3 SPDX-License-Identifier: BSD-2-Clause
5 Copyright (c) 2018-2020 Gavin D. Howard and contributors.
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33 bc - arbitrary-precision 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 : This option is a no-op.
132 This is a **non-portable extension**.
136 : Do not print copyright header. bc(1) will also suppress the header in
137 non-interactive mode.
139 This is mostly for compatibility with the [GNU bc(1)][2].
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 In other bc(1) implementations, this option causes the program to execute
171 the expressions and then exit. This bc(1) does not, unless the
172 **BC_EXPR_EXIT** is defined (see the **ENVIRONMENT VARIABLES** section).
174 This is a **non-portable extension**.
176 **-f** *file*, **--file**=*file*
178 : Reads in *file* and evaluates it, line by line, as though it were read
179 through **stdin**. If expressions are also given (see above), the
180 expressions are evaluated in the order given.
182 In other bc(1) implementations, this option causes the program to execute
183 the files and then exit. This bc(1) does not, unless the
184 **BC_EXPR_EXIT** is defined (see the **ENVIRONMENT VARIABLES** section).
186 This is a **non-portable extension**.
188 All long options are **non-portable extensions**.
192 Any non-error output is written to **stdout**.
194 **Note**: Unlike other bc(1) implementations, this bc(1) will issue a fatal
195 error (see the **EXIT STATUS** section) if it cannot write to **stdout**, so if
196 **stdout** is closed, as in **bc <file> >&-**, it will quit with an error. This
197 is done so that bc(1) can report problems when **stdout** is redirected to a
200 If there are scripts that depend on the behavior of other bc(1) implementations,
201 it is recommended that those scripts be changed to redirect **stdout** to
206 Any error output is written to **stderr**.
208 **Note**: Unlike other bc(1) implementations, this bc(1) will issue a fatal
209 error (see the **EXIT STATUS** section) if it cannot write to **stderr**, so if
210 **stderr** is closed, as in **bc <file> 2>&-**, it will quit with an error. This
211 is done so that bc(1) can exit with an error code when **stderr** is redirected
214 If there are scripts that depend on the behavior of other bc(1) implementations,
215 it is recommended that those scripts be changed to redirect **stderr** to
220 The syntax for bc(1) programs is mostly C-like, with some differences. This
221 bc(1) follows the [POSIX standard][1], which is a much more thorough resource
222 for the language this bc(1) accepts. This section is meant to be a summary and a
223 listing of all the extensions to the standard.
225 In the sections below, **E** means expression, **S** means statement, and **I**
228 Identifiers (**I**) start with a lowercase letter and can be followed by any
229 number (up to **BC_NAME_MAX-1**) of lowercase letters (**a-z**), digits
230 (**0-9**), and underscores (**\_**). The regex is **\[a-z\]\[a-z0-9\_\]\***.
231 Identifiers with more than one character (letter) are a
232 **non-portable extension**.
234 **ibase** is a global variable determining how to interpret constant numbers. It
235 is the "input" base, or the number base used for interpreting input numbers.
236 **ibase** is initially **10**. If the **-s** (**--standard**) and **-w**
237 (**--warn**) flags were not given on the command line, the max allowable value
238 for **ibase** is **36**. Otherwise, it is **16**. The min allowable value for
239 **ibase** is **2**. The max allowable value for **ibase** can be queried in
240 bc(1) programs with the **maxibase()** built-in function.
