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 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 In other dc(1) implementations, this option causes the program to execute
110 the expressions and then exit. This dc(1) does not, unless the
111 **DC_EXPR_EXIT** is defined (see the **ENVIRONMENT VARIABLES** section).
113 This is a **non-portable extension**.
115 **-f** *file*, **--file**=*file*
117 : Reads in *file* and evaluates it, line by line, as though it were read
118 through **stdin**. If expressions are also given (see above), the
119 expressions are evaluated in the order given.
121 In other dc(1) implementations, this option causes the program to execute
122 the files and then exit. This dc(1) does not, unless the
123 **DC_EXPR_EXIT** is defined (see the **ENVIRONMENT VARIABLES** section).
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 power (the portion after the **e**) must be an
239 integer. An example is **1.89237e9**, which is equal to **1892370000**. Negative
240 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.
360 The first value popped off of the stack must be an integer, and if that
361 value is negative, the second value popped off of the stack must be
366 : The top value is popped off the stack, its square root is computed, and the
367 result is pushed onto the stack. The *scale* of the result is equal to
370 The value popped off of the stack must be non-negative.
374 : If this command *immediately* precedes a number (i.e., no spaces or other
375 commands), then that number is input as a negative number.
377 Otherwise, the top value on the stack is popped and copied, and the copy is
378 negated and pushed onto the stack. This behavior without a number is a
379 **non-portable extension**.
383 : The top value is popped off the stack, and if it is zero, it is pushed back
384 onto the stack. Otherwise, its absolute value is pushed onto the stack.
386 This is a **non-portable extension**.
390 : The top three values are popped off the stack, a modular exponentiation is
391 computed, and the result is pushed onto the stack.
393 The first value popped is used as the reduction modulus and must be an
394 integer and non-zero. The second value popped is used as the exponent and
395 must be an integer and non-negative. The third value popped is the base and
398 This is a **non-portable extension**.
400 {{ A H N P HN HP NP HNP }}
403 : The top value is popped off the stack and copied, and the copy is truncated
404 and pushed onto the stack.
406 This is a **non-portable extension**.
410 : The top two values are popped off the stack, and the precision of the second
411 is set to the value of the first, whether by truncation or extension.
413 The first value popped off of the stack must be an integer and non-negative.
415 This is a **non-portable extension**.
419 : The top two values are popped off the stack, and the second is shifted left
420 (radix shifted right) to the value of the first.
422 The first value popped off of the stack must be an integer and non-negative.
424 This is a **non-portable extension**.
428 : The top two values are popped off the stack, and the second is shifted right
429 (radix shifted left) to the value of the first.
431 The first value popped off of the stack must be an integer and non-negative.
433 This is a **non-portable extension**.
438 : The top two values are popped off of the stack, they are compared, and a
439 **1** is pushed if they are equal, or **0** otherwise.
441 This is a **non-portable extension**.
445 : The top value is popped off of the stack, and if it a **0**, a **1** is
446 pushed; otherwise, a **0** is pushed.
448 This is a **non-portable extension**.
452 : The top two values are popped off of the stack, they are compared, and a
453 **1** is pushed if the first is less than the second, or **0** otherwise.
455 This is a **non-portable extension**.
459 : The top two values are popped off of the stack, they are compared, and a
460 **1** is pushed if the first is less than or equal to the second, or **0**
463 This is a **non-portable extension**.
467 : The top two values are popped off of the stack, they are compared, and a
468 **1** is pushed if the first is greater than the second, or **0** otherwise.
470 This is a **non-portable extension**.
474 : The top two values are popped off of the stack, they are compared, and a
475 **1** is pushed if the first is greater than or equal to the second, or
478 This is a **non-portable extension**.
482 : The top two values are popped off of the stack. If they are both non-zero, a
483 **1** is pushed onto the stack. If either of them is zero, or both of them
484 are, then a **0** is pushed onto the stack.
486 This is like the **&&** operator in bc(1), and it is *not* a short-circuit
489 This is a **non-portable extension**.
493 : The top two values are popped off of the stack. If at least one of them is
494 non-zero, a **1** is pushed onto the stack. If both of them are zero, then a
495 **0** is pushed onto the stack.
497 This is like the **||** operator in bc(1), and it is *not* a short-circuit
500 This is a **non-portable extension**.
502 {{ A H N P HN HP NP HNP }}
503 ## Pseudo-Random Number Generator
505 dc(1) has a built-in pseudo-random number generator. These commands query the
506 pseudo-random number generator. (See Parameters for more information about the
507 **seed** value that controls the pseudo-random number generator.)
