bc(1)                                                                    bc(1)



NAME
       bc - An arbitrary precision calculator language

SYNTAX
       bc [ -hlwsqv ] [long-options] [  file ... ]

DESCRIPTION
       bc  is a language that supports arbitrary precision numbers with inter‐
       active execution of statements.  There are  some  similarities  in  the
       syntax  to  the  C  programming  language.   A standard math library is
       available by command line option.  If requested, the  math  library  is
       defined before processing any files.  bc starts by processing code from
       all the files listed on the command line in the  order  listed.   After
       all  files  have been processed, bc reads from the standard input.  All
       code is executed as it is read.  (If a file contains a command to  halt
       the processor, bc will never read from the standard input.)

       This  version  of  bc contains several extensions beyond traditional bc
       implementations and the POSIX draft standard.  Command line options can
       cause these extensions to print a warning or to be rejected.  This doc‐
       ument describes the language accepted by  this  processor.   Extensions
       will be identified as such.

   OPTIONS
       -h, --help
              Print the usage and exit.

       -i, --interactive
              Force interactive mode.

       -l, --mathlib
              Define the standard math library.

       -w, --warn
              Give warnings for extensions to POSIX bc.

       -s, --standard
              Process exactly the POSIX bc language.

       -q, --quiet
              Do not print the normal GNU bc welcome.

       -v, --version
              Print the version number and copyright and quit.

   NUMBERS
       The most basic element in bc is the number.  Numbers are arbitrary pre‐
       cision numbers.  This precision is both in the  integer  part  and  the
       fractional part.  All numbers are represented internally in decimal and
       all computation is done in decimal.  (This  version  truncates  results
       from divide and multiply operations.)  There are two attributes of num‐
       bers, the length and the scale.  The length is the total number of sig‐
       nificant  decimal  digits in a number and the scale is the total number
       of decimal digits after the decimal point.  For example:
               .000001 has a length of 6 and scale of 6.
               1935.000 has a length of 7 and a scale of 3.

   VARIABLES
       Numbers are stored in two types  of  variables,  simple  variables  and
       arrays.   Both  simple  variables and array variables are named.  Names
       begin with a letter followed by  any  number  of  letters,  digits  and
       underscores.   All  letters  must  be  lower case.  (Full alpha-numeric
       names are an extension. In POSIX bc all names are a single  lower  case
       letter.)   The  type  of  variable  is clear by the context because all
       array variable names will be followed by brackets ([]).

       There are four special variables, scale, ibase, obase, and last.  scale
       defines  how  some  operations use digits after the decimal point.  The
       default value of scale is 0. ibase and obase define the conversion base
       for input and output numbers.  The default for both input and output is
       base 10.  last (an extension) is a variable that has the value  of  the
       last  printed  number.  These will be discussed in further detail where
       appropriate.  All of these variables may have values assigned  to  them
       as well as used in expressions.

   COMMENTS
       Comments in bc start with the characters /* and end with the characters
       */.  Comments may start anywhere and appear as a single  space  in  the
       input.   (This causes comments to delimit other input items.  For exam‐
       ple, a comment can not be found in the  middle  of  a  variable  name.)
       Comments  include  any newlines (end of line) between the start and the
       end of the comment.

       To support the use of scripts for bc, a single line  comment  has  been
       added  as  an extension.  A single line comment starts at a # character
       and continues to the next end of the line.  The end of  line  character
       is not part of the comment and is processed normally.

   EXPRESSIONS
       The  numbers  are manipulated by expressions and statements.  Since the
       language was designed to be interactive, statements and expressions are
       executed  as  soon  as possible.  There is no "main" program.  Instead,
       code is executed as it is encountered.  (Functions, discussed in detail
       later, are defined when encountered.)

       A  simple  expression  is  just  a constant. bc converts constants into
       internal decimal numbers using the current input base, specified by the
       variable ibase. (There is an exception in functions.)  The legal values
       of ibase are 2 through 16.  Assigning a value  outside  this  range  to
       ibase will result in a value of 2 or 16.  Input numbers may contain the
       characters 0-9 and A-F. (Note: They must be capitals.  Lower case  let‐
       ters  are  variable names.)  Single digit numbers always have the value
       of the digit regardless of the value of ibase.  (i.e.  A  =  10.)   For
       multi-digit  numbers,  bc  changes all input digits greater or equal to
       ibase to the value of ibase-1.  This makes the number FFF always be the
       largest 3 digit number of the input base.

