| BC(1) | General Commands Manual | BC(1) | 
bc —
| bc | [ -hilqsvw] [long-options] [file
      ...] | 
bc is a language that supports arbitrary precision
  numbers with interactive 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 document describes the language
    accepted by this processor. Extensions will be identified as such.
-h,
    --help-i,
    --interactive-l,
    --mathlib-q,
    --quiet-s,
    --standardbc language.-v,
    --version-w,
    --warnbc.bc is the number. Numbers are
  arbitrary precision 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 of bc
  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:
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.
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 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 processed normally.
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 36. (Base values greater than 16 are an extension.) Assigning
    a value outside this range to ibase will result in a
    value of 2 or 36. Input numbers may contain the characters 0-9 and A-Z.
    (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 ‘ZZZ’ 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 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++var--var++--+
    expr-
    expr*
    expr/
    exprscale.%
    exprscale 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.^
    exprscale 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 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)=
    expr=
    expr=
      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:
<
    expr2<=
    expr2>
    expr2>=
    expr2==
    expr2!=
    expr2Boolean 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&&
    expr||
    exprThe expression precedence is as follows: (lowest to highest)
||’ operator, left associative&&’ operator, left
      associative!’ operator, nonassociative+’ and
      ‘-’ operators, left associative*’,
      ‘/’ and
      ‘%’ operators, left associative^’ operator, right associative-’ operator,
    nonassociative++’ and
      ‘--’ operators, nonassociativeThis 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 < 5Most 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
    parentheses 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)read()ibase for the conversion base.scale(expression)sqrt(expression)bc statements are executed “as
  soon as possible”. Execution happens 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 newline. A statement list is a series of statements
  separated by semicolons and newlines. The following is a list of
  bc statements and what they do: (Things enclosed in
  brackets ([]) are optional parts of the statement.)
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 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 last.)"string"print
    listprint 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 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 }if
    (expression)
    statement1 [else
    statement2]if statement evaluates the
      expression and executes
      statement1 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)
    statementwhile 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
      execution of a break statement.for
    ([expression1];
    [expression2];
    [expression3])
    statementfor statement controls repeated execution of
      the statement. expression1 is
      evaluated before the loop. expression2 is evaluated
      before each execution of the statement. If it is
      non-zero, the statement is executed. If it is zero,
      the loop is terminated. After each execution of the
      statement, expression3 is
      evaluated before the reevaluation of expression2. If
      expression1 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;
}
    
    breakwhile statement or for
      statement.continuecontinue statement (an extension) causes the
      most recent enclosing for statement to start the
      next iteration.halthalt statement (an extension) is an executed
      statement that causes the bc processor to quit
      only when it is executed. For example,
    if (0 == 1) haltbc to terminate because the halt is
      not executed.returnreturn
    (expression)limitsbc This is an extension.quitquit statement is read, the
      bc processor is terminated, regardless of where
      the quit statement is found. For example,
    if (0 == 1) quitbc to terminate.warrantybc 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
    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 syntax 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 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 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 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 function 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.
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)c(x)a(x)l(x)e(x)j(n,
    x)bc:
POSIXLY_CORRECT-s option.BC_ENV_ARGSbc.
      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 environment
      variables would typically contain function definitions for functions the
      user wants defined every time bc is run.BC_LINE_LENGTHpi=$(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);
}
bc is compiled using the
  editline(3) 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. This adds to bc one more special variable. This
  special variable, history is the number of lines of
  history retained. The default 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. For more information, read the user manual for the
  editline(3) library.
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 “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 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
    environmentLANG environment variable and all environment
      variables starting with LC_.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.lastbc does not have a
      last variable. Some implementations of
      bc use the period
      (‘.’) in a similar way.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
    clausebc does not have an
      else clause.for
    statementbc requires all expressions to be present in
      the for statement.&&,
    ||, !bc does not have the logical operators.read() functionbc does not have a
      read() function.print
    statementbc does not have a
      print statement .continue
    statementbc does not have a
      continue statement.return
    statementbc requires parentheses around the return
      expression.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.bc requires the opening brace on the same
      line as the define key word and the
      auto statement on the next line.=+,
    =-, =*,
    =/, =%,
    =^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.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.
a = 1
b = 2
    
    
{ a = 1
  b = 2 }
    
    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
      interruption. 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.bc processor. Some of them may have been changed by an
  installation. Use the limits statement to see the
  actual values.
BC_BASE_MAXBC_DIM_MAXBC_SCALE_MAXINT_MAX digits. Also, the number of digits before
      the decimal point is limited to INT_MAX
    digits.BC_STRING_MAXINT_MAX characters.^’) is limited to
      LONG_MAX.bc
  will report that the file is unavailable and terminate. Also, there are
  compile and run time diagnostics that should be self-explanatory.
| April 16, 2017 | NetBSD 10.0 |