Add the DragonFly cvs id and perform general cleanups on cvs/rcs/sccs ids. Most
[dragonfly.git] / contrib / bc / doc / bc.1
CommitLineData
984263bc
MD
1.\"
2.\" bc.1 - the *roff document processor source for the bc manual
3.\"
4.\" This file is part of GNU bc.
5.\" Copyright (C) 1991-1994, 1997, 2000 Free Software Foundation, Inc.
6.\"
7.\" This program is free software; you can redistribute it and/or modify
8.\" it under the terms of the GNU General Public License as published by
9.\" the Free Software Foundation; either version 2 of the License , or
10.\" (at your option) any later version.
11.\"
12.\" This program is distributed in the hope that it will be useful,
13.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
14.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15.\" GNU General Public License for more details.
16.\"
17.\" You should have received a copy of the GNU General Public License
18.\" along with this program; see the file COPYING. If not, write to:
19.\" The Free Software Foundation, Inc.
20.\" 59 Temple Place, Suite 330
21.\" Boston, MA 02111 USA
22.\"
23.\" You may contact the author by:
24.\" e-mail: philnelson@acm.org
25.\" us-mail: Philip A. Nelson
26.\" Computer Science Department, 9062
27.\" Western Washington University
28.\" Bellingham, WA 98226-9062
29.\"
30.\" $FreeBSD: src/contrib/bc/doc/bc.1,v 1.4.6.2 2002/07/29 07:41:24 ru Exp $
1de703da 31.\" $DragonFly: src/contrib/bc/doc/Attic/bc.1,v 1.2 2003/06/17 04:23:58 dillon Exp $
984263bc
MD
32.\"
33.TH bc 1 .\" "Command Manual" v1.06 "Sept 12, 2000"
34.SH NAME
35bc - An arbitrary precision calculator language
36.SH SYNTAX
37\fBbc\fR [ \fB-hlwsqv\fR ] [long-options] [ \fI file ...\fR ]
38.SH VERSION
39This man page documents GNU bc version 1.06.
40.SH DESCRIPTION
41\fBbc\fR is a language that supports arbitrary precision numbers
42with interactive execution of statements. There are some similarities
43in the syntax to the C programming language.
44A standard math library is available by command line option.
45If requested, the math library is defined before processing any files.
46\fBbc\fR starts by processing code from all the files listed
47on the command line in the order listed. After all files have been
48processed, \fBbc\fR reads from the standard input. All code is
49executed as it is read. (If a file contains a command to halt the
50processor, \fBbc\fR will never read from the standard input.)
51.PP
52This version of \fBbc\fR contains several extensions beyond
53traditional \fBbc\fR implementations and the POSIX draft standard.
54Command line options can cause these extensions to print a warning
55or to be rejected. This
56document describes the language accepted by this processor.
57Extensions will be identified as such.
58.SS OPTIONS
59.IP "-h, --help"
60Print the usage and exit.
61.IP "-i, --interactive"
62Force interactive mode.
63.IP "-l, --mathlib"
64Define the standard math library.
65.IP "-w, --warn"
66Give warnings for extensions to POSIX \fBbc\fR.
67.IP "-s, --standard"
68Process exactly the POSIX \fBbc\fR language.
69.IP "-q, --quiet"
70Do not print the normal GNU bc welcome.
71.IP "-v, --version"
72Print the version number and copyright and quit.
73.SS NUMBERS
74The most basic element in \fBbc\fR is the number. Numbers are
75arbitrary precision numbers. This precision is both in the integer
76part and the fractional part. All numbers are represented internally
77in decimal and all computation is done in decimal. (This version
78truncates results from divide and multiply operations.) There are two
79attributes of numbers, the length and the scale. The length is the
80total number of significant decimal digits in a number and the scale
81is the total number of decimal digits after the decimal point. For
82example:
83.nf
84.RS
85 .000001 has a length of 6 and scale of 6.
86 1935.000 has a length of 7 and a scale of 3.
87.RE
88.fi
89.SS VARIABLES
90Numbers are stored in two types of variables, simple variables and
91arrays. Both simple variables and array variables are named. Names
92begin with a letter followed by any number of letters, digits and
93underscores. All letters must be lower case. (Full alpha-numeric
94names are an extension. In POSIX \fBbc\fR all names are a single
95lower case letter.) The type of variable is clear by the context
96because all array variable names will be followed by brackets ([]).
