1bc(1) General Commands Manual bc(1)
2
6 bc - An arbitrary precision calculator language
7
9 bc [ -hlwsqv ] [long-options] [ file ... ]
10
12 This man page documents GNU bc version 1.06.
13
15 bc is a language that supports arbitrary precision numbers with inter‐
16 active execution of statements. There are some similarities in the
17 syntax to the C programming language. A standard math library is
18 available by command line option. If requested, the math library is
19 defined before processing any files. bc starts by processing code from
20 all the files listed on the command line in the order listed. After
21 all files have been processed, bc reads from the standard input. All
22 code is executed as it is read. (If a file contains a command to halt
23 the processor, bc will never read from the standard input.)
24 This version of bc contains several extensions beyond traditional bc
26 implementations and the POSIX draft standard. Command line options can
27 cause these extensions to print a warning or to be rejected. This doc‐
28 ument describes the language accepted by this processor. Extensions
29 will be identified as such.
30 OPTIONS
32 -h, --help
33 Print the usage and exit.
34 -i, --interactive
36 Force interactive mode.
37 -l, --mathlib
39 Define the standard math library.
40 -w, --warn
42 Give warnings for extensions to POSIX bc.
43 -s, --standard
45 Process exactly the POSIX bc language.
46 -q, --quiet
48 Do not print the normal GNU bc welcome.
49 -v, --version
51 Print the version number and copyright and quit.
52 NUMBERS
54 The most basic element in bc is the number. Numbers are arbitrary pre‐
55 cision numbers. This precision is both in the integer part and the
56 fractional part. All numbers are represented internally in decimal and
57 all computation is done in decimal. (This version truncates results
58 from divide and multiply operations.) There are two attributes of num‐
59 bers, the length and the scale. The length is the total number of sig‐
60 nificant decimal digits in a number and the scale is the total number
61 of decimal digits after the decimal point. For example:
62 .000001 has a length of 6 and scale of 6.
63 1935.000 has a length of 7 and a scale of 3.
64 VARIABLES
66 Numbers are stored in two types of variables, simple variables and
67 arrays. Both simple variables and array variables are named. Names
68 begin with a letter followed by any number of letters, digits and
69 underscores. All letters must be lower case. (Full alpha-numeric
70 names are an extension. In POSIX bc all names are a single lower case
71 letter.) The type of variable is clear by the context because all
72 array variable names will be followed by brackets ([]).
73 There are four special variables, scale, ibase, obase, and last. scale
75 defines how some operations use digits after the decimal point. The
76 default value of scale is 0. ibase and obase define the conversion base
77 for input and output numbers. The default for both input and output is
78 base 10. last (an extension) is a variable that has the value of the
79 last printed number. These will be discussed in further detail where
80 appropriate. All of these variables may have values assigned to them
81 as well as used in expressions.
82 COMMENTS
84 Comments in bc start with the characters /* and end with the characters
85 */. Comments may start anywhere and appear as a single space in the
86 input. (This causes comments to delimit other input items. For exam‐
87 ple, a comment can not be found in the middle of a variable name.)
88 Comments include any newlines (end of line) between the start and the
89 end of the comment.
90 To support the use of scripts for bc, a single line comment has been
92 added as an extension. A single line comment starts at a # character
93 and continues to the next end of the line. The end of line character
94 is not part of the comment and is processed normally.
95 EXPRESSIONS
97 The numbers are manipulated by expressions and statements. Since the
98 language was designed to be interactive, statements and expressions are
99 executed as soon as possible. There is no "main" program. Instead,
100 code is executed as it is encountered. (Functions, discussed in detail
101 later, are defined when encountered.)
102 A simple expression is just a constant. bc converts constants into
104 internal decimal numbers using the current input base, specified by the
105 variable ibase. (There is an exception in functions.) The legal values
106 of ibase are 2 through 16. Assigning a value outside this range to
107 ibase will result in a value of 2 or 16. Input numbers may contain the
108 characters 0-9 and A-F. (Note: They must be capitals. Lower case let‐
109 ters are variable names.) Single digit numbers always have the value
110 of the digit regardless of the value of ibase. (i.e. A = 10.) For
111 multi-digit numbers, bc changes all input digits greater or equal to
112 ibase to the value of ibase-1. This makes the number FFF always be the
113 largest 3 digit number of the input base.
