3 SPDX-License-Identifier: BSD-2-Clause
5 Copyright (c) 2018-2020 Gavin D. Howard and contributors.
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8 modification, are permitted provided that the following conditions are met:
10 * Redistributions of source code must retain the above copyright notice, this
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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 {{ A E H N EH EN HN EHN }}
84 : Disables the prompt in TTY mode. (The prompt is only enabled in TTY mode.
85 See the **TTY MODE** section) This is mostly for those users that do not
86 want a prompt or are not used to having them in dc(1). Most of those users
87 would want to put this option in **DC_ENV_ARGS**.
89 {{ P EP HP NP EHP ENP HNP EHNP }}
90 : This option is a no-op.
93 This is a **non-portable extension**.
95 **-x** **--extended-register**
97 : Enables extended register mode. See the *Extended Register Mode* subsection
98 of the **REGISTERS** section for more information.
100 This is a **non-portable extension**.
102 **-e** *expr*, **--expression**=*expr*
104 : Evaluates *expr*. If multiple expressions are given, they are evaluated in
105 order. If files are given as well (see below), the expressions and files are
106 evaluated in the order given. This means that if a file is given before an
107 expression, the file is read in and evaluated first.
109 After processing all expressions and files, dc(1) will exit, unless **-**
110 (**stdin**) was given as an argument at least once to **-f** or **--file**.
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 After processing all expressions and files, dc(1) will exit, unless **-**
121 (**stdin**) was given as an argument at least once to **-f** or **--file**.
122 However, if any other **-e**, **--expression**, **-f**, or **--file**
123 arguments are given after that, bc(1) will give a fatal error and exit.
125 This is a **non-portable extension**.
127 All long options are **non-portable extensions**.
131 Any non-error output is written to **stdout**.
133 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
134 error (see the **EXIT STATUS** section) if it cannot write to **stdout**, so if
135 **stdout** is closed, as in **dc <file> >&-**, it will quit with an error. This
136 is done so that dc(1) can report problems when **stdout** is redirected to a
139 If there are scripts that depend on the behavior of other dc(1) implementations,
140 it is recommended that those scripts be changed to redirect **stdout** to
145 Any error output is written to **stderr**.
147 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
148 error (see the **EXIT STATUS** section) if it cannot write to **stderr**, so if
149 **stderr** is closed, as in **dc <file> 2>&-**, it will quit with an error. This
150 is done so that dc(1) can exit with an error code when **stderr** is redirected
153 If there are scripts that depend on the behavior of other dc(1) implementations,
154 it is recommended that those scripts be changed to redirect **stderr** to
159 Each item in the input source code, either a number (see the **NUMBERS**
160 section) or a command (see the **COMMANDS** section), is processed and executed,
161 in order. Input is processed immediately when entered.
163 **ibase** is a register (see the **REGISTERS** section) that determines how to
164 interpret constant numbers. It is the "input" base, or the number base used for
165 interpreting input numbers. **ibase** is initially **10**. The max allowable
166 value for **ibase** is **16**. The min allowable value for **ibase** is **2**.
167 The max allowable value for **ibase** can be queried in dc(1) programs with the
170 **obase** is a register (see the **REGISTERS** section) that determines how to
171 output results. It is the "output" base, or the number base used for outputting
172 numbers. **obase** is initially **10**. The max allowable value for **obase** is
173 **DC_BASE_MAX** and can be queried with the **U** command. The min allowable
174 {{ A H N P HN HP NP HNP }}
175 value for **obase** is **0**. If **obase** is **0**, values are output in
176 scientific notation, and if **obase** is **1**, values are output in engineering
177 notation. Otherwise, values are output in the specified base.
179 Outputting in scientific and engineering notations are **non-portable
182 {{ E EH EN EP EHN EHP ENP EHNP }}
183 value for **obase** is **2**. Values are output in the specified base.
