3 SPDX-License-Identifier: BSD-2-Clause
5 Copyright (c) 2018-2021 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 If this option is given on the command-line (i.e., not in **DC_ENV_ARGS**,
105 see the **ENVIRONMENT VARIABLES** section), then after processing all
106 expressions and files, dc(1) will exit, unless **-** (**stdin**) was given
107 as an argument at least once to **-f** or **-\-file**, whether on the
108 command-line or in **DC_ENV_ARGS**. However, if any other **-e**,
109 **-\-expression**, **-f**, or **-\-file** arguments are given after **-f-**
110 or equivalent is given, dc(1) will give a fatal error and exit.
112 This is a **non-portable extension**.
114 **-f** *file*, **-\-file**=*file*
116 : Reads in *file* and evaluates it, line by line, as though it were read
117 through **stdin**. If expressions are also given (see above), the
118 expressions are evaluated in the order given.
120 If this option is given on the command-line (i.e., not in **DC_ENV_ARGS**,
121 see the **ENVIRONMENT VARIABLES** section), then after processing all
122 expressions and files, dc(1) will exit, unless **-** (**stdin**) was given
123 as an argument at least once to **-f** or **-\-file**. However, if any other
124 **-e**, **-\-expression**, **-f**, or **-\-file** arguments are given after
125 **-f-** or equivalent is given, dc(1) will give a fatal error and exit.
127 This is a **non-portable extension**.
129 All long options are **non-portable extensions**.
133 Any non-error output is written to **stdout**. In addition, if history (see the
134 **HISTORY** section) and the prompt (see the **TTY MODE** section) are enabled,
135 both are output to **stdout**.
137 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
138 error (see the **EXIT STATUS** section) if it cannot write to **stdout**, so if
139 **stdout** is closed, as in **dc <file> >&-**, it will quit with an error. This
140 is done so that dc(1) can report problems when **stdout** is redirected to a
143 If there are scripts that depend on the behavior of other dc(1) implementations,
144 it is recommended that those scripts be changed to redirect **stdout** to
149 Any error output is written to **stderr**.
151 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
152 error (see the **EXIT STATUS** section) if it cannot write to **stderr**, so if
153 **stderr** is closed, as in **dc <file> 2>&-**, it will quit with an error. This
154 is done so that dc(1) can exit with an error code when **stderr** is redirected
157 If there are scripts that depend on the behavior of other dc(1) implementations,
158 it is recommended that those scripts be changed to redirect **stderr** to
163 Each item in the input source code, either a number (see the **NUMBERS**
164 section) or a command (see the **COMMANDS** section), is processed and executed,
165 in order. Input is processed immediately when entered.
167 **ibase** is a register (see the **REGISTERS** section) that determines how to
168 interpret constant numbers. It is the "input" base, or the number base used for
169 interpreting input numbers. **ibase** is initially **10**. The max allowable
170 value for **ibase** is **16**. The min allowable value for **ibase** is **2**.
171 The max allowable value for **ibase** can be queried in dc(1) programs with the
174 **obase** is a register (see the **REGISTERS** section) that determines how to
175 output results. It is the "output" base, or the number base used for outputting
176 numbers. **obase** is initially **10**. The max allowable value for **obase** is
177 **DC_BASE_MAX** and can be queried with the **U** command. The min allowable
178 value for **obase** is **0**. If **obase** is **0**, values are output in
179 scientific notation, and if **obase** is **1**, values are output in engineering
180 notation. Otherwise, values are output in the specified base.
182 Outputting in scientific and engineering notations are **non-portable
185 The *scale* of an expression is the number of digits in the result of the
186 expression right of the decimal point, and **scale** is a register (see the
187 **REGISTERS** section) that sets the precision of any operations (with
188 exceptions). **scale** is initially **0**. **scale** cannot be negative. The max
189 allowable value for **scale** can be queried in dc(1) programs with the **V**
192 **seed** is a register containing the current seed for the pseudo-random number
193 generator. If the current value of **seed** is queried and stored, then if it is
194 assigned to **seed** later, the pseudo-random number generator is guaranteed to
195 produce the same sequence of pseudo-random numbers that were generated after the
196 value of **seed** was first queried.
