#!/bin/bash

# calc--A command line calculator that acts as a frontend to bc

# Establishing the amount of decimal places bc will expect, in this case the default 2
scale=2
# Establishing a show_help() function that will display a message to the user if they invoke calc, and then type help or ?
show_help()
{
cat << EOF
    In addition to standard math functions, calc also supports:

    a % b       remainder of a/b
    a ^ b       exponential: a raised to the b power
    s(x)        sine of x, x in radians
    c(x)        cosine of x, x in radians
    a(x)        arctangent of x, in radians
    l(x)        natural log of x
    e(x)        exponential log of raising e to the x
    j(n,x)      Bessel function of intenger order n of x
    scale N     show N fractional digits (default = 2)
EOF
}

# This is a very simple script, here, as long as the arguments passed to calc are greater than 0, calc simply executes the scriptbc script we wrote earlier.
if [ $# -gt 0 ] ; then
    exec scriptbc "$@"
fi

# Otherwise if no arguments are passed to calc, it opens up a prompt that displays this message
echo "Calc--a simple calculator. Enter 'help' for help, 'quit' to quit."

# the read command is what keeps the prompt open, here the while loop invokes the read command,
# which awaits bash command, and then takes the newly created $args variable...
while read command args
do
    case $command # if the $command variable is...
        in
        quit|exit)      exit 0                                       ;; # quit/exit causes an exit of the program with a success/ok status...
        help|\?)        show_help                                    ;; # help/? brings up the help message above
        scale)          scale=$args                                  ;; # if scale is invoked, you can change the default value of the $scale variable
        *)              scriptbc -p $scale "$command" "$args"         ;; # otherwise any other commands will simply invoke the scriptbc script
    esac

    /bin/echo -n "calc>" # afterwards which you will be returned to the calc> prompt
done

echo "" # after invoking calc with arguments, a blank line is printed.

exit 0 # and an success/ok status is passed upon exit.