97.PP
98There are four special variables, \fBscale, ibase, obase,\fR and
99\fBlast\fR. \fBscale\fR defines how some operations use digits after the
100decimal point. The default value of \fBscale\fR is 0. \fBibase\fR
101and \fBobase\fR define the conversion base for input and output
102numbers. The default for both input and output is base 10.
103\fBlast\fR (an extension) is a variable that has the value of the last
104printed number. These will be discussed in further detail where
105appropriate. All of these variables may have values assigned to them
106as well as used in expressions.
107.SS COMMENTS
108Comments in \fBbc\fR start with the characters \fB/*\fR and end with
109the characters \fB*/\fR. Comments may start anywhere and appear as a
110single space in the input. (This causes comments to delimit other
111input items. For example, a comment can not be found in the middle of
112a variable name.) Comments include any newlines (end of line) between
113the start and the end of the comment.
114.PP
115To support the use of scripts for \fBbc\fR, a single line comment has been
116added as an extension. A single line comment starts at a \fB#\fR
117character and continues to the next end of the line. The end of line
118character is not part of the comment and is processed normally.
119.SS EXPRESSIONS
120The numbers are manipulated by expressions and statements. Since
121the language was designed to be interactive, statements and expressions
122are executed as soon as possible. There is no "main" program. Instead,
123code is executed as it is encountered. (Functions, discussed in
124detail later, are defined when encountered.)
125.PP
126A simple expression is just a constant. \fBbc\fR converts constants
127into internal decimal numbers using the current input base, specified
128by the variable \fBibase\fR. (There is an exception in functions.)
129The legal values of \fBibase\fR are 2 through 16. Assigning a
130value outside this range to \fBibase\fR will result in a value of 2
131or 16. Input numbers may contain the characters 0-9 and A-F. (Note:
132They must be capitals. Lower case letters are variable names.)
133Single digit numbers always have the value of the digit regardless of
134the value of \fBibase\fR. (i.e. A = 10.) For multi-digit numbers,
135\fBbc\fR changes all input digits greater or equal to ibase to the
136value of \fBibase\fR-1. This makes the number \fBFFF\fR always be
137the largest 3 digit number of the input base.
138.PP
139Full expressions are similar to many other high level languages.
140Since there is only one kind of number, there are no rules for mixing
141types. Instead, there are rules on the scale of expressions. Every
142expression has a scale. This is derived from the scale of original
143numbers, the operation performed and in many cases, the value of the
144variable \fBscale\fR. Legal values of the variable \fBscale\fR are
1450 to the maximum number representable by a C integer.
146.PP
147In the following descriptions of legal expressions, "expr" refers to a
148complete expression and "var" refers to a simple or an array variable.
149A simple variable is just a
150.RS
151\fIname\fR
152.RE
153and an array variable is specified as
154.RS
155\fIname\fR[\fIexpr\fR]
156.RE
157Unless specifically
158mentioned the scale of the result is the maximum scale of the
159expressions involved.
160.IP "- expr"
161The result is the negation of the expression.
162.IP "++ var"
163The variable is incremented by one and the new value is the result of
164the expression.
165.IP "-- var"
166The variable
167is decremented by one and the new value is the result of the
168expression.
169.IP "var ++"
170 The result of the expression is the value of
171the variable and then the variable is incremented by one.
172.IP "var --"
173The result of the expression is the value of the variable and then
174the variable is decremented by one.
175.IP "expr + expr"
176The result of the expression is the sum of the two expressions.
177.IP "expr - expr"
178The result of the expression is the difference of the two expressions.
179.IP "expr * expr"
180The result of the expression is the product of the two expressions.
181.IP "expr / expr"
182The result of the expression is the quotient of the two expressions.
183The scale of the result is the value of the variable \fBscale\fR.