198 Multiple values assigned to **seed** can produce the same sequence of
199 pseudo-random numbers. Likewise, when a value is assigned to **seed**, it is not
200 guaranteed that querying **seed** immediately after will return the same value.
201 In addition, the value of **seed** will change after any call to the **'**
202 command or the **"** command that does not get receive a value of **0** or
203 **1**. The maximum integer returned by the **'** command can be queried with the
206 **Note**: The values returned by the pseudo-random number generator with the
207 **'** and **"** commands are guaranteed to **NOT** be cryptographically secure.
208 This is a consequence of using a seeded pseudo-random number generator. However,
209 they *are* guaranteed to be reproducible with identical **seed** values. This
210 means that the pseudo-random values from dc(1) should only be used where a
211 reproducible stream of pseudo-random numbers is *ESSENTIAL*. In any other case,
212 use a non-seeded pseudo-random number generator.
214 The pseudo-random number generator, **seed**, and all associated operations are
215 **non-portable extensions**.
219 Comments go from **#** until, and not including, the next newline. This is a
220 **non-portable extension**.
224 Numbers are strings made up of digits, uppercase letters up to **F**, and at
225 most **1** period for a radix. Numbers can have up to **DC_NUM_MAX** digits.
226 Uppercase letters are equal to **9** + their position in the alphabet (i.e.,
227 **A** equals **10**, or **9+1**). If a digit or letter makes no sense with the
228 current value of **ibase**, they are set to the value of the highest valid digit
231 Single-character numbers (i.e., **A** alone) take the value that they would have
232 if they were valid digits, regardless of the value of **ibase**. This means that
233 **A** alone always equals decimal **10** and **F** alone always equals decimal
236 In addition, dc(1) accepts numbers in scientific notation. These have the form
237 **\<number\>e\<integer\>**. The exponent (the portion after the **e**) must be
238 an integer. An example is **1.89237e9**, which is equal to **1892370000**.
239 Negative exponents are also allowed, so **4.2890e_3** is equal to **0.0042890**.
241 **WARNING**: Both the number and the exponent in scientific notation are
242 interpreted according to the current **ibase**, but the number is still
243 multiplied by **10\^exponent** regardless of the current **ibase**. For example,
244 if **ibase** is **16** and dc(1) is given the number string **FFeA**, the
245 resulting decimal number will be **2550000000000**, and if dc(1) is given the
246 number string **10e_4**, the resulting decimal number will be **0.0016**.
248 Accepting input as scientific notation is a **non-portable extension**.
252 The valid commands are listed below.
256 These commands are used for printing.
258 Note that both scientific notation and engineering notation are available for
259 printing numbers. Scientific notation is activated by assigning **0** to
260 **obase** using **0o**, and engineering notation is activated by assigning **1**
261 to **obase** using **1o**. To deactivate them, just assign a different value to
264 Printing numbers in scientific notation and/or engineering notation is a
265 **non-portable extension**.
269 : Prints the value on top of the stack, whether number or string, and prints a
272 This does not alter the stack.
276 : Prints the value on top of the stack, whether number or string, and pops it
281 : Pops a value off the stack.
283 If the value is a number, it is truncated and the absolute value of the
284 result is printed as though **obase** is **UCHAR_MAX+1** and each digit is
285 interpreted as an ASCII character, making it a byte stream.
287 If the value is a string, it is printed without a trailing newline.
289 This is a **non-portable extension**.
293 : Prints the entire contents of the stack, in order from newest to oldest,
294 without altering anything.
296 Users should use this command when they get lost.
300 These are the commands used for arithmetic.
304 : The top two values are popped off the stack, added, and the result is pushed
305 onto the stack. The *scale* of the result is equal to the max *scale* of
310 : The top two values are popped off the stack, subtracted, and the result is
311 pushed onto the stack. The *scale* of the result is equal to the max
312 *scale* of both operands.
