3 SPDX-License-Identifier: BSD-2-Clause
5 Copyright (c) 2018-2020 Gavin D. Howard and contributors.
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33 dc - arbitrary-precision decimal reverse-Polish notation calculator
37 **dc** [**-hiPvVx**] [**--version**] [**--help**] [**--interactive**] [**--no-prompt**] [**--extended-register**] [**-e** *expr*] [**--expression**=*expr*...] [**-f** *file*...] [**-file**=*file*...] [*file*...]
41 dc(1) is an arbitrary-precision calculator. It uses a stack (reverse Polish
42 notation) to store numbers and results of computations. Arithmetic operations
43 pop arguments off of the stack and push the results.
45 If no files are given on the command-line as extra arguments (i.e., not as
46 **-f** or **--file** arguments), then dc(1) reads from **stdin**. Otherwise,
47 those files are processed, and dc(1) will then exit.
49 This is different from the dc(1) on OpenBSD and possibly other dc(1)
50 implementations, where **-e** (**--expression**) and **-f** (**--file**)
51 arguments cause dc(1) to execute them and exit. The reason for this is that this
52 dc(1) allows users to set arguments in the environment variable **DC_ENV_ARGS**
53 (see the **ENVIRONMENT VARIABLES** section). Any expressions given on the
54 command-line should be used to set up a standard environment. For example, if a
55 user wants the **scale** always set to **10**, they can set **DC_ENV_ARGS** to
56 **-e 10k**, and this dc(1) will always start with a **scale** of **10**.
58 If users want to have dc(1) exit after processing all input from **-e** and
59 **-f** arguments (and their equivalents), then they can just simply add **-e q**
60 as the last command-line argument or define the environment variable
65 The following are the options that dc(1) accepts.
69 : Prints a usage message and quits.
71 **-v**, **-V**, **--version**
73 : Print the version information (copyright header) and exit.
75 **-i**, **--interactive**
77 : Forces interactive mode. (See the **INTERACTIVE MODE** section.)
79 This is a **non-portable extension**.
81 **-P**, **--no-prompt**
83 : Disables the prompt in TTY mode. (The prompt is only enabled in TTY mode.
84 See the **TTY MODE** section) This is mostly for those users that do not
85 want a prompt or are not used to having them in dc(1). Most of those users
86 would want to put this option in **DC_ENV_ARGS**.
88 This is a **non-portable extension**.
90 **-x** **--extended-register**
92 : Enables extended register mode. See the *Extended Register Mode* subsection
93 of the **REGISTERS** section for more information.
95 This is a **non-portable extension**.
97 **-e** *expr*, **--expression**=*expr*
99 : Evaluates *expr*. If multiple expressions are given, they are evaluated in
100 order. If files are given as well (see below), the expressions and files are
101 evaluated in the order given. This means that if a file is given before an
102 expression, the file is read in and evaluated first.
104 After processing all expressions and files, dc(1) will exit, unless **-**
105 (**stdin**) was given as an argument at least once to **-f** or **--file**.
107 This is a **non-portable extension**.
109 **-f** *file*, **--file**=*file*
111 : Reads in *file* and evaluates it, line by line, as though it were read
112 through **stdin**. If expressions are also given (see above), the
113 expressions are evaluated in the order given.
115 After processing all expressions and files, dc(1) will exit, unless **-**
116 (**stdin**) was given as an argument at least once to **-f** or **--file**.
117 However, if any other **-e**, **--expression**, **-f**, or **--file**
118 arguments are given after that, bc(1) will give a fatal error and exit.
120 This is a **non-portable extension**.
122 All long options are **non-portable extensions**.
126 Any non-error output is written to **stdout**.
128 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
129 error (see the **EXIT STATUS** section) if it cannot write to **stdout**, so if
130 **stdout** is closed, as in **dc <file> >&-**, it will quit with an error. This
131 is done so that dc(1) can report problems when **stdout** is redirected to a
134 If there are scripts that depend on the behavior of other dc(1) implementations,
135 it is recommended that those scripts be changed to redirect **stdout** to
140 Any error output is written to **stderr**.
142 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
143 error (see the **EXIT STATUS** section) if it cannot write to **stderr**, so if
144 **stderr** is closed, as in **dc <file> 2>&-**, it will quit with an error. This
145 is done so that dc(1) can exit with an error code when **stderr** is redirected
148 If there are scripts that depend on the behavior of other dc(1) implementations,
149 it is recommended that those scripts be changed to redirect **stderr** to
154 Each item in the input source code, either a number (see the **NUMBERS**
155 section) or a command (see the **COMMANDS** section), is processed and executed,
156 in order. Input is processed immediately when entered.
