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*...]
42 bc(1) is an interactive processor for a language first standardized in 1991 by
43 POSIX. (The current standard is [here][1].) The language provides unlimited
44 precision decimal arithmetic and is somewhat C-like, but there are differences.
45 Such differences will be noted in this document.
47 After parsing and handling options, this bc(1) reads any files given on the
48 command line and executes them before reading from **stdin**.
50 This bc(1) is a drop-in replacement for *any* bc(1), including (and
51 especially) the GNU bc(1).
55 The following are the options that bc(1) accepts.
57 **-g**, **--global-stacks**
59 Turns the globals **ibase**, **obase**, and **scale** into stacks.
61 This has the effect that a copy of the current value of all three are pushed
62 onto a stack for every function call, as well as popped when every function
63 returns. This means that functions can assign to any and all of those
64 globals without worrying that the change will affect other functions.
65 Thus, a hypothetical function named **output(x,b)** that simply printed
66 **x** in base **b** could be written like this:
68 define void output(x, b) {
75 define void output(x, b) {
83 This makes writing functions much easier.
85 However, since using this flag means that functions cannot set **ibase**,
86 **obase**, or **scale** globally, functions that are made to do so cannot
87 work anymore. There are two possible use cases for that, and each has a
90 First, if a function is called on startup to turn bc(1) into a number
91 converter, it is possible to replace that capability with various shell
94 alias d2o="bc -e ibase=A -e obase=8"
95 alias h2b="bc -e ibase=G -e obase=2"
97 Second, if the purpose of a function is to set **ibase**, **obase**, or
98 **scale** globally for any other purpose, it could be split into one to
99 three functions (based on how many globals it sets) and each of those
100 functions could return the desired value for a global.
102 If the behavior of this option is desired for every run of bc(1), then users
103 could make sure to define **BC_ENV_ARGS** and include this option (see the
104 **ENVIRONMENT VARIABLES** section for more details).
106 If **-s**, **-w**, or any equivalents are used, this option is ignored.
108 This is a **non-portable extension**.
112 : Prints a usage message and quits.
114 **-i**, **--interactive**
116 : Forces interactive mode. (See the **INTERACTIVE MODE** section.)
118 This is a **non-portable extension**.
120 **-l**, **--mathlib**
122 : Sets **scale** (see the **SYNTAX** section) to **20** and loads the included
123 math library before running any code, including any expressions or files
124 specified on the command line.
126 To learn what is in the library, see the **LIBRARY** section.
128 **-P**, **--no-prompt**
130 : Disables the prompt in TTY mode. (The prompt is only enabled in TTY mode.
131 See the **TTY MODE** section) This is mostly for those users that do not
132 want a prompt or are not used to having them in bc(1). Most of those users
133 would want to put this option in **BC_ENV_ARGS** (see the
134 **ENVIRONMENT VARIABLES** section).
136 This is a **non-portable extension**.
140 : This option is for compatibility with the [GNU bc(1)][2]; it is a no-op.
141 Without this option, GNU bc(1) prints a copyright header. This bc(1) only
142 prints the copyright header if one or more of the **-v**, **-V**, or
143 **--version** options are given.
145 This is a **non-portable extension**.
147 **-s**, **--standard**
149 : Process exactly the language defined by the [standard][1] and error if any
152 This is a **non-portable extension**.
154 **-v**, **-V**, **--version**
156 : Print the version information (copyright header) and exit.
158 This is a **non-portable extension**.
162 : Like **-s** and **--standard**, except that warnings (and not errors) are
163 printed for non-standard extensions and execution continues normally.
165 This is a **non-portable extension**.
167 **-e** *expr*, **--expression**=*expr*
169 : Evaluates *expr*. If multiple expressions are given, they are evaluated in
170 order. If files are given as well (see below), the expressions and files are
171 evaluated in the order given. This means that if a file is given before an
172 expression, the file is read in and evaluated first.
