How to write a bash script to set global environment variable?

Question

Recently I wrote a script which sets an environment variable, take a look:

#!/bin/bash

echo "Pass a path:"
read path
echo $path

defaultPath=/home/$(whoami)/Desktop

if [ -n "$path" ]; then
    export my_var=$path
else
    echo "Path is empty! Exporting default path ..."
    export my_var=$defaultPath
fi

echo "Exported path: $my_var"

It works just great but the problem is that my_var is available just locally, I mean in console window where I ran the script.

How to write a script which allow me to export global environment variable which can be seen everywhere?

Similar question was already asked. See http://stackoverflow.com/questions/1464253/global-environment-variables-in-a-shell-script — Maciej, Sep 10 '12 at 12:32
The post http://stackoverflow.com/questions/1464253/global-environment-variables-in-a-shell-script pointed to by @Maciej shows that you do not **run** a script that modifies an environment variable; you **source** it instead. The dot **.** shown in the answers below and around is an alias for the `source` command. Clearly, not to be confused with the dot for the current directory, which indicates an argument instead of a command. — XavierStuvw, Jan 09 '22 at 15:51
Just a note, you must have equals sign between export my_var and the path. I was attempting with a space there (as I was taught old school maybe? or maybe that's the syntax for another shell?), and only got it to work once I replaced space with = Thanks! — skittlebiz, Feb 22 '22 at 20:10

score 159 · Answer 1 · edited Apr 17 '17 at 20:27

159

Just run your shell script preceded by "." (dot space).

This causes the script to run the instructions in the original shell. Thus the variables still exist after the script finish

Ex:

cat setmyvar.sh
export myvar=exists

. ./setmyvar.sh

echo $myvar
exists

edited Apr 17 '17 at 20:27

Løiten

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answered May 29 '14 at 15:22

JDembinski

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Bingo. This solves the problem described in the question (setting an environment variable in the calling shell). – Tim Stewart Jul 07 '14 at 10:34
The accepted answer, by David W., adds a more comprehensive explanation to anyone looking for that. Adding this note in the answer would probably be better but this should be sufficient to point those in a hurry in the right direction. – Fernando Cordeiro Aug 08 '22 at 18:56

score 58 · Accepted Answer · edited Nov 02 '19 at 07:46

Each and every shell has its own environment. There's no Universal environment that will magically appear in all console windows. An environment variable created in one shell cannot be accessed in another shell.

It's even more restrictive. If one shell spawns a subshell, that subshell has access to the parent's environment variables, but if that subshell creates an environment variable, it's not accessible in the parent shell.

If all of your shells need access to the same set of variables, you can create a startup file that will set them for you. This is done in BASH via the $HOME/.bash_profile file (or through $HOME/.profile if $HOME/.bash_profile doesn't exist) or through $HOME/.bashrc. Other shells have their own set of startup files. One is used for logins, and one is used for shells spawned without logins (and, as with bash, a third for non-interactive shells). See the manpage to learn exactly what startup scripts are used and what order they're executed).

You can try using shared memory, but I believe that only works while processes are running, so even if you figured out a way to set a piece of shared memory, it would go away as soon as that command is finished. (I've rarely used shared memory except for named pipes). Otherwise, there's really no way to set an environment variable in one shell and have another shell automatically pick it up. You can try using named pipes or writing that environment variable to a file for other shells to pick it up.

Imagine the problems that could happen if someone could change the environment of one shell without my knowledge.

One shell changing another without its knowledge or consent would indeed be bad. But the original question, although having a badly worded title, asks how to change a variable in the console window that "ran the script", i.e. with its knowledge and consent, which is legitimate and useful. JDembinski's answer shows how. — Tim Stewart, Jul 07 '14 at 10:39
It is possible to use system-wide environment files, such as `/etc/environment`, `/etc/profile` and `/etc/profile.d/` or `/etc/bash.bashrc`. In my case, I use `/etc/environment` to store variables for `cron` tasks. — antonbormotov, Jan 16 '17 at 02:25
this should not be the accepted answer. it doesn't address the question with a useful answer whereas the answer by JDembinski does. — bravery, Mar 09 '21 at 03:09
@bravery while I do agree with you to some extent, this answer covers a lot more, and includes a more in-depth explanation. IMHO, the answers both complement each other. And since this one is by far the most complete, I think it'd be unfair to give all the credit to JDembinski, as much as I like his addition. — Fernando Cordeiro, Aug 08 '22 at 18:59

score 9 · Answer 3 · answered Feb 20 '17 at 10:07

9

Actually I found an way to achieve this (which in my case was to use a bash script to set a number of security credentials)

I just call bash from inside the script and the spawned shell now has the export values

export API_USERNAME=abc
export API_PASSWORD=bbbb
bash

now calling the file using ~/.app-x-setup.sh will give me an interactive shell with those environment values setup

answered Feb 20 '17 at 10:07

Dinis Cruz

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Or you could just source it instead of execute this. Now you have a nested shell. – grepsedawk May 22 '17 at 21:00

score 7 · Answer 4 · answered Nov 05 '14 at 23:59

The following were extracted from 2nd paragraph from David W.'s answer: "If one shell spawns a subshell, that subshell has access to the parent's environment variables, but if that subshell creates an environment variable, it's not accessible in the parent shell."