509 The pseudo-random number generator is guaranteed to **NOT** be
510 cryptographically secure.
514 : Generates an integer between 0 and **DC_RAND_MAX**, inclusive (see the
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 : Pops a value off of the stack, which is used as an **exclusive** upper bound
525 on the integer that will be generated. If the bound is negative or is a
526 non-integer, an error is raised, and dc(1) resets (see the **RESET**
527 section) while **seed** remains unchanged. If the bound is larger than
528 **DC_RAND_MAX**, the higher bound is honored by generating several
529 pseudo-random integers, multiplying them by appropriate powers of
530 **DC_RAND_MAX+1**, and adding them together. Thus, the size of integer that
531 can be generated with this command is unbounded. Using this command will
532 change the value of **seed**, unless the operand is **0** or **1**. In that
533 case, **0** is pushed onto the stack, and **seed** is *not* changed.
535 The generated integer is made as unbiased as possible, subject to the
536 limitations of the pseudo-random number generator.
538 This is a **non-portable extension**.
543 These commands control the stack.
547 : Removes all items from ("clears") the stack.
551 : Copies the item on top of the stack ("duplicates") and pushes the copy onto
556 : Swaps ("reverses") the two top items on the stack.
560 : Pops ("removes") the top value from the stack.
564 These commands control registers (see the **REGISTERS** section).
568 : Pops the value off the top of the stack and stores it into register *r*.
572 : Copies the value in register *r* and pushes it onto the stack. This does not
573 alter the contents of *r*.
577 : Pops the value off the top of the (main) stack and pushes it onto the stack
578 of register *r*. The previous value of the register becomes inaccessible.
582 : Pops the value off the top of the stack for register *r* and push it onto
583 the main stack. The previous value in the stack for register *r*, if any, is
584 now accessible via the **l***r* command.
588 {{ A H N P HN HP NP HNP }}
589 These commands control the values of **ibase**, **obase**, **scale**, and
590 **seed**. Also see the **SYNTAX** section.
592 {{ E EH EN EP EHN EHP ENP EHNP }}
593 These commands control the values of **ibase**, **obase**, and **scale**. Also
594 see the **SYNTAX** section.
599 : Pops the value off of the top of the stack and uses it to set **ibase**,
600 which must be between **2** and **16**, inclusive.
602 If the value on top of the stack has any *scale*, the *scale* is ignored.
606 : Pops the value off of the top of the stack and uses it to set **obase**,
607 {{ A H N P HN HP NP HNP }}
608 which must be between **0** and **DC_BASE_MAX**, inclusive (see the
609 **LIMITS** section and the **NUMBERS** section).
611 {{ E EH EN EP EHN EHP ENP EHNP }}
612 which must be between **2** and **DC_BASE_MAX**, inclusive (see the
616 If the value on top of the stack has any *scale*, the *scale* is ignored.
620 : Pops the value off of the top of the stack and uses it to set **scale**,
621 which must be non-negative.
623 If the value on top of the stack has any *scale*, the *scale* is ignored.
625 {{ A H N P HN HP NP HNP }}
628 : Pops the value off of the top of the stack and uses it to set **seed**. The
629 meaning of **seed** is dependent on the current pseudo-random number
630 generator but is guaranteed to not change except for new major versions.
632 The *scale* and sign of the value may be significant.
634 If a previously used **seed** value is used again, the pseudo-random number
635 generator is guaranteed to produce the same sequence of pseudo-random
636 numbers as it did when the **seed** value was previously used.
638 The exact value assigned to **seed** is not guaranteed to be returned if the
639 **J** command is used. However, if **seed** *does* return a different value,
640 both values, when assigned to **seed**, are guaranteed to produce the same
641 sequence of pseudo-random numbers. This means that certain values assigned
642 to **seed** will not produce unique sequences of pseudo-random numbers.
644 There is no limit to the length (number of significant decimal digits) or
645 *scale* of the value that can be assigned to **seed**.
647 This is a **non-portable extension**.
652 : Pushes the current value of **ibase** onto the main stack.
656 : Pushes the current value of **obase** onto the main stack.
660 : Pushes the current value of **scale** onto the main stack.