186 The *scale* of an expression is the number of digits in the result of the
187 expression right of the decimal point, and **scale** is a register (see the
188 **REGISTERS** section) that sets the precision of any operations (with
189 exceptions). **scale** is initially **0**. **scale** cannot be negative. The max
190 allowable value for **scale** can be queried in dc(1) programs with the **V**
193 {{ A H N P HN HP NP HNP }}
194 **seed** is a register containing the current seed for the pseudo-random number
195 generator. If the current value of **seed** is queried and stored, then if it is
196 assigned to **seed** later, the pseudo-random number generator is guaranteed to
197 produce the same sequence of pseudo-random numbers that were generated after the
198 value of **seed** was first queried.
200 Multiple values assigned to **seed** can produce the same sequence of
201 pseudo-random numbers. Likewise, when a value is assigned to **seed**, it is not
202 guaranteed that querying **seed** immediately after will return the same value.
203 In addition, the value of **seed** will change after any call to the **'**
204 command or the **"** command that does not get receive a value of **0** or
205 **1**. The maximum integer returned by the **'** command can be queried with the
208 **Note**: The values returned by the pseudo-random number generator with the
209 **'** and **"** commands are guaranteed to **NOT** be cryptographically secure.
210 This is a consequence of using a seeded pseudo-random number generator. However,
211 they **are** guaranteed to be reproducible with identical **seed** values.
213 The pseudo-random number generator, **seed**, and all associated operations are
214 **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 {{ A H N P HN HP NP HNP }}
237 In addition, dc(1) accepts numbers in scientific notation. These have the form
238 **\<number\>e\<integer\>**. The exponent (the portion after the **e**) must be
239 an integer. An example is **1.89237e9**, which is equal to **1892370000**.
240 Negative exponents are also allowed, so **4.2890e_3** is equal to **0.0042890**.
242 **WARNING**: Both the number and the exponent in scientific notation are
243 interpreted according to the current **ibase**, but the number is still
244 multiplied by **10\^exponent** regardless of the current **ibase**. For example,
245 if **ibase** is **16** and dc(1) is given the number string **FFeA**, the
246 resulting decimal number will be **2550000000000**, and if dc(1) is given the
247 number string **10e_4**, the resulting decimal number will be **0.0016**.
249 Accepting input as scientific notation is a **non-portable extension**.
254 The valid commands are listed below.
258 These commands are used for printing.
260 {{ A H N P HN HP NP HNP }}
261 Note that both scientific notation and engineering notation are available for
262 printing numbers. Scientific notation is activated by assigning **0** to
263 **obase** using **0o**, and engineering notation is activated by assigning **1**
264 to **obase** using **1o**. To deactivate them, just assign a different value to
267 Printing numbers in scientific notation and/or engineering notation is a
268 **non-portable extension**.
273 : Prints the value on top of the stack, whether number or string, and prints a
276 This does not alter the stack.
280 : Prints the value on top of the stack, whether number or string, and pops it
285 : Pops a value off the stack.
287 If the value is a number, it is truncated and the absolute value of the
288 result is printed as though **obase** is **UCHAR_MAX+1** and each digit is
289 interpreted as an ASCII character, making it a byte stream.
291 If the value is a string, it is printed without a trailing newline.
293 This is a **non-portable extension**.
297 : Prints the entire contents of the stack, in order from newest to oldest,
298 without altering anything.
300 Users should use this command when they get lost.
304 These are the commands used for arithmetic.
308 : The top two values are popped off the stack, added, and the result is pushed
309 onto the stack. The *scale* of the result is equal to the max *scale* of
314 : The top two values are popped off the stack, subtracted, and the result is
315 pushed onto the stack. The *scale* of the result is equal to the max
316 *scale* of both operands.
320 : The top two values are popped off the stack, multiplied, and the result is
321 pushed onto the stack. If **a** is the *scale* of the first expression and
322 **b** is the *scale* of the second expression, the *scale* of the result
323 is equal to **min(a+b,max(scale,a,b))** where **min()** and **max()** return
328 : The top two values are popped off the stack, divided, and the result is
329 pushed onto the stack. The *scale* of the result is equal to **scale**.
331 The first value popped off of the stack must be non-zero.
335 : The top two values are popped off the stack, remaindered, and the result is
336 pushed onto the stack.
338 Remaindering is equivalent to 1) Computing **a/b** to current **scale**, and
339 2) Using the result of step 1 to calculate **a-(a/b)\*b** to *scale*
340 **max(scale+scale(b),scale(a))**.
