3 SPDX-License-Identifier: BSD-2-Clause
5 Copyright (c) 2018-2021 Gavin D. Howard and contributors.
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33 bc - arbitrary-precision decimal arithmetic language and calculator
37 **bc** [**-ghilPqsvVw**] [**-\-global-stacks**] [**-\-help**] [**-\-interactive**] [**-\-mathlib**] [**-\-no-prompt**] [**-\-quiet**] [**-\-standard**] [**-\-warn**] [**-\-version**] [**-e** *expr*] [**-\-expression**=*expr*...] [**-f** *file*...] [**-\-file**=*file*...] [*file*...]
41 bc(1) is an interactive processor for a language first standardized in 1991 by
42 POSIX. (The current standard is [here][1].) The language provides unlimited
43 precision decimal arithmetic and is somewhat C-like, but there are differences.
44 Such differences will be noted in this document.
46 After parsing and handling options, this bc(1) reads any files given on the
47 command line and executes them before reading from **stdin**.
51 The following are the options that bc(1) accepts.
53 **-g**, **-\-global-stacks**
55 Turns the globals **ibase**, **obase**, and **scale** into stacks.
57 This has the effect that a copy of the current value of all three are pushed
58 onto a stack for every function call, as well as popped when every function
59 returns. This means that functions can assign to any and all of those
60 globals without worrying that the change will affect other functions.
61 Thus, a hypothetical function named **output(x,b)** that simply printed
62 **x** in base **b** could be written like this:
64 define void output(x, b) {
71 define void output(x, b) {
79 This makes writing functions much easier.
81 However, since using this flag means that functions cannot set **ibase**,
82 **obase**, or **scale** globally, functions that are made to do so cannot
83 work anymore. There are two possible use cases for that, and each has a
86 First, if a function is called on startup to turn bc(1) into a number
87 converter, it is possible to replace that capability with various shell
90 alias d2o="bc -e ibase=A -e obase=8"
91 alias h2b="bc -e ibase=G -e obase=2"
93 Second, if the purpose of a function is to set **ibase**, **obase**, or
94 **scale** globally for any other purpose, it could be split into one to
95 three functions (based on how many globals it sets) and each of those
96 functions could return the desired value for a global.
98 If the behavior of this option is desired for every run of bc(1), then users
99 could make sure to define **BC_ENV_ARGS** and include this option (see the
100 **ENVIRONMENT VARIABLES** section for more details).
102 If **-s**, **-w**, or any equivalents are used, this option is ignored.
104 This is a **non-portable extension**.
108 : Prints a usage message and quits.
110 **-i**, **-\-interactive**
112 : Forces interactive mode. (See the **INTERACTIVE MODE** section.)
114 This is a **non-portable extension**.
116 **-l**, **-\-mathlib**
118 : Sets **scale** (see the **SYNTAX** section) to **20** and loads the included
119 math library before running any code, including any expressions or files
120 specified on the command line.
122 To learn what is in the library, see the **LIBRARY** section.
124 **-P**, **-\-no-prompt**
126 : Disables the prompt in TTY mode. (The prompt is only enabled in TTY mode.
127 See the **TTY MODE** section) This is mostly for those users that do not
128 want a prompt or are not used to having them in bc(1). Most of those users
129 would want to put this option in **BC_ENV_ARGS** (see the
130 **ENVIRONMENT VARIABLES** section).
132 This is a **non-portable extension**.
136 : This option is for compatibility with the [GNU bc(1)][2]; it is a no-op.
137 Without this option, GNU bc(1) prints a copyright header. This bc(1) only
138 prints the copyright header if one or more of the **-v**, **-V**, or
139 **-\-version** options are given.
141 This is a **non-portable extension**.
143 **-s**, **-\-standard**
145 : Process exactly the language defined by the [standard][1] and error if any
148 This is a **non-portable extension**.
150 **-v**, **-V**, **-\-version**
152 : Print the version information (copyright header) and exit.
