dc  an arbitrary precision calculator
dc [V] [version] [h] [help]
[e scriptexpression] [expression=scriptexpression]
[f scriptfile] [file=scriptfile]
[file ...]
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 standard 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.
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
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.
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 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 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 command has been.
+ 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 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 quotient 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 nonnegative
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 integer. For small integers this is
like the sequence Sm^Lm%, but, unlike ^, this command 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.
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.
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.
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 numbers 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.
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 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 topofstack 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, executing 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 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.
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.
! 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.
Email bug reports to bugdc@gnu.org.
GNU Project 19970325 DC(1)
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