| 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 $ |
| 31 | .\" $DragonFly: src/contrib/bc/doc/Attic/bc.1,v 1.2 2003/06/17 04:23:58 dillon Exp $ |
| 32 | .\" |
| 33 | .TH bc 1 .\" "Command Manual" v1.06 "Sept 12, 2000" |
| 34 | .SH NAME |
| 35 | bc - An arbitrary precision calculator language |
| 36 | .SH SYNTAX |
| 37 | \fBbc\fR [ \fB-hlwsqv\fR ] [long-options] [ \fI file ...\fR ] |
| 38 | .SH VERSION |
| 39 | This man page documents GNU bc version 1.06. |
| 40 | .SH DESCRIPTION |
| 41 | \fBbc\fR is a language that supports arbitrary precision numbers |
| 42 | with interactive execution of statements. There are some similarities |
| 43 | in the syntax to the C programming language. |
| 44 | A standard math library is available by command line option. |
| 45 | If requested, the math library is defined before processing any files. |
| 46 | \fBbc\fR starts by processing code from all the files listed |
| 47 | on the command line in the order listed. After all files have been |
| 48 | processed, \fBbc\fR reads from the standard input. All code is |
| 49 | executed as it is read. (If a file contains a command to halt the |
| 50 | processor, \fBbc\fR will never read from the standard input.) |
| 51 | .PP |
| 52 | This version of \fBbc\fR contains several extensions beyond |
| 53 | traditional \fBbc\fR implementations and the POSIX draft standard. |
| 54 | Command line options can cause these extensions to print a warning |
| 55 | or to be rejected. This |
| 56 | document describes the language accepted by this processor. |
| 57 | Extensions will be identified as such. |
| 58 | .SS OPTIONS |
| 59 | .IP "-h, --help" |
| 60 | Print the usage and exit. |
| 61 | .IP "-i, --interactive" |
| 62 | Force interactive mode. |
| 63 | .IP "-l, --mathlib" |
| 64 | Define the standard math library. |
| 65 | .IP "-w, --warn" |
| 66 | Give warnings for extensions to POSIX \fBbc\fR. |
| 67 | .IP "-s, --standard" |
| 68 | Process exactly the POSIX \fBbc\fR language. |
| 69 | .IP "-q, --quiet" |
| 70 | Do not print the normal GNU bc welcome. |
| 71 | .IP "-v, --version" |
| 72 | Print the version number and copyright and quit. |
| 73 | .SS NUMBERS |
| 74 | The most basic element in \fBbc\fR is the number. Numbers are |
| 75 | arbitrary precision numbers. This precision is both in the integer |
| 76 | part and the fractional part. All numbers are represented internally |
| 77 | in decimal and all computation is done in decimal. (This version |
| 78 | truncates results from divide and multiply operations.) There are two |
| 79 | attributes of numbers, the length and the scale. The length is the |
| 80 | total number of significant decimal digits in a number and the scale |
| 81 | is the total number of decimal digits after the decimal point. For |
| 82 | example: |
| 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 |
| 90 | Numbers are stored in two types of variables, simple variables and |
| 91 | arrays. Both simple variables and array variables are named. Names |
| 92 | begin with a letter followed by any number of letters, digits and |
| 93 | underscores. All letters must be lower case. (Full alpha-numeric |
| 94 | names are an extension. In POSIX \fBbc\fR all names are a single |
| 95 | lower case letter.) The type of variable is clear by the context |
| 96 | because all array variable names will be followed by brackets ([]). |
| 97 | .PP |
| 98 | There are four special variables, \fBscale, ibase, obase,\fR and |
| 99 | \fBlast\fR. \fBscale\fR defines how some operations use digits after the |
| 100 | decimal point. The default value of \fBscale\fR is 0. \fBibase\fR |
| 101 | and \fBobase\fR define the conversion base for input and output |
| 102 | numbers. 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 |
| 104 | printed number. These will be discussed in further detail where |
| 105 | appropriate. All of these variables may have values assigned to them |
| 106 | as well as used in expressions. |
| 107 | .SS COMMENTS |
| 108 | Comments in \fBbc\fR start with the characters \fB/*\fR and end with |
| 109 | the characters \fB*/\fR. Comments may start anywhere and appear as a |
| 110 | single space in the input. (This causes comments to delimit other |
| 111 | input items. For example, a comment can not be found in the middle of |
| 112 | a variable name.) Comments include any newlines (end of line) between |
| 113 | the start and the end of the comment. |
| 114 | .PP |
| 115 | To support the use of scripts for \fBbc\fR, a single line comment has been |
| 116 | added as an extension. A single line comment starts at a \fB#\fR |
| 117 | character and continues to the next end of the line. The end of line |
| 118 | character is not part of the comment and is processed normally. |