114 Full expressions are similar to many other high level languages. Since
116 there is only one kind of number, there are no rules for mixing types.
117 Instead, there are rules on the scale of expressions. Every expression
118 has a scale. This is derived from the scale of original numbers, the
119 operation performed and in many cases, the value of the variable scale.
120 Legal values of the variable scale are 0 to the maximum number repre‐
121 sentable by a C integer.
122 In the following descriptions of legal expressions, "expr" refers to a
124 complete expression and "var" refers to a simple or an array variable.
125 A simple variable is just a
126 name
127 and an array variable is specified as
128 name[expr]
129 Unless specifically mentioned the scale of the result is the maximum
130 scale of the expressions involved.
131 - expr The result is the negation of the expression.
133 ++ var The variable is incremented by one and the new value is the
135 result of the expression.
136 -- var The variable is decremented by one and the new value is the
138 result of the expression.
139 var ++
141 The result of the expression is the value of the variable and
142 then the variable is incremented by one.
143 var -- The result of the expression is the value of the variable and
145 then the variable is decremented by one.
146 expr + expr
148 The result of the expression is the sum of the two expressions.
149 expr - expr
151 The result of the expression is the difference of the two
152 expressions.
153 expr * expr
155 The result of the expression is the product of the two expres‐
156 sions.
157 expr / expr
159 The result of the expression is the quotient of the two expres‐
160 sions. The scale of the result is the value of the variable
161 scale.
162 expr % expr
164 The result of the expression is the "remainder" and it is com‐
165 puted in the following way. To compute a%b, first a/b is com‐
166 puted to scale digits. That result is used to compute a-(a/b)*b
167 to the scale of the maximum of scale+scale(b) and scale(a). If
168 scale is set to zero and both expressions are integers this
169 expression is the integer remainder function.
170 expr ^ expr
172 The result of the expression is the value of the first raised to
173 the second. The second expression must be an integer. (If the
174 second expression is not an integer, a warning is generated and
175 the expression is truncated to get an integer value.) The scale
176 of the result is scale if the exponent is negative. If the
177 exponent is positive the scale of the result is the minimum of
178 the scale of the first expression times the value of the expo‐
179 nent and the maximum of scale and the scale of the first expres‐
180 sion. (e.g. scale(a^b) = min(scale(a)*b, max( scale,
181 scale(a))).) It should be noted that expr^0 will always return
182 the value of 1.
183 ( expr )
185 This alters the standard precedence to force the evaluation of
186 the expression.
187 var = expr
189 The variable is assigned the value of the expression.
190 var <op>= expr
192 This is equivalent to "var = var <op> expr" with the exception
193 that the "var" part is evaluated only once. This can make a
194 difference if "var" is an array.
195 Relational expressions are a special kind of expression that always
197 evaluate to 0 or 1, 0 if the relation is false and 1 if the relation is
198 true. These may appear in any legal expression. (POSIX bc requires
199 that relational expressions are used only in if, while, and for state‐
200 ments and that only one relational test may be done in them.) The
201 relational operators are
202 expr1 < expr2
204 The result is 1 if expr1 is strictly less than expr2.
205 expr1 <= expr2
207 The result is 1 if expr1 is less than or equal to expr2.
208 expr1 > expr2
210 The result is 1 if expr1 is strictly greater than expr2.
211 expr1 >= expr2
213 The result is 1 if expr1 is greater than or equal to expr2.
214 expr1 == expr2
216 The result is 1 if expr1 is equal to expr2.
217 expr1 != expr2
219 The result is 1 if expr1 is not equal to expr2.
220 Boolean operations are also legal. (POSIX bc does NOT have boolean
222 operations). The result of all boolean operations are 0 and 1 (for
223 false and true) as in relational expressions. The boolean operators
224 are:
225 !expr The result is 1 if expr is 0.