158 **ibase** is a register (see the **REGISTERS** section) that determines how to
159 interpret constant numbers. It is the "input" base, or the number base used for
160 interpreting input numbers. **ibase** is initially **10**. The max allowable
161 value for **ibase** is **16**. The min allowable value for **ibase** is **2**.
162 The max allowable value for **ibase** can be queried in dc(1) programs with the
165 **obase** is a register (see the **REGISTERS** section) that determines how to
166 output results. It is the "output" base, or the number base used for outputting
167 numbers. **obase** is initially **10**. The max allowable value for **obase** is
168 **DC_BASE_MAX** and can be queried with the **U** command. The min allowable
169 value for **obase** is **0**. If **obase** is **0**, values are output in
170 scientific notation, and if **obase** is **1**, values are output in engineering
171 notation. Otherwise, values are output in the specified base.
173 Outputting in scientific and engineering notations are **non-portable
176 The *scale* of an expression is the number of digits in the result of the
177 expression right of the decimal point, and **scale** is a register (see the
178 **REGISTERS** section) that sets the precision of any operations (with
179 exceptions). **scale** is initially **0**. **scale** cannot be negative. The max
180 allowable value for **scale** can be queried in dc(1) programs with the **V**
183 **seed** is a register containing the current seed for the pseudo-random number
184 generator. If the current value of **seed** is queried and stored, then if it is
185 assigned to **seed** later, the pseudo-random number generator is guaranteed to
186 produce the same sequence of pseudo-random numbers that were generated after the
187 value of **seed** was first queried.
189 Multiple values assigned to **seed** can produce the same sequence of
190 pseudo-random numbers. Likewise, when a value is assigned to **seed**, it is not
191 guaranteed that querying **seed** immediately after will return the same value.
192 In addition, the value of **seed** will change after any call to the **'**
193 command or the **"** command that does not get receive a value of **0** or
194 **1**. The maximum integer returned by the **'** command can be queried with the
197 **Note**: The values returned by the pseudo-random number generator with the
198 **'** and **"** commands are guaranteed to **NOT** be cryptographically secure.
199 This is a consequence of using a seeded pseudo-random number generator. However,
200 they **are** guaranteed to be reproducible with identical **seed** values.
202 The pseudo-random number generator, **seed**, and all associated operations are
203 **non-portable extensions**.
207 Comments go from **#** until, and not including, the next newline. This is a
208 **non-portable extension**.
212 Numbers are strings made up of digits, uppercase letters up to **F**, and at
213 most **1** period for a radix. Numbers can have up to **DC_NUM_MAX** digits.
214 Uppercase letters are equal to **9** + their position in the alphabet (i.e.,
215 **A** equals **10**, or **9+1**). If a digit or letter makes no sense with the
216 current value of **ibase**, they are set to the value of the highest valid digit
219 Single-character numbers (i.e., **A** alone) take the value that they would have
220 if they were valid digits, regardless of the value of **ibase**. This means that
221 **A** alone always equals decimal **10** and **F** alone always equals decimal
224 In addition, dc(1) accepts numbers in scientific notation. These have the form
225 **\<number\>e\<integer\>**. The exponent (the portion after the **e**) must be
226 an integer. An example is **1.89237e9**, which is equal to **1892370000**.
227 Negative exponents are also allowed, so **4.2890e_3** is equal to **0.0042890**.
229 **WARNING**: Both the number and the exponent in scientific notation are
230 interpreted according to the current **ibase**, but the number is still
231 multiplied by **10\^exponent** regardless of the current **ibase**. For example,
232 if **ibase** is **16** and dc(1) is given the number string **FFeA**, the
233 resulting decimal number will be **2550000000000**, and if dc(1) is given the
234 number string **10e_4**, the resulting decimal number will be **0.0016**.