       Full expressions are similar to many other high level languages.  Since
       there is only one kind of number, there are no rules for mixing  types.
       Instead, there are rules on the scale of expressions.  Every expression
       has a scale.  This is derived from the scale of original  numbers,  the
       operation performed and in many cases, the value of the variable scale.
       Legal values of the variable scale are 0 to the maximum  number  repre‐
       sentable by a C integer.

       In  the following descriptions of legal expressions, "expr" refers to a
       complete expression and "var" refers to a simple or an array  variable.
       A simple variable is just a
              name
       and an array variable is specified as
              name[expr]
       Unless  specifically  mentioned  the scale of the result is the maximum
       scale of the expressions involved.

       - expr The result is the negation of the expression.

       ++ var The variable is incremented by one and  the  new  value  is  the
              result of the expression.

       -- var The  variable  is  decremented  by  one and the new value is the
              result of the expression.

       var ++
               The result of the expression is the value of the  variable  and
              then the variable is incremented by one.

       var -- The  result  of  the expression is the value of the variable and
              then the variable is decremented by one.

       expr + expr
              The result of the expression is the sum of the two expressions.

       expr - expr
              The result of the  expression  is  the  difference  of  the  two
              expressions.

       expr * expr
              The  result  of the expression is the product of the two expres‐
              sions.

       expr / expr
              The result of the expression is the quotient of the two  expres‐
              sions.   The  scale  of  the result is the value of the variable
              scale.

       expr % expr
              The result of the expression is the "remainder" and it  is  com‐
              puted  in  the following way.  To compute a%b, first a/b is com‐
              puted to scale digits.  That result is used to compute a-(a/b)*b
              to  the scale of the maximum of scale+scale(b) and scale(a).  If
              scale is set to zero and  both  expressions  are  integers  this
              expression is the integer remainder function.

       expr ^ expr
              The result of the expression is the value of the first raised to
              the second. The second expression must be an integer.   (If  the
              second  expression is not an integer, a warning is generated and
              the expression is truncated to get an integer value.)  The scale
              of  the  result  is  scale  if the exponent is negative.  If the
              exponent is positive the scale of the result is the  minimum  of
              the  scale  of the first expression times the value of the expo‐
              nent and the maximum of scale and the scale of the first expres‐
              sion.    (e.g.   scale(a^b)   =   min(scale(a)*b,   max(  scale,
              scale(a))).)  It should be noted that expr^0 will always  return
              the value of 1.

       ( expr )
              This  alters  the standard precedence to force the evaluation of
              the expression.

       var = expr
              The variable is assigned the value of the expression.

       var = expr
              This is equivalent to "var = var  expr" with  the  exception
              that  the  "var"  part  is evaluated only once.  This can make a
              difference if "var" is an array.

       Relational expressions are a special kind  of  expression  that  always
       evaluate to 0 or 1, 0 if the relation is false and 1 if the relation is
       true.  These may appear in any legal expression.   (POSIX  bc  requires
       that  relational expressions are used only in if, while, and for state‐
       ments and that only one relational test may  be  done  in  them.)   The
       relational operators are

       expr1 < expr2
              The result is 1 if expr1 is strictly less than expr2.

       expr1 <= expr2
              The result is 1 if expr1 is less than or equal to expr2.

       expr1 > expr2
              The result is 1 if expr1 is strictly greater than expr2.

       expr1 >= expr2
              The result is 1 if expr1 is greater than or equal to expr2.

       expr1 == expr2
              The result is 1 if expr1 is equal to expr2.

       expr1 != expr2
              The result is 1 if expr1 is not equal to expr2.

       Boolean  operations  are  also  legal.  (POSIX bc does NOT have boolean
       operations). The result of all boolean operations  are  0  and  1  (for
       false  and  true)  as in relational expressions.  The boolean operators
       are:

       !expr  The result is 1 if expr is 0.

       expr && expr
              The result is 1 if both expressions are non-zero.

       expr || expr
              The result is 1 if either expression is non-zero.