227 expr && expr
229 The result is 1 if both expressions are non-zero.
230 expr || expr
232 The result is 1 if either expression is non-zero.
233 The expression precedence is as follows: (lowest to highest)
235 || operator, left associative
236 && operator, left associative
237 ! operator, nonassociative
238 Relational operators, left associative
239 Assignment operator, right associative
240 + and - operators, left associative
241 *, / and % operators, left associative
242 ^ operator, right associative
243 unary - operator, nonassociative
244 ++ and -- operators, nonassociative
245 This precedence was chosen so that POSIX compliant bc programs will run
247 correctly. This will cause the use of the relational and logical opera‐
248 tors to have some unusual behavior when used with assignment expres‐
249 sions. Consider the expression:
250 a = 3 < 5
251 Most C programmers would assume this would assign the result of "3 < 5"
253 (the value 1) to the variable "a". What this does in bc is assign the
254 value 3 to the variable "a" and then compare 3 to 5. It is best to use
255 parenthesis when using relational and logical operators with the
256 assignment operators.
257 There are a few more special expressions that are provided in bc.
259 These have to do with user defined functions and standard functions.
260 They all appear as "name(parameters)". See the section on functions
261 for user defined functions. The standard functions are:
262 length ( expression )
264 The value of the length function is the number of significant
265 digits in the expression.
266 read ( )
268 The read function (an extension) will read a number from the
269 standard input, regardless of where the function occurs.
270 Beware, this can cause problems with the mixing of data and pro‐
271 gram in the standard input. The best use for this function is
272 in a previously written program that needs input from the user,
273 but never allows program code to be input from the user. The
274 value of the read function is the number read from the standard
275 input using the current value of the variable ibase for the con‐
276 version base.
277 scale ( expression )
279 The value of the scale function is the number of digits after
280 the decimal point in the expression.
281 sqrt ( expression )
283 The value of the sqrt function is the square root of the expres‐
284 sion. If the expression is negative, a run time error is gener‐
285 ated.
286 STATEMENTS
288 Statements (as in most algebraic languages) provide the sequencing of
289 expression evaluation. In bc statements are executed "as soon as pos‐
290 sible." Execution happens when a newline in encountered and there is
291 one or more complete statements. Due to this immediate execution, new‐
292 lines are very important in bc. In fact, both a semicolon and a newline
293 are used as statement separators. An improperly placed newline will
294 cause a syntax error. Because newlines are statement separators, it is
295 possible to hide a newline by using the backslash character. The
296 sequence "\<nl>", where <nl> is the newline appears to bc as whitespace
297 instead of a newline. A statement list is a series of statements sepa‐
298 rated by semicolons and newlines. The following is a list of bc state‐
299 ments and what they do: (Things enclosed in brackets ([]) are optional
300 parts of the statement.)
301 expression
303 This statement does one of two things. If the expression starts
304 with "<variable> <assignment> ...", it is considered to be an
305 assignment statement. If the expression is not an assignment
306 statement, the expression is evaluated and printed to the out‐
307 put. After the number is printed, a newline is printed. For
308 example, "a=1" is an assignment statement and "(a=1)" is an
309 expression that has an embedded assignment. All numbers that
310 are printed are printed in the base specified by the variable
311 obase. The legal values for obase are 2 through BC_BASE_MAX.
312 (See the section LIMITS.) For bases 2 through 16, the usual
313 method of writing numbers is used. For bases greater than 16,
314 bc uses a multi-character digit method of printing the numbers
315 where each higher base digit is printed as a base 10 number.
316 The multi-character digits are separated by spaces. Each digit
317 contains the number of characters required to represent the base
318 ten value of "obase-1". Since numbers are of arbitrary preci‐
319 sion, some numbers may not be printable on a single output line.
320 These long numbers will be split across lines using the "\" as
321 the last character on a line. The maximum number of characters
322 printed per line is 70. Due to the interactive nature of bc,
323 printing a number causes the side effect of assigning the
324 printed value to the special variable last. This allows the user
325 to recover the last value printed without having to retype the
326 expression that printed the number. Assigning to last is legal
327 and will overwrite the last printed value with the assigned
328 value. The newly assigned value will remain until the next num‐
329 ber is printed or another value is assigned to last. (Some
330 installations may allow the use of a single period (.) which is
331 not part of a number as a short hand notation for for last.)
