[Linux 常見問題] How to export variables that are set, all at once?

Source From Here
Question
If I defined environment variable(s) in a file, how do I export these variables all at once?

How-To
Assume we have a configuration file .env:

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1. MY_NAME='John'  
2. MY_AGE='39'  

Then we can test it by test.sh:

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1. #!/bin/sh  
2. echo -e "===== Setting from .env ====="  
3. cat .env  
4.   
5. echo -e "\n===== My setting ====="  
6. env | grep 'MY'  
7.   
8. source ./.env  
9. echo -e "\n===== After .env, My setting ====="  
10. env | grep 'MY'  

The execution result:

# ./test.sh
===== Setting from .env =====
MY_NAME='John'
MY_AGE='39'

===== My setting =====

===== After .env, My setting =====

Run the following command, before setting the variables:

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1. set -a   

From man page:

-a
When this option is on, the export attribute shall be set for each variable to which an assignment is performed;

To turn this option off, run set +a afterwards. Let's update test.sh:

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1. #!/bin/sh  
2. echo -e "===== Setting from .env ====="  
3. cat .env  
4.   
5. echo -e "\n===== My setting ====="  
6. env | grep 'MY'  
7. set -a  
8. source ./.env  
9. set +a  
10. echo -e "\n===== After .env, My setting ====="  
11. env | grep 'MY'  

This time, the execution will look like:

# ./test.sh
===== Setting from .env =====
MY_NAME='John'
MY_AGE='39'

===== My setting =====

===== After .env, My setting =====
MY_AGE=39
MY_NAME=John