184.IP "expr % expr"
185The result of the expression is the "remainder" and it is computed in the
186following way. To compute a%b, first a/b is computed to \fBscale\fR
187digits. That result is used to compute a-(a/b)*b to the scale of the
188maximum of \fBscale\fR+scale(b) and scale(a). If \fBscale\fR is set
189to zero and both expressions are integers this expression is the
190integer remainder function.
191.IP "expr ^ expr"
192The result of the expression is the value of the first raised to the
193second. The second expression must be an integer. (If the second
194expression is not an integer, a warning is generated and the
195expression is truncated to get an integer value.) The scale of the
196result is \fBscale\fR if the exponent is negative. If the exponent
197is positive the scale of the result is the minimum of the scale of the
198first expression times the value of the exponent and the maximum of
199\fBscale\fR and the scale of the first expression. (e.g. scale(a^b)
200= min(scale(a)*b, max( \fBscale,\fR scale(a))).) It should be noted
201that expr^0 will always return the value of 1.
202.IP "( expr )"
203This alters the standard precedence to force the evaluation of the
204expression.
205.IP "var = expr"
206The variable is assigned the value of the expression.
207.IP "var <op>= expr"
208This is equivalent to "var = var <op> expr" with the exception that
209the "var" part is evaluated only once. This can make a difference if
210"var" is an array.
211.PP
212 Relational expressions are a special kind of expression
213that always evaluate to 0 or 1, 0 if the relation is false and 1 if
214the relation is true. These may appear in any legal expression.
215(POSIX bc requires that relational expressions are used only in if,
216while, and for statements and that only one relational test may be
217done in them.) The relational operators are
218.IP "expr1 < expr2"
219The result is 1 if expr1 is strictly less than expr2.
220.IP "expr1 <= expr2"
221The result is 1 if expr1 is less than or equal to expr2.
222.IP "expr1 > expr2"
223The result is 1 if expr1 is strictly greater than expr2.
224.IP "expr1 >= expr2"
225The result is 1 if expr1 is greater than or equal to expr2.
226.IP "expr1 == expr2"
227The result is 1 if expr1 is equal to expr2.
228.IP "expr1 != expr2"
229The result is 1 if expr1 is not equal to expr2.
230.PP
231Boolean operations are also legal. (POSIX \fBbc\fR does NOT have
232boolean operations). The result of all boolean operations are 0 and 1
233(for false and true) as in relational expressions. The boolean
234operators are:
235.IP "!expr"
236The result is 1 if expr is 0.
237.IP "expr && expr"
238The result is 1 if both expressions are non-zero.
239.IP "expr || expr"
240The result is 1 if either expression is non-zero.
241.PP
242The expression precedence is as follows: (lowest to highest)
243.nf
244.RS
245|| operator, left associative
246&& operator, left associative
247! operator, nonassociative
248Relational operators, left associative
249Assignment operator, right associative
250+ and - operators, left associative
251*, / and % operators, left associative
252^ operator, right associative
253unary - operator, nonassociative
254++ and -- operators, nonassociative
255.RE
256.fi
257.PP
258This precedence was chosen so that POSIX compliant \fBbc\fR programs
259will run correctly. This will cause the use of the relational and
260logical operators to have some unusual behavior when used with
261assignment expressions. Consider the expression:
262.RS
263a = 3 < 5
264.RE
265.PP
266Most C programmers would assume this would assign the result of "3 <
2675" (the value 1) to the variable "a". What this does in \fBbc\fR is
268assign the value 3 to the variable "a" and then compare 3 to 5. It is
269best to use parenthesis when using relational and logical operators
270with the assignment operators.
271.PP
272There are a few more special expressions that are provided in \fBbc\fR.
273These have to do with user defined functions and standard
274functions. They all appear as "\fIname\fB(\fIparameters\fB)\fR".
275See the section on functions for user defined functions. The standard
276functions are:
277.IP "length ( expression )"
278The value of the length function is the number of significant digits in the
279expression.
280.IP "read ( )"
281The read function (an extension) will read a number from the standard
282input, regardless of where the function occurs. Beware, this can
283cause problems with the mixing of data and program in the standard input.
284The best use for this function is in a previously written program that
285needs input from the user, but never allows program code to be input
286from the user. The value of the read function is the number read from
287the standard input using the current value of the variable
288\fBibase\fR for the conversion base.