       The expression precedence is as follows: (lowest to highest)
              || operator, left associative
              && operator, left associative
              ! operator, nonassociative
              Relational operators, left associative
              Assignment operator, right associative
              + and - operators, left associative
              *, / and % operators, left associative
              ^ operator, right associative
              unary - operator, nonassociative
              ++ and -- operators, nonassociative

       This precedence was chosen so that POSIX compliant bc programs will run
       correctly. This will cause the use of the relational and logical opera‐
       tors to have some unusual behavior when used  with  assignment  expres‐
       sions.  Consider the expression:
              a = 3 < 5

       Most C programmers would assume this would assign the result of "3 < 5"
       (the value 1) to the variable "a".  What this does in bc is assign  the
       value 3 to the variable "a" and then compare 3 to 5.  It is best to use
       parenthesis when  using  relational  and  logical  operators  with  the
       assignment operators.

       There  are  a  few  more  special  expressions that are provided in bc.
       These have to do with user defined functions  and  standard  functions.
       They  all  appear  as "name(parameters)".  See the section on functions
       for user defined functions.  The standard functions are:

       length ( expression )
              The value of the length function is the  number  of  significant
              digits in the expression.

       read ( )
              The  read  function  (an  extension) will read a number from the
              standard  input,  regardless  of  where  the  function   occurs.
              Beware, this can cause problems with the mixing of data and pro‐
              gram in the standard input.  The best use for this  function  is
              in  a previously written program that needs input from the user,
              but never allows program code to be input from  the  user.   The
              value  of the read function is the number read from the standard
              input using the current value of the variable ibase for the con‐
              version base.

       scale ( expression )
              The  value  of  the scale function is the number of digits after
              the decimal point in the expression.

       sqrt ( expression )
              The value of the sqrt function is the square root of the expres‐
              sion.  If the expression is negative, a run time error is gener‐
              ated.

   STATEMENTS
       Statements (as in most algebraic languages) provide the  sequencing  of
       expression  evaluation.  In bc statements are executed "as soon as pos‐
       sible."  Execution happens when a newline in encountered and  there  is
       one or more complete statements.  Due to this immediate execution, new‐
       lines are very important in bc. In fact, both a semicolon and a newline
       are  used  as  statement separators.  An improperly placed newline will
       cause a syntax error.  Because newlines are statement separators, it is
       possible  to  hide  a  newline  by  using the backslash character.  The
       sequence "\", where  is the newline appears to bc as whitespace
       instead of a newline.  A statement list is a series of statements sepa‐
       rated by semicolons and newlines.  The following is a list of bc state‐
       ments  and what they do: (Things enclosed in brackets ([]) are optional
       parts of the statement.)

       expression
              This statement does one of two things.  If the expression starts
              with  "    ...", it is considered to be an
              assignment statement.  If the expression is  not  an  assignment
              statement,  the  expression is evaluated and printed to the out‐
              put.  After the number is printed, a newline  is  printed.   For
              example,  "a=1"  is  an  assignment  statement and "(a=1)" is an
              expression that has an embedded assignment.   All  numbers  that
              are  printed  are  printed in the base specified by the variable
              obase. The legal values for obase  are  2  through  BC_BASE_MAX.
              (See  the  section  LIMITS.)   For bases 2 through 16, the usual
              method of writing numbers is used.  For bases greater  than  16,
              bc  uses  a multi-character digit method of printing the numbers
              where each higher base digit is printed as  a  base  10  number.
              The  multi-character digits are separated by spaces.  Each digit
              contains the number of characters required to represent the base
              ten  value  of "obase-1".  Since numbers are of arbitrary preci‐
              sion, some numbers may not be printable on a single output line.
              These  long  numbers will be split across lines using the "\" as
              the last character on a line.  The maximum number of  characters
              printed  per  line  is 70.  Due to the interactive nature of bc,
              printing a number  causes  the  side  effect  of  assigning  the
              printed value to the special variable last. This allows the user
              to recover the last value printed without having to  retype  the
              expression  that printed the number.  Assigning to last is legal
              and will overwrite the last  printed  value  with  the  assigned
              value.  The newly assigned value will remain until the next num‐
              ber is printed or another value  is  assigned  to  last.   (Some
              installations  may allow the use of a single period (.) which is
              not part of a number as a short hand notation for for last.)

       string The string is printed to the output.  Strings start with a  dou‐
              ble  quote  character  and contain all characters until the next
              double quote character.   All  characters  are  take  literally,
              including  any  newline.   No newline character is printed after
              the string.

       print list
              The print statement (an extension) provides  another  method  of
              output.   The  "list" is a list of strings and expressions sepa‐
              rated by commas.  Each string or expression is  printed  in  the
              order  of the list.  No terminating newline is printed.  Expres‐
              sions are evaluated and their value is printed and  assigned  to
              the variable last. Strings in the print statement are printed to
              the output and may contain special characters.  Special  charac‐
              ters  start with the backslash character (\).  The special char‐
              acters  recognized  by  bc  are  "a"  (alert   or   bell),   "b"
              (backspace),  "f"  (form  feed),  "n"  (newline),  "r" (carriage
              return), "q" (double quote), "t"  (tab),  and  "\"  (backslash).
              Any other character following the backslash will be ignored.