242 **obase** is a global variable determining how to output results. It is the
243 "output" base, or the number base used for outputting numbers. **obase** is
244 initially **10**. The max allowable value for **obase** is **BC_BASE_MAX** and
245 can be queried in bc(1) programs with the **maxobase()** built-in function. The
246 min allowable value for **obase** is **2**. Values are output in the specified
249 The *scale* of an expression is the number of digits in the result of the
250 expression right of the decimal point, and **scale** is a global variable that
251 sets the precision of any operations, with exceptions. **scale** is initially
252 **0**. **scale** cannot be negative. The max allowable value for **scale** is
253 **BC_SCALE_MAX** and can be queried in bc(1) programs with the **maxscale()**
256 bc(1) has both *global* variables and *local* variables. All *local*
257 variables are local to the function; they are parameters or are introduced in
258 the **auto** list of a function (see the **FUNCTIONS** section). If a variable
259 is accessed which is not a parameter or in the **auto** list, it is assumed to
260 be *global*. If a parent function has a *local* variable version of a variable
261 that a child function considers *global*, the value of that *global* variable in
262 the child function is the value of the variable in the parent function, not the
263 value of the actual *global* variable.
265 All of the above applies to arrays as well.
267 The value of a statement that is an expression (i.e., any of the named
268 expressions or operands) is printed unless the lowest precedence operator is an
269 assignment operator *and* the expression is notsurrounded by parentheses.
271 The value that is printed is also assigned to the special variable **last**. A
272 single dot (**.**) may also be used as a synonym for **last**. These are
273 **non-portable extensions**.
275 Either semicolons or newlines may separate statements.
279 There are two kinds of comments:
281 1. Block comments are enclosed in **/\*** and **\*/**.
282 2. Line comments go from **#** until, and not including, the next newline. This
283 is a **non-portable extension**.
287 The following are named expressions in bc(1):
290 2. Array Elements: **I[E]**
294 6. **last** or a single dot (**.**)
296 Number 6 is a **non-portable extension**.
298 Variables and arrays do not interfere; users can have arrays named the same as
299 variables. This also applies to functions (see the **FUNCTIONS** section), so a
300 user can have a variable, array, and function that all have the same name, and
301 they will not shadow each other, whether inside of functions or not.
303 Named expressions are required as the operand of **increment**/**decrement**
304 operators and as the left side of **assignment** operators (see the *Operators*
309 The following are valid operands in bc(1):
311 1. Numbers (see the *Numbers* subsection below).
312 2. Array indices (**I[E]**).
313 3. **(E)**: The value of **E** (used to change precedence).
314 4. **sqrt(E)**: The square root of **E**. **E** must be non-negative.
315 5. **length(E)**: The number of significant decimal digits in **E**.
316 6. **length(I[])**: The number of elements in the array **I**. This is a
317 **non-portable extension**.
318 7. **scale(E)**: The *scale* of **E**.
319 8. **abs(E)**: The absolute value of **E**. This is a **non-portable
321 9. **I()**, **I(E)**, **I(E, E)**, and so on, where **I** is an identifier for
322 a non-**void** function (see the *Void Functions* subsection of the
323 **FUNCTIONS** section). The **E** argument(s) may also be arrays of the form
324 **I[]**, which will automatically be turned into array references (see the
325 *Array References* subsection of the **FUNCTIONS** section) if the
326 corresponding parameter in the function definition is an array reference.
327 10. **read()**: Reads a line from **stdin** and uses that as an expression. The
328 result of that expression is the result of the **read()** operand. This is a
329 **non-portable extension**.
330 11. **maxibase()**: The max allowable **ibase**. This is a **non-portable
332 12. **maxobase()**: The max allowable **obase**. This is a **non-portable
334 13. **maxscale()**: The max allowable **scale**. This is a **non-portable
339 Numbers are strings made up of digits, uppercase letters, and at most **1**
340 period for a radix. Numbers can have up to **BC_NUM_MAX** digits. Uppercase
341 letters are equal to **9** + their position in the alphabet (i.e., **A** equals
342 **10**, or **9+1**). If a digit or letter makes no sense with the current value
343 of **ibase**, they are set to the value of the highest valid digit in **ibase**.
