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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 reverse-polish desk calculator which supports unlimited preci-
sion arithmetic. It also allows you to define and call macros. Nor-
mally dc reads from the standard input; if any command arguments are
given to it, they are filenames, and dc reads and executes the con-
tents of the files before reading from standard input. All normal
output is to standard output; all error output is to standard error.
A reverse-polish 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 num-
bers in succession, separate them with spaces or newlines. These have
no meaning as commands.
OPTIONS
Dc may be invoked with the following command-line 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 command-line
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 script-file
--file=script-file
Add the commands contained in the file script-file to the set
of commands to be run while processing the input.
If any command-line 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 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 8-bit
bytes), the sequence KSK 0k1/ [_1*]sx d0>x [256~aPd0as 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 divi-
sion 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 frac-
tion 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 non-zero number, and should be an integer. The sec-
ond 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 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 subtrac-
tion 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 regis-
ter 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 in the result of most arithmetic opera-
tions. 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 mea-
sured 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 bal-
anced [ and ] characters), and pushes it on the stack. For
example, [foo]P prints the characters foo (with no newline).
a The top-of-stack is popped. If it was a number, then the low-
order byte of this number is converted into a string and pushed
onto the stack. Otherwise the top-of-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. Nor-
mally 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 top-of-stack 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 top-of-stack is
not greater than (less than or equal to) what was the second-
to-top.
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 second-
to-top value will be stored in the array r, indexed by the old
top-of-stack value.
;r Pops the top-of-stack 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 asso-
ciated 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 bug-dc@gnu.org.
GNU Project 1997-03-25 DC(1)
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