174 If this option is given on the command-line (i.e., not in **BC_ENV_ARGS**,
175 see the **ENVIRONMENT VARIABLES** section), then after processing all
176 expressions and files, bc(1) will exit, unless **-** (**stdin**) was given
177 as an argument at least once to **-f** or **--file**, whether on the
178 command-line or in **BC_ENV_ARGS**. However, if any other **-e**,
179 **--expression**, **-f**, or **--file** arguments are given after **-f-** or
180 equivalent is given, bc(1) will give a fatal error and exit.
182 This is a **non-portable extension**.
184 **-f** *file*, **--file**=*file*
186 : Reads in *file* and evaluates it, line by line, as though it were read
187 through **stdin**. If expressions are also given (see above), the
188 expressions are evaluated in the order given.
190 If this option is given on the command-line (i.e., not in **BC_ENV_ARGS**,
191 see the **ENVIRONMENT VARIABLES** section), then after processing all
192 expressions and files, bc(1) will exit, unless **-** (**stdin**) was given
193 as an argument at least once to **-f** or **--file**. However, if any other
194 **-e**, **--expression**, **-f**, or **--file** arguments are given after
195 **-f-** or equivalent is given, bc(1) will give a fatal error and exit.
197 This is a **non-portable extension**.
199 All long options are **non-portable extensions**.
203 Any non-error output is written to **stdout**. In addition, if history (see the
204 **HISTORY** section) and the prompt (see the **TTY MODE** section) are enabled,
205 both are output to **stdout**.
207 **Note**: Unlike other bc(1) implementations, this bc(1) will issue a fatal
208 error (see the **EXIT STATUS** section) if it cannot write to **stdout**, so if
209 **stdout** is closed, as in **bc <file> >&-**, it will quit with an error. This
210 is done so that bc(1) can report problems when **stdout** is redirected to a
213 If there are scripts that depend on the behavior of other bc(1) implementations,
214 it is recommended that those scripts be changed to redirect **stdout** to
219 Any error output is written to **stderr**.
221 **Note**: Unlike other bc(1) implementations, this bc(1) will issue a fatal
222 error (see the **EXIT STATUS** section) if it cannot write to **stderr**, so if
223 **stderr** is closed, as in **bc <file> 2>&-**, it will quit with an error. This
224 is done so that bc(1) can exit with an error code when **stderr** is redirected
227 If there are scripts that depend on the behavior of other bc(1) implementations,
228 it is recommended that those scripts be changed to redirect **stderr** to
233 The syntax for bc(1) programs is mostly C-like, with some differences. This
234 bc(1) follows the [POSIX standard][1], which is a much more thorough resource
235 for the language this bc(1) accepts. This section is meant to be a summary and a
236 listing of all the extensions to the standard.
238 In the sections below, **E** means expression, **S** means statement, and **I**
241 Identifiers (**I**) start with a lowercase letter and can be followed by any
242 number (up to **BC_NAME_MAX-1**) of lowercase letters (**a-z**), digits
243 (**0-9**), and underscores (**\_**). The regex is **\[a-z\]\[a-z0-9\_\]\***.
244 Identifiers with more than one character (letter) are a
245 **non-portable extension**.
247 **ibase** is a global variable determining how to interpret constant numbers. It
248 is the "input" base, or the number base used for interpreting input numbers.
249 **ibase** is initially **10**. If the **-s** (**--standard**) and **-w**
250 (**--warn**) flags were not given on the command line, the max allowable value
251 for **ibase** is **36**. Otherwise, it is **16**. The min allowable value for
252 **ibase** is **2**. The max allowable value for **ibase** can be queried in
253 bc(1) programs with the **maxibase()** built-in function.
