DragonFly On-Line Manual Pages
DC(1) DragonFly General Commands Manual DC(1)
NAME
dc -- desk calculator
SYNOPSIS
dc [-x] [-e expression] [file]
DESCRIPTION
dc is an arbitrary precision arithmetic package. The overall structure
of dc is a stacking (reverse Polish) calculator i.e. numbers are stored
on a stack. Adding a number pushes it onto the stack. Arithmetic opera-
tions pop arguments off the stack and push the results. See also the
bc(1) utility, which is a preprocessor for dc providing infix notation
and a C-like syntax which implements functions and reasonable control
structures for programs. The options are as follows:
-e expression
Evaluate expression. If multiple -e options are specified, they
will be processed in the order given. If no file argument is
given, execution will stop after processing the expressions given
on the command line, otherwise processing will continue with the
contents of file.
-x Enable extended register mode. This mode is used by bc(1) to
allow more than 256 registers. See Registers for a more detailed
description.
Ordinarily, dc operates on decimal integers, but one may specify an input
base, output base, and a number of fractional digits (scale) to be main-
tained. If an argument is given, input is taken from that file until its
end, then from the standard input. Whitespace is ignored, expect where
it signals the end of a number, end of a line or when a register name is
expected. 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 and letters A-F. It may be
preceded by an underscore (`_') to input a negative number. A
number may contain a single decimal point. A number may also
contain the characters A-F, with the values 10-15.
* - / * % ~ ^
The top two values on the stack are added (+), subtracted (-),
multiplied (*), divided (/), remaindered (%), divided and remain-
dered (~), 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.
For addition and subtraction, the scale of the result is the max-
imum of scales of the operands. For division the scale of the
result is defined by the scale set by the k operation. For mul-
tiplication, the scale is defined by the expression
min(a+b,max(a,b,scale)), where a and b are the scales of the op-
erands, and scale is the scale defined by the k operation. For
exponentiation with a non-negative exponent, the scale of the
result is min(a*b,max(scale,a)), where a is the scale of the
base, and b is the value of the exponent. If the exponent is
negative, the scale of the result is the scale defined by the k
operation.
In the case of the division and modulus operator (~), the resul-
tant quotient is pushed first followed by the remainder. This is
a shorthand for the sequence:
x y / x y %
The division and modulus operator is a non-portable extension.
a Pop the top value from the stack. If that value is a number,
compute the integer part of the number modulo 256. If the result
is zero, push an empty string. Otherwise push a one character
string by interpreting the computed value as an ASCII character.
If the top value is a string, push a string containing the first
character of the original string. If the original string is
empty, an empty string is pushed back. The a operator is a non-
portable extension.
c All values on the stack are popped.
d The top value on the stack is duplicated.
f All values on the stack are printed, separated by newlines.
G The top two numbers are popped from the stack and compared. A
one is pushed if the top of the stack is equal to the second num-
ber on the stack. A zero is pushed otherwise. This is a non-
portable extension.
i The top value on the stack is popped and used as the base for
further input. The initial input base is 10.
I Pushes the input base on the top of the stack.
J Pop the top value from the stack. The recursion level is popped
by that value and, following that, the input is skipped until the
first occurrence of the M operator. The J operator is a non-por-
table extension, used by the bc(1) command.
K The current scale factor is pushed onto 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, divi-
sion, and exponentiation. The interaction of scale factor, input
base, and output base will be reasonable if all are changed
together.
Lx Register x is treated as a stack and its top value is popped onto
the main stack.
lx The value in register x is pushed on the stack. The register x
is not altered. Initially, all registers contain the value zero.
M Mark used by the J operator. The M operator is a non-portable
extensions, used by the bc(1) command.
N The top of the stack is replaced by one if the top of the stack
is equal to zero. If the top of the stack is unequal to zero, it
is replaced by zero. This is a non-portable extension.
n The top value on the stack is popped and printed without a new-
line. This is a non-portable extension.
O Pushes the output base on the top of the stack.
o The top value on the stack is popped and used as the base for
further output. The initial output base is 10.
P The top of the stack is popped. If the top of the stack is a
string, it is printed without a trailing newline. If the top of
the stack is a number, it is interpreted as a base 256 number,
and each digit of this base 256 number is printed as an ASCII
character, without a trailing newline.
p The top value on the stack is printed with a trailing newline.
The top value remains unchanged.
Q The top value on the stack is popped and the string execution
level is popped by that value.
q Exits the program. If executing a string, the recursion level is
popped by two.
R The top of the stack is removed (popped). This is a non-portable
extension.
r The top two values on the stack are reversed (swapped). This is
a non-portable extension.
Sx Register x is treated as a stack. The top value of the main
stack is popped and pushed on it.
sx The top of the stack is popped and stored into a register named
x.
v Replaces the top element on the stack by its square root. The
scale of the result is the maximum of the scale of the argument
and the current value of scale.