316 : The top two values are popped off the stack, multiplied, and the result is
317 pushed onto the stack. If **a** is the *scale* of the first expression and
318 **b** is the *scale* of the second expression, the *scale* of the result
319 is equal to **min(a+b,max(scale,a,b))** where **min()** and **max()** return
324 : The top two values are popped off the stack, divided, and the result is
325 pushed onto the stack. The *scale* of the result is equal to **scale**.
327 The first value popped off of the stack must be non-zero.
331 : The top two values are popped off the stack, remaindered, and the result is
332 pushed onto the stack.
334 Remaindering is equivalent to 1) Computing **a/b** to current **scale**, and
335 2) Using the result of step 1 to calculate **a-(a/b)\*b** to *scale*
336 **max(scale+scale(b),scale(a))**.
338 The first value popped off of the stack must be non-zero.
342 : The top two values are popped off the stack, divided and remaindered, and
343 the results (divided first, remainder second) are pushed onto the stack.
344 This is equivalent to **x y / x y %** except that **x** and **y** are only
347 The first value popped off of the stack must be non-zero.
349 This is a **non-portable extension**.
353 : The top two values are popped off the stack, the second is raised to the
354 power of the first, and the result is pushed onto the stack. The *scale* of
355 the result is equal to **scale**.
357 The first value popped off of the stack must be an integer, and if that
358 value is negative, the second value popped off of the stack must be
363 : The top value is popped off the stack, its square root is computed, and the
364 result is pushed onto the stack. The *scale* of the result is equal to
367 The value popped off of the stack must be non-negative.
371 : If this command *immediately* precedes a number (i.e., no spaces or other
372 commands), then that number is input as a negative number.
374 Otherwise, the top value on the stack is popped and copied, and the copy is
375 negated and pushed onto the stack. This behavior without a number is a
376 **non-portable extension**.
380 : The top value is popped off the stack, and if it is zero, it is pushed back
381 onto the stack. Otherwise, its absolute value is pushed onto the stack.
383 This is a **non-portable extension**.
387 : The top three values are popped off the stack, a modular exponentiation is
388 computed, and the result is pushed onto the stack.
390 The first value popped is used as the reduction modulus and must be an
391 integer and non-zero. The second value popped is used as the exponent and
392 must be an integer and non-negative. The third value popped is the base and
395 This is a **non-portable extension**.
399 : The top value is popped off the stack and copied, and the copy is truncated
400 and pushed onto the stack.
402 This is a **non-portable extension**.
406 : The top two values are popped off the stack, and the precision of the second
407 is set to the value of the first, whether by truncation or extension.
409 The first value popped off of the stack must be an integer and non-negative.
411 This is a **non-portable extension**.
415 : The top two values are popped off the stack, and the second is shifted left
416 (radix shifted right) to the value of the first.
418 The first value popped off of the stack must be an integer and non-negative.
420 This is a **non-portable extension**.
424 : The top two values are popped off the stack, and the second is shifted right
425 (radix shifted left) to the value of the first.
427 The first value popped off of the stack must be an integer and non-negative.
429 This is a **non-portable extension**.
433 : The top two values are popped off of the stack, they are compared, and a
434 **1** is pushed if they are equal, or **0** otherwise.
436 This is a **non-portable extension**.
440 : The top value is popped off of the stack, and if it a **0**, a **1** is
441 pushed; otherwise, a **0** is pushed.
443 This is a **non-portable extension**.
447 : The top two values are popped off of the stack, they are compared, and a
448 **1** is pushed if the first is less than the second, or **0** otherwise.
450 This is a **non-portable extension**.
454 : The top two values are popped off of the stack, they are compared, and a
455 **1** is pushed if the first is less than or equal to the second, or **0**
458 This is a **non-portable extension**.
462 : The top two values are popped off of the stack, they are compared, and a
463 **1** is pushed if the first is greater than the second, or **0** otherwise.