342 The first value popped off of the stack must be non-zero.
346 : The top two values are popped off the stack, divided and remaindered, and
347 the results (divided first, remainder second) are pushed onto the stack.
348 This is equivalent to **x y / x y %** except that **x** and **y** are only
351 The first value popped off of the stack must be non-zero.
353 This is a **non-portable extension**.
357 : The top two values are popped off the stack, the second is raised to the
358 power of the first, and the result is pushed onto the stack. The *scale* of
359 the result is equal to **scale**.
361 The first value popped off of the stack must be an integer, and if that
362 value is negative, the second value popped off of the stack must be
367 : The top value is popped off the stack, its square root is computed, and the
368 result is pushed onto the stack. The *scale* of the result is equal to
371 The value popped off of the stack must be non-negative.
375 : If this command *immediately* precedes a number (i.e., no spaces or other
376 commands), then that number is input as a negative number.
378 Otherwise, the top value on the stack is popped and copied, and the copy is
379 negated and pushed onto the stack. This behavior without a number is a
380 **non-portable extension**.
384 : The top value is popped off the stack, and if it is zero, it is pushed back
385 onto the stack. Otherwise, its absolute value is pushed onto the stack.
387 This is a **non-portable extension**.
391 : The top three values are popped off the stack, a modular exponentiation is
392 computed, and the result is pushed onto the stack.
394 The first value popped is used as the reduction modulus and must be an
395 integer and non-zero. The second value popped is used as the exponent and
396 must be an integer and non-negative. The third value popped is the base and
399 This is a **non-portable extension**.
401 {{ A H N P HN HP NP HNP }}
404 : The top value is popped off the stack and copied, and the copy is truncated
405 and pushed onto the stack.
407 This is a **non-portable extension**.
411 : The top two values are popped off the stack, and the precision of the second
412 is set to the value of the first, whether by truncation or extension.
414 The first value popped off of the stack must be an integer and non-negative.
416 This is a **non-portable extension**.
420 : The top two values are popped off the stack, and the second is shifted left
421 (radix shifted right) to the value of the first.
423 The first value popped off of the stack must be an integer and non-negative.
425 This is a **non-portable extension**.
429 : The top two values are popped off the stack, and the second is shifted right
430 (radix shifted left) to the value of the first.
432 The first value popped off of the stack must be an integer and non-negative.
434 This is a **non-portable extension**.
439 : The top two values are popped off of the stack, they are compared, and a
440 **1** is pushed if they are equal, or **0** otherwise.
442 This is a **non-portable extension**.
446 : The top value is popped off of the stack, and if it a **0**, a **1** is
447 pushed; otherwise, a **0** is pushed.
449 This is a **non-portable extension**.
453 : The top two values are popped off of the stack, they are compared, and a
454 **1** is pushed if the first is less than the second, or **0** otherwise.
456 This is a **non-portable extension**.
460 : The top two values are popped off of the stack, they are compared, and a
461 **1** is pushed if the first is less than or equal to the second, or **0**
464 This is a **non-portable extension**.
468 : The top two values are popped off of the stack, they are compared, and a
469 **1** is pushed if the first is greater than the second, or **0** otherwise.
471 This is a **non-portable extension**.
475 : The top two values are popped off of the stack, they are compared, and a
476 **1** is pushed if the first is greater than or equal to the second, or
479 This is a **non-portable extension**.
483 : The top two values are popped off of the stack. If they are both non-zero, a
484 **1** is pushed onto the stack. If either of them is zero, or both of them
485 are, then a **0** is pushed onto the stack.
487 This is like the **&&** operator in bc(1), and it is *not* a short-circuit
490 This is a **non-portable extension**.
494 : The top two values are popped off of the stack. If at least one of them is
495 non-zero, a **1** is pushed onto the stack. If both of them are zero, then a
496 **0** is pushed onto the stack.
498 This is like the **||** operator in bc(1), and it is *not* a short-circuit
501 This is a **non-portable extension**.
503 {{ A H N P HN HP NP HNP }}
504 ## Pseudo-Random Number Generator
506 dc(1) has a built-in pseudo-random number generator. These commands query the
507 pseudo-random number generator. (See Parameters for more information about the
508 **seed** value that controls the pseudo-random number generator.)