154 This is a **non-portable extension**.
158 : Like **-s** and **-\-standard**, except that warnings (and not errors) are
159 printed for non-standard extensions and execution continues normally.
161 This is a **non-portable extension**.
163 **-e** *expr*, **-\-expression**=*expr*
165 : Evaluates *expr*. If multiple expressions are given, they are evaluated in
166 order. If files are given as well (see below), the expressions and files are
167 evaluated in the order given. This means that if a file is given before an
168 expression, the file is read in and evaluated first.
170 If this option is given on the command-line (i.e., not in **BC_ENV_ARGS**,
171 see the **ENVIRONMENT VARIABLES** section), then after processing all
172 expressions and files, bc(1) will exit, unless **-** (**stdin**) was given
173 as an argument at least once to **-f** or **-\-file**, whether on the
174 command-line or in **BC_ENV_ARGS**. However, if any other **-e**,
175 **-\-expression**, **-f**, or **-\-file** arguments are given after **-f-**
176 or equivalent is given, bc(1) will give a fatal error and exit.
178 This is a **non-portable extension**.
180 **-f** *file*, **-\-file**=*file*
182 : Reads in *file* and evaluates it, line by line, as though it were read
183 through **stdin**. If expressions are also given (see above), the
184 expressions are evaluated in the order given.
186 If this option is given on the command-line (i.e., not in **BC_ENV_ARGS**,
187 see the **ENVIRONMENT VARIABLES** section), then after processing all
188 expressions and files, bc(1) will exit, unless **-** (**stdin**) was given
189 as an argument at least once to **-f** or **-\-file**. However, if any other
190 **-e**, **-\-expression**, **-f**, or **-\-file** arguments are given after
191 **-f-** or equivalent is given, bc(1) will give a fatal error and exit.
193 This is a **non-portable extension**.
195 All long options are **non-portable extensions**.
199 Any non-error output is written to **stdout**. In addition, if history (see the
200 **HISTORY** section) and the prompt (see the **TTY MODE** section) are enabled,
201 both are output to **stdout**.
203 **Note**: Unlike other bc(1) implementations, this bc(1) will issue a fatal
204 error (see the **EXIT STATUS** section) if it cannot write to **stdout**, so if
205 **stdout** is closed, as in **bc <file> >&-**, it will quit with an error. This
206 is done so that bc(1) can report problems when **stdout** is redirected to a
209 If there are scripts that depend on the behavior of other bc(1) implementations,
210 it is recommended that those scripts be changed to redirect **stdout** to
215 Any error output is written to **stderr**.
217 **Note**: Unlike other bc(1) implementations, this bc(1) will issue a fatal
218 error (see the **EXIT STATUS** section) if it cannot write to **stderr**, so if
219 **stderr** is closed, as in **bc <file> 2>&-**, it will quit with an error. This
220 is done so that bc(1) can exit with an error code when **stderr** is redirected
223 If there are scripts that depend on the behavior of other bc(1) implementations,
224 it is recommended that those scripts be changed to redirect **stderr** to
229 The syntax for bc(1) programs is mostly C-like, with some differences. This
230 bc(1) follows the [POSIX standard][1], which is a much more thorough resource
231 for the language this bc(1) accepts. This section is meant to be a summary and a
232 listing of all the extensions to the standard.
234 In the sections below, **E** means expression, **S** means statement, and **I**
237 Identifiers (**I**) start with a lowercase letter and can be followed by any
238 number (up to **BC_NAME_MAX-1**) of lowercase letters (**a-z**), digits
239 (**0-9**), and underscores (**\_**). The regex is **\[a-z\]\[a-z0-9\_\]\***.
240 Identifiers with more than one character (letter) are a
241 **non-portable extension**.
243 **ibase** is a global variable determining how to interpret constant numbers. It
244 is the "input" base, or the number base used for interpreting input numbers.
