Dc is an arbitrary precision arithmetic package. Ordinarily
it operates on decimal integers, but one may specify an input base, output
base, and a number of fractional digits to be maintained. The overall
structure of dc is a stacking (reverse Polish) calculator. If an
argument is given, input is taken from that file until its end, then from
the standard input. The following constructions are recognized:
number
The value of the number is pushed on the stack. A number is an unbroken string
of the digits 0-9. It may be preceded by an underscore _ to input a negative
number. Numbers may contain decimal points.
+ - / * % ^
The top two values on the stack are added (+), subtracted (-), multiplied (*),
divided (/), remaindered (%), or exponentiated (^). The two entries are
popped off the stack; the result is pushed on the stack in their place. Any
fractional part of an exponent is ignored.
- sx
- The top of the stack is popped and stored into a register named x,
where x may be any character. If the s is capitalized,
x is treated as a stack and the value is pushed on it.
- lx
- The value in register x is pushed on the stack. The register
x is not altered. All registers start with zero value. If the
l is capitalized, register x is treated as a stack and its
top value is popped onto the main stack.
- d
- The top value on the stack is duplicated.
- p
- The top value on the stack is printed. The top value remains unchanged.
P interprets the top of the stack as an ascii string, removes it,
and prints it.
- f
- All values on the stack and in registers are printed.
- q
- exits the program. If executing a string, the recursion level is popped by
two. If q is capitalized, the top value on the stack is popped and
the string execution level is popped by that value.
- x
- treats the top element of the stack as a character string and executes it
as a string of dc commands.
- X
- replaces the number on the top of the stack with its scale factor.
- [ ... ]
- puts the bracketed ascii string onto the top of the stack.
<x >x =x
The top two elements of the stack are popped and compared. Register x
is executed if they obey the stated relation.
- v
- replaces the top element on the stack by its square root. Any existing
fractional part of the argument is taken into account, but otherwise the
scale factor is ignored.
- !
- interprets the rest of the line as a UNIX command.
- c
- All values on the stack are popped.
- i
- The top value on the stack is popped and used as the number radix for
further input. I pushes the input base on the top of the
stack.
- o
- The top value on the stack is popped and used as the number radix for
further output.
- O
- pushes the output base on the top of the stack.
- k
- the top of the stack is popped, and that value is used as a non-negative
scale factor: the appropriate number of places are printed on output, and
maintained during multiplication, division, and exponentiation. The
interaction of scale factor, input base, and output base will be
reasonable if all are changed together.
- z
- The stack level is pushed onto the stack.
- Z
- replaces the number on the top of the stack with its length.
- ?
- A line of input is taken from the input source (usually the terminal) and
executed.
- ; :
- are used by bc for array operations.
An example which prints the first ten values of n! is
[la1+dsa*pla10>y]sy
0sa1
lyx
bc(1), which is a preprocessor for dc providing infix
notation and a C-like syntax which implements functions and reasonable
control structures for programs.
`x is unimplemented' where x is an octal number.
`stack empty' for not enough elements on the stack to do what was asked.
`Out of space' when the free list is exhausted (too many digits).
`Out of headers' for too many numbers being kept around.
`Out of pushdown' for too many items on the stack.
`Nesting Depth' for too many levels of nested execution.