Bash variable that outlives the shell script

Question

We have an issue that I am able to recreate with this simple example. I have the following sample shell script file, named SO-shell.txt

#!/bin/bash
export my_var="A quick bown fox"
echo my_var was set to "$my_var"

When I run SO-shell.txt I get the following output:
my_var was set to A quick bown fox

After the script has finished execution, if I execute the following at the shell command line:
shell> echo "$my_var"

I don't see anything (i.e. shell variable did not get assigned beyond the lifespan of the shell script)

Q) How to make a shell variable outlive the lifespan of its defining shell script?

You can't. Nor would you want to. Perhaps you want to source the file rather than execute it. — William Pursell, Dec 03 '20 at 18:24
Possible duplicate questions: ["Can I export a variable to the environment from a bash script without sourcing it?"](https://stackoverflow.com/questions/16618071/can-i-export-a-variable-to-the-environment-from-a-bash-script-without-sourcing-i), ["bash forgets export variable"](https://stackoverflow.com/questions/10457725/bash-forgets-export-variable), and ["How to export a variable in bash"](https://stackoverflow.com/questions/307120/how-to-export-a-variable-in-bash). — Gordon Davisson, Dec 03 '20 at 18:30

vsergi · Accepted Answer · 2020-12-03T18:42:43.947

The export and ‘declare -x’ commands allow parameters and functions to be added to and deleted from the environment.

Bash Reference Manual - Environment

By using export command, basically you are declaring the variable for this specific process and its child-processes.

However, as workaround you can execute your script in the next way . SO-shell.tx

As example:

[19:30:50][/]# bash test.sh
my_var was set to A quick bown fox
[19:30:59][/]# echo $my_var

[19:31:11][/]# . test.sh
my_var was set to A quick bown fox
[19:31:15][/]# echo $my_var
A quick bown fox

You have more information about this here: Export variable from bash script

score 0 · Answer 2 · answered Dec 03 '20 at 18:29

How to make a shell variable outlive the lifespan of its defining shell script?

It's impossible (in normal shell implementations). Because shell variables are stored in memory inside the shell process and after a process dies all process memory is returned to the operating system, all information stored there is lost including the variable.

You can basically use any method of interprocess communication:

Use a file.
- Store the variable value to a file from child shell and restore it in parent shell.
- Store the variable definition (ie. declare -p my_var) in the file in child shell and source the file in parent shell.
Output the variable and grab the output in parent shell with command substitution.
Use a fifo between child and parent shell
Write your own tooling or your own shell implementation that would for example use shared memory to store the variable.

Bash variable that outlives the shell script

2 Answers2