The purpose of this project is to take the XDG Base Directory Standard and XDG User Directory Standard (collectively XDG), as a starting point for a universal standard suitable for inclusion in the File Hierarchy Standard.
$HOME_ETC$HOME_USR$HOME_VAR$HOME_TMP
The defaults for each respectively:
~/.etcor~/.config~/.usror~/.local~/.varor~/.variable~/.tmpor~/.cache
The later are for compatibility with XDG. (Note: .variable might be replaced with a more succinct name if a good alternative can be determined.)
$DIRS_ETC$DIRS_USR$DIRS_VAR$DIRS_TMP
The defaults for each respectively:
/etc/usr/local:/usr/var/tmp
Notice we did not provide and equivalent for XDG's $XDG_DATA_HOME or $XDG_DATA_DIRS. In XDG the default home location points to ~/.local/share. To access the same location via BDS use $HOME_USR/share. However, if deemed necessary, $HOME_SHARE and $DIRS_SHARE can be added.
Although the latest XDG standard provides for $XDG_RUNTIME_DIR which corresponds to /var/run in the FHS, XDG lacks any corresponding locals for /var itself. In BDS the equivalent to /var is supported by $HOME_VAR and $DIRS_VAR and defaults to the locations ~/.var and /var, respectively.
The ~/.local directory that is the prefix of the default $XDG_DATA_HOME
path is an explicit part of the BDS standard. (In the Ruby XDG library
this had been labeled $XDG_RESOURCE_HOME.) This directory is simply the per-user equivalent of the system wide /usr/local or /usr directory.
For a universal standard, the sub-directory path of $XDG_CONFIG_DIRS
should not be required. So instead of /etc/xdg, the default is /etc.
By reversing the word order, no special prefix is needed for the environment variable names.