465 This is a **non-portable extension**.
469 : The top two values are popped off of the stack, they are compared, and a
470 **1** is pushed if the first is greater than or equal to the second, or
473 This is a **non-portable extension**.
477 : The top two values are popped off of the stack. If they are both non-zero, a
478 **1** is pushed onto the stack. If either of them is zero, or both of them
479 are, then a **0** is pushed onto the stack.
481 This is like the **&&** operator in bc(1), and it is *not* a short-circuit
484 This is a **non-portable extension**.
488 : The top two values are popped off of the stack. If at least one of them is
489 non-zero, a **1** is pushed onto the stack. If both of them are zero, then a
490 **0** is pushed onto the stack.
492 This is like the **||** operator in bc(1), and it is *not* a short-circuit
495 This is a **non-portable extension**.
497 ## Pseudo-Random Number Generator
499 dc(1) has a built-in pseudo-random number generator. These commands query the
500 pseudo-random number generator. (See Parameters for more information about the
501 **seed** value that controls the pseudo-random number generator.)
503 The pseudo-random number generator is guaranteed to **NOT** be
504 cryptographically secure.
508 : Generates an integer between 0 and **DC_RAND_MAX**, inclusive (see the
511 The generated integer is made as unbiased as possible, subject to the
512 limitations of the pseudo-random number generator.
514 This is a **non-portable extension**.
518 : Pops a value off of the stack, which is used as an **exclusive** upper bound
519 on the integer that will be generated. If the bound is negative or is a
520 non-integer, an error is raised, and dc(1) resets (see the **RESET**
521 section) while **seed** remains unchanged. If the bound is larger than
522 **DC_RAND_MAX**, the higher bound is honored by generating several
523 pseudo-random integers, multiplying them by appropriate powers of
524 **DC_RAND_MAX+1**, and adding them together. Thus, the size of integer that
525 can be generated with this command is unbounded. Using this command will
526 change the value of **seed**, unless the operand is **0** or **1**. In that
527 case, **0** is pushed onto the stack, and **seed** is *not* changed.
529 The generated integer is made as unbiased as possible, subject to the
530 limitations of the pseudo-random number generator.
532 This is a **non-portable extension**.
536 These commands control the stack.
540 : Removes all items from ("clears") the stack.
544 : Copies the item on top of the stack ("duplicates") and pushes the copy onto
549 : Swaps ("reverses") the two top items on the stack.
553 : Pops ("removes") the top value from the stack.
557 These commands control registers (see the **REGISTERS** section).
561 : Pops the value off the top of the stack and stores it into register *r*.
565 : Copies the value in register *r* and pushes it onto the stack. This does not
566 alter the contents of *r*.
570 : Pops the value off the top of the (main) stack and pushes it onto the stack
571 of register *r*. The previous value of the register becomes inaccessible.
575 : Pops the value off the top of the stack for register *r* and push it onto
576 the main stack. The previous value in the stack for register *r*, if any, is
577 now accessible via the **l***r* command.
581 These commands control the values of **ibase**, **obase**, **scale**, and
582 **seed**. Also see the **SYNTAX** section.
586 : Pops the value off of the top of the stack and uses it to set **ibase**,
587 which must be between **2** and **16**, inclusive.
589 If the value on top of the stack has any *scale*, the *scale* is ignored.
593 : Pops the value off of the top of the stack and uses it to set **obase**,
594 which must be between **0** and **DC_BASE_MAX**, inclusive (see the
595 **LIMITS** section and the **NUMBERS** section).
597 If the value on top of the stack has any *scale*, the *scale* is ignored.
601 : Pops the value off of the top of the stack and uses it to set **scale**,
602 which must be non-negative.
604 If the value on top of the stack has any *scale*, the *scale* is ignored.
608 : Pops the value off of the top of the stack and uses it to set **seed**. The
609 meaning of **seed** is dependent on the current pseudo-random number
610 generator but is guaranteed to not change except for new major versions.