345 Single-character numbers (i.e., **A** alone) take the value that they would have
346 if they were valid digits, regardless of the value of **ibase**. This means that
347 **A** alone always equals decimal **10** and **Z** alone always equals decimal
352 The following arithmetic and logical operators can be used. They are listed in
353 order of decreasing precedence. Operators in the same group have the same
358 : Type: Prefix and Postfix
362 Description: **increment**, **decrement**
370 Description: **negation**, **boolean not**
378 Description: **power**
386 Description: **multiply**, **divide**, **modulus**
394 Description: **add**, **subtract**
396 **=** **+=** **-=** **\*=** **/=** **%=** **\^=**
402 Description: **assignment**
404 **==** **\<=** **\>=** **!=** **\<** **\>**
410 Description: **relational**
418 Description: **boolean and**
426 Description: **boolean or**
428 The operators will be described in more detail below.
432 : The prefix and postfix **increment** and **decrement** operators behave
433 exactly like they would in C. They require a named expression (see the
434 *Named Expressions* subsection) as an operand.
436 The prefix versions of these operators are more efficient; use them where
441 : The **negation** operator returns **0** if a user attempts to negate any
442 expression with the value **0**. Otherwise, a copy of the expression with
443 its sign flipped is returned.
447 : The **boolean not** operator returns **1** if the expression is **0**, or
450 This is a **non-portable extension**.
454 : The **power** operator (not the **exclusive or** operator, as it would be in
455 C) takes two expressions and raises the first to the power of the value of
458 The second expression must be an integer (no *scale*), and if it is
459 negative, the first value must be non-zero.
463 : The **multiply** operator takes two expressions, multiplies them, and
464 returns the product. If **a** is the *scale* of the first expression and
465 **b** is the *scale* of the second expression, the *scale* of the result is
466 equal to **min(a+b,max(scale,a,b))** where **min()** and **max()** return
471 : The **divide** operator takes two expressions, divides them, and returns the
472 quotient. The *scale* of the result shall be the value of **scale**.
474 The second expression must be non-zero.
478 : The **modulus** operator takes two expressions, **a** and **b**, and
479 evaluates them by 1) Computing **a/b** to current **scale** and 2) Using the
480 result of step 1 to calculate **a-(a/b)\*b** to *scale*
481 **max(scale+scale(b),scale(a))**.
483 The second expression must be non-zero.
487 : The **add** operator takes two expressions, **a** and **b**, and returns the
488 sum, with a *scale* equal to the max of the *scale*s of **a** and **b**.
492 : The **subtract** operator takes two expressions, **a** and **b**, and
493 returns the difference, with a *scale* equal to the max of the *scale*s of
496 **=** **+=** **-=** **\*=** **/=** **%=** **\^=**
498 : The **assignment** operators take two expressions, **a** and **b** where
499 **a** is a named expression (see the *Named Expressions* subsection).
501 For **=**, **b** is copied and the result is assigned to **a**. For all
502 others, **a** and **b** are applied as operands to the corresponding
503 arithmetic operator and the result is assigned to **a**.
505 **==** **\<=** **\>=** **!=** **\<** **\>**
507 : The **relational** operators compare two expressions, **a** and **b**, and
508 if the relation holds, according to C language semantics, the result is
509 **1**. Otherwise, it is **0**.
511 Note that unlike in C, these operators have a lower precedence than the
512 **assignment** operators, which means that **a=b\>c** is interpreted as
515 Also, unlike the [standard][1] requires, these operators can appear anywhere
516 any other expressions can be used. This allowance is a
517 **non-portable extension**.
521 : The **boolean and** operator takes two expressions and returns **1** if both
522 expressions are non-zero, **0** otherwise.
524 This is *not* a short-circuit operator.
526 This is a **non-portable extension**.
530 : The **boolean or** operator takes two expressions and returns **1** if one
531 of the expressions is non-zero, **0** otherwise.