236 Accepting input as scientific notation is a **non-portable extension**.
240 The valid commands are listed below.
244 These commands are used for printing.
246 Note that both scientific notation and engineering notation are available for
247 printing numbers. Scientific notation is activated by assigning **0** to
248 **obase** using **0o**, and engineering notation is activated by assigning **1**
249 to **obase** using **1o**. To deactivate them, just assign a different value to
252 Printing numbers in scientific notation and/or engineering notation is a
253 **non-portable extension**.
257 : Prints the value on top of the stack, whether number or string, and prints a
260 This does not alter the stack.
264 : Prints the value on top of the stack, whether number or string, and pops it
269 : Pops a value off the stack.
271 If the value is a number, it is truncated and the absolute value of the
272 result is printed as though **obase** is **UCHAR_MAX+1** and each digit is
273 interpreted as an ASCII character, making it a byte stream.
275 If the value is a string, it is printed without a trailing newline.
277 This is a **non-portable extension**.
281 : Prints the entire contents of the stack, in order from newest to oldest,
282 without altering anything.
284 Users should use this command when they get lost.
288 These are the commands used for arithmetic.
292 : The top two values are popped off the stack, added, and the result is pushed
293 onto the stack. The *scale* of the result is equal to the max *scale* of
298 : The top two values are popped off the stack, subtracted, and the result is
299 pushed onto the stack. The *scale* of the result is equal to the max
300 *scale* of both operands.
304 : The top two values are popped off the stack, multiplied, and the result is
305 pushed onto the stack. If **a** is the *scale* of the first expression and
306 **b** is the *scale* of the second expression, the *scale* of the result
307 is equal to **min(a+b,max(scale,a,b))** where **min()** and **max()** return
312 : The top two values are popped off the stack, divided, and the result is
313 pushed onto the stack. The *scale* of the result is equal to **scale**.
315 The first value popped off of the stack must be non-zero.
319 : The top two values are popped off the stack, remaindered, and the result is
320 pushed onto the stack.
322 Remaindering is equivalent to 1) Computing **a/b** to current **scale**, and
323 2) Using the result of step 1 to calculate **a-(a/b)\*b** to *scale*
324 **max(scale+scale(b),scale(a))**.
326 The first value popped off of the stack must be non-zero.
330 : The top two values are popped off the stack, divided and remaindered, and
331 the results (divided first, remainder second) are pushed onto the stack.
332 This is equivalent to **x y / x y %** except that **x** and **y** are only
335 The first value popped off of the stack must be non-zero.
337 This is a **non-portable extension**.
341 : The top two values are popped off the stack, the second is raised to the
342 power of the first, and the result is pushed onto the stack. The *scale* of
343 the result is equal to **scale**.
345 The first value popped off of the stack must be an integer, and if that
346 value is negative, the second value popped off of the stack must be
351 : The top value is popped off the stack, its square root is computed, and the
352 result is pushed onto the stack. The *scale* of the result is equal to
355 The value popped off of the stack must be non-negative.
359 : If this command *immediately* precedes a number (i.e., no spaces or other
360 commands), then that number is input as a negative number.
362 Otherwise, the top value on the stack is popped and copied, and the copy is
363 negated and pushed onto the stack. This behavior without a number is a
364 **non-portable extension**.
368 : The top value is popped off the stack, and if it is zero, it is pushed back
369 onto the stack. Otherwise, its absolute value is pushed onto the stack.
371 This is a **non-portable extension**.
375 : The top three values are popped off the stack, a modular exponentiation is
376 computed, and the result is pushed onto the stack.
378 The first value popped is used as the reduction modulus and must be an
379 integer and non-zero. The second value popped is used as the exponent and
380 must be an integer and non-negative. The third value popped is the base and
383 This is a **non-portable extension**.
387 : The top value is popped off the stack and copied, and the copy is truncated
388 and pushed onto the stack.
390 This is a **non-portable extension**.
394 : The top two values are popped off the stack, and the precision of the second
395 is set to the value of the first, whether by truncation or extension.
397 The first value popped off of the stack must be an integer and non-negative.
399 This is a **non-portable extension**.
403 : The top two values are popped off the stack, and the second is shifted left
404 (radix shifted right) to the value of the first.
406 The first value popped off of the stack must be an integer and non-negative.
408 This is a **non-portable extension**.
412 : The top two values are popped off the stack, and the second is shifted right
413 (radix shifted left) to the value of the first.