245 **ibase** is initially **10**. If the **-s** (**-\-standard**) and **-w**
246 (**-\-warn**) flags were not given on the command line, the max allowable value
247 for **ibase** is **36**. Otherwise, it is **16**. The min allowable value for
248 **ibase** is **2**. The max allowable value for **ibase** can be queried in
249 bc(1) programs with the **maxibase()** built-in function.
251 **obase** is a global variable determining how to output results. It is the
252 "output" base, or the number base used for outputting numbers. **obase** is
253 initially **10**. The max allowable value for **obase** is **BC_BASE_MAX** and
254 can be queried in bc(1) programs with the **maxobase()** built-in function. The
255 min allowable value for **obase** is **2**. Values are output in the specified
258 The *scale* of an expression is the number of digits in the result of the
259 expression right of the decimal point, and **scale** is a global variable that
260 sets the precision of any operations, with exceptions. **scale** is initially
261 **0**. **scale** cannot be negative. The max allowable value for **scale** is
262 **BC_SCALE_MAX** and can be queried in bc(1) programs with the **maxscale()**
265 bc(1) has both *global* variables and *local* variables. All *local*
266 variables are local to the function; they are parameters or are introduced in
267 the **auto** list of a function (see the **FUNCTIONS** section). If a variable
268 is accessed which is not a parameter or in the **auto** list, it is assumed to
269 be *global*. If a parent function has a *local* variable version of a variable
270 that a child function considers *global*, the value of that *global* variable in
271 the child function is the value of the variable in the parent function, not the
272 value of the actual *global* variable.
274 All of the above applies to arrays as well.
276 The value of a statement that is an expression (i.e., any of the named
277 expressions or operands) is printed unless the lowest precedence operator is an
278 assignment operator *and* the expression is notsurrounded by parentheses.
280 The value that is printed is also assigned to the special variable **last**. A
281 single dot (**.**) may also be used as a synonym for **last**. These are
282 **non-portable extensions**.
284 Either semicolons or newlines may separate statements.
288 There are two kinds of comments:
290 1. Block comments are enclosed in **/\*** and **\*/**.
291 2. Line comments go from **#** until, and not including, the next newline. This
292 is a **non-portable extension**.
296 The following are named expressions in bc(1):
299 2. Array Elements: **I[E]**
303 6. **last** or a single dot (**.**)
305 Number 6 is a **non-portable extension**.
307 Variables and arrays do not interfere; users can have arrays named the same as
308 variables. This also applies to functions (see the **FUNCTIONS** section), so a
309 user can have a variable, array, and function that all have the same name, and
310 they will not shadow each other, whether inside of functions or not.
312 Named expressions are required as the operand of **increment**/**decrement**
313 operators and as the left side of **assignment** operators (see the *Operators*
318 The following are valid operands in bc(1):
320 1. Numbers (see the *Numbers* subsection below).
321 2. Array indices (**I[E]**).
322 3. **(E)**: The value of **E** (used to change precedence).
323 4. **sqrt(E)**: The square root of **E**. **E** must be non-negative.
324 5. **length(E)**: The number of significant decimal digits in **E**.
325 6. **length(I[])**: The number of elements in the array **I**. This is a
326 **non-portable extension**.
327 7. **scale(E)**: The *scale* of **E**.
328 8. **abs(E)**: The absolute value of **E**. This is a **non-portable
330 9. **I()**, **I(E)**, **I(E, E)**, and so on, where **I** is an identifier for
331 a non-**void** function (see the *Void Functions* subsection of the
332 **FUNCTIONS** section). The **E** argument(s) may also be arrays of the form
333 **I[]**, which will automatically be turned into array references (see the
334 *Array References* subsection of the **FUNCTIONS** section) if the
335 corresponding parameter in the function definition is an array reference.
336 10. **read()**: Reads a line from **stdin** and uses that as an expression. The
337 result of that expression is the result of the **read()** operand. This is a
338 **non-portable extension**.