533 This is *not* a short-circuit operator.
535 This is a **non-portable extension**.
539 The following items are statements:
542 2. **{** **S** **;** ... **;** **S** **}**
543 3. **if** **(** **E** **)** **S**
544 4. **if** **(** **E** **)** **S** **else** **S**
545 5. **while** **(** **E** **)** **S**
546 6. **for** **(** **E** **;** **E** **;** **E** **)** **S**
547 7. An empty statement
553 13. A string of characters, enclosed in double quotes
554 14. **print** **E** **,** ... **,** **E**
555 15. **I()**, **I(E)**, **I(E, E)**, and so on, where **I** is an identifier for
556 a **void** function (see the *Void Functions* subsection of the
557 **FUNCTIONS** section). The **E** argument(s) may also be arrays of the form
558 **I[]**, which will automatically be turned into array references (see the
559 *Array References* subsection of the **FUNCTIONS** section) if the
560 corresponding parameter in the function definition is an array reference.
562 Numbers 4, 9, 11, 12, 14, and 15 are **non-portable extensions**.
564 Also, as a **non-portable extension**, any or all of the expressions in the
565 header of a for loop may be omitted. If the condition (second expression) is
566 omitted, it is assumed to be a constant **1**.
568 The **break** statement causes a loop to stop iterating and resume execution
569 immediately following a loop. This is only allowed in loops.
571 The **continue** statement causes a loop iteration to stop early and returns to
572 the start of the loop, including testing the loop condition. This is only
575 The **if** **else** statement does the same thing as in C.
577 The **quit** statement causes bc(1) to quit, even if it is on a branch that will
578 not be executed (it is a compile-time command).
580 The **halt** statement causes bc(1) to quit, if it is executed. (Unlike **quit**
581 if it is on a branch of an **if** statement that is not executed, bc(1) does not
584 The **limits** statement prints the limits that this bc(1) is subject to. This
585 is like the **quit** statement in that it is a compile-time command.
587 An expression by itself is evaluated and printed, followed by a newline.
591 The "expressions" in a **print** statement may also be strings. If they are, there
592 are backslash escape sequences that are interpreted specially. What those
593 sequences are, and what they cause to be printed, are shown below:
607 Any other character following a backslash causes the backslash and character to
610 Any non-string expression in a print statement shall be assigned to **last**,
611 like any other expression that is printed.
613 ## Order of Evaluation
615 All expressions in a statment are evaluated left to right, except as necessary
616 to maintain order of operations. This means, for example, assuming that **i** is
617 equal to **0**, in the expression
621 the first (or 0th) element of **a** is set to **1**, and **i** is equal to **2**
622 at the end of the expression.
624 This includes function arguments. Thus, assuming **i** is equal to **0**, this
625 means that in the expression
629 the first argument passed to **x()** is **0**, and the second argument is **1**,
630 while **i** is equal to **2** before the function starts executing.
634 Function definitions are as follows:
644 Any **I** in the parameter list or **auto** list may be replaced with **I[]** to
645 make a parameter or **auto** var an array, and any **I** in the parameter list
646 may be replaced with **\*I[]** to make a parameter an array reference. Callers
647 of functions that take array references should not put an asterisk in the call;
648 they must be called with just **I[]** like normal array parameters and will be
649 automatically converted into references.
651 As a **non-portable extension**, the opening brace of a **define** statement may
652 appear on the next line.
654 As a **non-portable extension**, the return statement may also be in one of the
658 2. **return** **(** **)**
661 The first two, or not specifying a **return** statement, is equivalent to
662 **return (0)**, unless the function is a **void** function (see the *Void
663 Functions* subsection below).
667 Functions can also be **void** functions, defined as follows:
670 define void I(I,...,I){
677 They can only be used as standalone expressions, where such an expression would
678 be printed alone, except in a print statement.
680 Void functions can only use the first two **return** statements listed above.
681 They can also omit the return statement entirely.
683 The word "void" is not treated as a keyword; it is still possible to have
684 variables, arrays, and functions named **void**. The word "void" is only
685 treated specially right after the **define** keyword.
687 This is a **non-portable extension**.
691 For any array in the parameter list, if the array is declared in the form
697 it is a **reference**. Any changes to the array in the function are reflected,
698 when the function returns, to the array that was passed in.