612 The *scale* and sign of the value may be significant.
614 If a previously used **seed** value is used again, the pseudo-random number
615 generator is guaranteed to produce the same sequence of pseudo-random
616 numbers as it did when the **seed** value was previously used.
618 The exact value assigned to **seed** is not guaranteed to be returned if the
619 **J** command is used. However, if **seed** *does* return a different value,
620 both values, when assigned to **seed**, are guaranteed to produce the same
621 sequence of pseudo-random numbers. This means that certain values assigned
622 to **seed** will not produce unique sequences of pseudo-random numbers.
624 There is no limit to the length (number of significant decimal digits) or
625 *scale* of the value that can be assigned to **seed**.
627 This is a **non-portable extension**.
631 : Pushes the current value of **ibase** onto the main stack.
635 : Pushes the current value of **obase** onto the main stack.
639 : Pushes the current value of **scale** onto the main stack.
643 : Pushes the current value of **seed** onto the main stack.
645 This is a **non-portable extension**.
649 : Pushes the maximum allowable value of **ibase** onto the main stack.
651 This is a **non-portable extension**.
655 : Pushes the maximum allowable value of **obase** onto the main stack.
657 This is a **non-portable extension**.
661 : Pushes the maximum allowable value of **scale** onto the main stack.
663 This is a **non-portable extension**.
667 : Pushes the maximum (inclusive) integer that can be generated with the **'**
668 pseudo-random number generator command.
670 This is a **non-portable extension**.
674 The following commands control strings.
676 dc(1) can work with both numbers and strings, and registers (see the
677 **REGISTERS** section) can hold both strings and numbers. dc(1) always knows
678 whether the contents of a register are a string or a number.
680 While arithmetic operations have to have numbers, and will print an error if
681 given a string, other commands accept strings.
683 Strings can also be executed as macros. For example, if the string **[1pR]** is
684 executed as a macro, then the code **1pR** is executed, meaning that the **1**
685 will be printed with a newline after and then popped from the stack.
687 **\[**_characters_**\]**
689 : Makes a string containing *characters* and pushes it onto the stack.
691 If there are brackets (**\[** and **\]**) in the string, then they must be
692 balanced. Unbalanced brackets can be escaped using a backslash (**\\**)
695 If there is a backslash character in the string, the character after it
696 (even another backslash) is put into the string verbatim, but the (first)
701 : The value on top of the stack is popped.
703 If it is a number, it is truncated and its absolute value is taken. The
704 result mod **UCHAR_MAX+1** is calculated. If that result is **0**, push an
705 empty string; otherwise, push a one-character string where the character is
706 the result of the mod interpreted as an ASCII character.
708 If it is a string, then a new string is made. If the original string is
709 empty, the new string is empty. If it is not, then the first character of
710 the original string is used to create the new string as a one-character
711 string. The new string is then pushed onto the stack.
713 This is a **non-portable extension**.
717 : Pops a value off of the top of the stack.
719 If it is a number, it is pushed back onto the stack.
721 If it is a string, it is executed as a macro.
723 This behavior is the norm whenever a macro is executed, whether by this
724 command or by the conditional execution commands below.
728 : Pops two values off of the stack that must be numbers and compares them. If
729 the first value is greater than the second, then the contents of register
732 For example, **0 1>a** will execute the contents of register **a**, and
735 If either or both of the values are not numbers, dc(1) will raise an error
736 and reset (see the **RESET** section).
740 : Like the above, but will execute register *s* if the comparison fails.
742 If either or both of the values are not numbers, dc(1) will raise an error
743 and reset (see the **RESET** section).
745 This is a **non-portable extension**.
749 : Pops two values off of the stack that must be numbers and compares them. If
750 the first value is not greater than the second (less than or equal to), then
751 the contents of register *r* are executed.
753 If either or both of the values are not numbers, dc(1) will raise an error
754 and reset (see the **RESET** section).
758 : Like the above, but will execute register *s* if the comparison fails.