339 11. **maxibase()**: The max allowable **ibase**. This is a **non-portable
341 12. **maxobase()**: The max allowable **obase**. This is a **non-portable
343 13. **maxscale()**: The max allowable **scale**. This is a **non-portable
348 Numbers are strings made up of digits, uppercase letters, and at most **1**
349 period for a radix. Numbers can have up to **BC_NUM_MAX** digits. Uppercase
350 letters are equal to **9** + their position in the alphabet (i.e., **A** equals
351 **10**, or **9+1**). If a digit or letter makes no sense with the current value
352 of **ibase**, they are set to the value of the highest valid digit in **ibase**.
354 Single-character numbers (i.e., **A** alone) take the value that they would have
355 if they were valid digits, regardless of the value of **ibase**. This means that
356 **A** alone always equals decimal **10** and **Z** alone always equals decimal
361 The following arithmetic and logical operators can be used. They are listed in
362 order of decreasing precedence. Operators in the same group have the same
367 : Type: Prefix and Postfix
371 Description: **increment**, **decrement**
379 Description: **negation**, **boolean not**
387 Description: **power**
395 Description: **multiply**, **divide**, **modulus**
403 Description: **add**, **subtract**
405 **=** **+=** **-=** **\*=** **/=** **%=** **\^=**
411 Description: **assignment**
413 **==** **\<=** **\>=** **!=** **\<** **\>**
419 Description: **relational**
427 Description: **boolean and**
435 Description: **boolean or**
437 The operators will be described in more detail below.
441 : The prefix and postfix **increment** and **decrement** operators behave
442 exactly like they would in C. They require a named expression (see the
443 *Named Expressions* subsection) as an operand.
445 The prefix versions of these operators are more efficient; use them where
450 : The **negation** operator returns **0** if a user attempts to negate any
451 expression with the value **0**. Otherwise, a copy of the expression with
452 its sign flipped is returned.
456 : The **boolean not** operator returns **1** if the expression is **0**, or
459 This is a **non-portable extension**.
463 : The **power** operator (not the **exclusive or** operator, as it would be in
464 C) takes two expressions and raises the first to the power of the value of
465 the second. The *scale* of the result is equal to **scale**.
467 The second expression must be an integer (no *scale*), and if it is
468 negative, the first value must be non-zero.
472 : The **multiply** operator takes two expressions, multiplies them, and
473 returns the product. If **a** is the *scale* of the first expression and
474 **b** is the *scale* of the second expression, the *scale* of the result is
475 equal to **min(a+b,max(scale,a,b))** where **min()** and **max()** return
480 : The **divide** operator takes two expressions, divides them, and returns the
481 quotient. The *scale* of the result shall be the value of **scale**.
483 The second expression must be non-zero.
487 : The **modulus** operator takes two expressions, **a** and **b**, and
488 evaluates them by 1) Computing **a/b** to current **scale** and 2) Using the
489 result of step 1 to calculate **a-(a/b)\*b** to *scale*
490 **max(scale+scale(b),scale(a))**.
492 The second expression must be non-zero.
496 : The **add** operator takes two expressions, **a** and **b**, and returns the
497 sum, with a *scale* equal to the max of the *scale*s of **a** and **b**.
501 : The **subtract** operator takes two expressions, **a** and **b**, and
502 returns the difference, with a *scale* equal to the max of the *scale*s of
505 **=** **+=** **-=** **\*=** **/=** **%=** **\^=**
507 : The **assignment** operators take two expressions, **a** and **b** where
508 **a** is a named expression (see the *Named Expressions* subsection).
510 For **=**, **b** is copied and the result is assigned to **a**. For all
511 others, **a** and **b** are applied as operands to the corresponding
512 arithmetic operator and the result is assigned to **a**.
514 **==** **\<=** **\>=** **!=** **\<** **\>**
516 : The **relational** operators compare two expressions, **a** and **b**, and
517 if the relation holds, according to C language semantics, the result is
518 **1**. Otherwise, it is **0**.