| 119 | .SS EXPRESSIONS |
| 120 | The numbers are manipulated by expressions and statements. Since |
| 121 | the language was designed to be interactive, statements and expressions |
| 122 | are executed as soon as possible. There is no "main" program. Instead, |
| 123 | code is executed as it is encountered. (Functions, discussed in |
| 124 | detail later, are defined when encountered.) |
| 125 | .PP |
| 126 | A simple expression is just a constant. \fBbc\fR converts constants |
| 127 | into internal decimal numbers using the current input base, specified |
| 128 | by the variable \fBibase\fR. (There is an exception in functions.) |
| 129 | The legal values of \fBibase\fR are 2 through 16. Assigning a |
| 130 | value outside this range to \fBibase\fR will result in a value of 2 |
| 131 | or 16. Input numbers may contain the characters 0-9 and A-F. (Note: |
| 132 | They must be capitals. Lower case letters are variable names.) |
| 133 | Single digit numbers always have the value of the digit regardless of |
| 134 | the 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 |
| 136 | value of \fBibase\fR-1. This makes the number \fBFFF\fR always be |
| 137 | the largest 3 digit number of the input base. |
| 138 | .PP |
| 139 | Full expressions are similar to many other high level languages. |
| 140 | Since there is only one kind of number, there are no rules for mixing |
| 141 | types. Instead, there are rules on the scale of expressions. Every |
| 142 | expression has a scale. This is derived from the scale of original |
| 143 | numbers, the operation performed and in many cases, the value of the |
| 144 | variable \fBscale\fR. Legal values of the variable \fBscale\fR are |
| 145 | 0 to the maximum number representable by a C integer. |
| 146 | .PP |
| 147 | In the following descriptions of legal expressions, "expr" refers to a |
| 148 | complete expression and "var" refers to a simple or an array variable. |
| 149 | A simple variable is just a |
| 150 | .RS |
| 151 | \fIname\fR |
| 152 | .RE |
| 153 | and an array variable is specified as |
| 154 | .RS |
| 155 | \fIname\fR[\fIexpr\fR] |
| 156 | .RE |
| 157 | Unless specifically |
| 158 | mentioned the scale of the result is the maximum scale of the |
| 159 | expressions involved. |
| 160 | .IP "- expr" |
| 161 | The result is the negation of the expression. |
| 162 | .IP "++ var" |
| 163 | The variable is incremented by one and the new value is the result of |
| 164 | the expression. |
| 165 | .IP "-- var" |
| 166 | The variable |
| 167 | is decremented by one and the new value is the result of the |
| 168 | expression. |
| 169 | .IP "var ++" |
| 170 | The result of the expression is the value of |
| 171 | the variable and then the variable is incremented by one. |
| 172 | .IP "var --" |
| 173 | The result of the expression is the value of the variable and then |
| 174 | the variable is decremented by one. |
| 175 | .IP "expr + expr" |
| 176 | The result of the expression is the sum of the two expressions. |
| 177 | .IP "expr - expr" |
| 178 | The result of the expression is the difference of the two expressions. |
| 179 | .IP "expr * expr" |
| 180 | The result of the expression is the product of the two expressions. |
| 181 | .IP "expr / expr" |
| 182 | The result of the expression is the quotient of the two expressions. |
| 183 | The scale of the result is the value of the variable \fBscale\fR. |
| 184 | .IP "expr % expr" |
| 185 | The result of the expression is the "remainder" and it is computed in the |
| 186 | following way. To compute a%b, first a/b is computed to \fBscale\fR |
| 187 | digits. That result is used to compute a-(a/b)*b to the scale of the |
| 188 | maximum of \fBscale\fR+scale(b) and scale(a). If \fBscale\fR is set |
| 189 | to zero and both expressions are integers this expression is the |
| 190 | integer remainder function. |
| 191 | .IP "expr ^ expr" |
| 192 | The result of the expression is the value of the first raised to the |
| 193 | second. The second expression must be an integer. (If the second |
| 194 | expression is not an integer, a warning is generated and the |
| 195 | expression is truncated to get an integer value.) The scale of the |
| 196 | result is \fBscale\fR if the exponent is negative. If the exponent |
| 197 | is positive the scale of the result is the minimum of the scale of the |
| 198 | first 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 |
| 201 | that expr^0 will always return the value of 1. |
| 202 | .IP "( expr )" |
| 203 | This alters the standard precedence to force the evaluation of the |
| 204 | expression. |
| 205 | .IP "var = expr" |
| 206 | The variable is assigned the value of the expression. |