255 **obase** is a global variable determining how to output results. It is the
256 "output" base, or the number base used for outputting numbers. **obase** is
257 initially **10**. The max allowable value for **obase** is **BC_BASE_MAX** and
258 can be queried in bc(1) programs with the **maxobase()** built-in function. The
259 min allowable value for **obase** is **2**. Values are output in the specified
262 The *scale* of an expression is the number of digits in the result of the
263 expression right of the decimal point, and **scale** is a global variable that
264 sets the precision of any operations, with exceptions. **scale** is initially
265 **0**. **scale** cannot be negative. The max allowable value for **scale** is
266 **BC_SCALE_MAX** and can be queried in bc(1) programs with the **maxscale()**
269 bc(1) has both *global* variables and *local* variables. All *local*
270 variables are local to the function; they are parameters or are introduced in
271 the **auto** list of a function (see the **FUNCTIONS** section). If a variable
272 is accessed which is not a parameter or in the **auto** list, it is assumed to
273 be *global*. If a parent function has a *local* variable version of a variable
274 that a child function considers *global*, the value of that *global* variable in
275 the child function is the value of the variable in the parent function, not the
276 value of the actual *global* variable.
278 All of the above applies to arrays as well.
280 The value of a statement that is an expression (i.e., any of the named
281 expressions or operands) is printed unless the lowest precedence operator is an
282 assignment operator *and* the expression is notsurrounded by parentheses.
284 The value that is printed is also assigned to the special variable **last**. A
285 single dot (**.**) may also be used as a synonym for **last**. These are
286 **non-portable extensions**.
288 Either semicolons or newlines may separate statements.
292 There are two kinds of comments:
294 1. Block comments are enclosed in **/\*** and **\*/**.
295 2. Line comments go from **#** until, and not including, the next newline. This
296 is a **non-portable extension**.
300 The following are named expressions in bc(1):
303 2. Array Elements: **I[E]**
307 6. **last** or a single dot (**.**)
309 Number 6 is a **non-portable extension**.
311 Variables and arrays do not interfere; users can have arrays named the same as
312 variables. This also applies to functions (see the **FUNCTIONS** section), so a
313 user can have a variable, array, and function that all have the same name, and
314 they will not shadow each other, whether inside of functions or not.
316 Named expressions are required as the operand of **increment**/**decrement**
317 operators and as the left side of **assignment** operators (see the *Operators*
322 The following are valid operands in bc(1):
324 1. Numbers (see the *Numbers* subsection below).
325 2. Array indices (**I[E]**).
326 3. **(E)**: The value of **E** (used to change precedence).
327 4. **sqrt(E)**: The square root of **E**. **E** must be non-negative.
328 5. **length(E)**: The number of significant decimal digits in **E**.
329 6. **length(I[])**: The number of elements in the array **I**. This is a
330 **non-portable extension**.
331 7. **scale(E)**: The *scale* of **E**.
332 8. **abs(E)**: The absolute value of **E**. This is a **non-portable
334 9. **I()**, **I(E)**, **I(E, E)**, and so on, where **I** is an identifier for
335 a non-**void** function (see the *Void Functions* subsection of the
336 **FUNCTIONS** section). The **E** argument(s) may also be arrays of the form
337 **I[]**, which will automatically be turned into array references (see the
338 *Array References* subsection of the **FUNCTIONS** section) if the
339 corresponding parameter in the function definition is an array reference.
340 10. **read()**: Reads a line from **stdin** and uses that as an expression. The
341 result of that expression is the result of the **read()** operand. This is a
342 **non-portable extension**.
343 11. **maxibase()**: The max allowable **ibase**. This is a **non-portable
345 12. **maxobase()**: The max allowable **obase**. This is a **non-portable
347 13. **maxscale()**: The max allowable **scale**. This is a **non-portable
352 Numbers are strings made up of digits, uppercase letters, and at most **1**
353 period for a radix. Numbers can have up to **BC_NUM_MAX** digits. Uppercase
354 letters are equal to **9** + their position in the alphabet (i.e., **A** equals
355 **10**, or **9+1**). If a digit or letter makes no sense with the current value
356 of **ibase**, they are set to the value of the highest valid digit in **ibase**.