289.IP "scale ( expression )"
290The value of the scale function is the number of digits after the decimal
291point in the expression.
292.IP "sqrt ( expression )"
293The value of the sqrt function is the square root of the expression. If
294the expression is negative, a run time error is generated.
295.SS STATEMENTS
296Statements (as in most algebraic languages) provide the sequencing of
297expression evaluation. In \fBbc\fR statements are executed "as soon
298as possible." Execution happens when a newline in encountered and
299there is one or more complete statements. Due to this immediate
300execution, newlines are very important in \fBbc\fR. In fact, both a
301semicolon and a newline are used as statement separators. An
302improperly placed newline will cause a syntax error. Because newlines
303are statement separators, it is possible to hide a newline by using
304the backslash character. The sequence "\e<nl>", where <nl> is the
305newline appears to \fBbc\fR as whitespace instead of a newline. A
306statement list is a series of statements separated by semicolons and
307newlines. The following is a list of \fBbc\fR statements and what
308they do: (Things enclosed in brackets ([]) are optional parts of the
309statement.)
310.IP "expression"
311This statement does one of two things. If the expression starts with
312"<variable> <assignment> ...", it is considered to be an assignment
313statement. If the expression is not an assignment statement, the
314expression is evaluated and printed to the output. After the number
315is printed, a newline is printed. For example, "a=1" is an assignment
316statement and "(a=1)" is an expression that has an embedded
317assignment. All numbers that are printed are printed in the base
318specified by the variable \fBobase\fR. The legal values for \fB
319obase\fR are 2 through BC_BASE_MAX. (See the section LIMITS.) For
320bases 2 through 16, the usual method of writing numbers is used. For
321bases greater than 16, \fBbc\fR uses a multi-character digit method
322of printing the numbers where each higher base digit is printed as a
323base 10 number. The multi-character digits are separated by spaces.
324Each digit contains the number of characters required to represent the
325base ten value of "obase-1". Since numbers are of arbitrary
326precision, some numbers may not be printable on a single output line.
327These long numbers will be split across lines using the "\e" as the
328last character on a line. The maximum number of characters printed
329per line is 70. Due to the interactive nature of \fBbc\fR, printing
330a number causes the side effect of assigning the printed value to the
331special variable \fBlast\fR. This allows the user to recover the
332last value printed without having to retype the expression that
333printed the number. Assigning to \fBlast\fR is legal and will
334overwrite the last printed value with the assigned value. The newly
335assigned value will remain until the next number is printed or another
336value is assigned to \fBlast\fR. (Some installations may allow the
337use of a single period (.) which is not part of a number as a short
338hand notation for for \fBlast\fR.)
339.IP "string"
340The string is printed to the output. Strings start with a double quote
341character and contain all characters until the next double quote character.
342All characters are take literally, including any newline. No newline
343character is printed after the string.
344.IP "\fBprint\fR list"
345The print statement (an extension) provides another method of output.
346The "list" is a list of strings and expressions separated by commas.
347Each string or expression is printed in the order of the list. No
348terminating newline is printed. Expressions are evaluated and their
349value is printed and assigned to the variable \fBlast\fR. Strings
350in the print statement are printed to the output and may contain
351special characters. Special characters start with the backslash
352character (\e). The special characters recognized by \fBbc\fR are
353"a" (alert or bell), "b" (backspace), "f" (form feed), "n" (newline),
354"r" (carriage return), "q" (double quote), "t" (tab), and "\e" (backslash).
355Any other character following the backslash will be ignored.
356.IP "{ statement_list }"
357This is the compound statement. It allows multiple statements to be
358grouped together for execution.
359.IP "\fBif\fR ( expression ) statement1 [\fBelse\fR statement2]"
360The if statement evaluates the expression and executes statement1 or
361statement2 depending on the value of the expression. If the expression
362is non-zero, statement1 is executed. If statement2 is present and
363the value of the expression is 0, then statement2 is executed. (The
364else clause is an extension.)
365.IP "\fBwhile\fR ( expression ) statement"
366The while statement will execute the statement while the expression
367is non-zero. It evaluates the expression before each execution of
368the statement. Termination of the loop is caused by a zero
369expression value or the execution of a break statement.