520 Note that unlike in C, these operators have a lower precedence than the
521 **assignment** operators, which means that **a=b\>c** is interpreted as
524 Also, unlike the [standard][1] requires, these operators can appear anywhere
525 any other expressions can be used. This allowance is a
526 **non-portable extension**.
530 : The **boolean and** operator takes two expressions and returns **1** if both
531 expressions are non-zero, **0** otherwise.
533 This is *not* a short-circuit operator.
535 This is a **non-portable extension**.
539 : The **boolean or** operator takes two expressions and returns **1** if one
540 of the expressions is non-zero, **0** otherwise.
542 This is *not* a short-circuit operator.
544 This is a **non-portable extension**.
548 The following items are statements:
551 2. **{** **S** **;** ... **;** **S** **}**
552 3. **if** **(** **E** **)** **S**
553 4. **if** **(** **E** **)** **S** **else** **S**
554 5. **while** **(** **E** **)** **S**
555 6. **for** **(** **E** **;** **E** **;** **E** **)** **S**
556 7. An empty statement
562 13. A string of characters, enclosed in double quotes
563 14. **print** **E** **,** ... **,** **E**
564 15. **I()**, **I(E)**, **I(E, E)**, and so on, where **I** is an identifier for
565 a **void** function (see the *Void Functions* subsection of the
566 **FUNCTIONS** section). The **E** argument(s) may also be arrays of the form
567 **I[]**, which will automatically be turned into array references (see the
568 *Array References* subsection of the **FUNCTIONS** section) if the
569 corresponding parameter in the function definition is an array reference.
571 Numbers 4, 9, 11, 12, 14, and 15 are **non-portable extensions**.
573 Also, as a **non-portable extension**, any or all of the expressions in the
574 header of a for loop may be omitted. If the condition (second expression) is
575 omitted, it is assumed to be a constant **1**.
577 The **break** statement causes a loop to stop iterating and resume execution
578 immediately following a loop. This is only allowed in loops.
580 The **continue** statement causes a loop iteration to stop early and returns to
581 the start of the loop, including testing the loop condition. This is only
584 The **if** **else** statement does the same thing as in C.
586 The **quit** statement causes bc(1) to quit, even if it is on a branch that will
587 not be executed (it is a compile-time command).
589 The **halt** statement causes bc(1) to quit, if it is executed. (Unlike **quit**
590 if it is on a branch of an **if** statement that is not executed, bc(1) does not
593 The **limits** statement prints the limits that this bc(1) is subject to. This
594 is like the **quit** statement in that it is a compile-time command.
596 An expression by itself is evaluated and printed, followed by a newline.
600 The "expressions" in a **print** statement may also be strings. If they are, there
601 are backslash escape sequences that are interpreted specially. What those
602 sequences are, and what they cause to be printed, are shown below:
616 Any other character following a backslash causes the backslash and character to
619 Any non-string expression in a print statement shall be assigned to **last**,
620 like any other expression that is printed.
622 ## Order of Evaluation
624 All expressions in a statment are evaluated left to right, except as necessary
625 to maintain order of operations. This means, for example, assuming that **i** is
626 equal to **0**, in the expression
630 the first (or 0th) element of **a** is set to **1**, and **i** is equal to **2**
631 at the end of the expression.
633 This includes function arguments. Thus, assuming **i** is equal to **0**, this
634 means that in the expression
638 the first argument passed to **x()** is **0**, and the second argument is **1**,
639 while **i** is equal to **2** before the function starts executing.
643 Function definitions are as follows:
653 Any **I** in the parameter list or **auto** list may be replaced with **I[]** to
654 make a parameter or **auto** var an array, and any **I** in the parameter list
655 may be replaced with **\*I[]** to make a parameter an array reference. Callers
656 of functions that take array references should not put an asterisk in the call;
657 they must be called with just **I[]** like normal array parameters and will be
658 automatically converted into references.
660 As a **non-portable extension**, the opening brace of a **define** statement may
661 appear on the next line.