510 The pseudo-random number generator is guaranteed to **NOT** be
511 cryptographically secure.
515 : Generates an integer between 0 and **DC_RAND_MAX**, inclusive (see the
518 The generated integer is made as unbiased as possible, subject to the
519 limitations of the pseudo-random number generator.
521 This is a **non-portable extension**.
525 : Pops a value off of the stack, which is used as an **exclusive** upper bound
526 on the integer that will be generated. If the bound is negative or is a
527 non-integer, an error is raised, and dc(1) resets (see the **RESET**
528 section) while **seed** remains unchanged. If the bound is larger than
529 **DC_RAND_MAX**, the higher bound is honored by generating several
530 pseudo-random integers, multiplying them by appropriate powers of
531 **DC_RAND_MAX+1**, and adding them together. Thus, the size of integer that
532 can be generated with this command is unbounded. Using this command will
533 change the value of **seed**, unless the operand is **0** or **1**. In that
534 case, **0** is pushed onto the stack, and **seed** is *not* changed.
536 The generated integer is made as unbiased as possible, subject to the
537 limitations of the pseudo-random number generator.
539 This is a **non-portable extension**.
544 These commands control the stack.
548 : Removes all items from ("clears") the stack.
552 : Copies the item on top of the stack ("duplicates") and pushes the copy onto
557 : Swaps ("reverses") the two top items on the stack.
561 : Pops ("removes") the top value from the stack.
565 These commands control registers (see the **REGISTERS** section).
569 : Pops the value off the top of the stack and stores it into register *r*.
573 : Copies the value in register *r* and pushes it onto the stack. This does not
574 alter the contents of *r*.
578 : Pops the value off the top of the (main) stack and pushes it onto the stack
579 of register *r*. The previous value of the register becomes inaccessible.
583 : Pops the value off the top of the stack for register *r* and push it onto
584 the main stack. The previous value in the stack for register *r*, if any, is
585 now accessible via the **l***r* command.
589 {{ A H N P HN HP NP HNP }}
590 These commands control the values of **ibase**, **obase**, **scale**, and
591 **seed**. Also see the **SYNTAX** section.
593 {{ E EH EN EP EHN EHP ENP EHNP }}
594 These commands control the values of **ibase**, **obase**, and **scale**. Also
595 see the **SYNTAX** section.
600 : Pops the value off of the top of the stack and uses it to set **ibase**,
601 which must be between **2** and **16**, inclusive.
603 If the value on top of the stack has any *scale*, the *scale* is ignored.
607 : Pops the value off of the top of the stack and uses it to set **obase**,
608 {{ A H N P HN HP NP HNP }}
609 which must be between **0** and **DC_BASE_MAX**, inclusive (see the
610 **LIMITS** section and the **NUMBERS** section).
612 {{ E EH EN EP EHN EHP ENP EHNP }}
613 which must be between **2** and **DC_BASE_MAX**, inclusive (see the
617 If the value on top of the stack has any *scale*, the *scale* is ignored.
621 : Pops the value off of the top of the stack and uses it to set **scale**,
622 which must be non-negative.
624 If the value on top of the stack has any *scale*, the *scale* is ignored.
626 {{ A H N P HN HP NP HNP }}
629 : Pops the value off of the top of the stack and uses it to set **seed**. The
630 meaning of **seed** is dependent on the current pseudo-random number
631 generator but is guaranteed to not change except for new major versions.
633 The *scale* and sign of the value may be significant.
635 If a previously used **seed** value is used again, the pseudo-random number
636 generator is guaranteed to produce the same sequence of pseudo-random
637 numbers as it did when the **seed** value was previously used.
639 The exact value assigned to **seed** is not guaranteed to be returned if the
640 **J** command is used. However, if **seed** *does* return a different value,
641 both values, when assigned to **seed**, are guaranteed to produce the same
642 sequence of pseudo-random numbers. This means that certain values assigned
643 to **seed** will not produce unique sequences of pseudo-random numbers.
645 There is no limit to the length (number of significant decimal digits) or
646 *scale* of the value that can be assigned to **seed**.