332 string The string is printed to the output. Strings start with a dou‐
334 ble quote character and contain all characters until the next
335 double quote character. All characters are take literally,
336 including any newline. No newline character is printed after
337 the string.
338 print list
340 The print statement (an extension) provides another method of
341 output. The "list" is a list of strings and expressions sepa‐
342 rated by commas. Each string or expression is printed in the
343 order of the list. No terminating newline is printed. Expres‐
344 sions are evaluated and their value is printed and assigned to
345 the variable last. Strings in the print statement are printed to
346 the output and may contain special characters. Special charac‐
347 ters start with the backslash character (\). The special char‐
348 acters recognized by bc are "a" (alert or bell), "b"
349 (backspace), "f" (form feed), "n" (newline), "r" (carriage
350 return), "q" (double quote), "t" (tab), and "\" (backslash).
351 Any other character following the backslash will be ignored.
352 { statement_list }
354 This is the compound statement. It allows multiple statements
355 to be grouped together for execution.
356 if ( expression ) statement1 [else statement2]
358 The if statement evaluates the expression and executes state‐
359 ment1 or statement2 depending on the value of the expression.
360 If the expression is non-zero, statement1 is executed. If
361 statement2 is present and the value of the expression is 0, then
362 statement2 is executed. (The else clause is an extension.)
363 while ( expression ) statement
365 The while statement will execute the statement while the expres‐
366 sion is non-zero. It evaluates the expression before each exe‐
367 cution of the statement. Termination of the loop is caused by
368 a zero expression value or the execution of a break statement.
369 for ( [expression1] ; [expression2] ; [expression3] ) statement
371 The for statement controls repeated execution of the statement.
372 Expression1 is evaluated before the loop. Expression2 is evalu‐
373 ated before each execution of the statement. If it is non-zero,
374 the statement is evaluated. If it is zero, the loop is termi‐
375 nated. After each execution of the statement, expression3 is
376 evaluated before the reevaluation of expression2. If expres‐
377 sion1 or expression3 are missing, nothing is evaluated at the
378 point they would be evaluated. If expression2 is missing, it is
379 the same as substituting the value 1 for expression2. (The
380 optional expressions are an extension. POSIX bc requires all
381 three expressions.) The following is equivalent code for the
382 for statement:
383 expression1;
384 while (expression2) {
385 statement;
386 expression3;
387 }
388 break This statement causes a forced exit of the most recent enclosing
390 while statement or for statement.
391 continue
393 The continue statement (an extension) causes the most recent
394 enclosing for statement to start the next iteration.
395 halt The halt statement (an extension) is an executed statement that
397 causes the bc processor to quit only when it is executed. For
398 example, "if (0 == 1) halt" will not cause bc to terminate
399 because the halt is not executed.
400 return Return the value 0 from a function. (See the section on func‐
402 tions.)
403 return ( expression )
405 Return the value of the expression from a function. (See the
406 section on functions.) As an extension, the parenthesis are not
407 required.
408 PSEUDO STATEMENTS
410 These statements are not statements in the traditional sense. They are
411 not executed statements. Their function is performed at "compile"
412 time.
413 limits Print the local limits enforced by the local version of bc.
415 This is an extension.
416 quit When the quit statement is read, the bc processor is terminated,
418 regardless of where the quit statement is found. For example,
419 "if (0 == 1) quit" will cause bc to terminate.
420 warranty
422 Print a longer warranty notice. This is an extension.
423 FUNCTIONS
425 Functions provide a method of defining a computation that can be exe‐
426 cuted later. Functions in bc always compute a value and return it to
427 the caller. Function definitions are "dynamic" in the sense that a
428 function is undefined until a definition is encountered in the input.
