This is ../../doc/bc.info, produced by makeinfo version 4.8 from

../../doc/bc.texi.

START-INFO-DIR-ENTRY

* bc: (bc).                    An arbitrary precision calculator language.

END-INFO-DIR-ENTRY

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File: bc.info,  Node: Top,  Next: Introduction,  Prev: (dir),  Up: (dir)

* Menu:

* Introduction::

* Basic Elements::

* Expressions::

* Statements::

* Functions::

* Examples::

* Readline and Libedit Options::

* Comparison with Other Implementations::

* Limits::

* Environment Variables::

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File: bc.info,  Node: Introduction,  Next: Basic Elements,  Prev: Top,  Up: Top

1 Introduction

**************

* Menu:

* Description::

* Command Line Options::

?

File: bc.info,  Node: Description,  Next: Command Line Options,  Prev: Introduction,  Up: Introduction

1.1 Description

===============

`bc' [ -hlwsqv ] [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.

   The author would like to thank Steve Sommars

(<Steve.Sommars@att.com>) for his extensive help in testing the

implementation.  Many great suggestions were given.  This is a much

better product due to his involvement.

   Email bug reports to <bug-bc@gnu.org>.  Be sure to include the word

"bc" somewhere in the "Subject:" field.

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File: bc.info,  Node: Command Line Options,  Next: Numbers,  Prev: Description,  Up: Introduction

1.2 Command Line Options

========================

`bc' takes the following options from the command line:

`-h, --help'

     Print the usage and exit.

`-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.

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File: bc.info,  Node: Basic Elements,  Next: Expressions,  Prev: Introduction,  Up: Top

2 Basic Elements

****************

* Menu:

* Numbers::

* Variables::

* Comments::

?

File: bc.info,  Node: Numbers,  Next: Variables,  Prev: Command Line Options,  Up: Basic Elements

2.1 Numbers

===========

The most basic element in `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 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

digits used by `bc' to represent 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, while 1935.000 has a length of 7 and

a scale of 3.

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File: bc.info,  Node: Variables,  Next: Comments,  Prev: Numbers,  Up: Basic Elements

2.2 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 alphanumeric 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.

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File: bc.info,  Node: Comments,  Prev: Variables,  Up: Basic Elements

2.3 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 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.

?

File: bc.info,  Node: Expressions,  Next: Statements,  Prev: Basic Elements,  Up: Top

3 Expressions

*************

* Menu:

* About Expressions and Special Variables::

* Basic Expressions::

* Relational Expressions::

* Boolean Expressions::

* Precedence::

* Special Expressions::

?

File: bc.info,  Node: About Expressions and Special Variables,  Next: Basic Expressions,  Prev: Expressions,  Up: Expressions

3.1 About Expressions and Special Variables

===========================================

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 36.  (Bases 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.

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File: bc.info,  Node: Basic Expressions,  Next: Relational Expressions,  Prev: About Expressions and Special Variables,  Up: Expressions

3.2 Basic Expressions

=====================

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 expressions.

`expr / expr'

     The result of the expression is the quotient of the two

     expressions.  The scale of the result is the value of the variable

     `scale'

`expr % expr'

     The result of the expression is the "remainder" and it is computed

     in the following way.  To compute a%b, first a/b is computed to

     SCALE digits.  That result is used to compute a-(a/b)*b to the

     scale of the maximum of SCALE+scale(b) and scale(a).  If SCALE is

     set to zero and both expressions are integers this expression is

     the integer remainder function.

`expr ^ expr'

     The result of the expression is the value of the first raised to

     the second. The second expression must be an integer.  (If the

     second expression is not an integer, a warning is generated and the

     expression is truncated to get an integer value.)  The scale of the

     result is SCALE if the exponent is 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 )'

     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.

?

File: bc.info,  Node: Relational Expressions,  Next: Boolean Expressions,  Prev: Basic Expressions,  Up: Expressions

3.3 Relational Expressions

==========================

Relational expressions are a special kind of expression that always

evaluate to 0 or 1, 0 if the relation is false and 1 if the relation is

true.  These may appear in any legal expression.  (POSIX `bc' requires

that relational expressions are used only in `if', `while', and `for'

statements and that only one relational test may be done in them.)  The

relational operators are

`expr1 < expr2'

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

`expr1 <= expr2'

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

`expr1 > expr2'

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

`expr1 >= expr2'

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

`expr1 == expr2'

     The result is 1 if expr1 is equal to expr2.

`expr1 != expr2'

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

?

File: bc.info,  Node: Boolean Expressions,  Next: Precedence,  Prev: Relational Expressions,  Up: Expressions

3.4 Boolean Expressions

=======================

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.

?

File: bc.info,  Node: Precedence,  Next: Special Expressions,  Prev: Boolean Expressions,  Up: Expressions

3.5 Precedence

==============

The expression precedence is as follows: (lowest to highest)

     || operator, left associative

     && operator, left associative

     ! operator, nonassociative

     Relational operators, left associative

     Assignment operator, right associative

     + and - operators, left associative

     *, / and % operators, left associative

     ^ operator, right associative

     unary - operator, nonassociative

     ++ and -- operators, nonassociative

   This precedence was chosen so that POSIX compliant `bc' programs

will run correctly. This will cause the use of the relational and

logical operators to have some unusual behavior when used with

assignment expressions.  Consider the expression:

     a = 3 < 5

   Most C programmers would assume this would assign the result of "3 <

5" (the value 1) to the variable "a".  What this does in `bc' is assign

the value 3 to the variable "a" and then compare 3 to 5.  It is best to

use parentheses when using relational and logical operators with the

assignment operators.

?