700 Other than this, all function arguments are passed by value.
702 This is a **non-portable extension**.
706 All of the functions below are available when the **-l** or **--mathlib**
707 command-line flags are given.
711 The [standard][1] defines the following functions for the math library:
715 : Returns the sine of **x**, which is assumed to be in radians.
717 This is a transcendental function (see the *Transcendental Functions*
722 : Returns the cosine of **x**, which is assumed to be in radians.
724 This is a transcendental function (see the *Transcendental Functions*
729 : Returns the arctangent of **x**, in radians.
731 This is a transcendental function (see the *Transcendental Functions*
736 : Returns the natural logarithm of **x**.
738 This is a transcendental function (see the *Transcendental Functions*
743 : Returns the mathematical constant **e** raised to the power of **x**.
745 This is a transcendental function (see the *Transcendental Functions*
750 : Returns the bessel integer order **n** (truncated) of **x**.
752 This is a transcendental function (see the *Transcendental Functions*
755 ## Transcendental Functions
757 All transcendental functions can return slightly inaccurate results (up to 1
758 [ULP][4]). This is unavoidable, and [this article][5] explains why it is
759 impossible and unnecessary to calculate exact results for the transcendental
762 Because of the possible inaccuracy, I recommend that users call those functions
763 with the precision (**scale**) set to at least 1 higher than is necessary. If
764 exact results are *absolutely* required, users can double the precision
765 (**scale**) and then truncate.
767 The transcendental functions in the standard math library are:
778 When bc(1) encounters an error or a signal that it has a non-default handler
779 for, it resets. This means that several things happen.
781 First, any functions that are executing are stopped and popped off the stack.
782 The behavior is not unlike that of exceptions in programming languages. Then
783 the execution point is set so that any code waiting to execute (after all
784 functions returned) is skipped.
786 Thus, when bc(1) resets, it skips any remaining code waiting to be executed.
787 Then, if it is interactive mode, and the error was not a fatal error (see the
788 **EXIT STATUS** section), it asks for more input; otherwise, it exits with the
789 appropriate return code.
791 Note that this reset behavior is different from the GNU bc(1), which attempts to
792 start executing the statement right after the one that caused an error.
796 Most bc(1) implementations use **char** types to calculate the value of **1**
797 decimal digit at a time, but that can be slow. This bc(1) does something
800 It uses large integers to calculate more than **1** decimal digit at a time. If
801 built in a environment where **BC_LONG_BIT** (see the **LIMITS** section) is
802 **64**, then each integer has **9** decimal digits. If built in an environment
803 where **BC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
804 value (the number of decimal digits per large integer) is called
807 The actual values of **BC_LONG_BIT** and **BC_BASE_DIGS** can be queried with
808 the **limits** statement.
810 In addition, this bc(1) uses an even larger integer for overflow checking. This
811 integer type depends on the value of **BC_LONG_BIT**, but is always at least
812 twice as large as the integer type used to store digits.
816 The following are the limits on bc(1):
820 : The number of bits in the **long** type in the environment where bc(1) was
821 built. This determines how many decimal digits can be stored in a single
822 large integer (see the **PERFORMANCE** section).
826 : The number of decimal digits per large integer (see the **PERFORMANCE**
827 section). Depends on **BC_LONG_BIT**.
831 : The max decimal number that each large integer can store (see
832 **BC_BASE_DIGS**) plus **1**. Depends on **BC_BASE_DIGS**.
836 : The max number that the overflow type (see the **PERFORMANCE** section) can
837 hold. Depends on **BC_LONG_BIT**.
841 : The maximum output base. Set at **BC_BASE_POW**.
845 : The maximum size of arrays. Set at **SIZE_MAX-1**.
849 : The maximum **scale**. Set at **BC_OVERFLOW_MAX-1**.
853 : The maximum length of strings. Set at **BC_OVERFLOW_MAX-1**.
857 : The maximum length of identifiers. Set at **BC_OVERFLOW_MAX-1**.
861 : The maximum length of a number (in decimal digits), which includes digits
862 after the decimal point. Set at **BC_OVERFLOW_MAX-1**.
