
DC(1) DC(1)
NAME
dc  an arbitrary precision calculator
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 standard 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 stan
dard output; all error output is to standard 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 succession, 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 bug
reporting 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
file=scriptfile
Add the commands contained in the file scriptfile to the set of commands to be run
while processing the input.
If any commandline parameters remain after processing the above, these parameters are
interpreted as the names of input files to be processed. A file name of  refers to the
standard input stream. The standard input will processed if no file names are specified.
Printing Commands
p Prints the value on the top of the stack, without altering the stack. A newline is
printed after the value.
n Prints the value on the top of the stack, popping it off, and does not print a new
line 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 clobbering 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 com
mand 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 frac
tion 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 precision
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 computed by the
sequence Sd dld/ Ld* .
~ Pops two values, divides the second one popped from the first one popped. The quo
tient is pushed first, and the remainder is pushed next. The number of fraction
digits used in the division is specified by the precision value. (The sequence
SdSn lnld/ LnLd% could also accomplish this function, with slightly different error
checking.)
^ Pops two values and exponentiates, using the first value popped as the exponent and
the second popped as the base. The fraction part of the exponent is ignored. The
precision value specifies the number of fraction digits in the result.
 Pops three values and computes a modular exponentiation. The first value popped is
used as the reduction modulus; this value must be a nonzero number, and should be
an integer. The second popped is used as the exponent; this value must be a non
negative number, and any fractional part of this exponent will be ignored. The
third value popped is the base which gets exponentiated, which should be an inte
ger. 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, pushing 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 regis
ter 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 com
mand.
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 in the
result of most arithmetic operations. The input radix controls the interpretation of num
bers typed in; all numbers typed in use this radix. The output radix is used for printing
numbers.
The input and output radices are separate parameters; you can make them unequal, which can
be useful or confusing. The input radix must be between 2 and 16 inclusive. The output
radix must be at least 2. The precision must be zero or greater. The precision is always
measured in decimal digits, regardless of the current input or output radix.
i Pops the value off the top of the stack and uses it 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 ] charac
ters), and pushes it on the stack. For example, [foo]P prints the characters 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 topof
stack was a string, and the first character 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, execut
ing the contents of register r as a macro if the original topofstack is greater.
Thus, 1 2>a will invoke register a's contents and 2 1>a will not.
!>r Similar but invokes the macro if the original topofstack is not greater than
(less than or equal to) what was the secondtotop.
<r Similar but invokes the macro if the original topofstack is less.
!<r Similar but invokes the macro if the original topofstack is not less than
(greater than or equal to) what was the secondtotop.
=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 com
mand 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 exe
cution 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 array associated with it. Thus
1 0:a 0Sa 2 0:a La 0;ap will print 1, because the 2 was stored in an instance of 0:a that
was later popped.
BUGS
Email bug reports to bugdc@gnu.org.
GNU Project 19970325 DC(1) 