648 This is a **non-portable extension**.
653 : Pushes the current value of **ibase** onto the main stack.
657 : Pushes the current value of **obase** onto the main stack.
661 : Pushes the current value of **scale** onto the main stack.
663 {{ A H N P HN HP NP HNP }}
666 : Pushes the current value of **seed** onto the main stack.
668 This is a **non-portable extension**.
673 : Pushes the maximum allowable value of **ibase** onto the main stack.
675 This is a **non-portable extension**.
679 : Pushes the maximum allowable value of **obase** onto the main stack.
681 This is a **non-portable extension**.
685 : Pushes the maximum allowable value of **scale** onto the main stack.
687 This is a **non-portable extension**.
689 {{ A H N P HN HP NP HNP }}
692 : Pushes the maximum (inclusive) integer that can be generated with the **'**
693 pseudo-random number generator command.
695 This is a **non-portable extension**.
700 The following commands control strings.
702 dc(1) can work with both numbers and strings, and registers (see the
703 **REGISTERS** section) can hold both strings and numbers. dc(1) always knows
704 whether the contents of a register are a string or a number.
706 While arithmetic operations have to have numbers, and will print an error if
707 given a string, other commands accept strings.
709 Strings can also be executed as macros. For example, if the string **[1pR]** is
710 executed as a macro, then the code **1pR** is executed, meaning that the **1**
711 will be printed with a newline after and then popped from the stack.
713 **\[**_characters_**\]**
715 : Makes a string containing *characters* and pushes it onto the stack.
717 If there are brackets (**\[** and **\]**) in the string, then they must be
718 balanced. Unbalanced brackets can be escaped using a backslash (**\\**)
721 If there is a backslash character in the string, the character after it
722 (even another backslash) is put into the string verbatim, but the (first)
727 : The value on top of the stack is popped.
729 If it is a number, it is truncated and its absolute value is taken. The
730 result mod **UCHAR_MAX+1** is calculated. If that result is **0**, push an
731 empty string; otherwise, push a one-character string where the character is
732 the result of the mod interpreted as an ASCII character.
734 If it is a string, then a new string is made. If the original string is
735 empty, the new string is empty. If it is not, then the first character of
736 the original string is used to create the new string as a one-character
737 string. The new string is then pushed onto the stack.
739 This is a **non-portable extension**.
743 : Pops a value off of the top of the stack.
745 If it is a number, it is pushed back onto the stack.
747 If it is a string, it is executed as a macro.
749 This behavior is the norm whenever a macro is executed, whether by this
750 command or by the conditional execution commands below.
754 : Pops two values off of the stack that must be numbers and compares them. If
755 the first value is greater than the second, then the contents of register
758 For example, **0 1>a** will execute the contents of register **a**, and
761 If either or both of the values are not numbers, dc(1) will raise an error
762 and reset (see the **RESET** section).
766 : Like the above, but will execute register *s* if the comparison fails.
768 If either or both of the values are not numbers, dc(1) will raise an error
769 and reset (see the **RESET** section).
771 This is a **non-portable extension**.
775 : Pops two values off of the stack that must be numbers and compares them. If
776 the first value is not greater than the second (less than or equal to), then
777 the contents of register *r* are executed.
779 If either or both of the values are not numbers, dc(1) will raise an error
780 and reset (see the **RESET** section).
784 : Like the above, but will execute register *s* if the comparison fails.
786 If either or both of the values are not numbers, dc(1) will raise an error
787 and reset (see the **RESET** section).
789 This is a **non-portable extension**.
793 : Pops two values off of the stack that must be numbers and compares them. If
794 the first value is less than the second, then the contents of register *r*
797 If either or both of the values are not numbers, dc(1) will raise an error
798 and reset (see the **RESET** section).
802 : Like the above, but will execute register *s* if the comparison fails.
804 If either or both of the values are not numbers, dc(1) will raise an error
805 and reset (see the **RESET** section).
807 This is a **non-portable extension**.
811 : Pops two values off of the stack that must be numbers and compares them. If
812 the first value is not less than the second (greater than or equal to), then
813 the contents of register *r* are executed.
815 If either or both of the values are not numbers, dc(1) will raise an error
816 and reset (see the **RESET** section).