| 207 | .IP "var <op>= expr" |
| 208 | This is equivalent to "var = var <op> expr" with the exception that |
| 209 | the "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 |
| 213 | that always evaluate to 0 or 1, 0 if the relation is false and 1 if |
| 214 | the relation is true. These may appear in any legal expression. |
| 215 | (POSIX bc requires that relational expressions are used only in if, |
| 216 | while, and for statements and that only one relational test may be |
| 217 | done in them.) The relational operators are |
| 218 | .IP "expr1 < expr2" |
| 219 | The result is 1 if expr1 is strictly less than expr2. |
| 220 | .IP "expr1 <= expr2" |
| 221 | The result is 1 if expr1 is less than or equal to expr2. |
| 222 | .IP "expr1 > expr2" |
| 223 | The result is 1 if expr1 is strictly greater than expr2. |
| 224 | .IP "expr1 >= expr2" |
| 225 | The result is 1 if expr1 is greater than or equal to expr2. |
| 226 | .IP "expr1 == expr2" |
| 227 | The result is 1 if expr1 is equal to expr2. |
| 228 | .IP "expr1 != expr2" |
| 229 | The result is 1 if expr1 is not equal to expr2. |
| 230 | .PP |
| 231 | Boolean operations are also legal. (POSIX \fBbc\fR does NOT have |
| 232 | boolean operations). The result of all boolean operations are 0 and 1 |
| 233 | (for false and true) as in relational expressions. The boolean |
| 234 | operators are: |
| 235 | .IP "!expr" |
| 236 | The result is 1 if expr is 0. |
| 237 | .IP "expr && expr" |
| 238 | The result is 1 if both expressions are non-zero. |
| 239 | .IP "expr || expr" |
| 240 | The result is 1 if either expression is non-zero. |
| 241 | .PP |
| 242 | The expression precedence is as follows: (lowest to highest) |
| 243 | .nf |
| 244 | .RS |
| 245 | || operator, left associative |
| 246 | && operator, left associative |
| 247 | ! operator, nonassociative |
| 248 | Relational operators, left associative |
| 249 | Assignment operator, right associative |
| 250 | + and - operators, left associative |
| 251 | *, / and % operators, left associative |
| 252 | ^ operator, right associative |
| 253 | unary - operator, nonassociative |
| 254 | ++ and -- operators, nonassociative |
| 255 | .RE |
| 256 | .fi |
| 257 | .PP |
| 258 | This precedence was chosen so that POSIX compliant \fBbc\fR programs |
| 259 | will run correctly. This will cause the use of the relational and |
| 260 | logical operators to have some unusual behavior when used with |
| 261 | assignment expressions. Consider the expression: |
| 262 | .RS |
| 263 | a = 3 < 5 |
| 264 | .RE |
| 265 | .PP |
| 266 | Most C programmers would assume this would assign the result of "3 < |
| 267 | 5" (the value 1) to the variable "a". What this does in \fBbc\fR is |
| 268 | assign the value 3 to the variable "a" and then compare 3 to 5. It is |
| 269 | best to use parenthesis when using relational and logical operators |
| 270 | with the assignment operators. |
| 271 | .PP |
| 272 | There are a few more special expressions that are provided in \fBbc\fR. |
| 273 | These have to do with user defined functions and standard |
| 274 | functions. They all appear as "\fIname\fB(\fIparameters\fB)\fR". |
| 275 | See the section on functions for user defined functions. The standard |
| 276 | functions are: |
| 277 | .IP "length ( expression )" |
| 278 | The value of the length function is the number of significant digits in the |
| 279 | expression. |
| 280 | .IP "read ( )" |
| 281 | The read function (an extension) will read a number from the standard |
| 282 | input, regardless of where the function occurs. Beware, this can |
| 283 | cause problems with the mixing of data and program in the standard input. |
| 284 | The best use for this function is in a previously written program that |
| 285 | needs input from the user, but never allows program code to be input |
| 286 | from the user. The value of the read function is the number read from |
| 287 | the standard input using the current value of the variable |
| 288 | \fBibase\fR for the conversion base. |
| 289 | .IP "scale ( expression )" |
| 290 | The value of the scale function is the number of digits after the decimal |
| 291 | point in the expression. |
| 292 | .IP "sqrt ( expression )" |
| 293 | The value of the sqrt function is the square root of the expression. If |
| 294 | the expression is negative, a run time error is generated. |
| 295 | .SS STATEMENTS |
| 296 | Statements (as in most algebraic languages) provide the sequencing of |
| 297 | expression evaluation. In \fBbc\fR statements are executed "as soon |
| 298 | as possible." Execution happens when a newline in encountered and |
| 299 | there is one or more complete statements. Due to this immediate |
| 300 | execution, newlines are very important in \fBbc\fR. In fact, both a |
