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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 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 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 (using upper case letters A through F as "digits"
       when working with input bases greater than ten), with an optional decimal point.  Exponen-
       tial 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 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 script  files  or  expres-
       sions 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  8-bit  bytes),  the
	      sequence	    KSK0k1/_1Ss      [ls*]Sxd0>x     [256~Ssd0<x]dsxxsx[q]Sq[Lsd0>qaPlxx]
	      dsxxsx0sqLqsxLxLK+k could also accomplish this function.	(Much of  the  complexity
	      of the above native-dc code is due to the ~ computing the characters backwards, and
	      the desire to ensure that all registers wind up back in their original states.)

       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 non-zero 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.	(This can also be
	      accomplished with the sequence SaSbLaLb.)

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  has a limited ability to 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  con-
       tents  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  com-
       mands  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  com-
       mand 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  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.  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 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.

       <r     Similar but invokes the macro if the original top-of-stack is less.

       !<r    Similar but invokes the macro  if  the  original	top-of-stack  is  not  less  than
	      (greater than or equal to) what was the second-to-top.

       =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.  The digit count for a num-
	      ber does not include any leading zeros, even if those appear to the  right  of  the
	      radix point.

       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 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 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 bug-dc@gnu.org.

GNU Project				    2006-06-11					    dc(1)
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