bash: defining a variable with or without export

Question

What is export for? What is the difference between:

export name=value

and

name=value

Answer 1

export will make the variable available to all shells forked from the current shell.

Answer 2

export makes the variable available to sub-processes.

That is,

export name=value

means that the variable name is available to any process you run from that shell process. If you want a process to make use of this variable, use export, and run the process from that shell.

name=value

means the variable scope is restricted to the shell, and is not available to any other process. You would use this for (say) loop variables, temporary variables etc.

Answer 3

To illustrate what the other answers are saying:

al$ foo="Hello, World"
al$ echo $foo
Hello, World
al$ bar="Goodbye"
al$ export foo
al$ bash
bash-3.2$ echo $foo
Hello, World
bash-3.2$ echo $bar

bash-3.2$

Answer 4

Others have answered that export makes the variable available to subshells, and that is correct but merely a side effect. When you export a variable, it puts that variable in the environment of the current shell (ie the shell calls putenv(3) or setenv(3)). The environment of a process is inherited across exec, making the variable visible in subshells.

Answer 5

Yeah, export actually makes environment variables available to all subprocesses; subshells are just one subtype of subprocesses. Not to subvert the conversation. XD

Answer 6

Here's yet another example:

VARTEST="value of VARTEST" 
#export VARTEST="value of VARTEST" 
sudo env | grep -i vartest 
sudo echo ${SUDO_USER} ${SUDO_UID}:${SUDO_GID} "${VARTEST}" 
sudo bash -c 'echo ${SUDO_USER} ${SUDO_UID}:${SUDO_GID} "${VARTEST}"'

Only by using export VARTEST the value of VARTEST is available in sudo bash -c '...'!

For further examples see:

• http://mywiki.wooledge.org/SubShell

• bash-hackers.org/wiki/doku.php/scripting/processtree