"export" Command

Learn all about export command

HOME

export - Set export attribute for shell variables.

root:~# help export

It's a named object that can be used by multiple applications as it contains valuable information required by these applications.

Example-1

1.1 - Print all Exported variables and functions (-p).

root@:~# export -p
declare -x HISTFILESIZE="1000"
declare -x HISTSIZE="1000"
declare -x HISTTIMEFORMAT="%F %T "
declare -x HOME="/root"
declare -x SHELL="/bin/bash"
declare -x USER="root"

OR

root@:~# export
declare -x HISTFILESIZE="1000"
declare -x HISTSIZE="1000"
declare -x HISTTIMEFORMAT="%F %T "
declare -x HOME="/root"
declare -x SHELL="/bin/bash"
declare -x USER="root"

Example-2

2.1 - Export Desired Variable.

There are many situations where we need to create new variable in parent process and that should be available in child process. In that case, if we dont use export then those variables wont be available in child process

root@:~# MY_HOME='1/2/3'
root@:~# echo $MY_HOME
1/2/3
root@:~# bash
root@:~# echo $MY_HOME

root@:~# exit
exit
root@:~# echo $MY_HOME
1/2/3
root@:~#

Description:
Line-1, new variable MY_HOME is created.
Line-2, printed new variable on terminal.
Line-3, created child process using 'bash' command.
Line-4, Again printed defined variable on terminal. As its expected, child process doesnt have the new defined variable.
Line-5, exit from the child process.
Line-6, print the new variable again in parent process.

As observed again, by default child process does not inherit parent's variables. It only inherits parent's exported variables. This is where export command is useful.

root@:~# export MY_HOME='1/2/3'
root@:~# echo $MY_HOME
1/2/3
root@:~# bash
root@:~# echo $MY_HOME
1/2/3
root@:~# exit
exit
root@:~# echo $MY_HOME
1/2/3
root@:~#

Example-3

3.1 - Modify Existing Exported Variable

root@:~# export MY_HOME='1/2/3'
root@:~# echo $MY_HOME
1/2/3
root@:~# export MY_HOME=$MY_HOME/45/4343/232/323
root@:~# echo $MY_HOME
1/2/3/45/4343/232/323