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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 interactive execu-
       tion 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  implementa-
       tions  and  the  POSIX draft standard.  Command line options can cause these exten-
       sions to print a warning or to be rejected.  This document 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 precision num-
       bers.  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 deci-
       mal.  (This version truncates results from divide and multiply operations.)   There
       are  two  attributes of numbers, the length and the scale.  The length is the total
       number of significant 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  */.   Com-
       ments  may  start anywhere and appear as a single space in the input.  (This causes
       comments to delimit other input items.  For example, 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  pro-
       cessed 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 pos-
       sible.   There  is  no  "main" program.  Instead, code is executed as it is encoun-
       tered.  (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
       letters  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  maxi-
       mum number representable 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 vari-
              able 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 expressions.

       expr / expr
              The result of the expression is the quotient of the  two  expressions.   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 computed in the
              following way.  To compute a%b, first a/b is computed 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  nega-
              tive.  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  exponent  and  the
              maximum  of scale and the scale of the first expression.  (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 expres-
              sion.

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

       var <op>= expr
              This is equivalent to "var = var <op> 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 statements 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 rela-
       tional 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 operators to have some
       unusual behavior when used with assignment expressions.  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 program 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  cur-
              rent value of the variable ibase for the conversion 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 expression.  If the
              expression is negative, a run time error is generated.

   STATEMENTS
       Statements  (as  in  most algebraic languages) provide the sequencing of expression
       evaluation.  In bc statements are executed "as soon as possible."   Execution  hap-
       pens  when  a  newline in encountered and there is one or more complete statements.
       Due to this immediate execution, newlines 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
       "\<nl>", where <nl> is the newline appears to bc as whitespace instead  of  a  new-
       line.   A statement list is a series of statements separated by semicolons and new-
       lines.  The following is a list of bc statements 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
              "<variable> <assignment> ...", it is considered to be an  assignment  state-
              ment.   If  the expression is not an assignment statement, the expression is
              evaluated and printed to the output.  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 precision, 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 with-
              out 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  number  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 double quote
              character and contain all characters until the next double quote  character.
              All  characters are take literally, including any newline.  No newline char-
              acter 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 separated by commas.  Each
              string or expression is printed in the order of the  list.   No  terminating
              newline  is  printed.   Expressions 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 characters  recog-
              nized  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 statement1 or  state-
              ment2  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 exten-
              sion.)

       while ( expression ) statement
              The while statement will execute the statement while the expression is  non-
              zero.   It  evaluates the expression before each execution of the statement.
              Termination of the loop is caused by a zero expression value or  the  execu-
              tion 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 evaluated before  each  execu-
              tion  of  the statement.  If it is non-zero, the statement is evaluated.  If
              it is zero, the loop is terminated.  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 substitut-
              ing the value 1 for expression2.  (The optional expressions  are  an  exten-
              sion. 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 functions.)

       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 exe-
       cuted 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 executed later.
       Functions in bc always compute a value and return it to the caller.  Function defi-
       nitions  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 definition,  zero
       or  more  parameters  are  defined by listing their names separated 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 defining array parameters.  The named array is passed by value to the
       function.  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 syn-
       tax of the auto list (if present)  is  "auto  name,  ...  ;".   (The  semicolon  is
       optional.)   Each name is the name of an auto variable.  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 initial-
       ized 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 func-
       tion 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 termination of a function  and
       the  return of a value.  There are two versions of the return statement.  The first
       form, "return", returns the value 0 to the calling expression.   The  second  form,
       "return  (  expression  )",  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 without an
       explicit return statement.

       Functions also change the usage of the variable ibase.  All constants in the  func-
       tion  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  defini-
       tion  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 out-
       put when called by itself on an input line.  The key word void  is  placed  between
       the  key  word  define  and the function 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 implement 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 edi-
       tor 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  spe-
       cial variable, history is the number 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 feature.  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  implemen-
       tations.   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 "undocumented" option (-c) that causes the program to output the byte
       code to the standard output instead of running it.  It was mainly used  for  debug-
       ging 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 processing 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-character 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 charac-
              ters 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" assignments.  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 example,  "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 interactive 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  execution  of  the
       current  execution  block.  A runtime warning will not terminate the current execu-
       tion block.

       Interrupts
              During an interactive session, the SIGINT signal (usually generated  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 inter-
              ruption.   All auto variables and function parameters 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  instal-
              lation 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 arguments 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 environ-
              ment 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  newline  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 AT gnu.org.  Be sure to include the word ''bc'' somewhere
       in the ''Subject:'' field.

AUTHOR
       Philip A. Nelson
       philnelson AT acm.org

ACKNOWLEDGEMENTS
       The author would like to thank Steve Sommars (Steve.Sommars AT att.com) for his exten-
       sive  help in testing the implementation.  Many great suggestions were given.  This
       is a much better product due to his involvement.



GNU Project                       2006-06-11                             bc(1)

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