358 Single-character numbers (i.e., **A** alone) take the value that they would have
359 if they were valid digits, regardless of the value of **ibase**. This means that
360 **A** alone always equals decimal **10** and **Z** alone always equals decimal
365 The following arithmetic and logical operators can be used. They are listed in
366 order of decreasing precedence. Operators in the same group have the same
371 : Type: Prefix and Postfix
375 Description: **increment**, **decrement**
383 Description: **negation**, **boolean not**
391 Description: **power**
399 Description: **multiply**, **divide**, **modulus**
407 Description: **add**, **subtract**
409 **=** **+=** **-=** **\*=** **/=** **%=** **\^=**
415 Description: **assignment**
417 **==** **\<=** **\>=** **!=** **\<** **\>**
423 Description: **relational**
431 Description: **boolean and**
439 Description: **boolean or**
441 The operators will be described in more detail below.
445 : The prefix and postfix **increment** and **decrement** operators behave
446 exactly like they would in C. They require a named expression (see the
447 *Named Expressions* subsection) as an operand.
449 The prefix versions of these operators are more efficient; use them where
454 : The **negation** operator returns **0** if a user attempts to negate any
455 expression with the value **0**. Otherwise, a copy of the expression with
456 its sign flipped is returned.
460 : The **boolean not** operator returns **1** if the expression is **0**, or
463 This is a **non-portable extension**.
467 : The **power** operator (not the **exclusive or** operator, as it would be in
468 C) takes two expressions and raises the first to the power of the value of
469 the second. The *scale* of the result is equal to **scale**.
471 The second expression must be an integer (no *scale*), and if it is
472 negative, the first value must be non-zero.
476 : The **multiply** operator takes two expressions, multiplies them, and
477 returns the product. If **a** is the *scale* of the first expression and
478 **b** is the *scale* of the second expression, the *scale* of the result is
479 equal to **min(a+b,max(scale,a,b))** where **min()** and **max()** return
484 : The **divide** operator takes two expressions, divides them, and returns the
485 quotient. The *scale* of the result shall be the value of **scale**.
487 The second expression must be non-zero.
491 : The **modulus** operator takes two expressions, **a** and **b**, and
492 evaluates them by 1) Computing **a/b** to current **scale** and 2) Using the
493 result of step 1 to calculate **a-(a/b)\*b** to *scale*
494 **max(scale+scale(b),scale(a))**.
496 The second expression must be non-zero.
500 : The **add** operator takes two expressions, **a** and **b**, and returns the
501 sum, with a *scale* equal to the max of the *scale*s of **a** and **b**.
505 : The **subtract** operator takes two expressions, **a** and **b**, and
506 returns the difference, with a *scale* equal to the max of the *scale*s of
509 **=** **+=** **-=** **\*=** **/=** **%=** **\^=**
511 : The **assignment** operators take two expressions, **a** and **b** where
512 **a** is a named expression (see the *Named Expressions* subsection).
514 For **=**, **b** is copied and the result is assigned to **a**. For all
515 others, **a** and **b** are applied as operands to the corresponding
516 arithmetic operator and the result is assigned to **a**.
518 **==** **\<=** **\>=** **!=** **\<** **\>**
520 : The **relational** operators compare two expressions, **a** and **b**, and
521 if the relation holds, according to C language semantics, the result is
522 **1**. Otherwise, it is **0**.
524 Note that unlike in C, these operators have a lower precedence than the
525 **assignment** operators, which means that **a=b\>c** is interpreted as
528 Also, unlike the [standard][1] requires, these operators can appear anywhere
529 any other expressions can be used. This allowance is a
530 **non-portable extension**.
534 : The **boolean and** operator takes two expressions and returns **1** if both
535 expressions are non-zero, **0** otherwise.
537 This is *not* a short-circuit operator.
539 This is a **non-portable extension**.
543 : The **boolean or** operator takes two expressions and returns **1** if one
544 of the expressions is non-zero, **0** otherwise.