| 301 | semicolon and a newline are used as statement separators. An |
| 302 | improperly placed newline will cause a syntax error. Because newlines |
| 303 | are statement separators, it is possible to hide a newline by using |
| 304 | the backslash character. The sequence "\e<nl>", where <nl> is the |
| 305 | newline appears to \fBbc\fR as whitespace instead of a newline. A |
| 306 | statement list is a series of statements separated by semicolons and |
| 307 | newlines. The following is a list of \fBbc\fR statements and what |
| 308 | they do: (Things enclosed in brackets ([]) are optional parts of the |
| 309 | statement.) |
| 310 | .IP "expression" |
| 311 | This statement does one of two things. If the expression starts with |
| 312 | "<variable> <assignment> ...", it is considered to be an assignment |
| 313 | statement. If the expression is not an assignment statement, the |
| 314 | expression is evaluated and printed to the output. After the number |
| 315 | is printed, a newline is printed. For example, "a=1" is an assignment |
| 316 | statement and "(a=1)" is an expression that has an embedded |
| 317 | assignment. All numbers that are printed are printed in the base |
| 318 | specified by the variable \fBobase\fR. The legal values for \fB |
| 319 | obase\fR are 2 through BC_BASE_MAX. (See the section LIMITS.) For |
| 320 | bases 2 through 16, the usual method of writing numbers is used. For |
| 321 | bases greater than 16, \fBbc\fR uses a multi-character digit method |
| 322 | of printing the numbers where each higher base digit is printed as a |
| 323 | base 10 number. The multi-character digits are separated by spaces. |
| 324 | Each digit contains the number of characters required to represent the |
| 325 | base ten value of "obase-1". Since numbers are of arbitrary |
| 326 | precision, some numbers may not be printable on a single output line. |
| 327 | These long numbers will be split across lines using the "\e" as the |
| 328 | last character on a line. The maximum number of characters printed |
| 329 | per line is 70. Due to the interactive nature of \fBbc\fR, printing |
| 330 | a number causes the side effect of assigning the printed value to the |
| 331 | special variable \fBlast\fR. This allows the user to recover the |
| 332 | last value printed without having to retype the expression that |
| 333 | printed the number. Assigning to \fBlast\fR is legal and will |
| 334 | overwrite the last printed value with the assigned value. The newly |
| 335 | assigned value will remain until the next number is printed or another |
| 336 | value is assigned to \fBlast\fR. (Some installations may allow the |
| 337 | use of a single period (.) which is not part of a number as a short |
| 338 | hand notation for for \fBlast\fR.) |
| 339 | .IP "string" |
| 340 | The string is printed to the output. Strings start with a double quote |
| 341 | character and contain all characters until the next double quote character. |
| 342 | All characters are take literally, including any newline. No newline |
| 343 | character is printed after the string. |
| 344 | .IP "\fBprint\fR list" |
| 345 | The print statement (an extension) provides another method of output. |
| 346 | The "list" is a list of strings and expressions separated by commas. |
| 347 | Each string or expression is printed in the order of the list. No |
| 348 | terminating newline is printed. Expressions are evaluated and their |
| 349 | value is printed and assigned to the variable \fBlast\fR. Strings |
| 350 | in the print statement are printed to the output and may contain |
| 351 | special characters. Special characters start with the backslash |
| 352 | character (\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). |
| 355 | Any other character following the backslash will be ignored. |
| 356 | .IP "{ statement_list }" |
| 357 | This is the compound statement. It allows multiple statements to be |
| 358 | grouped together for execution. |
| 359 | .IP "\fBif\fR ( expression ) statement1 [\fBelse\fR statement2]" |
| 360 | The if statement evaluates the expression and executes statement1 or |
| 361 | statement2 depending on the value of the expression. If the expression |
| 362 | is non-zero, statement1 is executed. If statement2 is present and |
| 363 | the value of the expression is 0, then statement2 is executed. (The |
| 364 | else clause is an extension.) |
| 365 | .IP "\fBwhile\fR ( expression ) statement" |
| 366 | The while statement will execute the statement while the expression |
| 367 | is non-zero. It evaluates the expression before each execution of |
| 368 | the statement. Termination of the loop is caused by a zero |