415 The first value popped off of the stack must be an integer and non-negative.
417 This is a **non-portable extension**.
421 : The top two values are popped off of the stack, they are compared, and a
422 **1** is pushed if they are equal, or **0** otherwise.
424 This is a **non-portable extension**.
428 : The top value is popped off of the stack, and if it a **0**, a **1** is
429 pushed; otherwise, a **0** is pushed.
431 This is a **non-portable extension**.
435 : The top two values are popped off of the stack, they are compared, and a
436 **1** is pushed if the first is less than the second, or **0** otherwise.
438 This is a **non-portable extension**.
442 : The top two values are popped off of the stack, they are compared, and a
443 **1** is pushed if the first is less than or equal to the second, or **0**
446 This is a **non-portable extension**.
450 : The top two values are popped off of the stack, they are compared, and a
451 **1** is pushed if the first is greater than the second, or **0** otherwise.
453 This is a **non-portable extension**.
457 : The top two values are popped off of the stack, they are compared, and a
458 **1** is pushed if the first is greater than or equal to the second, or
461 This is a **non-portable extension**.
465 : The top two values are popped off of the stack. If they are both non-zero, a
466 **1** is pushed onto the stack. If either of them is zero, or both of them
467 are, then a **0** is pushed onto the stack.
469 This is like the **&&** operator in bc(1), and it is *not* a short-circuit
472 This is a **non-portable extension**.
476 : The top two values are popped off of the stack. If at least one of them is
477 non-zero, a **1** is pushed onto the stack. If both of them are zero, then a
478 **0** is pushed onto the stack.
480 This is like the **||** operator in bc(1), and it is *not* a short-circuit
483 This is a **non-portable extension**.
485 ## Pseudo-Random Number Generator
487 dc(1) has a built-in pseudo-random number generator. These commands query the
488 pseudo-random number generator. (See Parameters for more information about the
489 **seed** value that controls the pseudo-random number generator.)
491 The pseudo-random number generator is guaranteed to **NOT** be
492 cryptographically secure.
496 : Generates an integer between 0 and **DC_RAND_MAX**, inclusive (see the
499 The generated integer is made as unbiased as possible, subject to the
500 limitations of the pseudo-random number generator.
502 This is a **non-portable extension**.
506 : Pops a value off of the stack, which is used as an **exclusive** upper bound
507 on the integer that will be generated. If the bound is negative or is a
508 non-integer, an error is raised, and dc(1) resets (see the **RESET**
509 section) while **seed** remains unchanged. If the bound is larger than
510 **DC_RAND_MAX**, the higher bound is honored by generating several
511 pseudo-random integers, multiplying them by appropriate powers of
512 **DC_RAND_MAX+1**, and adding them together. Thus, the size of integer that
513 can be generated with this command is unbounded. Using this command will
514 change the value of **seed**, unless the operand is **0** or **1**. In that
515 case, **0** is pushed onto the stack, and **seed** is *not* changed.
517 The generated integer is made as unbiased as possible, subject to the
518 limitations of the pseudo-random number generator.
520 This is a **non-portable extension**.
524 These commands control the stack.
528 : Removes all items from ("clears") the stack.
532 : Copies the item on top of the stack ("duplicates") and pushes the copy onto
537 : Swaps ("reverses") the two top items on the stack.
541 : Pops ("removes") the top value from the stack.
545 These commands control registers (see the **REGISTERS** section).
549 : Pops the value off the top of the stack and stores it into register *r*.
553 : Copies the value in register *r* and pushes it onto the stack. This does not
554 alter the contents of *r*.
558 : Pops the value off the top of the (main) stack and pushes it onto the stack
559 of register *r*. The previous value of the register becomes inaccessible.
563 : Pops the value off the top of the stack for register *r* and push it onto
564 the main stack. The previous value in the stack for register *r*, if any, is
565 now accessible via the **l***r* command.
569 These commands control the values of **ibase**, **obase**, **scale**, and
570 **seed**. Also see the **SYNTAX** section.
574 : Pops the value off of the top of the stack and uses it to set **ibase**,
575 which must be between **2** and **16**, inclusive.
