How to Set a User Environment Variable Permanently

environment-variablespath

This is irritating me. I seen several suggestions (all using different files and syntax) and none of them worked.

How do I set an environment variable for a specific user? I am on debian squeeze.
What is the exact syntax I should put in the file to make ABC = "123"?

Best Answer

You have to put the declaration in the initialization files of your shell:

If you are using bash, ash, ksh or some other Bourne-style shell, you can add
```
ABC="123"; export ABC
```
in your .profile file (${HOME}/.profile). This is the default situation on most Unix installations, and in particular on Debian.

If your login shell is bash, you can use .bash_profile (${HOME}/.bash_profile) or .bash_login instead.

Note: If either of these files exists and your login shell is bash, .profile is not read when you log in over ssh or on a text console, but it might still be read instead of .bash_profile if you log in from the GUI. Also, if there is no .bash_profile, then use .bashrc.
If you've set zsh as your login shell, use ~/.zprofile instead of ~/.profile.
If you are using tcsh, add
```
setenv ABC "123"
```
in .login file (${HOME}/.login)
if you are using another shell look at the shell manual how to define environment variables and which files are executed at the shell startup.

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Is the $HOME environment variable always set on a Linux system

Yes. The POSIX specification requires the OS to set a value for $HOME:

HOME
The system shall initialize this variable at the time of login to be a pathname of the user's home directory. See pwd.h.

What about user nobody?

# su - nobody
No directory, logging in with HOME=/
$ echo $HOME
/

Even though nobody has no true home, HOME is set to the root directory.

To Export or Not to Export Bash PS1 Variable

That's correct: PS1 is only meaningful in interactive instances of bash, so it should be set in ~/.bashrc and should not be exported. PS1 is also meaningful in other shells, but it has a different meaning, because prompt expansions differ between shells. In fact, even between instances of bash, PS1 can have different meanings, since the meaning depends on shell options (at least promptvars).

Exporting PS1 to the environment from .profile is a throwback to the 1970s, when there was only one shell that used it (the Bourne shell) and it didn't have a configuration file. It still works today if you always use the same shell and never configure it differently. But all modern shells that aren't designed purely for scripting (csh, ksh, bash, zsh, …) read a configuration file when started interactively (.cshrc, .kshrc, .bashrc, .zshrc, …), so the 1970s method is no longer necessary. Setting PS1 and other shell-specific settings in a shell-specific file, and not exporting it to the environment, avoids breaking things when you use a different shell configuration or a different shell or a different terminal that isn't capable of showing your usual prompt fanciness. Setting PS1 in a shell-specific file works all the time, whereas setting it in .profile and exporting it only works in “simple” cases, so there's no reason not to do it the right way, but there are plenty of bad tutorials around the web and even bad default configurations in distributions. C'est la vie.

Best Answer

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