663 As a **non-portable extension**, the return statement may also be in one of the
667 2. **return** **(** **)**
670 The first two, or not specifying a **return** statement, is equivalent to
671 **return (0)**, unless the function is a **void** function (see the *Void
672 Functions* subsection below).
676 Functions can also be **void** functions, defined as follows:
679 define void I(I,...,I){
686 They can only be used as standalone expressions, where such an expression would
687 be printed alone, except in a print statement.
689 Void functions can only use the first two **return** statements listed above.
690 They can also omit the return statement entirely.
692 The word "void" is not treated as a keyword; it is still possible to have
693 variables, arrays, and functions named **void**. The word "void" is only
694 treated specially right after the **define** keyword.
696 This is a **non-portable extension**.
700 For any array in the parameter list, if the array is declared in the form
706 it is a **reference**. Any changes to the array in the function are reflected,
707 when the function returns, to the array that was passed in.
709 Other than this, all function arguments are passed by value.
711 This is a **non-portable extension**.
715 All of the functions below are available when the **-l** or **-\-mathlib**
716 command-line flags are given.
720 The [standard][1] defines the following functions for the math library:
724 : Returns the sine of **x**, which is assumed to be in radians.
726 This is a transcendental function (see the *Transcendental Functions*
731 : Returns the cosine of **x**, which is assumed to be in radians.
733 This is a transcendental function (see the *Transcendental Functions*
738 : Returns the arctangent of **x**, in radians.
740 This is a transcendental function (see the *Transcendental Functions*
745 : Returns the natural logarithm of **x**.
747 This is a transcendental function (see the *Transcendental Functions*
752 : Returns the mathematical constant **e** raised to the power of **x**.
754 This is a transcendental function (see the *Transcendental Functions*
759 : Returns the bessel integer order **n** (truncated) of **x**.
761 This is a transcendental function (see the *Transcendental Functions*
764 ## Transcendental Functions
766 All transcendental functions can return slightly inaccurate results (up to 1
767 [ULP][4]). This is unavoidable, and [this article][5] explains why it is
768 impossible and unnecessary to calculate exact results for the transcendental
771 Because of the possible inaccuracy, I recommend that users call those functions
772 with the precision (**scale**) set to at least 1 higher than is necessary. If
773 exact results are *absolutely* required, users can double the precision
774 (**scale**) and then truncate.
776 The transcendental functions in the standard math library are:
787 When bc(1) encounters an error or a signal that it has a non-default handler
788 for, it resets. This means that several things happen.
790 First, any functions that are executing are stopped and popped off the stack.
791 The behavior is not unlike that of exceptions in programming languages. Then
792 the execution point is set so that any code waiting to execute (after all
793 functions returned) is skipped.
795 Thus, when bc(1) resets, it skips any remaining code waiting to be executed.
796 Then, if it is interactive mode, and the error was not a fatal error (see the
797 **EXIT STATUS** section), it asks for more input; otherwise, it exits with the
798 appropriate return code.
800 Note that this reset behavior is different from the GNU bc(1), which attempts to
801 start executing the statement right after the one that caused an error.
805 Most bc(1) implementations use **char** types to calculate the value of **1**
806 decimal digit at a time, but that can be slow. This bc(1) does something
809 It uses large integers to calculate more than **1** decimal digit at a time. If
810 built in a environment where **BC_LONG_BIT** (see the **LIMITS** section) is
811 **64**, then each integer has **9** decimal digits. If built in an environment
812 where **BC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
813 value (the number of decimal digits per large integer) is called
816 The actual values of **BC_LONG_BIT** and **BC_BASE_DIGS** can be queried with
817 the **limits** statement.
819 In addition, this bc(1) uses an even larger integer for overflow checking. This
820 integer type depends on the value of **BC_LONG_BIT**, but is always at least
821 twice as large as the integer type used to store digits.
825 The following are the limits on bc(1):
829 : The number of bits in the **long** type in the environment where bc(1) was
830 built. This determines how many decimal digits can be stored in a single
831 large integer (see the **PERFORMANCE** section).
