dc

dc(1)                        General Commands Manual                       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 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 (using upper case letters A
       through F as "digits" when working with input bases greater than ten),
       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 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 expressions 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 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 command 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 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 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 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
              maximum of the precision value and the precision of the argument
              is used to determine 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.)

       R      Pops the top-of-stack as an integer n.  Cyclically rotates the top
              n items on the updated stack.  If n is positive, then the rotation
              direction will make the topmost element the second-from top; if n
              is negative, then the rotation will make the topmost element the
              n-th element from the top.  If the stack depth is less than n,
              then the entire stack is rotated (in the appropriate direction),
              without any error being reported.

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.  The
              value 0 is retrieved if the register is uninitialized.  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.

       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 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 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, 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.

       <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 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 decimal
              digits it has (or number of characters, if it is a string) and
              pushes that number.  The digit count for a number 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 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
       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                        2008-05-22                              dc(1)