| 369 | expression value or the execution of a break statement. |
| 370 | .IP "\fBfor\fR ( [expression1] ; [expression2] ; [expression3] ) statement" |
| 371 | The for statement controls repeated execution of the statement. |
| 372 | Expression1 is evaluated before the loop. Expression2 is evaluated |
| 373 | before each execution of the statement. If it is non-zero, the statement |
| 374 | is evaluated. If it is zero, the loop is terminated. After each |
| 375 | execution of the statement, expression3 is evaluated before the reevaluation |
| 376 | of expression2. If expression1 or expression3 are missing, nothing is |
| 377 | evaluated at the point they would be evaluated. |
| 378 | If expression2 is missing, it is the same as substituting |
| 379 | the value 1 for expression2. (The optional expressions are an |
| 380 | extension. POSIX \fBbc\fR requires all three expressions.) |
| 381 | The following is equivalent code for the for statement: |
| 382 | .nf |
| 383 | .RS |
| 384 | expression1; |
| 385 | while (expression2) { |
| 386 | statement; |
| 387 | expression3; |
| 388 | } |
| 389 | .RE |
| 390 | .fi |
| 391 | .IP "\fBbreak\fR" |
| 392 | This statement causes a forced exit of the most recent enclosing while |
| 393 | statement or for statement. |
| 394 | .IP "\fBcontinue\fR" |
| 395 | The continue statement (an extension) causes the most recent enclosing |
| 396 | for statement to start the next iteration. |
| 397 | .IP "\fBhalt\fR" |
| 398 | The halt statement (an extension) is an executed statement that causes |
| 399 | the \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 |
| 401 | not executed. |
| 402 | .IP "\fBreturn\fR" |
| 403 | Return the value 0 from a function. (See the section on functions.) |
| 404 | .IP "\fBreturn\fR ( expression )" |
| 405 | Return the value of the expression from a function. (See the section on |
| 406 | functions.) As an extension, the parenthesis are not required. |
| 407 | .SS PSEUDO STATEMENTS |
| 408 | These statements are not statements in the traditional sense. They are |
| 409 | not executed statements. Their function is performed at "compile" time. |
| 410 | .IP "\fBlimits\fR" |
| 411 | Print the local limits enforced by the local version of \fBbc\fR. This |
| 412 | is an extension. |
| 413 | .IP "\fBquit\fR" |
| 414 | When the quit statement is read, the \fBbc\fR processor |
| 415 | is terminated, regardless of where the quit statement is found. For |
| 416 | example, "if (0 == 1) quit" will cause \fBbc\fR to terminate. |
| 417 | .IP "\fBwarranty\fR" |
| 418 | Print a longer warranty notice. This is an extension. |
| 419 | .SS FUNCTIONS |
| 420 | Functions provide a method of defining a computation that can be executed |
| 421 | later. Functions in |
| 422 | .B bc |
| 423 | always compute a value and return it to the caller. Function definitions |
| 424 | are "dynamic" in the sense that a function is undefined until a definition |
| 425 | is encountered in the input. That definition is then used until another |
| 426 | definition function for the same name is encountered. The new definition |
| 427 | then 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 |
| 434 | A function call is just an expression of the form |
| 435 | "\fIname\fB(\fIparameters\fB)\fR". |
| 436 | .PP |
| 437 | Parameters are numbers or arrays (an extension). In the function definition, |
| 438 | zero or more parameters are defined by listing their names separated by |
| 439 | commas. Numbers are only call by value parameters. Arrays are only |
| 440 | call by variable. Arrays are specified in the parameter definition by |
| 441 | the notation "\fIname\fB[]\fR". In the function call, actual parameters |
| 442 | are full expressions for number parameters. The same notation is used |
| 443 | for passing arrays as for defining array parameters. The named array is |
| 444 | passed by variable to the function. Since function definitions are dynamic, |
| 445 | parameter numbers and types are checked when a function is called. Any |
| 446 | mismatch in number or types of parameters will cause a runtime error. |
| 447 | A runtime error will also occur for the call to an undefined function. |
| 448 | .PP |
| 449 | The \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 |
| 452 | the name of an auto variable. Arrays may be specified by using the |
| 453 | same notation as used in parameters. These variables have their |
| 454 | values pushed onto a stack at the start of the function. The |
| 455 | variables are then initialized to zero and used throughout the |
| 456 | execution of the function. At function exit, these variables are |
| 457 | popped so that the original value (at the time of the function call) |