760 If either or both of the values are not numbers, dc(1) will raise an error
761 and reset (see the **RESET** section).
763 This is a **non-portable extension**.
767 : Pops two values off of the stack that must be numbers and compares them. If
768 the first value is less than the second, then the contents of register *r*
771 If either or both of the values are not numbers, dc(1) will raise an error
772 and reset (see the **RESET** section).
776 : Like the above, but will execute register *s* if the comparison fails.
778 If either or both of the values are not numbers, dc(1) will raise an error
779 and reset (see the **RESET** section).
781 This is a **non-portable extension**.
785 : Pops two values off of the stack that must be numbers and compares them. If
786 the first value is not less than the second (greater than or equal to), then
787 the contents of register *r* are executed.
789 If either or both of the values are not numbers, dc(1) will raise an error
790 and reset (see the **RESET** section).
794 : Like the above, but will execute register *s* if the comparison fails.
796 If either or both of the values are not numbers, dc(1) will raise an error
797 and reset (see the **RESET** section).
799 This is a **non-portable extension**.
803 : Pops two values off of the stack that must be numbers and compares them. If
804 the first value is equal to the second, then the contents of register *r*
807 If either or both of the values are not numbers, dc(1) will raise an error
808 and reset (see the **RESET** section).
812 : Like the above, but will execute register *s* if the comparison fails.
814 If either or both of the values are not numbers, dc(1) will raise an error
815 and reset (see the **RESET** section).
817 This is a **non-portable extension**.
821 : Pops two values off of the stack that must be numbers and compares them. If
822 the first value is not equal to the second, then the contents of register
825 If either or both of the values are not numbers, dc(1) will raise an error
826 and reset (see the **RESET** section).
830 : Like the above, but will execute register *s* if the comparison fails.
832 If either or both of the values are not numbers, dc(1) will raise an error
833 and reset (see the **RESET** section).
835 This is a **non-portable extension**.
839 : Reads a line from the **stdin** and executes it. This is to allow macros to
840 request input from users.
844 : During execution of a macro, this exits the execution of that macro and the
845 execution of the macro that executed it. If there are no macros, or only one
846 macro executing, dc(1) exits.
850 : Pops a value from the stack which must be non-negative and is used the
851 number of macro executions to pop off of the execution stack. If the number
852 of levels to pop is greater than the number of executing macros, dc(1)
857 These commands query status of the stack or its top value.
861 : Pops a value off of the stack.
863 If it is a number, calculates the number of significant decimal digits it
864 has and pushes the result.
866 If it is a string, pushes the number of characters the string has.
870 : Pops a value off of the stack.
872 If it is a number, pushes the *scale* of the value onto the stack.
874 If it is a string, pushes **0**.
878 : Pushes the current stack depth (before execution of this command).
882 These commands manipulate arrays.
886 : Pops the top two values off of the stack. The second value will be stored in
887 the array *r* (see the **REGISTERS** section), indexed by the first value.
891 : Pops the value on top of the stack and uses it as an index into the array
892 *r*. The selected value is then pushed onto the stack.
896 Registers are names that can store strings, numbers, and arrays. (Number/string
897 registers do not interfere with array registers.)
899 Each register is also its own stack, so the current register value is the top of
900 the stack for the register. All registers, when first referenced, have one value
901 (**0**) in their stack.
903 In non-extended register mode, a register name is just the single character that
904 follows any command that needs a register name. The only exception is a newline
905 (**'\\n'**); it is a parse error for a newline to be used as a register name.
907 ## Extended Register Mode
909 Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited
910 amounts of registers, if extended register mode is enabled.
912 If extended register mode is enabled (**-x** or **-\-extended-register**
913 command-line arguments are given), then normal single character registers are
914 used *unless* the character immediately following a command that needs a
915 register name is a space (according to **isspace()**) and not a newline
918 In that case, the register name is found according to the regex
919 **\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if
920 the next non-space characters do not match that regex.
924 When dc(1) encounters an error or a signal that it has a non-default handler
925 for, it resets. This means that several things happen.
