In this article we will understand how to set environment variables in Linux.
Set Environment Variable in Linux
You can define a linux variable using export command
export <variable-name>=<value> export MY_WEBSITE=dbagenesis.com export ARTICLE="Environment Variables in Linux" export TODAY="It's an exciting day" export PLAYER='The "ROCK" player'
Always use UPPERCASE for variable names
Put value under " " if it contains spaces or single quotes
Put value under ' ' if it contains double quotes
You can check the value of a stored environment variable using echo command
echo "Current website is $MY_WEBSITE" echo "You are reading $ARTICLE"
You have to use $ when you want to call a variable's stored value.
We don't put $ sign while exporting a linux variable, we put $ sign only while calling variables
Scope of Environment Variables
When you set environment variables using linux export command, these variables scope is only session level. You close the terminal and login again, the variables are cleared from the system.
To make the variables permanent so that they are available when you login again, you must set the variables inside .bashrc file last line
vi .bashrc --> user's home location export MY_WEBSITE=dbagenesis.com export ARTICLE="Environment Variables in Linux"
You need to source (or load) the .bashrc for Linux to load new environment variables
source .bashrc echo $MY_WEBSITE echo $ARTICLE
The variables set under .bashrc file are only available to the particular user. For example, if Oracle user sets environment variables under its own .bashrc file, then its only accessible to Oracle user.
To define system wide environment variables, add variables to /etc/environment file (last line)
As root user: ============= vi /etc/environment export MY_SYS_VAR="System Wide Variable"
Logout and login. Now MY_SYS_VAR is available to all the users on Linux server!
List Environment Variables
To list all the system variables and local variables (set by user), simply use env command
To filter all the variables listed by env command
env | grep MY --> prints all vars containing MY env | grep HOME --> prints all vars containing HOME