866 : The maximum allowable exponent (positive or negative). Set at
871 : The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
873 The actual values can be queried with the **limits** statement.
875 These limits are meant to be effectively non-existent; the limits are so large
876 (at least on 64-bit machines) that there should not be any point at which they
877 become a problem. In fact, memory should be exhausted before these limits should
880 # ENVIRONMENT VARIABLES
882 bc(1) recognizes the following environment variables:
886 : If this variable exists (no matter the contents), bc(1) behaves as if
887 the **-s** option was given.
891 : This is another way to give command-line arguments to bc(1). They should be
892 in the same format as all other command-line arguments. These are always
893 processed first, so any files given in **BC_ENV_ARGS** will be processed
894 before arguments and files given on the command-line. This gives the user
895 the ability to set up "standard" options and files to be used at every
896 invocation. The most useful thing for such files to contain would be useful
897 functions that the user might want every time bc(1) runs.
899 The code that parses **BC_ENV_ARGS** will correctly handle quoted arguments,
900 but it does not understand escape sequences. For example, the string
901 **"/home/gavin/some bc file.bc"** will be correctly parsed, but the string
902 **"/home/gavin/some \"bc\" file.bc"** will include the backslashes.
904 The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
905 if you have a file with any number of single quotes in the name, you can use
906 double quotes as the outside quotes, as in **"some 'bc' file.bc"**, and vice
907 versa if you have a file with double quotes. However, handling a file with
908 both kinds of quotes in **BC_ENV_ARGS** is not supported due to the
909 complexity of the parsing, though such files are still supported on the
910 command-line where the parsing is done by the shell.
914 : If this environment variable exists and contains an integer that is greater
915 than **1** and is less than **UINT16_MAX** (**2\^16-1**), bc(1) will output
916 lines to that length, including the backslash (**\\**). The default line
921 : If this variable exists (no matter the contents), bc(1) will exit
922 immediately after executing expressions and files given by the **-e** and/or
923 **-f** command-line options (and any equivalents).
927 bc(1) returns the following exit statuses:
935 : A math error occurred. This follows standard practice of using **1** for
936 expected errors, since math errors will happen in the process of normal
939 Math errors include divide by **0**, taking the square root of a negative
940 number, attempting to convert a negative number to a hardware integer,
941 overflow when converting a number to a hardware integer, and attempting to
942 use a non-integer where an integer is required.
944 Converting to a hardware integer happens for the second operand of the power
945 (**\^**) operator and the corresponding assignment operator.
949 : A parse error occurred.
951 Parse errors include unexpected **EOF**, using an invalid character, failing
952 to find the end of a string or comment, using a token where it is invalid,
953 giving an invalid expression, giving an invalid print statement, giving an
954 invalid function definition, attempting to assign to an expression that is
955 not a named expression (see the *Named Expressions* subsection of the
956 **SYNTAX** section), giving an invalid **auto** list, having a duplicate
957 **auto**/function parameter, failing to find the end of a code block,
958 attempting to return a value from a **void** function, attempting to use a
959 variable as a reference, and using any extensions when the option **-s** or
960 any equivalents were given.
964 : A runtime error occurred.
966 Runtime errors include assigning an invalid number to **ibase**, **obase**,
967 or **scale**; give a bad expression to a **read()** call, calling **read()**
968 inside of a **read()** call, type errors, passing the wrong number of
969 arguments to functions, attempting to call an undefined function, and
970 attempting to use a **void** function call as a value in an expression.
974 : A fatal error occurred.
976 Fatal errors include memory allocation errors, I/O errors, failing to open
977 files, attempting to use files that do not have only ASCII characters (bc(1)
978 only accepts ASCII characters), attempting to open a directory as a file,
979 and giving invalid command-line options.
981 The exit status **4** is special; when a fatal error occurs, bc(1) always exits
982 and returns **4**, no matter what mode bc(1) is in.