       { statement_list }
              This  is  the compound statement.  It allows multiple statements
              to be grouped together for execution.

       if ( expression ) statement1 [else statement2]
              The if statement evaluates the expression  and  executes  state‐
              ment1  or  statement2  depending on the value of the expression.
              If the expression  is  non-zero,  statement1  is  executed.   If
              statement2 is present and the value of the expression is 0, then
              statement2 is executed.  (The else clause is an extension.)

       while ( expression ) statement
              The while statement will execute the statement while the expres‐
              sion  is non-zero.  It evaluates the expression before each exe‐
              cution of the statement.   Termination of the loop is caused  by
              a zero expression value or the execution of a break statement.

       for ( [expression1] ; [expression2] ; [expression3] ) statement
              The  for statement controls repeated execution of the statement.
              Expression1 is evaluated before the loop.  Expression2 is evalu‐
              ated before each execution of the statement.  If it is non-zero,
              the statement is evaluated.  If it is zero, the loop  is  termi‐
              nated.   After  each  execution of the statement, expression3 is
              evaluated before the reevaluation of  expression2.   If  expres‐
              sion1  or  expression3  are missing, nothing is evaluated at the
              point they would be evaluated.  If expression2 is missing, it is
              the  same  as  substituting  the  value 1 for expression2.  (The
              optional expressions are an extension.  POSIX  bc  requires  all
              three  expressions.)   The  following is equivalent code for the
              for statement:
              expression1;
              while (expression2) {
                 statement;
                 expression3;
              }

       break  This statement causes a forced exit of the most recent enclosing
              while statement or for statement.

       continue
              The  continue  statement  (an extension)  causes the most recent
              enclosing for statement to start the next iteration.

       halt   The halt statement (an extension) is an executed statement  that
              causes  the  bc processor to quit only when it is executed.  For
              example, "if (0 == 1) halt"  will  not  cause  bc  to  terminate
              because the halt is not executed.

       return Return  the  value 0 from a function.  (See the section on func‐
              tions.)

       return ( expression )
              Return the value of the expression from a  function.   (See  the
              section on functions.)  As an extension, the parenthesis are not
              required.

   PSEUDO STATEMENTS
       These statements are not statements in the traditional sense.  They are
       not  executed  statements.   Their  function  is performed at "compile"
       time.

       limits Print the local limits enforced by  the  local  version  of  bc.
              This is an extension.

       quit   When the quit statement is read, the bc processor is terminated,
              regardless of where the quit statement is found.   For  example,
              "if (0 == 1) quit" will cause bc to terminate.

       warranty
              Print a longer warranty notice.  This is an extension.

   FUNCTIONS
       Functions  provide  a method of defining a computation that can be exe‐
       cuted later.  Functions in bc always compute a value and return  it  to
       the  caller.   Function  definitions  are "dynamic" in the sense that a
       function is undefined until a definition is encountered in  the  input.
       That  definition is then used until another definition function for the
       same name is encountered.  The new definition then replaces  the  older
       definition.  A function is defined as follows:
              define name ( parameters ) { newline
                  auto_list   statement_list }
       A function call is just an expression of the form "name(parameters)".

       Parameters are numbers or arrays (an extension).  In the function defi‐
       nition, zero or more parameters are defined by listing their names sep‐
       arated by commas.  All parameters are call by value parameters.  Arrays
       are specified in the parameter definition  by  the  notation  "name[]".
       In the function call, actual parameters are full expressions for number
       parameters.  The same notation is used for passing arrays as for defin‐
       ing  array parameters.  The named array is passed by value to the func‐
       tion.  Since function definitions are dynamic,  parameter  numbers  and
       types are checked when a function is called.  Any mismatch in number or
       types of parameters will cause a runtime error.  A runtime  error  will
       also occur for the call to an undefined function.

