rpn.pod

NAME

rpn - Programmable command-line calculator using reverse polish notation

SYNOPSIS

Usage: rpn [-bdvh] [<operator>]

Options:
  -b, --batchmode       enable batch mode
  -d, --debug           enable debug mode
  -s, --stack           show last 5 items of the stack (off by default)
  -i  --intermediate    print intermediate results
  -m, --manual          show manual
  -c, --config <file>   load <file> containing LUA code
  -p, --precision <int> floating point number precision (default 2)
  -v, --version         show version
  -h, --help            show help

When <operator>  is given, batch  mode ist automatically  enabled. Use
this only when working with stdin. E.g.: echo "2 3 4 5" | rpn +

DESCRIPTION

rpn is a command line calculator using reverse polish notation.

Working principle

Reverse Polish Notation (short: RPN) requires to have a stack where numbers and results are being put. So, you put numbers onto the stack and each math operation uses these for calculation, removes them and puts the result back.

To visualize it, let's look at a calculation:

((80 + 20) / 2) * 4

This is how you enter the formula int an RPN calculator and how the stack evolves during the operation:

| rpn commands | stack contents | calculation   |
|--------------|----------------|---------------|
|           80 |             80 |               |
|           20 |          80 20 |               |
|            + |            100 | 80 + 20 = 100 |
|            2 |          100 2 |               |
|            / |             50 | 100 / 2 = 50  |
|            4 |           50 4 |               |
|            x |            200 | 50 * 4 = 200  |

The last stack element 200 is the calculation result.

USAGE

The default mode of operation is the interactive mode. You'll get a prompt which shows you the current size of the stack. At the prompt you enter numbers followed by operators or mathematical functions. You can use completion for the functions. You can either enter each number or operator on its own line or separated by whitespace, that doesn't matter. After a calculation the result will be immediately displayed (and added to the stack). You can quit interactive mode using the commands quit or exit or hit one of the ctrl-d or ctrl-c key combinations.

If you feed data to standard input (STDIN), rpn just does the calculation denoted in the contet fed in via stdin, prints the result and exits. You can also specify a calculation on the commandline.

Here are the three variants ($ is the shell prompt):

$ rpn
rpn> 2
rpn> 2
rpn> +
= 4

$ rpn
rpn> 2 2 +
= 4

$ echo 2 2 + | rpn
4

$ rpn 2 2 +
4

The rpn calculator provides a batch mode which you can use to do math operations on many numbers. Batch mode can be enabled using the commandline option -b or toggled using the interactive command batch. Not all math operations and functions work in batch mode though.

Example of batch mode usage:

$ rpn -b
rpn->batch > 2 2 2 2 +
= 8

$ rpn
rpn> batch
rpn->batch> 2 2 2 2 +
8

$ echo 2 2 2 2 + | rpn -b
8

$ echo 2 2 2 2 | rpn +
8

If the first parameter to rpn is a math operator or function, batch mode is enabled automatically, see last example.

You can enter integers, floating point numbers (positive or negative) or hex numbers (prefixed with 0x).

STACK MANIPULATION

There are lots of stack manipulation commands provided. The most important one is undo which goes back to the stack before the last math operation.

You can use dump to display the stack. If debugging is enabled (-d switch or debug toggle command), then the backup stack is also being displayed.

The stack can be reversed using the reverse command. However, sometimes only the last two values are in the wrong order. Use the swap command to exchange them.

You can use the shift command to remove the last number from the stack.

BUILTIN OPERATORS AND FUNCTIONS

Basic operators:

+                    add
-                    subtract
/                    divide
x                    multiply (alias: *)
^                    power

Bitwise operators:

and                  bitwise and
or                   bitwise or
xor                  bitwise xor
<                    left shift
>                    right shift

Percent functions:

%                    percent
%-                   subtract percent
%+                   add percent

Batch functions:

sum                  sum of all values (alias: +)
max                  max of all values
min                  min of all values
mean                 mean of all values (alias: avg)
median               median of all values

Math functions:

mod sqrt abs acos acosh asin asinh atan atan2 atanh cbrt ceil cos cosh
erf erfc  erfcinv erfinv exp  exp2 expm1 floor  gamma ilogb j0  j1 log
log10 log1p log2 logb pow round roundtoeven sin sinh tan tanh trunc y0
y1 copysign dim hypot

Conversion functions:

cm-to-inch
inch-to-cm
gallons-to-liters
liters-to-gallons
yards-to-meters
meters-to-yards
miles-to-kilometers
kilometers-to-miles

