dc  Unix, Linux Command
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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 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.
OPTIONS
Dc may be invoked with the following commandline options:
Tag  Description 
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.
Printing Commands
Tag  Description 
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.

Arithmetic
Tag  Description 
+ 
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.
Stack Control
Tag  Description 
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.
Tag  Description 
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 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.
Tag  Description 
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.
Tag  Description 
[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.

Status Inquiry
Tag  Description 
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
Tag  Description 
! 
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.
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