$BACKGROUND Use by libcufo to choose the default style when none was explicitely specified.
$CU_DTAGS_PATH May point to a file containing debug tags to enable, one per line. The tag names correspond those passed to cu_dlog_def.
$CU_SEED48 Seed the random number generator at starup by calling seed48(t), where t is determined as follows. If the variable contains the literal "time", the system clock is used. Otherwise, it should contain a 12 digit hexadecimal value without base prefix which makes up the three components of the argument to seed48.
$CU_VERBOSITY An integer specifying the threshold for cu_verbf calls.
$CUFO_STYLEDIR A colon-separated list of directories to seach for cufo style files.
$CUFO_STYLE The name of the cufo-style to use. The name followed by a .style extension is searched for under $CUFO_STYLEDIR and some built-in paths.
$CULIBS_PREFIX, $CULIBS_EXEC_PREFIX, $CULIBS_SYSCONFDIR, ... Modifies culibs' idea of where it is installed.
$HOME libcufo to locate custom style definitions in $HOME/.config/culibs/cufo. $TMPDIR Where to create temporary files. Used by cuos_tmp_dir.