835 : The number of decimal digits per large integer (see the **PERFORMANCE**
836 section). Depends on **BC_LONG_BIT**.
840 : The max decimal number that each large integer can store (see
841 **BC_BASE_DIGS**) plus **1**. Depends on **BC_BASE_DIGS**.
845 : The max number that the overflow type (see the **PERFORMANCE** section) can
846 hold. Depends on **BC_LONG_BIT**.
850 : The maximum output base. Set at **BC_BASE_POW**.
854 : The maximum size of arrays. Set at **SIZE_MAX-1**.
858 : The maximum **scale**. Set at **BC_OVERFLOW_MAX-1**.
862 : The maximum length of strings. Set at **BC_OVERFLOW_MAX-1**.
866 : The maximum length of identifiers. Set at **BC_OVERFLOW_MAX-1**.
870 : The maximum length of a number (in decimal digits), which includes digits
871 after the decimal point. Set at **BC_OVERFLOW_MAX-1**.
875 : The maximum allowable exponent (positive or negative). Set at
880 : The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
882 The actual values can be queried with the **limits** statement.
884 These limits are meant to be effectively non-existent; the limits are so large
885 (at least on 64-bit machines) that there should not be any point at which they
886 become a problem. In fact, memory should be exhausted before these limits should
889 # ENVIRONMENT VARIABLES
891 bc(1) recognizes the following environment variables:
895 : If this variable exists (no matter the contents), bc(1) behaves as if
896 the **-s** option was given.
900 : This is another way to give command-line arguments to bc(1). They should be
901 in the same format as all other command-line arguments. These are always
902 processed first, so any files given in **BC_ENV_ARGS** will be processed
903 before arguments and files given on the command-line. This gives the user
904 the ability to set up "standard" options and files to be used at every
905 invocation. The most useful thing for such files to contain would be useful
906 functions that the user might want every time bc(1) runs.
908 The code that parses **BC_ENV_ARGS** will correctly handle quoted arguments,
909 but it does not understand escape sequences. For example, the string
910 **"/home/gavin/some bc file.bc"** will be correctly parsed, but the string
911 **"/home/gavin/some \"bc\" file.bc"** will include the backslashes.
913 The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
914 if you have a file with any number of single quotes in the name, you can use
915 double quotes as the outside quotes, as in **"some 'bc' file.bc"**, and vice
916 versa if you have a file with double quotes. However, handling a file with
917 both kinds of quotes in **BC_ENV_ARGS** is not supported due to the
918 complexity of the parsing, though such files are still supported on the
919 command-line where the parsing is done by the shell.
923 : If this environment variable exists and contains an integer that is greater
924 than **1** and is less than **UINT16_MAX** (**2\^16-1**), bc(1) will output
925 lines to that length, including the backslash (**\\**). The default line
930 bc(1) returns the following exit statuses:
938 : A math error occurred. This follows standard practice of using **1** for
939 expected errors, since math errors will happen in the process of normal
942 Math errors include divide by **0**, taking the square root of a negative
943 number, attempting to convert a negative number to a hardware integer,
944 overflow when converting a number to a hardware integer, and attempting to
945 use a non-integer where an integer is required.
947 Converting to a hardware integer happens for the second operand of the power
948 (**\^**) operator and the corresponding assignment operator.
952 : A parse error occurred.
954 Parse errors include unexpected **EOF**, using an invalid character, failing
955 to find the end of a string or comment, using a token where it is invalid,
956 giving an invalid expression, giving an invalid print statement, giving an
957 invalid function definition, attempting to assign to an expression that is
958 not a named expression (see the *Named Expressions* subsection of the
959 **SYNTAX** section), giving an invalid **auto** list, having a duplicate
960 **auto**/function parameter, failing to find the end of a code block,
961 attempting to return a value from a **void** function, attempting to use a
962 variable as a reference, and using any extensions when the option **-s** or
963 any equivalents were given.
967 : A runtime error occurred.