Configuration Commands:

[no]batch            toggle batch mode (nobatch turns it off)
[no]debug            toggle debug output (nodebug turns it off)
[no]showstack        show the last 5 items of the stack (noshowtack turns it off)

Show commands:

dump                 display the stack contents
hex                  show last stack item in hex form (converted to int)
history              display calculation history
vars                 show list of variables

Stack manipulation commands:

clear                clear the whole stack
shift                remove the last element of the stack
reverse              reverse the stack elements
swap                 exchange the last two stack elements
dup                  duplicate last stack item
undo                 undo last operation
edit                 edit the stack interactively using vi or $EDITOR

Other commands:

help|?               show this message
manual               show manual
quit|exit|c-d|c-c    exit program

Register variables:

>NAME                Put last stack element into variable NAME
<NAME                Retrieve variable NAME and put onto stack

Refer to https://pkg.go.dev/math for details about those functions.

There are also a number of shortcuts for some commands available:

d    debug
b    batch
s    showstack
h    history
p    dump (aka print)
v    vars
c    clear
u    undo

INTERACTIVE REPL

While you can use rpn in the command-line, the best experience you'll have is the interactive repl (read eval print loop). Just execute rpn and you'll be there.

In interactive mode you can use TAB completion to complete commands, operators and functions. There's also a history, which allows you to repeat complicated calculations (as long as you've entered them in one line).

There are also a lot of key bindings, here are the most important ones:

ctrl-c + ctrl-d

Exit interactive rpn

ctrl-z

Send rpn to the backgound.

ctrl-a

Beginning of line.

ctrl-e

End of line.

ctrl-l

Clear the screen.

ctrl-r

Search through history.

COMMENTS

Lines starting with # are being ignored as comments. You can also append comments to rpn input, e.g.:

# a comment
123   # another comment

In this case only 123 will be added to the stack.

VARIABLES

You can register the last item of the stack into a variable. Variable names must be all caps. Use the ">NAME" command to put a value into variable "NAME". Use "<NAME" to retrieve the value of variable "NAME" and put it onto the stack.

The command vars can be used to get a list of all variables.

EXTENDING RPN USING LUA

You can use a lua script with lua functions to extend the calculator. By default the tool looks for ~/.rpn.lua. You can also specify a script using the <kbd>-c</kbd> flag.

Here's an example of such a script:

function add(a,b)
  return a + b
end

function init()
  register("add", 2, "addition")
end

Here we created a function add() which adds two parameters. All parameters are FLOAT64 numbers. You don't have to worry about stack management, this is taken care of automatically.

The function init() MUST be defined, it will be called on startup. You can do anything you like in there, but you need to call the register() function to register your functions to the calculator. This function takes these parameters:

• function name

• number of arguments expected (see below)

  Number of expected arguments can be:

  - 0: expect 1 argument but do NOT modify the stack
  - 1-n: do a singular calculation
  - -1: batch mode work with all numbers on the stack 

• help text

Please refer to the lua language reference: https://www.lua.org/manual/5.4/ for more details about LUA.

Please note, that io, networking and system stuff is not allowed though. So you can't open files, execute other programs or open a connection to the outside!

CONFIGURATION

rpn can be configured via command line flags (see usage above). Most of the flags are also available as interactive commands, such as --batch has the same effect as the batch command.

The floating point number precision option -p, --precision however is not available as interactive command, it MUST be configured on the command line, if needed. The default precision is 2.

GETTING HELP

In interactive mode you can enter the help command (or ?) to get a short help along with a list of all supported operators and functions.

To read the manual you can use the manual command in interactive mode. The commandline option -m does the same thing.

If you have installed rpn as a package or using the distributed tarball, there will also be a manual page you can read using man rpn.

BUGS

In order to report a bug, unexpected behavior, feature requests or to submit a patch, please open an issue on github: https://github.com/TLINDEN/rpnc/issues.

LICENSE

This software is licensed under the GNU GENERAL PUBLIC LICENSE version 3.

Copyright (c) 2023-2024 by Thomas von Dein

This software uses the following GO modules:

readline (github.com/chzyer/readline)

Released under the MIT License, Copyright (c) 2016-2023 ChenYe

pflag (https://github.com/spf13/pflag)

Released under the BSD 3 license, Copyright 2013-2023 Steve Francia

gopher-lua (github.com/yuin/gopher-lua)

Released under the MIT License, Copyright (c) 2015-2023 Yusuke Inuzuka

AUTHORS

Thomas von Dein tom AT vondein DOT org