429 That definition is then used until another definition function for the
430 same name is encountered. The new definition then replaces the older
431 definition. A function is defined as follows:
432 define name ( parameters ) { newline
433 auto_list statement_list }
434 A function call is just an expression of the form "name(parameters)".
435 Parameters are numbers or arrays (an extension). In the function defi‐
437 nition, zero or more parameters are defined by listing their names sep‐
438 arated by commas. Numbers are only call by value parameters. Arrays
439 are only call by variable. Arrays are specified in the parameter defi‐
440 nition by the notation "name[]". In the function call, actual parame‐
441 ters are full expressions for number parameters. The same notation is
442 used for passing arrays as for defining array parameters. The named
443 array is passed by variable to the function. Since function defini‐
444 tions are dynamic, parameter numbers and types are checked when a func‐
445 tion is called. Any mismatch in number or types of parameters will
446 cause a runtime error. A runtime error will also occur for the call to
447 an undefined function.
448 The auto_list is an optional list of variables that are for "local"
450 use. The syntax of the auto list (if present) is "auto name, ... ;".
451 (The semicolon is optional.) Each name is the name of an auto vari‐
452 able. Arrays may be specified by using the same notation as used in
453 parameters. These variables have their values pushed onto a stack at
454 the start of the function. The variables are then initialized to zero
455 and used throughout the execution of the function. At function exit,
456 these variables are popped so that the original value (at the time of
457 the function call) of these variables are restored. The parameters are
458 really auto variables that are initialized to a value provided in the
459 function call. Auto variables are different than traditional local
460 variables because if function A calls function B, B may access function
461 A's auto variables by just using the same name, unless function B has
462 called them auto variables. Due to the fact that auto variables and
463 parameters are pushed onto a stack, bc supports recursive functions.
464 The function body is a list of bc statements. Again, statements are
466 separated by semicolons or newlines. Return statements cause the ter‐
467 mination of a function and the return of a value. There are two ver‐
468 sions of the return statement. The first form, "return", returns the
469 value 0 to the calling expression. The second form, "return ( expres‐
470 sion )", computes the value of the expression and returns that value to
471 the calling expression. There is an implied "return (0)" at the end of
472 every function. This allows a function to terminate and return 0 with‐
473 out an explicit return statement.
474 Functions also change the usage of the variable ibase. All constants
476 in the function body will be converted using the value of ibase at the
477 time of the function call. Changes of ibase will be ignored during the
478 execution of the function except for the standard function read, which
479 will always use the current value of ibase for conversion of numbers.
480 As an extension, the format of the definition has been slightly
482 relaxed. The standard requires the opening brace be on the same line
483 as the define keyword and all other parts must be on following lines.
484 This version of bc will allow any number of newlines before and after
485 the opening brace of the function. For example, the following defini‐
486 tions are legal.
487 define d (n) { return (2*n); }
488 define d (n)
489 { return (2*n); }
490 MATH LIBRARY
492 If bc is invoked with the -l option, a math library is preloaded and
493 the default scale is set to 20. The math functions will calculate
494 their results to the scale set at the time of their call. The math
495 library defines the following functions:
496 s (x) The sine of x, x is in radians.
498 c (x) The cosine of x, x is in radians.
500 a (x) The arctangent of x, arctangent returns radians.
502 l (x) The natural logarithm of x.
504 e (x) The exponential function of raising e to the value x.
506 j (n,x)
508 The bessel function of integer order n of x.
509 EXAMPLES
511 In /bin/sh, the following will assign the value of "pi" to the shell
512 variable pi.
513 pi=$(echo "scale=10; 4*a(1)" | bc -l)
514 The following is the definition of the exponential function used in the
516 math library. This function is written in POSIX bc.
517 scale = 20
518 /* Uses the fact that e^x = (e^(x/2))^2
520 When x is small enough, we use the series:
521 e^x = 1 + x + x^2/2! + x^3/3! + ...