| 458 | of these variables are restored. The parameters are really auto |
| 459 | variables that are initialized to a value provided in the function |
| 460 | call. Auto variables are different than traditional local variables |
| 461 | because if function A calls function B, B may access function |
| 462 | A's auto variables by just using the same name, unless function B has |
| 463 | called them auto variables. Due to the fact that auto variables and |
| 464 | parameters are pushed onto a stack, \fBbc\fR supports recursive functions. |
| 465 | .PP |
| 466 | The function body is a list of \fBbc\fR statements. Again, statements |
| 467 | are separated by semicolons or newlines. Return statements cause the |
| 468 | termination of a function and the return of a value. There are two |
| 469 | versions of the return statement. The first form, "\fBreturn\fR", returns |
| 470 | the value 0 to the calling expression. The second form, |
| 471 | "\fBreturn ( \fIexpression \fB)\fR", computes the value of the expression |
| 472 | and 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 |
| 474 | to terminate and return 0 without an explicit return statement. |
| 475 | .PP |
| 476 | Functions also change the usage of the variable \fBibase\fR. All |
| 477 | constants 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 |
| 479 | will be ignored during the execution of the function except for the |
| 480 | standard function \fBread\fR, which will always use the current value |
| 481 | of \fBibase\fR for conversion of numbers. |
| 482 | .PP |
| 483 | As an extension, the format of the definition has been slightly relaxed. |
| 484 | The 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. |
| 486 | This version of \fBbc\fR will allow any number of newlines before and |
| 487 | after the opening brace of the function. For example, the following |
| 488 | definitions are legal. |
| 489 | .nf |
| 490 | .RS |
| 491 | \f(CW |
| 492 | define d (n) { return (2*n); } |
| 493 | define d (n) |
| 494 | { return (2*n); } |
| 495 | \fR |
| 496 | .RE |
| 497 | .fi |
| 498 | .SS MATH LIBRARY |
| 499 | If \fBbc\fR is invoked with the \fB-l\fR option, a math library is preloaded |
| 500 | and the default scale is set to 20. The math functions will calculate their |
| 501 | results to the scale set at the time of their call. |
| 502 | The math library defines the following functions: |
| 503 | .IP "s (\fIx\fR)" |
| 504 | The sine of x, x is in radians. |
| 505 | .IP "c (\fIx\fR)" |
| 506 | The cosine of x, x is in radians. |
| 507 | .IP "a (\fIx\fR)" |
| 508 | The arctangent of x, arctangent returns radians. |
| 509 | .IP "l (\fIx\fR)" |
| 510 | The natural logarithm of x. |
| 511 | .IP "e (\fIx\fR)" |
| 512 | The exponential function of raising e to the value x. |
| 513 | .IP "j (\fIn,x\fR)" |
| 514 | The bessel function of integer order n of x. |
| 515 | .SS EXAMPLES |
| 516 | In /bin/sh, the following will assign the value of "pi" to the shell |
| 517 | variable \fBpi\fR. |
| 518 | .RS |
| 519 | \f(CW |
| 520 | pi=$(echo "scale=10; 4*a(1)" | bc -l) |
| 521 | \fR |
| 522 | .RE |
| 523 | .PP |
| 524 | The following is the definition of the exponential function used in the |
| 525 | math library. This function is written in POSIX \fBbc\fR. |
| 526 | .nf |
| 527 | .RS |
| 528 | \f(CW |
| 529 | scale = 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 | |
| 536 | define 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 |
| 573 | The following is code that uses the extended features of \fBbc\fR to |
| 574 | implement a simple program for calculating checkbook balances. This |
| 575 | program is best kept in a file so that it can be used many times |
| 576 | without having to retype it at every use. |
| 577 | .nf |
| 578 | .RS |
| 579 | \f(CW |
| 580 | scale=2 |
| 581 | print "\enCheck book program!\en" |
| 582 | print " Remember, deposits are negative transactions.\en" |
| 583 | print " Exit by a 0 transaction.\en\en" |
| 584 | |
| 585 | print "Initial balance? "; bal = read() |
| 586 | bal /= 1 |
| 587 | print "\en" |
| 588 | while (1) { |
| 589 | "current balance = "; bal |
| 590 | "transaction? "; trans = read() |
| 591 | if (trans == 0) break; |
| 592 | bal -= trans |
| 593 | bal /= 1 |
| 594 | } |
| 595 | quit |
| 596 | \fR |
| 597 | .RE |
| 598 | .fi |
| 599 | .PP |
| 600 | The following is the definition of the recursive factorial function. |
| 601 | .nf |
| 602 | .RS |
| 603 | \f(CW |
| 604 | define 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 |
| 612 | GNU \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. |
| 614 | This allows the user to do editing of lines before sending them |
| 615 | to \fBbc\fR. It also allows for a history of previous lines typed. |