File: bc.info,  Node: Special Expressions,  Prev: Precedence,  Up: Expressions

3.6 Special Expressions

=======================

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`)'".  *Note Functions::, for

user-defined functions.  The standard functions are:

`length ( EXPRESSION )'

     The value of the length function is the number of significant

     digits in the expression.

`read ( )'

     The `read' function (an extension) will read a number from the

     standard input, regardless of where the function occurs.  Beware,

     this can cause problems with the mixing of data and program in the

     standard input.  The best use for this function is in a previously

     written program that needs input from the user, but never allows

     program code to be input from the user.  The value of the `read'

     function is the number read from the standard input using the

     current value of the variable IBASE for the conversion base.

`scale ( EXPRESSION )'

     The value of the `scale' function is the number of digits after the

     decimal point in the expression.

`sqrt ( EXPRESSION )'

     The value of the `sqrt' function is the square root of the

     expression.  If the expression is negative, a run time error is

     generated.

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File: bc.info,  Node: Statements,  Next: Functions,  Prev: Expressions,  Up: Top

4 Statements

************

* Menu:

* Pseudo Statements::

   Statements (as in most algebraic languages) provide the sequencing of

expression evaluation.  In `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.)

`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 output.

     After the number is printed, a newline is printed.  For example,

     "a=1" is an assignment statement and "(a=1)" is an expression that

     has an embedded assignment.  All numbers that are printed are

     printed in the base specified by the variable OBASE. The legal

     values for OBASE are 2 through BC_BASE_MAX (*note Environment

     Variables::).  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 for LAST.)

`STRING'

     The string is printed to the output.  Strings start with a double

     quote character and contain all characters until the next double

     quote character.  All characters are taken 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 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 (\e).  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 "\e" (backslash).  Any other character following the

     backslash will be ignored.

`{ STATEMENT_LIST }'

     This is the compound statement.  It allows multiple statements to

     be grouped together for execution.

`if ( EXPRESSION ) STATEMENT1 [else STATEMENT2]'

     The if statement evaluates the expression and executes statement1

     or 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 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] ) STATEMENT'

     The `for' 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 evaluated.  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;

          }

`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.  (*Note Functions::.)

`return ( EXPRESSION )'

     Return the value of the expression from a function.  (*Note

     Functions::.)  As an extension, the parenthesis are not required.

?

File: bc.info,  Node: Pseudo Statements,  Prev: Statements,  Up: Statements

4.1 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.

?

File: bc.info,  Node: Functions,  Next: Examples,  Prev: Statements,  Up: Top

5 Functions

***********

* Menu:

* Math Library Functions::

   Functions provide a method of defining a computation that can be

executed later.  Functions in `bc' always compute a value and return it

to the caller.  Function 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.

?

File: bc.info,  Node: Math Library Functions,  Prev: Functions,  Up: Functions

5.1 Math Library Functions

==========================

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.

?

File: bc.info,  Node: Examples,  Next: Readline and Libedit Options,  Prev: Functions,  Up: Top

6 Examples

**********

In /bin/sh,  the following will assign the value of "pi" to the shell

variable PI.

     pi=$(echo "scale=10; 4*a(1)" | bc -l)

   The following is the definition of the exponential function used in

the math library.  This function is written in POSIX `bc'.

     scale = 20

     /* Uses the fact that e^x = (e^(x/2))^2

        When x is small enough, we use the series:

          e^x = 1 + x + x^2/2! + x^3/3! + ...

     */

     define e(x) {

       auto  a, d, e, f, i, m, v, z

       /* Check the sign of x. */

       if (x<0) {

         m = 1

         x = -x

       }

       /* Precondition x. */

       z = scale;

       scale = 4 + z + .44*x;

       while (x > 1) {

         f += 1;

         x /= 2;

       }

       /* Initialize the variables. */

       v = 1+x

       a = x

       d = 1

       for (i=2; 1; i++) {

         e = (a *= x) / (d *= i)

         if (e == 0) {

           if (f>0) while (f--)  v = v*v;

           scale = z

           if (m) return (1/v);

           return (v/1);

         }

         v += e

       }

     }

   The following is code that uses the extended features of `bc' to

implement a simple program for calculating checkbook balances.  This

program is best kept in a file so that it can be used many times

without having to retype it at every use.

     scale=2

     print "\nCheck book program\n!"

     print "  Remember, deposits are negative transactions.\n"

     print "  Exit by a 0 transaction.\n\n"

     print "Initial balance? "; bal = read()

     bal /= 1

     print "\n"

     while (1) {

       "current balance = "; bal

       "transaction? "; trans = read()

       if (trans == 0) break;

       bal -= trans

       bal /= 1

     }

     quit

   The following is the definition of the recursive factorial function.

     define f (x) {

       if (x <= 1) return (1);

       return (f(x-1) * x);

     }

?

File: bc.info,  Node: Readline and Libedit Options,  Next: Comparison with Other Implementations,  Prev: Examples,  Up: Top

7 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 more 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 number of lines of history retained.  A value

of -1 means that an unlimited number of history lines are retained.

This is the default value.  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 manuals for the GNU `readline', `history' and BSD `libedit'

libraries.  One can not enable both `readline' and `libedit' at the

same time.

?

File: bc.info,  Node: Comparison with Other Implementations,  Next: Limits,  Prev: Readline and Libedit Options,  Up: Top

8 Comparison with Other Implementations

***************************************

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'.  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 environment

     This version does not conform to the POSIX standard in the

     processing of the LANG environment variable and all environment

     variables starting with LC_.

names

     Traditional and POSIX `bc' have single letter names for functions,

     variables and arrays.  They have been extended to be

     multi-character names that start with a letter and may contain

     letters, numbers and the underscore character.

Strings

     Strings are not allowed to contain NUL characters.  POSIX says all

     characters must be included in strings.

last

     POSIX `bc' does not have a \fBlast 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.

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.