Environment variable settings

For more information about how to set environment variables-Linux general technology-Linux technology and application, see the following. I have asked questions in the Forum and consulted relevant materials. The following are some details about the environment configuration.
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Temporary environment variables (disappear after restart) can be viewed with set
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1. directly use the export command:
Test = abc
Echo $ test
Export test means that the test variable (echo $ test) can still be used in the sub-shell program ). This step cannot be used only in this shell. Enter the sub-shell method: Enter bash directly. Ps will see two bash processes.

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Permanent environment variables (do not disappear after restart) can be viewed with set
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1, so that all users can use
Global setting file: ①/etc/profile ②/etc/bashrc
You only need to add the environment variables you set in the preceding two files.

2, only for individual users
User setting file: ③. bash_profile ④. bashrc
These two files have ls-a in each user's directory.
You only need to add the environment variables you set in the preceding two files.

Note: It doesn't matter if the permanent environment variable is added without export. There is no sub-shell.
If there are any of the above shortcomings, we hope you can give them some advice.