927 First, any macros that are executing are stopped and popped off the stack.
928 The behavior is not unlike that of exceptions in programming languages. Then
929 the execution point is set so that any code waiting to execute (after all
930 macros returned) is skipped.
932 Thus, when dc(1) resets, it skips any remaining code waiting to be executed.
933 Then, if it is interactive mode, and the error was not a fatal error (see the
934 **EXIT STATUS** section), it asks for more input; otherwise, it exits with the
935 appropriate return code.
939 Most dc(1) implementations use **char** types to calculate the value of **1**
940 decimal digit at a time, but that can be slow. This dc(1) does something
943 It uses large integers to calculate more than **1** decimal digit at a time. If
944 built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is
945 **64**, then each integer has **9** decimal digits. If built in an environment
946 where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
947 value (the number of decimal digits per large integer) is called
950 In addition, this dc(1) uses an even larger integer for overflow checking. This
951 integer type depends on the value of **DC_LONG_BIT**, but is always at least
952 twice as large as the integer type used to store digits.
956 The following are the limits on dc(1):
960 : The number of bits in the **long** type in the environment where dc(1) was
961 built. This determines how many decimal digits can be stored in a single
962 large integer (see the **PERFORMANCE** section).
966 : The number of decimal digits per large integer (see the **PERFORMANCE**
967 section). Depends on **DC_LONG_BIT**.
971 : The max decimal number that each large integer can store (see
972 **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**.
976 : The max number that the overflow type (see the **PERFORMANCE** section) can
977 hold. Depends on **DC_LONG_BIT**.
981 : The maximum output base. Set at **DC_BASE_POW**.
985 : The maximum size of arrays. Set at **SIZE_MAX-1**.
989 : The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**.
993 : The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**.
997 : The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**.
1001 : The maximum length of a number (in decimal digits), which includes digits
1002 after the decimal point. Set at **DC_OVERFLOW_MAX-1**.
1006 : The maximum integer (inclusive) returned by the **'** command, if dc(1). Set
1007 at **2\^DC_LONG_BIT-1**.
1011 : The maximum allowable exponent (positive or negative). Set at
1012 **DC_OVERFLOW_MAX**.
1016 : The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
1018 These limits are meant to be effectively non-existent; the limits are so large
1019 (at least on 64-bit machines) that there should not be any point at which they
1020 become a problem. In fact, memory should be exhausted before these limits should
1023 # ENVIRONMENT VARIABLES
1025 dc(1) recognizes the following environment variables:
1029 : This is another way to give command-line arguments to dc(1). They should be
1030 in the same format as all other command-line arguments. These are always
1031 processed first, so any files given in **DC_ENV_ARGS** will be processed
1032 before arguments and files given on the command-line. This gives the user
1033 the ability to set up "standard" options and files to be used at every
1034 invocation. The most useful thing for such files to contain would be useful
1035 functions that the user might want every time dc(1) runs. Another use would
1036 be to use the **-e** option to set **scale** to a value other than **0**.
1038 The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments,
1039 but it does not understand escape sequences. For example, the string
1040 **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string
1041 **"/home/gavin/some \"dc\" file.dc"** will include the backslashes.
1043 The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
1044 if you have a file with any number of single quotes in the name, you can use
1045 double quotes as the outside quotes, as in **"some 'dc' file.dc"**, and vice
1046 versa if you have a file with double quotes. However, handling a file with
1047 both kinds of quotes in **DC_ENV_ARGS** is not supported due to the
1048 complexity of the parsing, though such files are still supported on the
1049 command-line where the parsing is done by the shell.
1053 : If this environment variable exists and contains an integer that is greater
1054 than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output
1055 lines to that length, including the backslash newline combo. The default
1056 line length is **70**.
1060 : If this variable exists (no matter the contents), dc(1) will exit
1061 immediately after executing expressions and files given by the **-e** and/or
1062 **-f** command-line options (and any equivalents).