820 : Like the above, but will execute register *s* if the comparison fails.
822 If either or both of the values are not numbers, dc(1) will raise an error
823 and reset (see the **RESET** section).
825 This is a **non-portable extension**.
829 : Pops two values off of the stack that must be numbers and compares them. If
830 the first value is equal to the second, then the contents of register *r*
833 If either or both of the values are not numbers, dc(1) will raise an error
834 and reset (see the **RESET** section).
838 : Like the above, but will execute register *s* if the comparison fails.
840 If either or both of the values are not numbers, dc(1) will raise an error
841 and reset (see the **RESET** section).
843 This is a **non-portable extension**.
847 : Pops two values off of the stack that must be numbers and compares them. If
848 the first value is not equal to the second, then the contents of register
851 If either or both of the values are not numbers, dc(1) will raise an error
852 and reset (see the **RESET** section).
856 : Like the above, but will execute register *s* if the comparison fails.
858 If either or both of the values are not numbers, dc(1) will raise an error
859 and reset (see the **RESET** section).
861 This is a **non-portable extension**.
865 : Reads a line from the **stdin** and executes it. This is to allow macros to
866 request input from users.
870 : During execution of a macro, this exits the execution of that macro and the
871 execution of the macro that executed it. If there are no macros, or only one
872 macro executing, dc(1) exits.
876 : Pops a value from the stack which must be non-negative and is used the
877 number of macro executions to pop off of the execution stack. If the number
878 of levels to pop is greater than the number of executing macros, dc(1)
883 These commands query status of the stack or its top value.
887 : Pops a value off of the stack.
889 If it is a number, calculates the number of significant decimal digits it
890 has and pushes the result.
892 If it is a string, pushes the number of characters the string has.
896 : Pops a value off of the stack.
898 If it is a number, pushes the *scale* of the value onto the stack.
900 If it is a string, pushes **0**.
904 : Pushes the current stack depth (before execution of this command).
908 These commands manipulate arrays.
912 : Pops the top two values off of the stack. The second value will be stored in
913 the array *r* (see the **REGISTERS** section), indexed by the first value.
917 : Pops the value on top of the stack and uses it as an index into the array
918 *r*. The selected value is then pushed onto the stack.
922 Registers are names that can store strings, numbers, and arrays. (Number/string
923 registers do not interfere with array registers.)
925 Each register is also its own stack, so the current register value is the top of
926 the stack for the register. All registers, when first referenced, have one value
927 (**0**) in their stack.
929 In non-extended register mode, a register name is just the single character that
930 follows any command that needs a register name. The only exception is a newline
931 (**'\\n'**); it is a parse error for a newline to be used as a register name.
933 ## Extended Register Mode
935 Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited
936 amounts of registers, if extended register mode is enabled.
938 If extended register mode is enabled (**-x** or **--extended-register**
939 command-line arguments are given), then normal single character registers are
940 used *unless* the character immediately following a command that needs a
941 register name is a space (according to **isspace()**) and not a newline
944 In that case, the register name is found according to the regex
945 **\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if
946 the next non-space characters do not match that regex.
950 When dc(1) encounters an error or a signal that it has a non-default handler
951 for, it resets. This means that several things happen.
953 First, any macros that are executing are stopped and popped off the stack.
954 The behavior is not unlike that of exceptions in programming languages. Then
955 the execution point is set so that any code waiting to execute (after all
956 macros returned) is skipped.
958 Thus, when dc(1) resets, it skips any remaining code waiting to be executed.
959 Then, if it is interactive mode, and the error was not a fatal error (see the
960 **EXIT STATUS** section), it asks for more input; otherwise, it exits with the
961 appropriate return code.
965 Most dc(1) implementations use **char** types to calculate the value of **1**
966 decimal digit at a time, but that can be slow. This dc(1) does something
969 It uses large integers to calculate more than **1** decimal digit at a time. If
970 built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is
971 **64**, then each integer has **9** decimal digits. If built in an environment
972 where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
973 value (the number of decimal digits per large integer) is called
976 In addition, this dc(1) uses an even larger integer for overflow checking. This
977 integer type depends on the value of **DC_LONG_BIT**, but is always at least
978 twice as large as the integer type used to store digits.
