bc(1)



bc(1)                       General Commands Manual                      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 out-
       put 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 <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 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 oper-
       ators 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  new-
       line  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 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  "<variable>  <assignment>  ...", 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 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 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 char-
              acters start with the  backslash  character  (\).   The  special
              characters  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 function 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, "<---", "\n"; }
              define void px (x) { print "--->", x, "<---", "\n"; }
              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
              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@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)

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