roll is a program to roll dices specified in a simple and intuitive way.
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README.md

roll

roll is a program to roll dices specified in a simple and intuitive way.

see INSTALL on how to compile and install roll and the man page for instructions

Synopsis

roll [-hpsv] [--version] expression

Description

Rolls a user-defined dice sequence. The dices to roll are defined using dN where N is the number of sides. Dices can be rolled multiple times by prepending the number of repetitions (e.g., 3d6) and used in simple mathematical expressions (e.g., 2d8+4).

Options

--help, -h
       help

--positive, -p
       allow only positive results

--sum-series, -s
       show the sum of roll series

--verbose, -v
       verbose (displays the result for each roll)

--version
       prints the version of the program

Expressions

Expressions are in dice notation (also known as dice algebra, common dice notation or RPG dice notation).

Die rolls are expressed in the form NdX or NDX where N is the number of dices (1 if omitted) and X the number of dice faces.

roll also accepts W (German) or T (Swedish) to specify a dice (D in English)

If the final number is omitted, it is assumed to be a six.

To this basic notation, an additive modifier can be appended, yielding expressions of the form, NdX+C. The plus can be replaced by a minus sign ("-") for subtraction. C is a number to be added subtracted from the final total.

See: http://en.wikipedia.org/wiki/Dice_notation

Percentile dice (d%)

Often, the variable X in the above notation will be "%". Although a 100-sided die does exist, it is both more common and more uniformly random to use a combination of two ten-sided dice known as percentile dice, where one die represents tens and the other units. A roll of two zeroes means 100.

If you want to roll a single 100-sided die use the "d100" notation.

d10x

d10x is equivalent to d10 x d10 and gives a non-linear distribution.

Fudge dice (dF or df)

The Fudge role-playing game system uses customized "Fudge dice" which have an equal number of plus, minus and blank sides.

Multipliers

In some games, the above notation is expanded to allow for a multiplier, as in NdXxC or CxNdX, where "x" or "*" denotes multiplication (can be replaced by "/" for division) and C is a natural number.

Results are rounded up.

Reroll filters

It is possible to specify restrictions on dice rolls telling which values to keep and which values to discard by putting a filter after the dice. If a value is to be discarded the dice is re-rolled until the result is valid value. You can specify to keep only values bigger (>), bigger or equal (>=), smaller (<), smaller or equal (<=) or different (!=) from a given number. The comparator is specified right after the the die specification (e.g., 1D6>2).

Selective results

It is possible to keep only the M highest or lowest dices with the following notation:

  • NdXhM: roll N dices with X sides and keep the highest M results (M must be less or equal N)
  • NdXkM: K for keep is equivalent to H for highest
  • NdXlM: roll N dices with X sides and keep the lowest M results (M must be less or equal N)

Or using the abbreviated notation NdX-L to drop the lowest and NdX-H to drop the highest result.

Series and repetitions

It is possible to concatenate top-level expressions with a comma ("expression, expression") and to repeat the execution of an expression or a set of expressions by using a counter and curly brackets ("N{ expression}")

Examples

3d6        rolls 3 6-sided dices and sums the results
           (can be abbreviated with "3d")
1d8 + 3    rolls 1 8-sided die and adds 3
                  (can be abbreviated by "d8+3")
d%         rolls 2 10-sided dices: one represents the tens and
           the other units
1d6x5      rolls 1 6-sided dice and multiplies the result by 5
1d6 / 2    rolls 1 6-sided dice and divides the result by 2 (1d3)
4d6h3      rolls 4 6-sided dices and keeps the 3 highest results
           (discarding the lowest)
4d6-L      rolls 4 6-sided dices and discards the lowest
"6{3d6}"   rolls 3d6 6 times (expression
           is quoted to avoid the > being interpreted as
           redirection by the shell)
"1d6>2"    rolls 1d6 until the result is bigger than 2 (expression
           is quoted to avoid the > being interpreted as
           redirection by the shell)
4DF        rolls 4 Fudge dices
10dx       rolls 2 ten-sided dices and multiply the results

Grammar (EBNF)

expression   := term { "+" term | "-" term } .
term         := number | factor [ ("*"|"/") number |
                number ("*"|"/") factor | "(" expression ")" .
factor       := number FilteredDice [ ("h"|"H"|"l"|"L"|"k"|"K") number ] | number FilteredDice "-" [ ("h"|"H"|"l"|"L") | FilteredDice .
FilteredDice := dice | dice (">"|">="|"<"|"<="|"!=") number .
dice         := "d" | "D" | "w" | "W" | "t" | "T" [ number | "%" | "F" | "f" | "x" | "X" ]