546 This is *not* a short-circuit operator.
548 This is a **non-portable extension**.
552 The following items are statements:
555 2. **{** **S** **;** ... **;** **S** **}**
556 3. **if** **(** **E** **)** **S**
557 4. **if** **(** **E** **)** **S** **else** **S**
558 5. **while** **(** **E** **)** **S**
559 6. **for** **(** **E** **;** **E** **;** **E** **)** **S**
560 7. An empty statement
566 13. A string of characters, enclosed in double quotes
567 14. **print** **E** **,** ... **,** **E**
568 15. **I()**, **I(E)**, **I(E, E)**, and so on, where **I** is an identifier for
569 a **void** function (see the *Void Functions* subsection of the
570 **FUNCTIONS** section). The **E** argument(s) may also be arrays of the form
571 **I[]**, which will automatically be turned into array references (see the
572 *Array References* subsection of the **FUNCTIONS** section) if the
573 corresponding parameter in the function definition is an array reference.
575 Numbers 4, 9, 11, 12, 14, and 15 are **non-portable extensions**.
577 Also, as a **non-portable extension**, any or all of the expressions in the
578 header of a for loop may be omitted. If the condition (second expression) is
579 omitted, it is assumed to be a constant **1**.
581 The **break** statement causes a loop to stop iterating and resume execution
582 immediately following a loop. This is only allowed in loops.
584 The **continue** statement causes a loop iteration to stop early and returns to
585 the start of the loop, including testing the loop condition. This is only
588 The **if** **else** statement does the same thing as in C.
590 The **quit** statement causes bc(1) to quit, even if it is on a branch that will
591 not be executed (it is a compile-time command).
593 The **halt** statement causes bc(1) to quit, if it is executed. (Unlike **quit**
594 if it is on a branch of an **if** statement that is not executed, bc(1) does not
597 The **limits** statement prints the limits that this bc(1) is subject to. This
598 is like the **quit** statement in that it is a compile-time command.
600 An expression by itself is evaluated and printed, followed by a newline.
604 The "expressions" in a **print** statement may also be strings. If they are, there
605 are backslash escape sequences that are interpreted specially. What those
606 sequences are, and what they cause to be printed, are shown below:
620 Any other character following a backslash causes the backslash and character to
623 Any non-string expression in a print statement shall be assigned to **last**,
624 like any other expression that is printed.
626 ## Order of Evaluation
628 All expressions in a statment are evaluated left to right, except as necessary
629 to maintain order of operations. This means, for example, assuming that **i** is
630 equal to **0**, in the expression
634 the first (or 0th) element of **a** is set to **1**, and **i** is equal to **2**
635 at the end of the expression.
637 This includes function arguments. Thus, assuming **i** is equal to **0**, this
638 means that in the expression
642 the first argument passed to **x()** is **0**, and the second argument is **1**,
643 while **i** is equal to **2** before the function starts executing.
647 Function definitions are as follows:
657 Any **I** in the parameter list or **auto** list may be replaced with **I[]** to
658 make a parameter or **auto** var an array, and any **I** in the parameter list
659 may be replaced with **\*I[]** to make a parameter an array reference. Callers
660 of functions that take array references should not put an asterisk in the call;
661 they must be called with just **I[]** like normal array parameters and will be
662 automatically converted into references.
664 As a **non-portable extension**, the opening brace of a **define** statement may
665 appear on the next line.
667 As a **non-portable extension**, the return statement may also be in one of the
671 2. **return** **(** **)**
674 The first two, or not specifying a **return** statement, is equivalent to
675 **return (0)**, unless the function is a **void** function (see the *Void
676 Functions* subsection below).
680 Functions can also be **void** functions, defined as follows:
683 define void I(I,...,I){
690 They can only be used as standalone expressions, where such an expression would
691 be printed alone, except in a print statement.
693 Void functions can only use the first two **return** statements listed above.
694 They can also omit the return statement entirely.
696 The word "void" is not treated as a keyword; it is still possible to have
697 variables, arrays, and functions named **void**. The word "void" is only
698 treated specially right after the **define** keyword.
