bc(1) bc(1)

NAME bc - An arbitrary precision calculator language

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

VERSION This man page documents GNU bc version 1.06.

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 <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 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 “<nl>”, 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 "<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 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.
          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 characters 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 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.

                                   .                                 bc(1)