370.IP "\fBfor\fR ( [expression1] ; [expression2] ; [expression3] ) statement"
371The for statement controls repeated execution of the statement.
372Expression1 is evaluated before the loop. Expression2 is evaluated
373before each execution of the statement. If it is non-zero, the statement
374is evaluated. If it is zero, the loop is terminated. After each
375execution of the statement, expression3 is evaluated before the reevaluation
376of expression2. If expression1 or expression3 are missing, nothing is
377evaluated at the point they would be evaluated.
378If expression2 is missing, it is the same as substituting
379the value 1 for expression2. (The optional expressions are an
380extension. POSIX \fBbc\fR requires all three expressions.)
381The following is equivalent code for the for statement:
382.nf
383.RS
384expression1;
385while (expression2) {
386 statement;
387 expression3;
388}
389.RE
390.fi
391.IP "\fBbreak\fR"
392This statement causes a forced exit of the most recent enclosing while
393statement or for statement.
394.IP "\fBcontinue\fR"
395The continue statement (an extension) causes the most recent enclosing
396for statement to start the next iteration.
397.IP "\fBhalt\fR"
398The halt statement (an extension) is an executed statement that causes
399the \fBbc\fR processor to quit only when it is executed. For example,
400"if (0 == 1) halt" will not cause \fBbc\fR to terminate because the halt is
401not executed.
402.IP "\fBreturn\fR"
403Return the value 0 from a function. (See the section on functions.)
404.IP "\fBreturn\fR ( expression )"
405Return the value of the expression from a function. (See the section on
406functions.) As an extension, the parenthesis are not required.
407.SS PSEUDO STATEMENTS
408These statements are not statements in the traditional sense. They are
409not executed statements. Their function is performed at "compile" time.
410.IP "\fBlimits\fR"
411Print the local limits enforced by the local version of \fBbc\fR. This
412is an extension.
413.IP "\fBquit\fR"
414When the quit statement is read, the \fBbc\fR processor
415is terminated, regardless of where the quit statement is found. For
416example, "if (0 == 1) quit" will cause \fBbc\fR to terminate.
417.IP "\fBwarranty\fR"
418Print a longer warranty notice. This is an extension.
419.SS FUNCTIONS
420Functions provide a method of defining a computation that can be executed
421later. Functions in
422.B bc
423always compute a value and return it to the caller. Function definitions
424are "dynamic" in the sense that a function is undefined until a definition
425is encountered in the input. That definition is then used until another
426definition function for the same name is encountered. The new definition
427then replaces the older definition. A function is defined as follows:
428.nf
429.RS
430\fBdefine \fIname \fB( \fIparameters \fB) { \fInewline
431\fI auto_list statement_list \fB}\fR
432.RE
433.fi
434A function call is just an expression of the form
435"\fIname\fB(\fIparameters\fB)\fR".
436.PP
437Parameters are numbers or arrays (an extension). In the function definition,
438zero or more parameters are defined by listing their names separated by
439commas. Numbers are only call by value parameters. Arrays are only
440call by variable. Arrays are specified in the parameter definition by
441the notation "\fIname\fB[]\fR". In the function call, actual parameters
442are full expressions for number parameters. The same notation is used
443for passing arrays as for defining array parameters. The named array is
444passed by variable to the function. Since function definitions are dynamic,
445parameter numbers and types are checked when a function is called. Any
446mismatch in number or types of parameters will cause a runtime error.
447A runtime error will also occur for the call to an undefined function.
448.PP
449The \fIauto_list\fR is an optional list of variables that are for
450"local" use. The syntax of the auto list (if present) is "\fBauto
451\fIname\fR, ... ;". (The semicolon is optional.) Each \fIname\fR is
452the name of an auto variable. Arrays may be specified by using the
453same notation as used in parameters. These variables have their
454values pushed onto a stack at the start of the function. The
455variables are then initialized to zero and used throughout the
456execution of the function. At function exit, these variables are
457popped so that the original value (at the time of the function call)
458of these variables are restored. The parameters are really auto
459variables that are initialized to a value provided in the function
460call. Auto variables are different than traditional local variables
461because if function A calls function B, B may access function
462A's auto variables by just using the same name, unless function B has
463called them auto variables. Due to the fact that auto variables and
464parameters are pushed onto a stack, \fBbc\fR supports recursive functions.