| 616 | When this option is selected, \fBbc\fR has one more special variable. |
| 617 | This special variable, \fBhistory\fR is the number of lines of history |
| 618 | retained. For \fBreadline\fR, a value of -1 means that an unlimited |
| 619 | number of history lines are retained. Setting the value of |
| 620 | \fBhistory\fR to a positive number restricts the number of history |
| 621 | lines to the number given. The value of 0 disables the history |
| 622 | feature. The default value is 100. For more information, read the |
| 623 | user manuals for the GNU \fBreadline\fR, \fBhistory\fR and BSD \fBlibedit\fR |
| 624 | libraries. One can not enable both \fBreadline\fR and \fBlibedit\fR |
| 625 | at the same time. |
| 626 | .SS DIFFERENCES |
| 627 | This version of |
| 628 | .B bc |
| 629 | was implemented from the POSIX P1003.2/D11 draft and contains |
| 630 | several differences and extensions relative to the draft and |
| 631 | traditional implementations. |
| 632 | It is not implemented in the traditional way using |
| 633 | .I dc(1). |
| 634 | This version is a single process which parses and runs a byte code |
| 635 | translation of the program. There is an "undocumented" option (-c) |
| 636 | that causes the program to output the byte code to |
| 637 | the standard output instead of running it. It was mainly used for |
| 638 | debugging the parser and preparing the math library. |
| 639 | .PP |
| 640 | A major source of differences is |
| 641 | extensions, where a feature is extended to add more functionality and |
| 642 | additions, where new features are added. |
| 643 | The following is the list of differences and extensions. |
| 644 | .IP "LANG environment" |
| 645 | This version does not conform to the POSIX standard in the processing |
| 646 | of the LANG environment variable and all environment variables starting |
| 647 | with LC_. |
| 648 | .IP names |
| 649 | Traditional and POSIX |
| 650 | .B bc |
| 651 | have single letter names for functions, variables and arrays. They have |
| 652 | been extended to be multi-character names that start with a letter and |
| 653 | may contain letters, numbers and the underscore character. |
| 654 | .IP Strings |
| 655 | Strings are not allowed to contain NUL characters. POSIX says all characters |
| 656 | must be included in strings. |
| 657 | .IP last |
| 658 | POSIX \fBbc\fR does not have a \fBlast\fR variable. Some implementations |
| 659 | of \fBbc\fR use the period (.) in a similar way. |
| 660 | .IP comparisons |
| 661 | POSIX \fBbc\fR allows comparisons only in the if statement, the while |
| 662 | statement, and the second expression of the for statement. Also, only |
| 663 | one relational operation is allowed in each of those statements. |
| 664 | .IP "if statement, else clause" |
| 665 | POSIX \fBbc\fR does not have an else clause. |
| 666 | .IP "for statement" |
| 667 | POSIX \fBbc\fR requires all expressions to be present in the for statement. |
| 668 | .IP "&&, ||, !" |
| 669 | POSIX \fBbc\fR does not have the logical operators. |
| 670 | .IP "read function" |
| 671 | POSIX \fBbc\fR does not have a read function. |
| 672 | .IP "print statement" |
| 673 | POSIX \fBbc\fR does not have a print statement . |
| 674 | .IP "continue statement" |
| 675 | POSIX \fBbc\fR does not have a continue statement. |
| 676 | .IP "return statement" |
| 677 | POSIX \fBbc\fR requires parentheses around the return expression. |
| 678 | .IP "array parameters" |
| 679 | POSIX \fBbc\fR does not (currently) support array parameters in full. |
| 680 | The POSIX grammar allows for arrays in function definitions, but does |
| 681 | not provide a method to specify an array as an actual parameter. (This |
| 682 | is most likely an oversight in the grammar.) Traditional implementations |
| 683 | of \fBbc\fR have only call by value array parameters. |
| 684 | .IP "function format" |
| 685 | POSIX \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 "=+, =-, =*, =/, =%, =^" |
| 688 | POSIX \fBbc\fR does not require these "old style" assignment operators to |
| 689 | be defined. This version may allow these "old style" assignments. Use |
| 690 | the limits statement to see if the installed version supports them. If |
| 691 | it 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 |
| 693 | value -1. |
| 694 | .IP "spaces in numbers" |
| 695 | Other 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 |
| 697 | would cause a syntax error in this version of \fBbc\fR. |
| 698 | .IP "errors and execution" |
| 699 | This implementation varies from other implementations in terms of what |
| 700 | code will be executed when syntax and other errors are found in the |
| 701 | program. If a syntax error is found in a function definition, error |