577 If the value on top of the stack has any *scale*, the *scale* is ignored.
581 : Pops the value off of the top of the stack and uses it to set **obase**,
582 which must be between **0** and **DC_BASE_MAX**, inclusive (see the
583 **LIMITS** section and the **NUMBERS** section).
585 If the value on top of the stack has any *scale*, the *scale* is ignored.
589 : Pops the value off of the top of the stack and uses it to set **scale**,
590 which must be non-negative.
592 If the value on top of the stack has any *scale*, the *scale* is ignored.
596 : Pops the value off of the top of the stack and uses it to set **seed**. The
597 meaning of **seed** is dependent on the current pseudo-random number
598 generator but is guaranteed to not change except for new major versions.
600 The *scale* and sign of the value may be significant.
602 If a previously used **seed** value is used again, the pseudo-random number
603 generator is guaranteed to produce the same sequence of pseudo-random
604 numbers as it did when the **seed** value was previously used.
606 The exact value assigned to **seed** is not guaranteed to be returned if the
607 **J** command is used. However, if **seed** *does* return a different value,
608 both values, when assigned to **seed**, are guaranteed to produce the same
609 sequence of pseudo-random numbers. This means that certain values assigned
610 to **seed** will not produce unique sequences of pseudo-random numbers.
612 There is no limit to the length (number of significant decimal digits) or
613 *scale* of the value that can be assigned to **seed**.
615 This is a **non-portable extension**.
619 : Pushes the current value of **ibase** onto the main stack.
623 : Pushes the current value of **obase** onto the main stack.
627 : Pushes the current value of **scale** onto the main stack.
631 : Pushes the current value of **seed** onto the main stack.
633 This is a **non-portable extension**.
637 : Pushes the maximum allowable value of **ibase** onto the main stack.
639 This is a **non-portable extension**.
643 : Pushes the maximum allowable value of **obase** onto the main stack.
645 This is a **non-portable extension**.
649 : Pushes the maximum allowable value of **scale** onto the main stack.
651 This is a **non-portable extension**.
655 : Pushes the maximum (inclusive) integer that can be generated with the **'**
656 pseudo-random number generator command.
658 This is a **non-portable extension**.
662 The following commands control strings.
664 dc(1) can work with both numbers and strings, and registers (see the
665 **REGISTERS** section) can hold both strings and numbers. dc(1) always knows
666 whether the contents of a register are a string or a number.
668 While arithmetic operations have to have numbers, and will print an error if
669 given a string, other commands accept strings.
671 Strings can also be executed as macros. For example, if the string **[1pR]** is
672 executed as a macro, then the code **1pR** is executed, meaning that the **1**
673 will be printed with a newline after and then popped from the stack.
675 **\[**_characters_**\]**
677 : Makes a string containing *characters* and pushes it onto the stack.
679 If there are brackets (**\[** and **\]**) in the string, then they must be
680 balanced. Unbalanced brackets can be escaped using a backslash (**\\**)
683 If there is a backslash character in the string, the character after it
684 (even another backslash) is put into the string verbatim, but the (first)
689 : The value on top of the stack is popped.
691 If it is a number, it is truncated and its absolute value is taken. The
692 result mod **UCHAR_MAX+1** is calculated. If that result is **0**, push an
693 empty string; otherwise, push a one-character string where the character is
694 the result of the mod interpreted as an ASCII character.
696 If it is a string, then a new string is made. If the original string is
697 empty, the new string is empty. If it is not, then the first character of
698 the original string is used to create the new string as a one-character
699 string. The new string is then pushed onto the stack.
701 This is a **non-portable extension**.
705 : Pops a value off of the top of the stack.
707 If it is a number, it is pushed back onto the stack.
709 If it is a string, it is executed as a macro.
711 This behavior is the norm whenever a macro is executed, whether by this
712 command or by the conditional execution commands below.
716 : Pops two values off of the stack that must be numbers and compares them. If
717 the first value is greater than the second, then the contents of register
720 For example, **0 1>a** will execute the contents of register **a**, and
723 If either or both of the values are not numbers, dc(1) will raise an error
724 and reset (see the **RESET** section).
728 : Like the above, but will execute register *s* if the comparison fails.
730 If either or both of the values are not numbers, dc(1) will raise an error
731 and reset (see the **RESET** section).