522 */
523 define e(x) {
525 auto a, d, e, f, i, m, v, z
526 /* Check the sign of x. */
528 if (x<0) {
529 m = 1
530 x = -x
531 }
532 /* Precondition x. */
534 z = scale;
535 scale = 4 + z + .44*x;
536 while (x > 1) {
537 f += 1;
538 x /= 2;
539 }
540 /* Initialize the variables. */
542 v = 1+x
543 a = x
544 d = 1
545 for (i=2; 1; i++) {
547 e = (a *= x) / (d *= i)
548 if (e == 0) {
549 if (f>0) while (f--) v = v*v;
550 scale = z
551 if (m) return (1/v);
552 return (v/1);
553 }
554 v += e
555 }
556 }
557 The following is code that uses the extended features of bc to imple‐
559 ment a simple program for calculating checkbook balances. This program
560 is best kept in a file so that it can be used many times without having
561 to retype it at every use.
562 scale=2
563 print "\nCheck book program!\n"
564 print " Remember, deposits are negative transactions.\n"
565 print " Exit by a 0 transaction.\n\n"
566 print "Initial balance? "; bal = read()
568 bal /= 1
569 print "\n"
570 while (1) {
571 "current balance = "; bal
572 "transaction? "; trans = read()
573 if (trans == 0) break;
574 bal -= trans
575 bal /= 1
576 }
577 quit
578 The following is the definition of the recursive factorial function.
580 define f (x) {
581 if (x <= 1) return (1);
582 return (f(x-1) * x);
583 }
584 READLINE AND LIBEDIT OPTIONS
586 GNU bc can be compiled (via a configure option) to use the GNU readline
587 input editor library or the BSD libedit library. This allows the user
588 to do editing of lines before sending them to bc. It also allows for a
589 history of previous lines typed. When this option is selected, bc has
590 one more special variable. This special variable, history is the num‐
591 ber of lines of history retained. For readline, a value of -1 means
592 that an unlimited number of history lines are retained. Setting the
593 value of history to a positive number restricts the number of history
594 lines to the number given. The value of 0 disables the history fea‐
595 ture. The default value is 100. For more information, read the user
596 manuals for the GNU readline, history and BSD libedit libraries. One
597 can not enable both readline and libedit at the same time.
598 DIFFERENCES
600 This version of bc was implemented from the POSIX P1003.2/D11 draft and
601 contains several differences and extensions relative to the draft and
602 traditional implementations. It is not implemented in the traditional
603 way using dc(1). This version is a single process which parses and
604 runs a byte code translation of the program. There is an "undocu‐
605 mented" option (-c) that causes the program to output the byte code to
606 the standard output instead of running it. It was mainly used for
607 debugging the parser and preparing the math library.
608 A major source of differences is extensions, where a feature is
610 extended to add more functionality and additions, where new features
611 are added. The following is the list of differences and extensions.
612 LANG This version does not conform to the POSIX standard in the pro‐
614 cessing of the LANG environment variable and all environment
615 variables starting with LC_.
616 names Traditional and POSIX bc have single letter names for functions,
618 variables and arrays. They have been extended to be multi-char‐
619 acter names that start with a letter and may contain letters,
620 numbers and the underscore character.
621 Strings
623 Strings are not allowed to contain NUL characters. POSIX says
624 all characters must be included in strings.
625 last POSIX bc does not have a last variable. Some implementations of
627 bc use the period (.) in a similar way.
628 comparisons
630 POSIX bc allows comparisons only in the if statement, the while
631 statement, and the second expression of the for statement.
632 Also, only one relational operation is allowed in each of those
633 statements.
634 if statement, else clause
636 POSIX bc does not have an else clause.
637 for statement
639 POSIX bc requires all expressions to be present in the for
640 statement.
641 &&, ||, !
643 POSIX bc does not have the logical operators.
644 read function
646 POSIX bc does not have a read function.
647 print statement
649 POSIX bc does not have a print statement .
650 continue statement
652 POSIX bc does not have a continue statement.
653 return statement
655 POSIX bc requires parentheses around the return expression.
656 array parameters
658 POSIX bc does not (currently) support array parameters in full.
659 The POSIX grammar allows for arrays in function definitions, but
660 does not provide a method to specify an array as an actual
661 parameter. (This is most likely an oversight in the grammar.)
662 Traditional implementations of bc have only call by value array
663 parameters.
664 function format
666 POSIX bc requires the opening brace on the same line as the
667 define key word and the auto statement on the next line.