984 The other statuses will only be returned when bc(1) is not in interactive mode
985 (see the **INTERACTIVE MODE** section), since bc(1) resets its state (see the
986 **RESET** section) and accepts more input when one of those errors occurs in
987 interactive mode. This is also the case when interactive mode is forced by the
988 **-i** flag or **--interactive** option.
990 These exit statuses allow bc(1) to be used in shell scripting with error
991 checking, and its normal behavior can be forced by using the **-i** flag or
992 **--interactive** option.
996 Per the [standard][1], bc(1) has an interactive mode and a non-interactive mode.
997 Interactive mode is turned on automatically when both **stdin** and **stdout**
998 are hooked to a terminal, but the **-i** flag and **--interactive** option can
999 turn it on in other cases.
1001 In interactive mode, bc(1) attempts to recover from errors (see the **RESET**
1002 section), and in normal execution, flushes **stdout** as soon as execution is
1003 done for the current input.
1007 If **stdin**, **stdout**, and **stderr** are all connected to a TTY, bc(1) turns
1010 TTY mode is required for history to be enabled (see the **COMMAND LINE HISTORY**
1011 section). It is also required to enable special handling for **SIGINT** signals.
1013 TTY mode is different from interactive mode because interactive mode is required
1014 in the [bc(1) specification][1], and interactive mode requires only **stdin**
1015 and **stdout** to be connected to a terminal.
1019 Sending a **SIGINT** will cause bc(1) to stop execution of the current input. If
1020 bc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
1021 **RESET** section). Otherwise, it will clean up and exit.
1023 Note that "current input" can mean one of two things. If bc(1) is processing
1024 input from **stdin** in TTY mode, it will ask for more input. If bc(1) is
1025 processing input from a file in TTY mode, it will stop processing the file and
1026 start processing the next file, if one exists, or ask for input from **stdin**
1027 if no other file exists.
1029 This means that if a **SIGINT** is sent to bc(1) as it is executing a file, it
1030 can seem as though bc(1) did not respond to the signal since it will immediately
1031 start executing the next file. This is by design; most files that users execute
1032 when interacting with bc(1) have function definitions, which are quick to parse.
1033 If a file takes a long time to execute, there may be a bug in that file. The
1034 rest of the files could still be executed without problem, allowing the user to
1037 **SIGTERM** and **SIGQUIT** cause bc(1) to clean up and exit, and it uses the
1038 default handler for all other signals. The one exception is **SIGHUP**; in that
1039 case, when bc(1) is in TTY mode, a **SIGHUP** will cause bc(1) to clean up and
1042 # COMMAND LINE HISTORY
1044 bc(1) supports interactive command-line editing. If bc(1) is in TTY mode (see
1045 the **TTY MODE** section), history is enabled. Previous lines can be recalled
1046 and edited with the arrow keys.
1048 **Note**: tabs are converted to 8 spaces.
1052 This bc(1) ships with support for adding error messages for different locales
1053 and thus, supports **LC_MESSAGES**.
1061 bc(1) is compliant with the [IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1]
1062 specification. The flags **-efghiqsvVw**, all long options, and the extensions
1063 noted above are extensions to that specification.
1065 Note that the specification explicitly says that bc(1) only accepts numbers that
1066 use a period (**.**) as a radix point, regardless of the value of
1069 This bc(1) supports error messages for different locales, and thus, it supports
1074 None are known. Report bugs at https://git.yzena.com/gavin/bc.
1078 Gavin D. Howard <yzena.tech@gmail.com> and contributors.
1080 [1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html
1081 [2]: https://www.gnu.org/software/bc/
1082 [3]: https://en.wikipedia.org/wiki/Rounding#Round_half_away_from_zero
1083 [4]: https://en.wikipedia.org/wiki/Unit_in_the_last_place
1084 [5]: https://people.eecs.berkeley.edu/~wkahan/LOG10HAF.TXT
1085 [6]: https://en.wikipedia.org/wiki/Rounding#Rounding_away_from_zero