465.PP
466The function body is a list of \fBbc\fR statements. Again, statements
467are separated by semicolons or newlines. Return statements cause the
468termination of a function and the return of a value. There are two
469versions of the return statement. The first form, "\fBreturn\fR", returns
470the value 0 to the calling expression. The second form,
471"\fBreturn ( \fIexpression \fB)\fR", computes the value of the expression
472and returns that value to the calling expression. There is an implied
473"\fBreturn (0)\fR" at the end of every function. This allows a function
474to terminate and return 0 without an explicit return statement.
475.PP
476Functions also change the usage of the variable \fBibase\fR. All
477constants in the function body will be converted using the value of
478\fBibase\fR at the time of the function call. Changes of \fBibase\fR
479will be ignored during the execution of the function except for the
480standard function \fBread\fR, which will always use the current value
481of \fBibase\fR for conversion of numbers.
482.PP
483As an extension, the format of the definition has been slightly relaxed.
484The standard requires the opening brace be on the same line as the
485\fBdefine\fR keyword and all other parts must be on following lines.
486This version of \fBbc\fR will allow any number of newlines before and
487after the opening brace of the function. For example, the following
488definitions are legal.
489.nf
490.RS
491\f(CW
492define d (n) { return (2*n); }
493define d (n)
494 { return (2*n); }
495\fR
496.RE
497.fi
498.SS MATH LIBRARY
499If \fBbc\fR is invoked with the \fB-l\fR option, a math library is preloaded
500and the default scale is set to 20. The math functions will calculate their
501results to the scale set at the time of their call.
502The math library defines the following functions:
503.IP "s (\fIx\fR)"
504The sine of x, x is in radians.
505.IP "c (\fIx\fR)"
506The cosine of x, x is in radians.
507.IP "a (\fIx\fR)"
508The arctangent of x, arctangent returns radians.
509.IP "l (\fIx\fR)"
510The natural logarithm of x.
511.IP "e (\fIx\fR)"
512The exponential function of raising e to the value x.
513.IP "j (\fIn,x\fR)"
514The bessel function of integer order n of x.
515.SS EXAMPLES
516In /bin/sh, the following will assign the value of "pi" to the shell
517variable \fBpi\fR.
518.RS
519\f(CW
520pi=$(echo "scale=10; 4*a(1)" | bc -l)
521\fR
522.RE
523.PP
524The following is the definition of the exponential function used in the
525math library. This function is written in POSIX \fBbc\fR.
526.nf
527.RS
528\f(CW
529scale = 20
530
531/* Uses the fact that e^x = (e^(x/2))^2
532 When x is small enough, we use the series:
533 e^x = 1 + x + x^2/2! + x^3/3! + ...
534*/
535
536define e(x) {
537 auto a, d, e, f, i, m, v, z
538
539 /* Check the sign of x. */
540 if (x<0) {
541 m = 1
542 x = -x
543 }
544
545 /* Precondition x. */
546 z = scale;
547 scale = 4 + z + .44*x;
548 while (x > 1) {
549 f += 1;
550 x /= 2;
551 }
552
553 /* Initialize the variables. */
554 v = 1+x
555 a = x
556 d = 1
557
558 for (i=2; 1; i++) {
559 e = (a *= x) / (d *= i)
560 if (e == 0) {
561 if (f>0) while (f--) v = v*v;
562 scale = z
563 if (m) return (1/v);
564 return (v/1);
565 }
566 v += e
567 }
568}
569\fR
570.RE
571.fi
572.PP
573The following is code that uses the extended features of \fBbc\fR to
574implement a simple program for calculating checkbook balances. This
575program is best kept in a file so that it can be used many times
576without having to retype it at every use.
577.nf
578.RS
579\f(CW
580scale=2
581print "\enCheck book program!\en"
582print " Remember, deposits are negative transactions.\en"
583print " Exit by a 0 transaction.\en\en"
584
585print "Initial balance? "; bal = read()
586bal /= 1
587print "\en"
588while (1) {
589 "current balance = "; bal
590 "transaction? "; trans = read()
591 if (trans == 0) break;
592 bal -= trans
593 bal /= 1
594}
595quit
596\fR
597.RE
598.fi
599.PP
600The following is the definition of the recursive factorial function.
