You may be able to convert binary to decimal, octal, or hex in your head but it seems that you can’t do simple arithmetic anymore and you can never find a calculator when you need one. What to do?

Create a calculator using shell arithmetic and RPN notation:

#!/usr/bin/env bash # cookbook filename: rpncalc # # simple RPN command line (integer) calculator # # takes the arguments and computes with them # of the form a b op # allow the use of x instead of * # # error check our argument counts: if [ \( $# -lt 3 \) -o \( $(($# % 2)) -eq 0 \) ] then echo "usage: calc number number op [ number op ] ..." echo "use x or '*' for multiplication" exit 1 fi ANS=$(($1 ${3//x/*} $2)) shift 3 while [ $# -gt 0 ] do ANS=$((ANS ${2//x/*} $1)) shift 2 done echo $ANS

Any arithmetic done within $(( )) is integer arithmetic only.

The idea of RPN (or *postfix*) style of notation
puts the operands (the numbers) first, followed by the operator. If we
are using RPN, we don’t write `5 + 4`

but rather `5 4 +`

as our expression.
If you want to multiply the result by 2, then you just put `2`

* on the end, so the whole expression would
be `5 4 + 2`

*, which is great for
computers to parse because you can go left to right and never need
parentheses. The result of any operation becomes the first operand for
the next expression.

In our simple *bash* calculator we will allow
the use of lowercase `x`

as a substitute for the multiplication symbol since * has special meaning ...

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