700 This is a **non-portable extension**.
704 For any array in the parameter list, if the array is declared in the form
710 it is a **reference**. Any changes to the array in the function are reflected,
711 when the function returns, to the array that was passed in.
713 Other than this, all function arguments are passed by value.
715 This is a **non-portable extension**.
719 All of the functions below are available when the **-l** or **--mathlib**
720 command-line flags are given.
724 The [standard][1] defines the following functions for the math library:
728 : Returns the sine of **x**, which is assumed to be in radians.
730 This is a transcendental function (see the *Transcendental Functions*
735 : Returns the cosine of **x**, which is assumed to be in radians.
737 This is a transcendental function (see the *Transcendental Functions*
742 : Returns the arctangent of **x**, in radians.
744 This is a transcendental function (see the *Transcendental Functions*
749 : Returns the natural logarithm of **x**.
751 This is a transcendental function (see the *Transcendental Functions*
756 : Returns the mathematical constant **e** raised to the power of **x**.
758 This is a transcendental function (see the *Transcendental Functions*
763 : Returns the bessel integer order **n** (truncated) of **x**.
765 This is a transcendental function (see the *Transcendental Functions*
768 ## Transcendental Functions
770 All transcendental functions can return slightly inaccurate results (up to 1
771 [ULP][4]). This is unavoidable, and [this article][5] explains why it is
772 impossible and unnecessary to calculate exact results for the transcendental
775 Because of the possible inaccuracy, I recommend that users call those functions
776 with the precision (**scale**) set to at least 1 higher than is necessary. If
777 exact results are *absolutely* required, users can double the precision
778 (**scale**) and then truncate.
780 The transcendental functions in the standard math library are:
791 When bc(1) encounters an error or a signal that it has a non-default handler
792 for, it resets. This means that several things happen.
794 First, any functions that are executing are stopped and popped off the stack.
795 The behavior is not unlike that of exceptions in programming languages. Then
796 the execution point is set so that any code waiting to execute (after all
797 functions returned) is skipped.
799 Thus, when bc(1) resets, it skips any remaining code waiting to be executed.
800 Then, if it is interactive mode, and the error was not a fatal error (see the
801 **EXIT STATUS** section), it asks for more input; otherwise, it exits with the
802 appropriate return code.
804 Note that this reset behavior is different from the GNU bc(1), which attempts to
805 start executing the statement right after the one that caused an error.
809 Most bc(1) implementations use **char** types to calculate the value of **1**
810 decimal digit at a time, but that can be slow. This bc(1) does something
813 It uses large integers to calculate more than **1** decimal digit at a time. If
814 built in a environment where **BC_LONG_BIT** (see the **LIMITS** section) is
815 **64**, then each integer has **9** decimal digits. If built in an environment
816 where **BC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
817 value (the number of decimal digits per large integer) is called
820 The actual values of **BC_LONG_BIT** and **BC_BASE_DIGS** can be queried with
821 the **limits** statement.
823 In addition, this bc(1) uses an even larger integer for overflow checking. This
824 integer type depends on the value of **BC_LONG_BIT**, but is always at least
825 twice as large as the integer type used to store digits.
829 The following are the limits on bc(1):
833 : The number of bits in the **long** type in the environment where bc(1) was
834 built. This determines how many decimal digits can be stored in a single
835 large integer (see the **PERFORMANCE** section).
839 : The number of decimal digits per large integer (see the **PERFORMANCE**
840 section). Depends on **BC_LONG_BIT**.
844 : The max decimal number that each large integer can store (see
845 **BC_BASE_DIGS**) plus **1**. Depends on **BC_BASE_DIGS**.
849 : The max number that the overflow type (see the **PERFORMANCE** section) can
850 hold. Depends on **BC_LONG_BIT**.
854 : The maximum output base. Set at **BC_BASE_POW**.
858 : The maximum size of arrays. Set at **SIZE_MAX-1**.
862 : The maximum **scale**. Set at **BC_OVERFLOW_MAX-1**.