733 This is a **non-portable extension**.
737 : Pops two values off of the stack that must be numbers and compares them. If
738 the first value is not greater than the second (less than or equal to), then
739 the contents of register *r* are executed.
741 If either or both of the values are not numbers, dc(1) will raise an error
742 and reset (see the **RESET** section).
746 : Like the above, but will execute register *s* if the comparison fails.
748 If either or both of the values are not numbers, dc(1) will raise an error
749 and reset (see the **RESET** section).
751 This is a **non-portable extension**.
755 : Pops two values off of the stack that must be numbers and compares them. If
756 the first value is less than the second, then the contents of register *r*
759 If either or both of the values are not numbers, dc(1) will raise an error
760 and reset (see the **RESET** section).
764 : Like the above, but will execute register *s* if the comparison fails.
766 If either or both of the values are not numbers, dc(1) will raise an error
767 and reset (see the **RESET** section).
769 This is a **non-portable extension**.
773 : Pops two values off of the stack that must be numbers and compares them. If
774 the first value is not less than the second (greater than or equal to), then
775 the contents of register *r* are executed.
777 If either or both of the values are not numbers, dc(1) will raise an error
778 and reset (see the **RESET** section).
782 : Like the above, but will execute register *s* if the comparison fails.
784 If either or both of the values are not numbers, dc(1) will raise an error
785 and reset (see the **RESET** section).
787 This is a **non-portable extension**.
791 : Pops two values off of the stack that must be numbers and compares them. If
792 the first value is equal to the second, then the contents of register *r*
795 If either or both of the values are not numbers, dc(1) will raise an error
796 and reset (see the **RESET** section).
800 : Like the above, but will execute register *s* if the comparison fails.
802 If either or both of the values are not numbers, dc(1) will raise an error
803 and reset (see the **RESET** section).
805 This is a **non-portable extension**.
809 : Pops two values off of the stack that must be numbers and compares them. If
810 the first value is not equal to the second, then the contents of register
813 If either or both of the values are not numbers, dc(1) will raise an error
814 and reset (see the **RESET** section).
818 : Like the above, but will execute register *s* if the comparison fails.
820 If either or both of the values are not numbers, dc(1) will raise an error
821 and reset (see the **RESET** section).
823 This is a **non-portable extension**.
827 : Reads a line from the **stdin** and executes it. This is to allow macros to
828 request input from users.
832 : During execution of a macro, this exits the execution of that macro and the
833 execution of the macro that executed it. If there are no macros, or only one
834 macro executing, dc(1) exits.
838 : Pops a value from the stack which must be non-negative and is used the
839 number of macro executions to pop off of the execution stack. If the number
840 of levels to pop is greater than the number of executing macros, dc(1)
845 These commands query status of the stack or its top value.
849 : Pops a value off of the stack.
851 If it is a number, calculates the number of significant decimal digits it
852 has and pushes the result.
854 If it is a string, pushes the number of characters the string has.
858 : Pops a value off of the stack.
860 If it is a number, pushes the *scale* of the value onto the stack.
862 If it is a string, pushes **0**.
866 : Pushes the current stack depth (before execution of this command).
870 These commands manipulate arrays.
874 : Pops the top two values off of the stack. The second value will be stored in
875 the array *r* (see the **REGISTERS** section), indexed by the first value.
879 : Pops the value on top of the stack and uses it as an index into the array
880 *r*. The selected value is then pushed onto the stack.
884 Registers are names that can store strings, numbers, and arrays. (Number/string
885 registers do not interfere with array registers.)
887 Each register is also its own stack, so the current register value is the top of
888 the stack for the register. All registers, when first referenced, have one value
889 (**0**) in their stack.
891 In non-extended register mode, a register name is just the single character that
892 follows any command that needs a register name. The only exception is a newline
893 (**'\\n'**); it is a parse error for a newline to be used as a register name.
895 ## Extended Register Mode
897 Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited
898 amounts of registers, if extended register mode is enabled.
900 If extended register mode is enabled (**-x** or **--extended-register**
901 command-line arguments are given), then normal single character registers are
902 used *unless* the character immediately following a command that needs a
903 register name is a space (according to **isspace()**) and not a newline
906 In that case, the register name is found according to the regex
907 **\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if
908 the next non-space characters do not match that regex.
912 When dc(1) encounters an error or a signal that it has a non-default handler
913 for, it resets. This means that several things happen.