       The  auto_list  is  an  optional list of variables that are for "local"
       use.  The syntax of the auto list (if present) is "auto name,  ...  ;".
       (The  semicolon  is  optional.)  Each name is the name of an auto vari‐
       able.  Arrays may be specified by using the same notation  as  used  in
       parameters.   These  variables have their values pushed onto a stack at
       the start of the function.  The variables are then initialized to  zero
       and  used  throughout the execution of the function.  At function exit,
       these variables are popped so that the original value (at the  time  of
       the function call) of these variables are restored.  The parameters are
       really auto variables that are initialized to a value provided  in  the
       function  call.   Auto  variables  are different than traditional local
       variables because if function A calls function B, B may access function
       A's  auto  variables by just using the same name, unless function B has
       called them auto variables.  Due to the fact that  auto  variables  and
       parameters are pushed onto a stack, bc supports recursive functions.

       The  function  body  is a list of bc statements.  Again, statements are
       separated by semicolons or newlines.  Return statements cause the  ter‐
       mination  of  a function and the return of a value.  There are two ver‐
       sions of the return statement.  The first form, "return",  returns  the
       value  0 to the calling expression.  The second form, "return ( expres‐
       sion )", computes the value of the expression and returns that value to
       the calling expression.  There is an implied "return (0)" at the end of
       every function.  This allows a function to terminate and return 0 with‐
       out an explicit return statement.

       Functions  also  change the usage of the variable ibase.  All constants
       in the function body will be converted using the value of ibase at  the
       time of the function call.  Changes of ibase will be ignored during the
       execution of the function except for the standard function read,  which
       will always use the current value of ibase for conversion of numbers.

       Several  extensions have been added to functions.  First, the format of
       the definition has been slightly relaxed.  The  standard  requires  the
       opening  brace  be on the same line as the define keyword and all other
       parts must be on following lines.  This version of bc  will  allow  any
       number  of newlines before and after the opening brace of the function.
       For example, the following definitions are legal.
              define d (n) { return (2*n); }
              define d (n)
                { return (2*n); }

       Functions may be defined as void.  A void funtion returns no value  and
       thus  may not be used in any place that needs a value.  A void function
       does not produce any output when called by itself  on  an  input  line.
       The  key  word void is placed between the key word define and the func‐
       tion name.  For example, consider the following session.
              define py (y) { print "--->", y, "<---", "0; }
              define void px (x) { print "--->", x, "<---", "0; }
              py(1)
              --->1<---
              0
              px(1)
              --->1<---
       Since py is not a void function, the call of py(1) prints  the  desired
       output and then prints a second line that is the value of the function.
       Since the value of a function that is  not  given  an  explicit  return
       statement  is zero, the zero is printed.  For px(1), no zero is printed
       because the function is a void function.

       Also, call by variable for arrays was added.   To  declare  a  call  by
       variable  array, the declaration of the array parameter in the function
       definition looks like "*name[]".  The call to the function remains  the
       same as call by value arrays.

   MATH LIBRARY
       If  bc  is  invoked with the -l option, a math library is preloaded and
       the default scale is set to 20.   The  math  functions  will  calculate
       their  results  to  the  scale set at the time of their call.  The math
       library defines the following functions:

       s (x)  The sine of x, x is in radians.

       c (x)  The cosine of x, x is in radians.

       a (x)  The arctangent of x, arctangent returns radians.

       l (x)  The natural logarithm of x.

       e (x)  The exponential function of raising e to the value x.

       j (n,x)
              The Bessel function of integer order n of x.

   EXAMPLES
       In /bin/sh,  the following will assign the value of "pi" to  the  shell
       variable pi.
               pi=$(echo "scale=10; 4*a(1)" | bc -l)

       The following is the definition of the exponential function used in the
       math library.  This function is written in POSIX bc.
              scale = 20

              /* Uses the fact that e^x = (e^(x/2))^2
                 When x is small enough, we use the series:
                   e^x = 1 + x + x^2/2! + x^3/3! + ...
              */

              define e(x) {
                auto  a, d, e, f, i, m, v, z

                /* Check the sign of x. */
                if (x<0) {
                  m = 1
                  x = -x
                }

                /* Precondition x. */
                z = scale;
                scale = 4 + z + .44*x;
                while (x > 1) {
                  f += 1;
                  x /= 2;
                }