982 The following are the limits on dc(1):
986 : The number of bits in the **long** type in the environment where dc(1) was
987 built. This determines how many decimal digits can be stored in a single
988 large integer (see the **PERFORMANCE** section).
992 : The number of decimal digits per large integer (see the **PERFORMANCE**
993 section). Depends on **DC_LONG_BIT**.
997 : The max decimal number that each large integer can store (see
998 **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**.
1002 : The max number that the overflow type (see the **PERFORMANCE** section) can
1003 hold. Depends on **DC_LONG_BIT**.
1007 : The maximum output base. Set at **DC_BASE_POW**.
1011 : The maximum size of arrays. Set at **SIZE_MAX-1**.
1015 : The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**.
1019 : The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**.
1023 : The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**.
1027 : The maximum length of a number (in decimal digits), which includes digits
1028 after the decimal point. Set at **DC_OVERFLOW_MAX-1**.
1030 {{ A H N P HN HP NP HNP }}
1033 : The maximum integer (inclusive) returned by the **'** command, if dc(1). Set
1034 at **2\^DC_LONG_BIT-1**.
1039 : The maximum allowable exponent (positive or negative). Set at
1040 **DC_OVERFLOW_MAX**.
1044 : The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
1046 These limits are meant to be effectively non-existent; the limits are so large
1047 (at least on 64-bit machines) that there should not be any point at which they
1048 become a problem. In fact, memory should be exhausted before these limits should
1051 # ENVIRONMENT VARIABLES
1053 dc(1) recognizes the following environment variables:
1057 : This is another way to give command-line arguments to dc(1). They should be
1058 in the same format as all other command-line arguments. These are always
1059 processed first, so any files given in **DC_ENV_ARGS** will be processed
1060 before arguments and files given on the command-line. This gives the user
1061 the ability to set up "standard" options and files to be used at every
1062 invocation. The most useful thing for such files to contain would be useful
1063 functions that the user might want every time dc(1) runs. Another use would
1064 be to use the **-e** option to set **scale** to a value other than **0**.
1066 The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments,
1067 but it does not understand escape sequences. For example, the string
1068 **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string
1069 **"/home/gavin/some \"dc\" file.dc"** will include the backslashes.
1071 The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
1072 if you have a file with any number of single quotes in the name, you can use
1073 double quotes as the outside quotes, as in **"some 'bc' file.bc"**, and vice
1074 versa if you have a file with double quotes. However, handling a file with
1075 both kinds of quotes in **DC_ENV_ARGS** is not supported due to the
1076 complexity of the parsing, though such files are still supported on the
1077 command-line where the parsing is done by the shell.
1081 : If this environment variable exists and contains an integer that is greater
1082 than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output
1083 lines to that length, including the backslash newline combo. The default
1084 line length is **70**.
1088 : If this variable exists (no matter the contents), dc(1) will exit
1089 immediately after executing expressions and files given by the **-e** and/or
1090 **-f** command-line options (and any equivalents).
1094 dc(1) returns the following exit statuses:
1102 : A math error occurred. This follows standard practice of using **1** for
1103 expected errors, since math errors will happen in the process of normal
1106 Math errors include divide by **0**, taking the square root of a negative
1107 {{ A H N P HN HP NP HNP }}
1108 number, using a negative number as a bound for the pseudo-random number
1109 generator, attempting to convert a negative number to a hardware integer,
1110 overflow when converting a number to a hardware integer, and attempting to
1111 use a non-integer where an integer is required.
1113 Converting to a hardware integer happens for the second operand of the power
1114 (**\^**), places (**\@**), left shift (**H**), and right shift (**h**)
1117 {{ E EH EN EP EHN EHP ENP EHNP }}
1118 number, attempting to convert a negative number to a hardware integer,
1119 overflow when converting a number to a hardware integer, and attempting to
1120 use a non-integer where an integer is required.
1122 Converting to a hardware integer happens for the second operand of the power
1128 : A parse error occurred.
1130 Parse errors include unexpected **EOF**, using an invalid character, failing
1131 to find the end of a string or comment, and using a token where it is
1136 : A runtime error occurred.
