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.

Give warnings for extensions to POSIX bc.
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'.  
Display version number, short copyright and quits, see warranty.
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