                /* Initialize the variables. */
                v = 1+x
                a = x
                d = 1

                for (i=2; 1; i++) {
                  e = (a *= x) / (d *= i)
                  if (e == 0) {
                    if (f>0) while (f--)  v = v*v;
                    scale = z
                    if (m) return (1/v);
                    return (v/1);
                  }
                  v += e
                }
              }

       The following is code that uses the extended features of bc  to  imple‐
       ment a simple program for calculating checkbook balances.  This program
       is best kept in a file so that it can be used many times without having
       to retype it at every use.
              scale=2
              print "\nCheck book program!\n"
              print "  Remember, deposits are negative transactions.\n"
              print "  Exit by a 0 transaction.\n\n"

              print "Initial balance? "; bal = read()
              bal /= 1
              print "\n"
              while (1) {
                "current balance = "; bal
                "transaction? "; trans = read()
                if (trans == 0) break;
                bal -= trans
                bal /= 1
              }
              quit

       The following is the definition of the recursive factorial function.
              define f (x) {
                if (x <= 1) return (1);
                return (f(x-1) * x);
              }

   READLINE AND LIBEDIT OPTIONS
       GNU bc can be compiled (via a configure option) to use the GNU readline
       input editor library or the BSD libedit library.  This allows the  user
       to do editing of lines before sending them to bc.  It also allows for a
       history of previous lines typed.  When this option is selected, bc  has
       one  more special variable.  This special variable, history is the num‐
       ber of lines of history retained.  For readline, a value  of  -1  means
       that  an  unlimited  number of history lines are retained.  Setting the
       value of history to a positive number restricts the number  of  history
       lines  to  the  number given.  The value of 0 disables the history fea‐
       ture.  The default value is 100. For more information,  read  the  user
       manuals  for  the GNU readline, history and BSD libedit libraries.  One
       can not enable both readline and libedit at the same time.

   DIFFERENCES
       This version of bc was implemented from the POSIX P1003.2/D11 draft and
       contains  several  differences and extensions relative to the draft and
       traditional implementations.  It is not implemented in the  traditional
       way  using  dc(1).   This  version is a single process which parses and
       runs a byte code translation of the  program.   There  is  an  "undocu‐
       mented"  option (-c) that causes the program to output the byte code to
       the standard output instead of running it.   It  was  mainly  used  for
       debugging the parser and preparing the math library.

       A  major  source  of  differences  is  extensions,  where  a feature is
       extended to add more functionality and additions,  where  new  features
       are added.  The following is the list of differences and extensions.

       LANG environment
              This  version does not conform to the POSIX standard in the pro‐
              cessing of the LANG environment  variable  and  all  environment
              variables starting with LC_.

       names  Traditional and POSIX bc have single letter names for functions,
              variables and arrays.  They have been extended to be multi-char‐
              acter  names  that  start with a letter and may contain letters,
              numbers and the underscore character.

       Strings
              Strings are not allowed to contain NUL characters.   POSIX  says
              all characters must be included in strings.

       last   POSIX bc does not have a last variable.  Some implementations of
              bc use the period (.) in a similar way.

       comparisons
              POSIX bc allows comparisons only in the if statement, the  while
              statement,  and  the  second  expression  of  the for statement.
              Also, only one relational operation is allowed in each of  those
              statements.

       if statement, else clause
              POSIX bc does not have an else clause.

       for statement
              POSIX  bc  requires  all  expressions  to  be present in the for
              statement.

       &&, ||, !
              POSIX bc does not have the logical operators.

       read function
              POSIX bc does not have a read function.

       print statement
              POSIX bc does not have a print statement .

       continue statement
              POSIX bc does not have a continue statement.

       return statement
              POSIX bc requires parentheses around the return expression.

       array parameters
              POSIX bc does not (currently) support array parameters in  full.
              The POSIX grammar allows for arrays in function definitions, but
              does not provide a method to  specify  an  array  as  an  actual
              parameter.   (This  is most likely an oversight in the grammar.)
              Traditional implementations of bc have only call by value  array
              parameters.

       function format
              POSIX  bc  requires  the  opening  brace on the same line as the
              define key word and the auto statement on the next line.