1138 Runtime errors include assigning an invalid number to **ibase**, **obase**,
1139 or **scale**; give a bad expression to a **read()** call, calling **read()**
1140 inside of a **read()** call, type errors, and attempting an operation when
1141 the stack has too few elements.
1145 : A fatal error occurred.
1147 Fatal errors include memory allocation errors, I/O errors, failing to open
1148 files, attempting to use files that do not have only ASCII characters (dc(1)
1149 only accepts ASCII characters), attempting to open a directory as a file,
1150 and giving invalid command-line options.
1152 The exit status **4** is special; when a fatal error occurs, dc(1) always exits
1153 and returns **4**, no matter what mode dc(1) is in.
1155 The other statuses will only be returned when dc(1) is not in interactive mode
1156 (see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the
1157 **RESET** section) and accepts more input when one of those errors occurs in
1158 interactive mode. This is also the case when interactive mode is forced by the
1159 **-i** flag or **--interactive** option.
1161 These exit statuses allow dc(1) to be used in shell scripting with error
1162 checking, and its normal behavior can be forced by using the **-i** flag or
1163 **--interactive** option.
1167 Like bc(1), dc(1) has an interactive mode and a non-interactive mode.
1168 Interactive mode is turned on automatically when both **stdin** and **stdout**
1169 are hooked to a terminal, but the **-i** flag and **--interactive** option can
1170 turn it on in other cases.
1172 In interactive mode, dc(1) attempts to recover from errors (see the **RESET**
1173 section), and in normal execution, flushes **stdout** as soon as execution is
1174 done for the current input.
1178 If **stdin**, **stdout**, and **stderr** are all connected to a TTY, dc(1) turns
1181 {{ A E N P EN EP NP ENP }}
1182 TTY mode is required for history to be enabled (see the **COMMAND LINE HISTORY**
1183 section). It is also required to enable special handling for **SIGINT** signals.
1186 {{ A E H N EH EN HN EHN }}
1187 The prompt is enabled in TTY mode.
1190 TTY mode is different from interactive mode because interactive mode is required
1191 in the [bc(1) specification][1], and interactive mode requires only **stdin**
1192 and **stdout** to be connected to a terminal.
1196 Sending a **SIGINT** will cause dc(1) to stop execution of the current input. If
1197 dc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
1198 **RESET** section). Otherwise, it will clean up and exit.
1200 Note that "current input" can mean one of two things. If dc(1) is processing
1201 input from **stdin** in TTY mode, it will ask for more input. If dc(1) is
1202 processing input from a file in TTY mode, it will stop processing the file and
1203 start processing the next file, if one exists, or ask for input from **stdin**
1204 if no other file exists.
1206 This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it
1207 can seem as though dc(1) did not respond to the signal since it will immediately
1208 start executing the next file. This is by design; most files that users execute
1209 when interacting with dc(1) have function definitions, which are quick to parse.
1210 If a file takes a long time to execute, there may be a bug in that file. The
1211 rest of the files could still be executed without problem, allowing the user to
1214 **SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the
1215 {{ A E N P EN EP NP ENP }}
1216 default handler for all other signals. The one exception is **SIGHUP**; in that
1217 case, when dc(1) is in TTY mode, a **SIGHUP** will cause dc(1) to clean up and
1220 {{ H EH HN HP EHN EHP HNP EHNP }}
1221 default handler for all other signals.
1224 {{ A E N P EN EP NP ENP }}
1225 # COMMAND LINE HISTORY
1227 dc(1) supports interactive command-line editing. If dc(1) is in TTY mode (see
1228 the **TTY MODE** section), history is enabled. Previous lines can be recalled
1229 and edited with the arrow keys.
1231 **Note**: tabs are converted to 8 spaces.
1234 {{ A E H P EH EP HP EHP }}
1237 This dc(1) ships with support for adding error messages for different locales
1238 and thus, supports **LC_MESSAGS**.
1247 The dc(1) utility operators are compliant with the operators in the bc(1)
1248 [IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1] specification.
1252 None are known. Report bugs at https://git.yzena.com/gavin/bc.
1256 Gavin D. Howard <gavin@yzena.com> and contributors.
1258 [1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html