866 : The maximum length of strings. Set at **BC_OVERFLOW_MAX-1**.
870 : The maximum length of identifiers. Set at **BC_OVERFLOW_MAX-1**.
874 : The maximum length of a number (in decimal digits), which includes digits
875 after the decimal point. Set at **BC_OVERFLOW_MAX-1**.
879 : The maximum allowable exponent (positive or negative). Set at
884 : The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
886 The actual values can be queried with the **limits** statement.
888 These limits are meant to be effectively non-existent; the limits are so large
889 (at least on 64-bit machines) that there should not be any point at which they
890 become a problem. In fact, memory should be exhausted before these limits should
893 # ENVIRONMENT VARIABLES
895 bc(1) recognizes the following environment variables:
899 : If this variable exists (no matter the contents), bc(1) behaves as if
900 the **-s** option was given.
904 : This is another way to give command-line arguments to bc(1). They should be
905 in the same format as all other command-line arguments. These are always
906 processed first, so any files given in **BC_ENV_ARGS** will be processed
907 before arguments and files given on the command-line. This gives the user
908 the ability to set up "standard" options and files to be used at every
909 invocation. The most useful thing for such files to contain would be useful
910 functions that the user might want every time bc(1) runs.
912 The code that parses **BC_ENV_ARGS** will correctly handle quoted arguments,
913 but it does not understand escape sequences. For example, the string
914 **"/home/gavin/some bc file.bc"** will be correctly parsed, but the string
915 **"/home/gavin/some \"bc\" file.bc"** will include the backslashes.
917 The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
918 if you have a file with any number of single quotes in the name, you can use
919 double quotes as the outside quotes, as in **"some 'bc' file.bc"**, and vice
920 versa if you have a file with double quotes. However, handling a file with
921 both kinds of quotes in **BC_ENV_ARGS** is not supported due to the
922 complexity of the parsing, though such files are still supported on the
923 command-line where the parsing is done by the shell.
927 : If this environment variable exists and contains an integer that is greater
928 than **1** and is less than **UINT16_MAX** (**2\^16-1**), bc(1) will output
929 lines to that length, including the backslash (**\\**). The default line
934 bc(1) returns the following exit statuses:
942 : A math error occurred. This follows standard practice of using **1** for
943 expected errors, since math errors will happen in the process of normal
946 Math errors include divide by **0**, taking the square root of a negative
947 number, attempting to convert a negative number to a hardware integer,
948 overflow when converting a number to a hardware integer, and attempting to
949 use a non-integer where an integer is required.
951 Converting to a hardware integer happens for the second operand of the power
952 (**\^**) operator and the corresponding assignment operator.
956 : A parse error occurred.
958 Parse errors include unexpected **EOF**, using an invalid character, failing
959 to find the end of a string or comment, using a token where it is invalid,
960 giving an invalid expression, giving an invalid print statement, giving an
961 invalid function definition, attempting to assign to an expression that is
962 not a named expression (see the *Named Expressions* subsection of the
963 **SYNTAX** section), giving an invalid **auto** list, having a duplicate
964 **auto**/function parameter, failing to find the end of a code block,
965 attempting to return a value from a **void** function, attempting to use a
966 variable as a reference, and using any extensions when the option **-s** or
967 any equivalents were given.
971 : A runtime error occurred.
973 Runtime errors include assigning an invalid number to **ibase**, **obase**,
974 or **scale**; give a bad expression to a **read()** call, calling **read()**
975 inside of a **read()** call, type errors, passing the wrong number of
976 arguments to functions, attempting to call an undefined function, and
977 attempting to use a **void** function call as a value in an expression.
981 : A fatal error occurred.
983 Fatal errors include memory allocation errors, I/O errors, failing to open
984 files, attempting to use files that do not have only ASCII characters (bc(1)
985 only accepts ASCII characters), attempting to open a directory as a file,
986 and giving invalid command-line options.
