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::
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 AT 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 AT gnu.org>. Be sure to include the word
"bc" somewhere in the "Subject:" field.
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.
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.
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.
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.
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.
If a and b are the scales of the two expressions, then the scale of
the result is: min(a+b,max(SCALE,a,b))
'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.
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.
function format
POSIX 'bc' requires the opening brace on the same line as the
'define' key word and the 'auto' statement on the next line.
'=+', '=-', '=*', '=/', '=%', '=^'
POSIX 'bc' does not require these "old style" assignment operators
to be defined. This version may allow these "old style"
assignments. Use the 'limits' statement to see if the installed
version supports them. If it does support the "old style"
assignment operators, the statement "a =- 1" will decrement 'a' by
1 instead of setting 'a' to the value -1.
spaces in numbers
Other implementations of 'bc' allow spaces in numbers. For
example, "x=1 3" would assign the value 13 to the variable x. The
same statement would cause a syntax error in this version of 'bc'.
errors and execution
This implementation varies from other implementations in terms of
what code will be executed when syntax and other errors are found
in the program. If a syntax error is found in a function
definition, error recovery tries to find the beginning of a
statement and continue to parse the function. Once a syntax error
is found in the function, the function will not be callable and
becomes undefined. Syntax errors in the interactive execution code
will invalidate the current execution block. The execution block
is terminated by an end of line that appears after a complete
sequence of statements. For example,
a = 1
b = 2
has two execution blocks and
{ a = 1
b = 2 }
has one execution block. Any runtime error will terminate the
execution of the current execution block. A runtime warning will
not terminate the current execution block.
Interrupts
During an interactive session, the SIGINT signal (usually generated
by the control-C character from the terminal) will cause execution
of the current execution block to be interrupted. It will display
a "runtime" error indicating which function was interrupted. After
all runtime structures have been cleaned up, a message will be
printed to notify the user that 'bc' is ready for more input. All
previously defined functions remain defined and the value of all
non-auto variables are the value at the point of 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'.
File: bc.info, Node: Limits, Next: Environment Variables, Prev: Comparison with Other Implementations, Up: Top
9 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.
'multiply'
The multiply routine may yield incorrect results if a number has
more than LONG_MAX / 90 total digits. For 32 bit longs, this
number is 23,860,929 digits.
'variable names'
The current limit on the number of unique names is 32767 for each
of simple variables, arrays and functions.
File: bc.info, Node: Environment Variables, Prev: Limits, Up: Top
10 Environment Variables
************************
The following environment variables are processed by 'bc':
'POSIXLY_CORRECT'
This is the same as the -s option (*note Command Line Options::).
'BC_ENV_ARGS'
This is another mechanism to get arguments to 'bc'. The format is
the same as the command line arguments. These arguments are
processed first, so any files listed in the environment arguments
are processed before any command line argument files. This allows
the user to set up "standard" options and files to be processed at
every invocation of 'bc'. The files in the environment variables
would typically contain function definitions for functions the user
wants defined every time 'bc' is run.
'BC_LINE_LENGTH'
This should be an integer specifying the number of characters in an
output line for numbers. This includes the backslash and newline
characters for long numbers. As an extension, the value of zero
disables the multi-line feature. Any other value of this variable
that is less than 3 sets the line length to 70.
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