915 First, any macros that are executing are stopped and popped off the stack.
916 The behavior is not unlike that of exceptions in programming languages. Then
917 the execution point is set so that any code waiting to execute (after all
918 macros returned) is skipped.
920 Thus, when dc(1) resets, it skips any remaining code waiting to be executed.
921 Then, if it is interactive mode, and the error was not a fatal error (see the
922 **EXIT STATUS** section), it asks for more input; otherwise, it exits with the
923 appropriate return code.
927 Most dc(1) implementations use **char** types to calculate the value of **1**
928 decimal digit at a time, but that can be slow. This dc(1) does something
931 It uses large integers to calculate more than **1** decimal digit at a time. If
932 built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is
933 **64**, then each integer has **9** decimal digits. If built in an environment
934 where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
935 value (the number of decimal digits per large integer) is called
938 In addition, this dc(1) uses an even larger integer for overflow checking. This
939 integer type depends on the value of **DC_LONG_BIT**, but is always at least
940 twice as large as the integer type used to store digits.
944 The following are the limits on dc(1):
948 : The number of bits in the **long** type in the environment where dc(1) was
949 built. This determines how many decimal digits can be stored in a single
950 large integer (see the **PERFORMANCE** section).
954 : The number of decimal digits per large integer (see the **PERFORMANCE**
955 section). Depends on **DC_LONG_BIT**.
959 : The max decimal number that each large integer can store (see
960 **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**.
964 : The max number that the overflow type (see the **PERFORMANCE** section) can
965 hold. Depends on **DC_LONG_BIT**.
969 : The maximum output base. Set at **DC_BASE_POW**.
973 : The maximum size of arrays. Set at **SIZE_MAX-1**.
977 : The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**.
981 : The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**.
985 : The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**.
989 : The maximum length of a number (in decimal digits), which includes digits
990 after the decimal point. Set at **DC_OVERFLOW_MAX-1**.
994 : The maximum integer (inclusive) returned by the **'** command, if dc(1). Set
995 at **2\^DC_LONG_BIT-1**.
999 : The maximum allowable exponent (positive or negative). Set at
1000 **DC_OVERFLOW_MAX**.
1004 : The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
1006 These limits are meant to be effectively non-existent; the limits are so large
1007 (at least on 64-bit machines) that there should not be any point at which they
1008 become a problem. In fact, memory should be exhausted before these limits should
1011 # ENVIRONMENT VARIABLES
1013 dc(1) recognizes the following environment variables:
1017 : This is another way to give command-line arguments to dc(1). They should be
1018 in the same format as all other command-line arguments. These are always
1019 processed first, so any files given in **DC_ENV_ARGS** will be processed
1020 before arguments and files given on the command-line. This gives the user
1021 the ability to set up "standard" options and files to be used at every
1022 invocation. The most useful thing for such files to contain would be useful
1023 functions that the user might want every time dc(1) runs. Another use would
1024 be to use the **-e** option to set **scale** to a value other than **0**.
1026 The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments,
1027 but it does not understand escape sequences. For example, the string
1028 **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string
1029 **"/home/gavin/some \"dc\" file.dc"** will include the backslashes.
1031 The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
1032 if you have a file with any number of single quotes in the name, you can use
1033 double quotes as the outside quotes, as in **"some 'bc' file.bc"**, and vice
1034 versa if you have a file with double quotes. However, handling a file with
1035 both kinds of quotes in **DC_ENV_ARGS** is not supported due to the
1036 complexity of the parsing, though such files are still supported on the
1037 command-line where the parsing is done by the shell.
1041 : If this environment variable exists and contains an integer that is greater
1042 than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output
1043 lines to that length, including the backslash newline combo. The default
1044 line length is **70**.
1048 : If this variable exists (no matter the contents), dc(1) will exit
1049 immediately after executing expressions and files given by the **-e** and/or
1050 **-f** command-line options (and any equivalents).
1054 dc(1) returns the following exit statuses:
1062 : A math error occurred. This follows standard practice of using **1** for
1063 expected errors, since math errors will happen in the process of normal
1066 Math errors include divide by **0**, taking the square root of a negative
1067 number, using a negative number as a bound for the pseudo-random number
1068 generator, attempting to convert a negative number to a hardware integer,
1069 overflow when converting a number to a hardware integer, and attempting to
1070 use a non-integer where an integer is required.