601.nf
602.RS
603\f(CW
604define f (x) {
605 if (x <= 1) return (1);
606 return (f(x-1) * x);
607}
608\fR
609.RE
610.fi
611.SS READLINE AND LIBEDIT OPTIONS
612GNU \fBbc\fR can be compiled (via a configure option) to use the GNU
613\fBreadline\fR input editor library or the BSD \fBlibedit\fR library.
614This allows the user to do editing of lines before sending them
615to \fBbc\fR. It also allows for a history of previous lines typed.
616When this option is selected, \fBbc\fR has one more special variable.
617This special variable, \fBhistory\fR is the number of lines of history
618retained. For \fBreadline\fR, a value of -1 means that an unlimited
619number of history lines are retained. Setting the value of
620\fBhistory\fR to a positive number restricts the number of history
621lines to the number given. The value of 0 disables the history
622feature. The default value is 100. For more information, read the
623user manuals for the GNU \fBreadline\fR, \fBhistory\fR and BSD \fBlibedit\fR
624libraries. One can not enable both \fBreadline\fR and \fBlibedit\fR
625at the same time.
626.SS DIFFERENCES
627This version of
628.B bc
629was implemented from the POSIX P1003.2/D11 draft and contains
630several differences and extensions relative to the draft and
631traditional implementations.
632It is not implemented in the traditional way using
633.I dc(1).
634This version is a single process which parses and runs a byte code
635translation of the program. There is an "undocumented" option (-c)
636that causes the program to output the byte code to
637the standard output instead of running it. It was mainly used for
638debugging the parser and preparing the math library.
639.PP
640A major source of differences is
641extensions, where a feature is extended to add more functionality and
642additions, where new features are added.
643The following is the list of differences and extensions.
644.IP "LANG environment"
645This version does not conform to the POSIX standard in the processing
646of the LANG environment variable and all environment variables starting
647with LC_.
648.IP names
649Traditional and POSIX
650.B bc
651have single letter names for functions, variables and arrays. They have
652been extended to be multi-character names that start with a letter and
653may contain letters, numbers and the underscore character.
654.IP Strings
655Strings are not allowed to contain NUL characters. POSIX says all characters
656must be included in strings.
657.IP last
658POSIX \fBbc\fR does not have a \fBlast\fR variable. Some implementations
659of \fBbc\fR use the period (.) in a similar way.
660.IP comparisons
661POSIX \fBbc\fR allows comparisons only in the if statement, the while
662statement, and the second expression of the for statement. Also, only
663one relational operation is allowed in each of those statements.
664.IP "if statement, else clause"
665POSIX \fBbc\fR does not have an else clause.
666.IP "for statement"
667POSIX \fBbc\fR requires all expressions to be present in the for statement.
668.IP "&&, ||, !"
669POSIX \fBbc\fR does not have the logical operators.
670.IP "read function"
671POSIX \fBbc\fR does not have a read function.
672.IP "print statement"
673POSIX \fBbc\fR does not have a print statement .
674.IP "continue statement"
675POSIX \fBbc\fR does not have a continue statement.
676.IP "return statement"
677POSIX \fBbc\fR requires parentheses around the return expression.
678.IP "array parameters"
679POSIX \fBbc\fR does not (currently) support array parameters in full.
680The POSIX grammar allows for arrays in function definitions, but does
681not provide a method to specify an array as an actual parameter. (This
682is most likely an oversight in the grammar.) Traditional implementations
683of \fBbc\fR have only call by value array parameters.
684.IP "function format"
685POSIX \fBbc\fR requires the opening brace on the same line as the
686\fBdefine\fR key word and the \fBauto\fR statement on the next line.
687.IP "=+, =-, =*, =/, =%, =^"
688POSIX \fBbc\fR does not require these "old style" assignment operators to
689be defined. This version may allow these "old style" assignments. Use
690the limits statement to see if the installed version supports them. If
691it does support the "old style" assignment operators, the statement
692"a =- 1" will decrement \fBa\fR by 1 instead of setting \fBa\fR to the
693value -1.