988 The exit status **4** is special; when a fatal error occurs, bc(1) always exits
989 and returns **4**, no matter what mode bc(1) is in.
991 The other statuses will only be returned when bc(1) is not in interactive mode
992 (see the **INTERACTIVE MODE** section), since bc(1) resets its state (see the
993 **RESET** section) and accepts more input when one of those errors occurs in
994 interactive mode. This is also the case when interactive mode is forced by the
995 **-i** flag or **--interactive** option.
997 These exit statuses allow bc(1) to be used in shell scripting with error
998 checking, and its normal behavior can be forced by using the **-i** flag or
999 **--interactive** option.
1003 Per the [standard][1], bc(1) has an interactive mode and a non-interactive mode.
1004 Interactive mode is turned on automatically when both **stdin** and **stdout**
1005 are hooked to a terminal, but the **-i** flag and **--interactive** option can
1006 turn it on in other cases.
1008 In interactive mode, bc(1) attempts to recover from errors (see the **RESET**
1009 section), and in normal execution, flushes **stdout** as soon as execution is
1010 done for the current input.
1014 If **stdin**, **stdout**, and **stderr** are all connected to a TTY, bc(1) turns
1017 TTY mode is required for history to be enabled (see the **COMMAND LINE HISTORY**
1018 section). It is also required to enable special handling for **SIGINT** signals.
1020 The prompt is enabled in TTY mode.
1022 TTY mode is different from interactive mode because interactive mode is required
1023 in the [bc(1) specification][1], and interactive mode requires only **stdin**
1024 and **stdout** to be connected to a terminal.
1028 Sending a **SIGINT** will cause bc(1) to stop execution of the current input. If
1029 bc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
1030 **RESET** section). Otherwise, it will clean up and exit.
1032 Note that "current input" can mean one of two things. If bc(1) is processing
1033 input from **stdin** in TTY mode, it will ask for more input. If bc(1) is
1034 processing input from a file in TTY mode, it will stop processing the file and
1035 start processing the next file, if one exists, or ask for input from **stdin**
1036 if no other file exists.
1038 This means that if a **SIGINT** is sent to bc(1) as it is executing a file, it
1039 can seem as though bc(1) did not respond to the signal since it will immediately
1040 start executing the next file. This is by design; most files that users execute
1041 when interacting with bc(1) have function definitions, which are quick to parse.
1042 If a file takes a long time to execute, there may be a bug in that file. The
1043 rest of the files could still be executed without problem, allowing the user to
1046 **SIGTERM** and **SIGQUIT** cause bc(1) to clean up and exit, and it uses the
1047 default handler for all other signals. The one exception is **SIGHUP**; in that
1048 case, when bc(1) is in TTY mode, a **SIGHUP** will cause bc(1) to clean up and
1051 # COMMAND LINE HISTORY
1053 bc(1) supports interactive command-line editing. If bc(1) is in TTY mode (see
1054 the **TTY MODE** section), history is enabled. Previous lines can be recalled
1055 and edited with the arrow keys.
1057 **Note**: tabs are converted to 8 spaces.
1065 bc(1) is compliant with the [IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1]
1066 specification. The flags **-efghiqsvVw**, all long options, and the extensions
1067 noted above are extensions to that specification.
1069 Note that the specification explicitly says that bc(1) only accepts numbers that
1070 use a period (**.**) as a radix point, regardless of the value of
1075 None are known. Report bugs at https://git.yzena.com/gavin/bc.
1079 Gavin D. Howard <gavin@yzena.com> and contributors.
1081 [1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html
1082 [2]: https://www.gnu.org/software/bc/
1083 [3]: https://en.wikipedia.org/wiki/Rounding#Round_half_away_from_zero
1084 [4]: https://en.wikipedia.org/wiki/Unit_in_the_last_place
1085 [5]: https://people.eecs.berkeley.edu/~wkahan/LOG10HAF.TXT
1086 [6]: https://en.wikipedia.org/wiki/Rounding#Rounding_away_from_zero