1066 dc(1) returns the following exit statuses:
1074 : A math error occurred. This follows standard practice of using **1** for
1075 expected errors, since math errors will happen in the process of normal
1078 Math errors include divide by **0**, taking the square root of a negative
1079 number, using a negative number as a bound for the pseudo-random number
1080 generator, attempting to convert a negative number to a hardware integer,
1081 overflow when converting a number to a hardware integer, and attempting to
1082 use a non-integer where an integer is required.
1084 Converting to a hardware integer happens for the second operand of the power
1085 (**\^**), places (**\@**), left shift (**H**), and right shift (**h**)
1090 : A parse error occurred.
1092 Parse errors include unexpected **EOF**, using an invalid character, failing
1093 to find the end of a string or comment, and using a token where it is
1098 : A runtime error occurred.
1100 Runtime errors include assigning an invalid number to **ibase**, **obase**,
1101 or **scale**; give a bad expression to a **read()** call, calling **read()**
1102 inside of a **read()** call, type errors, and attempting an operation when
1103 the stack has too few elements.
1107 : A fatal error occurred.
1109 Fatal errors include memory allocation errors, I/O errors, failing to open
1110 files, attempting to use files that do not have only ASCII characters (dc(1)
1111 only accepts ASCII characters), attempting to open a directory as a file,
1112 and giving invalid command-line options.
1114 The exit status **4** is special; when a fatal error occurs, dc(1) always exits
1115 and returns **4**, no matter what mode dc(1) is in.
1117 The other statuses will only be returned when dc(1) is not in interactive mode
1118 (see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the
1119 **RESET** section) and accepts more input when one of those errors occurs in
1120 interactive mode. This is also the case when interactive mode is forced by the
1121 **-i** flag or **-\-interactive** option.
1123 These exit statuses allow dc(1) to be used in shell scripting with error
1124 checking, and its normal behavior can be forced by using the **-i** flag or
1125 **-\-interactive** option.
1129 Like bc(1), dc(1) has an interactive mode and a non-interactive mode.
1130 Interactive mode is turned on automatically when both **stdin** and **stdout**
1131 are hooked to a terminal, but the **-i** flag and **-\-interactive** option can
1132 turn it on in other cases.
1134 In interactive mode, dc(1) attempts to recover from errors (see the **RESET**
1135 section), and in normal execution, flushes **stdout** as soon as execution is
1136 done for the current input.
1140 If **stdin**, **stdout**, and **stderr** are all connected to a TTY, dc(1) turns
1143 The prompt is enabled in TTY mode.
1145 TTY mode is different from interactive mode because interactive mode is required
1146 in the [bc(1) specification][1], and interactive mode requires only **stdin**
1147 and **stdout** to be connected to a terminal.
1151 Sending a **SIGINT** will cause dc(1) to stop execution of the current input. If
1152 dc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
1153 **RESET** section). Otherwise, it will clean up and exit.
1155 Note that "current input" can mean one of two things. If dc(1) is processing
1156 input from **stdin** in TTY mode, it will ask for more input. If dc(1) is
1157 processing input from a file in TTY mode, it will stop processing the file and
1158 start processing the next file, if one exists, or ask for input from **stdin**
1159 if no other file exists.
1161 This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it
1162 can seem as though dc(1) did not respond to the signal since it will immediately
1163 start executing the next file. This is by design; most files that users execute
1164 when interacting with dc(1) have function definitions, which are quick to parse.
1165 If a file takes a long time to execute, there may be a bug in that file. The
1166 rest of the files could still be executed without problem, allowing the user to
1169 **SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the
1170 default handler for all other signals.
1174 This dc(1) ships with support for adding error messages for different locales
1175 and thus, supports **LC_MESSAGS**.
1183 The dc(1) utility operators are compliant with the operators in the bc(1)
1184 [IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1] specification.
1188 None are known. Report bugs at https://git.yzena.com/gavin/bc.
1192 Gavin D. Howard <gavin@yzena.com> and contributors.
1194 [1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html