In case a user need to let parent shell access your new environment variables, just issue the following command in parent shell:

source <your_subshell_script>

or using shortcut

. <your_subshell_script>

Even if no one values it in my opinion this is the best solution to the question. — Michael Hecht, Jun 18 '22 at 07:29

score 4 · Answer 5 · answered Sep 10 '12 at 12:38

4

You got to add the variable in your .profile located in /home/$USER/.profile

Yo can do that with this command:

echo 'TEST="hi"' >> $HOME/.profile

Or by edit the file with emacs, for example. If you want to set this variable for all users, you got to edit /etc/profile (root)

answered Sep 10 '12 at 12:38

MarcD

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it would be lovely but it doesnt work at all :( I mean, this: `echo 'TEST="hi"' >> $HOME/.profile` doesnt work :/ – Katie Sep 10 '12 at 12:41

score 3 · Answer 6 · answered Sep 10 '12 at 12:33

There is no global environment, really, in UNIX.

Each process has an environment, originally inherited from the parent, but it is local to the process after the initial creation.

You can only modify your own, unless you go digging around in the process using a debugger.

score 3 · Answer 7 · answered Jan 16 '17 at 02:11

3

write it to a temporary file, lets say ~/.myglobalvar and read it from anywhere

echo "$myglobal" > ~/.myglobalvar

answered Jan 16 '17 at 02:11

Sergio Abreu

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score 2 · Answer 8 · answered Sep 10 '12 at 12:33

2

Environment variables are always "local" to process execution the export command allow to set environment variables for sub processes. You can look at .bashrc to set environment variables at the start of a bash shell. What you are trying to do seems not possible as a process cannot modify (or access ?) to environment variables of another process.

answered Sep 10 '12 at 12:33

Nahuel Fouilleul

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So the only solution is to add `my_var` to .bashrc? Is it possible to make it with bash script? – Katie Sep 10 '12 at 12:36
you can add a line in .bashrc to source a file which will be generated by a script – Nahuel Fouilleul Sep 10 '12 at 12:39

score 1 · Answer 9 · answered Sep 10 '12 at 12:38

1

You can update the ~/.bashrc or ~/.bash_profile file which is used to initialize the environment.

answered Sep 10 '12 at 12:38

Jin Kim

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score 1 · Answer 10 · answered Sep 10 '12 at 12:39

Take a look at the loading behavior of your shell (explained in the manpage, usually referring to .XXXshrc or .profile). Some configuration files are loaded at login time of an interactive shell, some are loaded each time you run a shell. Placing your variable in the latter might result in the behavior you want, e.g. always having the variable set using that distinct shell (for example bash).

score 1 · Answer 11 · edited Jan 24 '14 at 06:28

~/.bin/SOURCED/lazy script to save and load data as flat files for system.

[ ! -d ~/.megadata ] && mkdir ~/.megadata

function save_data {
[ -z "$1" -o -z "$2" ] && echo 'save_data [:id:] [:data:]' && return
local overwrite=${3-false}
[ "$overwrite" = 'true' ] && echo "$2" > ~/.megadata/$1 && return
[ ! -f ~/.megadata/$1 ]   && echo "$2" > ~/.megadata/$1 || echo ID TAKEN set third param to true to overwrite
}

save_data computer engine
cat ~/.megadata/computer
save_data computer engine
save_data computer megaengine true

function get_data {
[ -z "$1" -o -f $1 ] && echo 'get_data [:id:]' && return


[ -f ~/.megadata/$1 ]   && cat ~/.megadata/$1 || echo ID NOT FOUND
:
}

get_data computer
get_data computer

score 1 · Answer 12 · answered Oct 04 '13 at 14:35

If you need to dynamically set and reference environment variables in shell scripts, there is a work around. Judge for yourself whether is worth doing, but here it is.

The strategy involves having a 'set' script which dynamically writes a 'load' script, which has code to set and export an environment variable. The 'load' script is then executed periodically by other scripts which need to reference the variable. BTW, the same strategy could be done by writing and reading a file instead of a variable.

Here's a quick example...

Set_Load_PROCESSING_SIGNAL.sh

#!/bin/bash
PROCESSING_SIGNAL_SCRIPT=./Load_PROCESSING_SIGNAL.sh
echo "#!/bin/bash" > $PROCESSING_SIGNAL_SCRIPT
echo "export PROCESSING_SIGNAL=$1" >> $PROCESSING_SIGNAL_SCRIPT
chmod ug+rwx $PROCESSING_SIGNAL_SCRIPT

Load_PROCESSING_SIGNAL.sh (this gets dynamically created when the above is run)

#!/bin/bash
export PROCESSING_SIGNAL=1

You can test this with Test_PROCESSING_SIGNAL.sh

#!/bin/bash
PROCESSING_SIGNAL_SCRIPT=./Load_PROCESSING_SIGNAL.sh
N=1
LIM=100
while [ $N -le $LIM ]
do
# DO WHATEVER LOOP PROCESSING IS NEEDED
echo "N = $N"
sleep 5
N=$(( $N + 1 ))

# CHECK PROCESSING_SIGNAL
source $PROCESSING_SIGNAL_SCRIPT
if [[ $PROCESSING_SIGNAL -eq 0 ]]; then
# Write log info indicating that the signal to stop processing was detected
# Write out all relevent info
# Send an alert email of this too
# Then exit
echo "Detected PROCESSING_SIGNAL for all stop. Exiting..."
exit 1
fi
done

SomeOne_1 · Answer 13 · 2021-05-29T07:51:20.473

Maybe a little off topic, but when you really need it to set it temporarily to execute some script and ended up here looking for answers:

If you need to run a script with certain environment variables that you don't need to keep after execution you could do something like this:

#!/usr/bin/env sh

export XDEBUG_SESSION=$(hostname);echo "running with xdebug: $XDEBUG_SESSION";$@

In my example I just use XDEBUG_SESSION with a hostname, but you can use multiple variables. Keep them separated with a semi-colon. Execution as follows (assuming you called the script debug.sh and placed it in the same directory as your php script):

$ debug.sh php yourscript.php

How to write a bash script to set global environment variable?

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