694.IP "spaces in numbers"
695Other implementations of \fBbc\fR allow spaces in numbers. For example,
696"x=1 3" would assign the value 13 to the variable x. The same statement
697would cause a syntax error in this version of \fBbc\fR.
698.IP "errors and execution"
699This implementation varies from other implementations in terms of what
700code will be executed when syntax and other errors are found in the
701program. If a syntax error is found in a function definition, error
702recovery tries to find the beginning of a statement and continue to
703parse the function. Once a syntax error is found in the function, the
704function will not be callable and becomes undefined.
705Syntax errors in the interactive execution code will invalidate the
706current execution block. The execution block is terminated by an
707end of line that appears after a complete sequence of statements.
708For example,
709.nf
710.RS
711a = 1
712b = 2
713.RE
714.fi
715has two execution blocks and
716.nf
717.RS
718{ a = 1
719 b = 2 }
720.RE
721.fi
722has one execution block. Any runtime error will terminate the execution
723of the current execution block. A runtime warning will not terminate the
724current execution block.
725.IP "Interrupts"
726During an interactive session, the SIGINT signal (usually generated by
727the control-C character from the terminal) will cause execution of the
728current execution block to be interrupted. It will display a "runtime"
729error indicating which function was interrupted. After all runtime
730structures have been cleaned up, a message will be printed to notify the
731user that \fBbc\fR is ready for more input. All previously defined functions
732remain defined and the value of all non-auto variables are the value at
733the point of interruption. All auto variables and function parameters
734are removed during the
735clean up process. During a non-interactive
736session, the SIGINT signal will terminate the entire run of \fBbc\fR.
737.SS LIMITS
738The following are the limits currently in place for this
739.B bc
740processor. Some of them may have been changed by an installation.
741Use the limits statement to see the actual values.
742.IP BC_BASE_MAX
743The maximum output base is currently set at 999. The maximum input base
744is 16.
745.IP BC_DIM_MAX
746This is currently an arbitrary limit of 65535 as distributed. Your
747installation may be different.
748.IP BC_SCALE_MAX
749The number of digits after the decimal point is limited to INT_MAX digits.
750Also, the number of digits before the decimal point is limited to INT_MAX
751digits.
752.IP BC_STRING_MAX
753The limit on the number of characters in a string is INT_MAX characters.
754.IP exponent
755The value of the exponent in the raise operation (^) is limited to LONG_MAX.
756.IP "variable names"
757The current limit on the number of unique names is 32767 for each of
758simple variables, arrays and functions.
759.SH ENVIRONMENT
760The following environment variables are processed by \fBbc\fR:
761.IP "POSIXLY_CORRECT"
762This is the same as the \fB-s\fR option.
763.IP "BC_ENV_ARGS"
764This is another mechanism to get arguments to \fBbc\fR. The
765format is the same as the command line arguments. These arguments
766are processed first, so any files listed in the environment arguments
767are processed before any command line argument files. This allows
768the user to set up "standard" options and files to be processed
769at every invocation of \fBbc\fR. The files in the environment
770variables would typically contain function definitions for functions
771the user wants defined every time \fBbc\fR is run.
772.IP "BC_LINE_LENGTH"
773This should be an integer specifying the number of characters in an
774output line for numbers. This includes the backslash and newline characters
775for long numbers.
776.SH DIAGNOSTICS
777If any file on the command line can not be opened, \fBbc\fR will report
778that the file is unavailable and terminate. Also, there are compile
779and run time diagnostics that should be self-explanatory.
780.SH BUGS
781Error recovery is not very good yet.
782.PP
783Email bug reports to
784.BR bug-bc@gnu.org .
785Be sure to include the word ``bc'' somewhere in the ``Subject:'' field.
786.SH AUTHOR
787.nf
788Philip A. Nelson
789philnelson@acm.org
790.fi
791.SH ACKNOWLEDGEMENTS
792The author would like to thank Steve Sommars (Steve.Sommars@att.com) for
793his extensive help in testing the implementation. Many great suggestions
794were given. This is a much better product due to his involvement.