       =+, =-, =*, =/, =%, =^
              POSIX bc does not require these "old style" assignment operators
              to be defined.  This version may allow these "old style" assign‐
              ments.  Use the limits statement to see if the installed version
              supports  them.   If  it does support the "old style" assignment
              operators, the statement "a =- 1" will decrement a by 1  instead
              of setting a to the value -1.

       spaces in numbers
              Other  implementations of bc allow spaces in numbers.  For exam‐
              ple, "x=1 3" would assign the value 13 to the variable  x.   The
              same statement would cause a syntax error in this version of bc.

       errors and execution
              This  implementation  varies from other implementations in terms
              of what code will be executed when syntax and other  errors  are
              found  in the program.  If a syntax error is found in a function
              definition, error recovery tries to  find  the  beginning  of  a
              statement  and  continue  to  parse the function.  Once a syntax
              error is found  in  the  function,  the  function  will  not  be
              callable  and  becomes undefined.  Syntax errors in the interac‐
              tive execution code will invalidate the current execution block.
              The execution block is terminated by an end of line that appears
              after a complete sequence of statements.  For example,
              a = 1
              b = 2
       has two execution blocks and
              { a = 1
                b = 2 }
       has one execution block.  Any runtime error will terminate  the  execu‐
       tion of the current execution block.  A runtime warning will not termi‐
       nate the current execution block.

       Interrupts
              During an interactive session, the SIGINT signal (usually gener‐
              ated  by  the  control-C character from the terminal) will cause
              execution of the current execution block to be interrupted.   It
              will  display  a  "runtime"  error indicating which function was
              interrupted.  After all runtime structures have been cleaned up,
              a  message  will  be printed to notify the user that bc is ready
              for more input.  All previously defined functions remain defined
              and  the  value  of  all non-auto variables are the value at the
              point of interruption.  All auto variables and function  parame‐
              ters  are  removed  during  the clean up process.  During a non-
              interactive session, the SIGINT signal will terminate the entire
              run of bc.

   LIMITS
       The  following are the limits currently in place for this bc processor.
       Some of them may have been changed by an installation.  Use the  limits
       statement to see the actual values.

       BC_BASE_MAX
              The  maximum  output  base is currently set at 999.  The maximum
              input base is 16.

       BC_DIM_MAX
              This is currently an arbitrary limit of  65535  as  distributed.
              Your installation may be different.

       BC_SCALE_MAX
              The  number  of  digits  after  the  decimal point is limited to
              INT_MAX digits.  Also, the number of digits before  the  decimal
              point is limited to INT_MAX digits.

       BC_STRING_MAX
              The  limit  on  the  number of characters in a string is INT_MAX
              characters.

       exponent
              The value of the exponent in the raise operation (^) is  limited
              to LONG_MAX.

       variable names
              The  current  limit  on  the number of unique names is 32767 for
              each of simple variables, arrays and functions.

ENVIRONMENT VARIABLES
       The following environment variables are processed by bc:

       POSIXLY_CORRECT
              This is the same as the -s option.

       BC_ENV_ARGS
              This is another mechanism to get arguments to bc.  The format is
              the  same  as  the  command line arguments.  These arguments are
              processed first, so any files listed in  the  environment  argu‐
              ments  are  processed  before  any  command line argument files.
              This allows the user to set up "standard" options and  files  to
              be  processed at every invocation of bc.  The files in the envi‐
              ronment variables would typically contain  function  definitions
              for functions the user wants defined every time bc is run.

       BC_LINE_LENGTH
              This should be an integer specifying the number of characters in
              an output line for numbers. This includes the backslash and new‐
              line characters for long numbers.  As an extension, the value of
              zero disables the multi-line feature.  Any other value  of  this
              variable that is less than 3 sets the line length to 70.

DIAGNOSTICS
       If  any file on the command line can not be opened, bc will report that
       the file is unavailable and terminate.  Also, there are compile and run
       time diagnostics that should be self-explanatory.

BUGS
       Error recovery is not very good yet.

       Email  bug  reports  to  bug-bc@gnu.org.   Be  sure to include the word
       ``bc'' somewhere in the ``Subject:'' field.

AUTHOR
       Philip A. Nelson
       philnelson@acm.org

ACKNOWLEDGEMENTS
       The author would like to thank  Steve  Sommars  (Steve.Sommars@att.com)
       for  his extensive help in testing the implementation.  Many great sug‐
       gestions were given.  This is a much better product due to his involve‐
       ment.



GNU Project                       2006-06-11                             bc(1)