X Replaces the number on the top of the stack with its scale fac-
tor. If the top of the stack is a string, replace it with the
integer 0.
x Treats the top element of the stack as a character string and
executes it as a string of dc commands.
Z Replaces the number on the top of the stack with its length. The
length of a string is its number of characters. The length of a
number is its number of digits, not counting the minus sign and
decimal point.
z The stack level is pushed onto the stack.
[...] Puts the bracketed ASCII string onto the top of the stack. If
the string includes brackets, these must be properly balanced.
The backslash character (`\') may be used as an escape character,
making it possible to include unbalanced brackets in strings. To
include a backslash in a string, use a double backslash.
<x >x =x !<x !>x !=x
The top two elements of the stack are popped and compared. Reg-
ister x is executed if they obey the stated relation.
<xey >xey =xey !<xey !>xey !=xey
These operations are variants of the comparison operations above.
The first register name is followed by the letter `e' and another
register name. Register x will be executed if the relation is
true, and register y will be executed if the relation is false.
This is a non-portable extension.
( The top two numbers are popped from the stack and compared. A
one is pushed if the top of the stack is less than the second
number on the stack. A zero is pushed otherwise. This is a non-
portable extension.
{ The top two numbers are popped from the stack and compared. A
one is pushed if the top of stack is less than or equal to the
second number on the stack. A zero is pushed otherwise. This is
a non-portable extension.
! Interprets the rest of the line as a UNIX command.
? A line of input is taken from the input source (usually the ter-
minal) and executed.
:r Pop two values from the stack. The second value on the stack is
stored into the array r indexed by the top of stack.
;r Pop a value from the stack. The value is used as an index into
register r. The value in this register is pushed onto the stack.
Array elements initially have the value zero. Each level of a
stacked register has its own array associated with it. The com-
mand sequence
[first] 0:a [dummy] Sa [second] 0:a 0;a p La 0;a p
will print
second
first
since the string `second' is written in an array that is later
popped, to reveal the array that stored `first'.
# Skip the rest of the line. This is a non-portable extension.
Registers
Registers have a single character name x, where x may be any character,
including space, tab or any other special character. If extended regis-
ter mode is enabled using the -x option and the register identifier x has
the value 255, the next two characters are interpreted as a two-byte reg-
ister index. The set of standard single character registers and the set
of extended registers do not overlap. Extended register mode is a non-
portable extension.
EXAMPLES
An example which prints the first ten values of n!:
[la1+dsa*pla10>y]sy
0sa1
lyx
Independent of the current input base, the command
Ai
will reset the input base to decimal 10.
DIAGNOSTICS
%c (0%o) is unimplemented an undefined operation was called.
stack empty for not enough elements on the stack to do what was asked.
stack register '%c' (0%o) is empty for an L operation from a stack reg-
ister that is empty.
Runtime warning: non-zero scale in exponent for a fractional part of an
exponent that is being ignored.
divide by zero for trying to divide by zero.
remainder by zero for trying to take a remainder by zero.
square root of negative number for trying to take the square root of a
negative number.
index too big for an array index that is larger than 2048.
negative index for a negative array index.
input base must be a number between 2 and 16 for trying to set an ille-
gal input base.
output base must be a number greater than 1 for trying to set an illegal
output base.
scale must be a nonnegative number for trying to set a negative or zero
scale.
scale too large for trying to set a scale that is too large. A scale
must be representable as a 32-bit unsigned number.
Q command argument exceeded string execution depth for trying to pop the
recursion level more than the current recursion level.
Q command requires a number >= 1 for trying to pop an illegal number of
recursion levels.
recursion too deep for too many levels of nested execution.
The recursion level is increased by one if the x or ? operation or one of
the compare operations resulting in the execution of register is exe-
cuted. As an exception, the recursion level is not increased if the
operation is executed as the last command of a string. For example, the
commands
[lax]sa
1 lax
will execute an endless loop, while the commands
[laxp]sa
1 lax
will terminate because of a too deep recursion level.
J command argument exceeded string execution depth for trying to pop the
recursion level more than the current recursion level.
mark not found for a failed scan for an occurrence of the M operator.
SEE ALSO
bc(1)
L. L. Cherry and R. Morris, "DC - An Interactive Desk Calculator",
USD:05.
STANDARDS
The arithmetic operations of the dc utility are expected to conform to
the definition listed in the bc(1) section of the IEEE Std 1003.2
(``POSIX.2'') specification.
HISTORY
The dc command first appeared in Version 6 AT&T UNIX. A complete rewrite
of the dc command using the bn(3) big number routines first appeared in
OpenBSD 3.5.
AUTHORS
The original version of the dc command was written by Robert Morris and
Lorinda Cherry. The current version of the dc utility was written by
Otto Moerbeek.
DragonFly 3.5 October 10, 2004 DragonFly 3.5