1072 Converting to a hardware integer happens for the second operand of the power
1073 (**\^**), places (**\@**), left shift (**H**), and right shift (**h**)
1078 : A parse error occurred.
1080 Parse errors include unexpected **EOF**, using an invalid character, failing
1081 to find the end of a string or comment, and using a token where it is
1086 : A runtime error occurred.
1088 Runtime errors include assigning an invalid number to **ibase**, **obase**,
1089 or **scale**; give a bad expression to a **read()** call, calling **read()**
1090 inside of a **read()** call, type errors, and attempting an operation when
1091 the stack has too few elements.
1095 : A fatal error occurred.
1097 Fatal errors include memory allocation errors, I/O errors, failing to open
1098 files, attempting to use files that do not have only ASCII characters (dc(1)
1099 only accepts ASCII characters), attempting to open a directory as a file,
1100 and giving invalid command-line options.
1102 The exit status **4** is special; when a fatal error occurs, dc(1) always exits
1103 and returns **4**, no matter what mode dc(1) is in.
1105 The other statuses will only be returned when dc(1) is not in interactive mode
1106 (see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the
1107 **RESET** section) and accepts more input when one of those errors occurs in
1108 interactive mode. This is also the case when interactive mode is forced by the
1109 **-i** flag or **--interactive** option.
1111 These exit statuses allow dc(1) to be used in shell scripting with error
1112 checking, and its normal behavior can be forced by using the **-i** flag or
1113 **--interactive** option.
1117 Like bc(1), dc(1) has an interactive mode and a non-interactive mode.
1118 Interactive mode is turned on automatically when both **stdin** and **stdout**
1119 are hooked to a terminal, but the **-i** flag and **--interactive** option can
1120 turn it on in other cases.
1122 In interactive mode, dc(1) attempts to recover from errors (see the **RESET**
1123 section), and in normal execution, flushes **stdout** as soon as execution is
1124 done for the current input.
1128 If **stdin**, **stdout**, and **stderr** are all connected to a TTY, dc(1) turns
1131 TTY mode is required for history to be enabled (see the **COMMAND LINE HISTORY**
1132 section). It is also required to enable special handling for **SIGINT** signals.
1134 The prompt is enabled in TTY mode.
1136 TTY mode is different from interactive mode because interactive mode is required
1137 in the [bc(1) specification][1], and interactive mode requires only **stdin**
1138 and **stdout** to be connected to a terminal.
1142 Sending a **SIGINT** will cause dc(1) to stop execution of the current input. If
1143 dc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
1144 **RESET** section). Otherwise, it will clean up and exit.
1146 Note that "current input" can mean one of two things. If dc(1) is processing
1147 input from **stdin** in TTY mode, it will ask for more input. If dc(1) is
1148 processing input from a file in TTY mode, it will stop processing the file and
1149 start processing the next file, if one exists, or ask for input from **stdin**
1150 if no other file exists.
1152 This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it
1153 can seem as though dc(1) did not respond to the signal since it will immediately
1154 start executing the next file. This is by design; most files that users execute
1155 when interacting with dc(1) have function definitions, which are quick to parse.
1156 If a file takes a long time to execute, there may be a bug in that file. The
1157 rest of the files could still be executed without problem, allowing the user to
1160 **SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the
1161 default handler for all other signals. The one exception is **SIGHUP**; in that
1162 case, when dc(1) is in TTY mode, a **SIGHUP** will cause dc(1) to clean up and
1165 # COMMAND LINE HISTORY
1167 dc(1) supports interactive command-line editing. If dc(1) is in TTY mode (see
1168 the **TTY MODE** section), history is enabled. Previous lines can be recalled
1169 and edited with the arrow keys.
1171 **Note**: tabs are converted to 8 spaces.
1175 This dc(1) ships with support for adding error messages for different locales
1176 and thus, supports **LC_MESSAGS**.
1184 The dc(1) utility operators are compliant with the operators in the bc(1)
1185 [IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1] specification.
1189 None are known. Report bugs at https://git.yzena.com/gavin/bc.
1193 Gavin D. Howard <gavin@yzena.com> and contributors.
1195 [1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html