dc
SYNOPSIS dc [V] [version] [h] [help]
[e scriptexpression] [expression=scriptexpression]
[f scriptfile] [file=scriptfile]
[file ...]
DESCRIPTION Dc is a reversepolish desk calculator which supports
unlimited precision arithmetic. It also allows you to
define and call macros. Normally dc reads from the stan
dard input; if any command arguments are given to it, they
are filenames, and dc reads and executes the contents of
the files before reading from standard input. All normal
output is to standard output; all error output is to stan
dard error.
A reversepolish calculator stores numbers on a stack.
Entering a number pushes it on the stack. Arithmetic
operations pop arguments off the stack and push the
results.
To enter a number in dc, type the digits with an optional
decimal point. Exponential notation is not supported. To
enter a negative number, begin the number with ``_''.
``'' cannot be used for this, as it is a binary operator
for subtraction instead. To enter two numbers in succes
sion, separate them with spaces or newlines. These have
no meaning as commands.
OPTIONS Dc may be invoked with the following commandline options:
V
version
Print out the version of dc that is being run and a
copyright notice, then exit.
h
help Print a usage message briefly summarizing these
commandline options and the bugreporting address,
then exit.
e script
expression=script
Add the commands in script to the set of commands
to be run while processing the input.
f scriptfile
value.
n Prints the value on the top of the stack, popping
it off, and does not print a newline after.
P Pops off the value on top of the stack. If it it a
string, it is simply printed without a trailing
newline. Otherwise it is a number, and the integer
portion of its absolute value is printed out as a
"base (UCHAR_MAX+1)" byte stream. Assuming that
(UCHAR_MAX+1) is 256 (as it is on most machines
with 8bit bytes), the sequence KSK 0k1/ [_1*]sx
d0>x [256~aPd0<x]dsxx sxLKk could also accomplish
this function, except for the sideeffect of clob
bering the x register.
f Prints the entire contents of the stack without
altering anything. This is a good command to use
if you are lost or want to figure out what the
effect of some command has been.
Arithmetic + Pops two values off the stack, adds them, and
pushes the result. The precision of the result is
determined only by the values of the arguments, and
is enough to be exact.
 Pops two values, subtracts the first one popped
from the second one popped, and pushes the result.
* Pops two values, multiplies them, and pushes the
result. The number of fraction digits in the
result depends on the current precision value and
the number of fraction digits in the two arguments.
/ Pops two values, divides the second one popped from
the first one popped, and pushes the result. The
number of fraction digits is specified by the pre
cision value.
% Pops two values, computes the remainder of the
division that the / command would do, and pushes
that. The value computed is the same as that com
puted by the sequence Sd dld/ Ld* .
~ Pops two values, divides the second one popped from
the first one popped. The quotient is pushed
first, and the remainder is pushed next. The num
ber of fraction digits used in the division is
specified by the precision value. (The sequence
SdSn lnld/ LnLd% could also accomplish this func
tion, with slightly different error checking.)
popped is the base which gets exponentiated, which
should be an integer. For small integers this is
like the sequence Sm^Lm%, but, unlike ^, this com
mand will work with arbitrarily large exponents.
v Pops one value, computes its square root, and
pushes that. The precision value specifies the
number of fraction digits in the result.
Most arithmetic operations are affected by the ``precision
value'', which you can set with the k command. The
default precision value is zero, which means that all
arithmetic except for addition and subtraction produces
integer results.
Stack Control c Clears the stack, rendering it empty.
d Duplicates the value on the top of the stack, push
ing another copy of it. Thus, ``4d*p'' computes 4
squared and prints it.
r Reverses the order of (swaps) the top two values on
the stack.
Registers Dc provides at least 256 memory registers, each named by a
single character. You can store a number or a string in a
register and retrieve it later.
sr Pop the value off the top of the stack and store it
into register r.
lr Copy the value in register r and push it onto the
stack. This does not alter the contents of r.
Each register also contains its own stack. The current
register value is the top of the register's stack.
Sr Pop the value off the top of the (main) stack and
push it onto the stack of register r. The previous
value of the register becomes inaccessible.
Lr Pop the value off the top of register r's stack and
push it onto the main stack. The previous value in
register r's stack, if any, is now accessible via
the lr command.
Parameters Dc has three parameters that control its operation: the
precision, the input radix, and the output radix. The
precision specifies the number of fraction digits to keep
to set the input radix.
o Pops the value off the top of the stack and uses it
to set the output radix.
k Pops the value off the top of the stack and uses it
to set the precision.
I Pushes the current input radix on the stack.
O Pushes the current output radix on the stack.
K Pushes the current precision on the stack.
Strings Dc can operate on strings as well as on numbers. The only
things you can do with strings are print them and execute
them as macros (which means that the contents of the
string are processed as dc commands). All registers and
the stack can hold strings, and dc always knows whether
any given object is a string or a number. Some commands
such as arithmetic operations demand numbers as arguments
and print errors if given strings. Other commands can
accept either a number or a string; for example, the p
command can accept either and prints the object according
to its type.
[characters]
Makes a string containing characters (contained
between balanced [ and ] characters), and pushes it
on the stack. For example, [foo]P prints the char
acters foo (with no newline).
a The topofstack is popped. If it was a number,
then the loworder byte of this number is converted
into a string and pushed onto the stack. Otherwise
the topofstack was a string, and the first char
acter of that string is pushed back.
x Pops a value off the stack and executes it as a
macro. Normally it should be a string; if it is a
number, it is simply pushed back onto the stack.
For example, [1p]x executes the macro 1p which
pushes 1 on the stack and prints 1 on a separate
line.
Macros are most often stored in registers; [1p]sa stores a
macro to print 1 into register a, and lax invokes this
macro.
>r Pops two values off the stack and compares them
assuming they are numbers, executing the contents
=r Similar but invokes the macro if the two numbers
popped are equal.
!=r Similar but invokes the macro if the two numbers
popped are not equal.
? Reads a line from the terminal and executes it.
This command allows a macro to request input from
the user.
q exits from a macro and also from the macro which
invoked it. If called from the top level, or from
a macro which was called directly from the top
level, the q command will cause dc to exit.
Q Pops a value off the stack and uses it as a count
of levels of macro execution to be exited. Thus,
3Q exits three levels. The Q command will never
cause dc to exit.
Status Inquiry Z Pops a value off the stack, calculates the number
of digits it has (or number of characters, if it is
a string) and pushes that number.
X Pops a value off the stack, calculates the number
of fraction digits it has, and pushes that number.
For a string, the value pushed is 0.
z Pushes the current stack depth: the number of
objects on the stack before the execution of the z
command.
Miscellaneous ! Will run the rest of the line as a system command.
Note that parsing of the !<, !=, and !> commands
take precedence, so if you want to run a command
starting with <, =, or > you will need to add a
space after the !.
# Will interpret the rest of the line as a comment.
:r Will pop the top two values off of the stack. The
old secondtotop value will be stored in the array
r, indexed by the old topofstack value.
;r Pops the topofstack and uses it as an index into
the array r. The selected value is then pushed
onto the stack.
Note that each stacked instance of a register has its own