969 Runtime errors include assigning an invalid number to **ibase**, **obase**,
970 or **scale**; give a bad expression to a **read()** call, calling **read()**
971 inside of a **read()** call, type errors, passing the wrong number of
972 arguments to functions, attempting to call an undefined function, and
973 attempting to use a **void** function call as a value in an expression.
977 : A fatal error occurred.
979 Fatal errors include memory allocation errors, I/O errors, failing to open
980 files, attempting to use files that do not have only ASCII characters (bc(1)
981 only accepts ASCII characters), attempting to open a directory as a file,
982 and giving invalid command-line options.
984 The exit status **4** is special; when a fatal error occurs, bc(1) always exits
985 and returns **4**, no matter what mode bc(1) is in.
987 The other statuses will only be returned when bc(1) is not in interactive mode
988 (see the **INTERACTIVE MODE** section), since bc(1) resets its state (see the
989 **RESET** section) and accepts more input when one of those errors occurs in
990 interactive mode. This is also the case when interactive mode is forced by the
991 **-i** flag or **-\-interactive** option.
993 These exit statuses allow bc(1) to be used in shell scripting with error
994 checking, and its normal behavior can be forced by using the **-i** flag or
995 **-\-interactive** option.
999 Per the [standard][1], bc(1) has an interactive mode and a non-interactive mode.
1000 Interactive mode is turned on automatically when both **stdin** and **stdout**
1001 are hooked to a terminal, but the **-i** flag and **-\-interactive** option can
1002 turn it on in other cases.
1004 In interactive mode, bc(1) attempts to recover from errors (see the **RESET**
1005 section), and in normal execution, flushes **stdout** as soon as execution is
1006 done for the current input.
1010 If **stdin**, **stdout**, and **stderr** are all connected to a TTY, bc(1) turns
1013 The prompt is enabled in TTY mode.
1015 TTY mode is different from interactive mode because interactive mode is required
1016 in the [bc(1) specification][1], and interactive mode requires only **stdin**
1017 and **stdout** to be connected to a terminal.
1021 Sending a **SIGINT** will cause bc(1) to stop execution of the current input. If
1022 bc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
1023 **RESET** section). Otherwise, it will clean up and exit.
1025 Note that "current input" can mean one of two things. If bc(1) is processing
1026 input from **stdin** in TTY mode, it will ask for more input. If bc(1) is
1027 processing input from a file in TTY mode, it will stop processing the file and
1028 start processing the next file, if one exists, or ask for input from **stdin**
1029 if no other file exists.
1031 This means that if a **SIGINT** is sent to bc(1) as it is executing a file, it
1032 can seem as though bc(1) did not respond to the signal since it will immediately
1033 start executing the next file. This is by design; most files that users execute
1034 when interacting with bc(1) have function definitions, which are quick to parse.
1035 If a file takes a long time to execute, there may be a bug in that file. The
1036 rest of the files could still be executed without problem, allowing the user to
1039 **SIGTERM** and **SIGQUIT** cause bc(1) to clean up and exit, and it uses the
1040 default handler for all other signals.
1048 bc(1) is compliant with the [IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1]
1049 specification. The flags **-efghiqsvVw**, all long options, and the extensions
1050 noted above are extensions to that specification.
1052 Note that the specification explicitly says that bc(1) only accepts numbers that
1053 use a period (**.**) as a radix point, regardless of the value of
1058 None are known. Report bugs at https://git.yzena.com/gavin/bc.
1062 Gavin D. Howard <gavin@yzena.com> and contributors.
1064 [1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html
1065 [2]: https://www.gnu.org/software/bc/
1066 [3]: https://en.wikipedia.org/wiki/Rounding#Round_half_away_from_zero
1067 [4]: https://en.wikipedia.org/wiki/Unit_in_the_last_place
1068 [5]: https://people.eecs.berkeley.edu/~wkahan/LOG10HAF.TXT
1069 [6]: https://en.wikipedia.org/wiki/Rounding#Rounding_away_from_zero