See also gnu

bc [ -lwsqv ] [long-options] [ file ... ]

bc supports arbitrary precision numbers with interactive execution of statements,
starts executing code from files on the command line, then reads from the standard input.

--warn
-w
Give warnings for extensions to POSIX bc.
--standard
-s
POSIX
--quiet
-q
Do not print the welcome.
bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.  
--version
-v
Display version number, short copyright and quits, see warranty.
--mathlib
-l
Set scale=20 Define the math library.

In .profile set up alias bc='/usr/bin/bc -q ~/.bin/bc.ini' and
create ~/.bin/bc.ini containing :scale=2
then echo 5/6|bc will output .83