| 702 | recovery tries to find the beginning of a statement and continue to |
| 703 | parse the function. Once a syntax error is found in the function, the |
| 704 | function will not be callable and becomes undefined. |
| 705 | Syntax errors in the interactive execution code will invalidate the |
| 706 | current execution block. The execution block is terminated by an |
| 707 | end of line that appears after a complete sequence of statements. |
| 708 | For example, |
| 709 | .nf |
| 710 | .RS |
| 711 | a = 1 |
| 712 | b = 2 |
| 713 | .RE |
| 714 | .fi |
| 715 | has two execution blocks and |
| 716 | .nf |
| 717 | .RS |
| 718 | { a = 1 |
| 719 | b = 2 } |
| 720 | .RE |
| 721 | .fi |
| 722 | has one execution block. Any runtime error will terminate the execution |
| 723 | of the current execution block. A runtime warning will not terminate the |
| 724 | current execution block. |
| 725 | .IP "Interrupts" |
| 726 | During an interactive session, the SIGINT signal (usually generated by |
| 727 | the control-C character from the terminal) will cause execution of the |
| 728 | current execution block to be interrupted. It will display a "runtime" |
| 729 | error indicating which function was interrupted. After all runtime |
| 730 | structures have been cleaned up, a message will be printed to notify the |
| 731 | user that \fBbc\fR is ready for more input. All previously defined functions |
| 732 | remain defined and the value of all non-auto variables are the value at |
| 733 | the point of interruption. All auto variables and function parameters |
| 734 | are removed during the |
| 735 | clean up process. During a non-interactive |
| 736 | session, the SIGINT signal will terminate the entire run of \fBbc\fR. |
| 737 | .SS LIMITS |
| 738 | The following are the limits currently in place for this |
| 739 | .B bc |
| 740 | processor. Some of them may have been changed by an installation. |
| 741 | Use the limits statement to see the actual values. |
| 742 | .IP BC_BASE_MAX |
| 743 | The maximum output base is currently set at 999. The maximum input base |
| 744 | is 16. |
| 745 | .IP BC_DIM_MAX |
| 746 | This is currently an arbitrary limit of 65535 as distributed. Your |
| 747 | installation may be different. |
| 748 | .IP BC_SCALE_MAX |
| 749 | The number of digits after the decimal point is limited to INT_MAX digits. |
| 750 | Also, the number of digits before the decimal point is limited to INT_MAX |
| 751 | digits. |
| 752 | .IP BC_STRING_MAX |
| 753 | The limit on the number of characters in a string is INT_MAX characters. |
| 754 | .IP exponent |
| 755 | The value of the exponent in the raise operation (^) is limited to LONG_MAX. |
| 756 | .IP "variable names" |
| 757 | The current limit on the number of unique names is 32767 for each of |
| 758 | simple variables, arrays and functions. |
| 759 | .SH ENVIRONMENT |
| 760 | The following environment variables are processed by \fBbc\fR: |
| 761 | .IP "POSIXLY_CORRECT" |
| 762 | This is the same as the \fB-s\fR option. |
| 763 | .IP "BC_ENV_ARGS" |
| 764 | This is another mechanism to get arguments to \fBbc\fR. The |
| 765 | format is the same as the command line arguments. These arguments |
| 766 | are processed first, so any files listed in the environment arguments |
| 767 | are processed before any command line argument files. This allows |
| 768 | the user to set up "standard" options and files to be processed |
| 769 | at every invocation of \fBbc\fR. The files in the environment |
| 770 | variables would typically contain function definitions for functions |
| 771 | the user wants defined every time \fBbc\fR is run. |
| 772 | .IP "BC_LINE_LENGTH" |
| 773 | This should be an integer specifying the number of characters in an |
| 774 | output line for numbers. This includes the backslash and newline characters |
| 775 | for long numbers. |
| 776 | .SH DIAGNOSTICS |
| 777 | If any file on the command line can not be opened, \fBbc\fR will report |
| 778 | that the file is unavailable and terminate. Also, there are compile |
| 779 | and run time diagnostics that should be self-explanatory. |
| 780 | .SH BUGS |
| 781 | Error recovery is not very good yet. |
| 782 | .PP |
| 783 | Email bug reports to |
| 784 | .BR bug-bc@gnu.org . |
| 785 | Be sure to include the word ``bc'' somewhere in the ``Subject:'' field. |
| 786 | .SH AUTHOR |
| 787 | .nf |
| 788 | Philip A. Nelson |
| 789 | philnelson@acm.org |
| 790 | .fi |
| 791 | .SH ACKNOWLEDGEMENTS |
| 792 | The author would like to thank Steve Sommars (Steve.Sommars@att.com) for |
| 793 | his extensive help in testing the implementation. Many great suggestions |
| 794 | were given. This is a much better product due to his involvement. |