Sqlplus is my second home, part 4: Getting sqlplus parameter value into a variable

I’m having some busy times, so can’t blog anything more serious than another sqlplus trick (which likely has value only to some hardcore sqlplus geeks though).
Ever wanted to load a sqlplus parameter (like linesize, pagesize or arraysize) into a sqlplus define variable?
This can sometimes be helpful for customizing your everyday DBA scripts to output (or not output) some columns based on linesize. Or you may want to use the SQL error code somewhere in your script.