668 =+, =-, =*, =/, =%, =^
670 POSIX bc does not require these "old style" assignment operators
671 to be defined. This version may allow these "old style" assign‐
672 ments. Use the limits statement to see if the installed version
673 supports them. If it does support the "old style" assignment
674 operators, the statement "a =- 1" will decrement a by 1 instead
675 of setting a to the value -1.
676 spaces in numbers
678 Other implementations of bc allow spaces in numbers. For exam‐
679 ple, "x=1 3" would assign the value 13 to the variable x. The
680 same statement would cause a syntax error in this version of bc.
681 errors and execution
683 This implementation varies from other implementations in terms
684 of what code will be executed when syntax and other errors are
685 found in the program. If a syntax error is found in a function
686 definition, error recovery tries to find the beginning of a
687 statement and continue to parse the function. Once a syntax
688 error is found in the function, the function will not be
689 callable and becomes undefined. Syntax errors in the interac‐
690 tive execution code will invalidate the current execution block.
691 The execution block is terminated by an end of line that appears
692 after a complete sequence of statements. For example,
693 a = 1
694 b = 2
695 has two execution blocks and
696 { a = 1
697 b = 2 }
698 has one execution block. Any runtime error will terminate the execu‐
699 tion of the current execution block. A runtime warning will not termi‐
700 nate the current execution block.
701 Interrupts
703 During an interactive session, the SIGINT signal (usually gener‐
704 ated by the control-C character from the terminal) will cause
705 execution of the current execution block to be interrupted. It
706 will display a "runtime" error indicating which function was
707 interrupted. After all runtime structures have been cleaned up,
708 a message will be printed to notify the user that bc is ready
709 for more input. All previously defined functions remain defined
710 and the value of all non-auto variables are the value at the
711 point of interruption. All auto variables and function parame‐
712 ters are removed during the clean up process. During a non-
713 interactive session, the SIGINT signal will terminate the entire
714 run of bc.
715 LIMITS
717 The following are the limits currently in place for this bc processor.
718 Some of them may have been changed by an installation. Use the limits
719 statement to see the actual values.
720 BC_BASE_MAX
722 The maximum output base is currently set at 999. The maximum
723 input base is 16.
724 BC_DIM_MAX
726 This is currently an arbitrary limit of 65535 as distributed.
727 Your installation may be different.
728 BC_SCALE_MAX
730 The number of digits after the decimal point is limited to
731 INT_MAX digits. Also, the number of digits before the decimal
732 point is limited to INT_MAX digits.
733 BC_STRING_MAX
735 The limit on the number of characters in a string is INT_MAX
736 characters.
737 exponent
739 The value of the exponent in the raise operation (^) is limited
740 to LONG_MAX.
741 variable names
743 The current limit on the number of unique names is 32767 for
744 each of simple variables, arrays and functions.
745
747 The following environment variables are processed by bc:
748 POSIXLY_CORRECT
750 This is the same as the -s option.
751 BC_ENV_ARGS
753 This is another mechanism to get arguments to bc. The format is
754 the same as the command line arguments. These arguments are
755 processed first, so any files listed in the environent arguments
756 are processed before any command line argument files. This
757 allows the user to set up "standard" options and files to be
758 processed at every invocation of bc. The files in the environ‐
759 ment variables would typically contain function definitions for
760 functions the user wants defined every time bc is run.
761 BC_LINE_LENGTH
763 This should be an integer specifing the number of characters in
764 an output line for numbers. This includes the backslash and new‐
765 line characters for long numbers.
766
768 If any file on the command line can not be opened, bc will report that
769 the file is unavailable and terminate. Also, there are compile and run
770 time diagnostics that should be self-explanatory.
771
773 Error recovery is not very good yet.
774 Email bug reports to bug-bc@gnu.org. Be sure to include the word
776 ``bc'' somewhere in the ``Subject:'' field.
777
779 Philip A. Nelson
780 philnelson@acm.org
781
783 The author would like to thank Steve Sommars (Steve.Sommars@att.com)
784 for his extensive help in testing the implementation. Many great sug‐
785 gestions were given. This is a much better product due to his involve‐
786 ment.
787 . bc(1)