Ubuntu – Why aren’t variables like $PS1 in printenv

bashcommand lineenvironment-variablesps1

From what I can tell printenv displays environment variables, but why don't I see other variables like PS1 for customizing the shell prompt?

What exactly is printenv outputting and why doesn't it pick up PS1? Is there a more comprehensive output command that does more than printenv?

Best Answer

That's because PS1 is not normally exported.

Environment variables are used to set the execution environment of child processes; since PS1 only really has significance within an interactive shell, there's not normally any point exporting it - it is just a plain shell variable.

If you start an interactive child shell, then it will read and set its PS1 from the shell's resource file such as ~/.bashrc

If you export PS1 then you will see it in the printenv output. Alternatively you can see plain shell variables using the bash builtin set as described here How to list all variables names and their current values?

Related Solutions

Ubuntu – How to add environment variables

To set variable only for current shell:

VARNAME="my value"

To set it for current shell and all processes started from current shell:

export VARNAME="my value"      # shorter, less portable version

To set it permanently for all future bash sessions add such line to your .bashrc file in your $HOME directory.

To set it permanently, and system wide (all users, all processes) add set variable in /etc/environment:

sudo -H gedit /etc/environment

This file only accepts variable assignments like:

VARNAME="my value"

Do not use the export keyword here.

You need to logout from current user and login again so environment variables changes take place.

Ubuntu – Why does “man x-terminal-emulator” return the output of “man gnome-terminal”

x-terminal-emulator is a virtual package. The terminal emulator is configured by Debian's alternative system.

On Ubuntu you can easily follow this symlink construction, e.g. for gnome-terminal:

$ which x-terminal-emulator
/usr/bin/x-terminal-emulator
$ ls -lF /usr/bin/x-terminal-emulator
/usr/bin/x-terminal-emulator -> /etc/alternatives/x-terminal-emulator*
$ ls -al /etc/alternatives/x-terminal-emulator
/etc/alternatives/x-terminal-emulator -> /usr/bin/gnome-terminal.wrapper*

Now regarding the man pages, update-alternatives also links the man page of gnome-terminal to x-terminal-emulator as explained in the update-alternatives manual:

   It is often useful for a number of alternatives to be synchronized,  so
   that they are changed as a group; for example, when several versions of
   the  vi(1)  editor  are  installed,  the   man   page   referenced   by
   /usr/share/man/man1/vi.1 should correspond to the executable referenced
   by /usr/bin/vi.  update-alternatives handles this by  means  of  master
   and  slave links; when the master is changed, any associated slaves are
   changed too.  A master link and its associated slaves make  up  a  link
   group.

Source

Best Answer

Related Solutions

Ubuntu – How to add environment variables

Ubuntu – Why does “man x-terminal-emulator” return the output of “man gnome-terminal”

Related Question