662 {{ A H N P HN HP NP HNP }}
665 : Pushes the current value of **seed** onto the main stack.
667 This is a **non-portable extension**.
672 : Pushes the maximum allowable value of **ibase** onto the main stack.
674 This is a **non-portable extension**.
678 : Pushes the maximum allowable value of **obase** onto the main stack.
680 This is a **non-portable extension**.
684 : Pushes the maximum allowable value of **scale** onto the main stack.
686 This is a **non-portable extension**.
688 {{ A H N P HN HP NP HNP }}
691 : Pushes the maximum (inclusive) integer that can be generated with the **'**
692 pseudo-random number generator command.
694 This is a **non-portable extension**.
699 The following commands control strings.
701 dc(1) can work with both numbers and strings, and registers (see the
702 **REGISTERS** section) can hold both strings and numbers. dc(1) always knows
703 whether the contents of a register are a string or a number.
705 While arithmetic operations have to have numbers, and will print an error if
706 given a string, other commands accept strings.
708 Strings can also be executed as macros. For example, if the string **[1pR]** is
709 executed as a macro, then the code **1pR** is executed, meaning that the **1**
710 will be printed with a newline after and then popped from the stack.
712 **\[**_characters_**\]**
714 : Makes a string containing *characters* and pushes it onto the stack.
716 If there are brackets (**\[** and **\]**) in the string, then they must be
717 balanced. Unbalanced brackets can be escaped using a backslash (**\\**)
720 If there is a backslash character in the string, the character after it
721 (even another backslash) is put into the string verbatim, but the (first)
726 : The value on top of the stack is popped.
728 If it is a number, it is truncated and its absolute value is taken. The
729 result mod **UCHAR_MAX+1** is calculated. If that result is **0**, push an
730 empty string; otherwise, push a one-character string where the character is
731 the result of the mod interpreted as an ASCII character.
733 If it is a string, then a new string is made. If the original string is
734 empty, the new string is empty. If it is not, then the first character of
735 the original string is used to create the new string as a one-character
736 string. The new string is then pushed onto the stack.
738 This is a **non-portable extension**.
742 : Pops a value off of the top of the stack.
744 If it is a number, it is pushed back onto the stack.
746 If it is a string, it is executed as a macro.
748 This behavior is the norm whenever a macro is executed, whether by this
749 command or by the conditional execution commands below.
753 : Pops two values off of the stack that must be numbers and compares them. If
754 the first value is greater than the second, then the contents of register
757 For example, **0 1>a** will execute the contents of register **a**, and
760 If either or both of the values are not numbers, dc(1) will raise an error
761 and reset (see the **RESET** section).
765 : Like the above, but will execute register *s* if the comparison fails.
767 If either or both of the values are not numbers, dc(1) will raise an error
768 and reset (see the **RESET** section).
770 This is a **non-portable extension**.
774 : Pops two values off of the stack that must be numbers and compares them. If
775 the first value is not greater than the second (less than or equal to), then
776 the contents of register *r* are executed.
778 If either or both of the values are not numbers, dc(1) will raise an error
779 and reset (see the **RESET** section).
783 : Like the above, but will execute register *s* if the comparison fails.
785 If either or both of the values are not numbers, dc(1) will raise an error
786 and reset (see the **RESET** section).
788 This is a **non-portable extension**.
792 : Pops two values off of the stack that must be numbers and compares them. If
793 the first value is less than the second, then the contents of register *r*
796 If either or both of the values are not numbers, dc(1) will raise an error
797 and reset (see the **RESET** section).
801 : Like the above, but will execute register *s* if the comparison fails.
803 If either or both of the values are not numbers, dc(1) will raise an error
804 and reset (see the **RESET** section).
806 This is a **non-portable extension**.
810 : Pops two values off of the stack that must be numbers and compares them. If
811 the first value is not less than the second (greater than or equal to), then
812 the contents of register *r* are executed.
814 If either or both of the values are not numbers, dc(1) will raise an error
815 and reset (see the **RESET** section).
819 : Like the above, but will execute register *s* if the comparison fails.
821 If either or both of the values are not numbers, dc(1) will raise an error
822 and reset (see the **RESET** section).
824 This is a **non-portable extension**.
828 : Pops two values off of the stack that must be numbers and compares them. If
829 the first value is equal to the second, then the contents of register *r*
832 If either or both of the values are not numbers, dc(1) will raise an error
833 and reset (see the **RESET** section).
837 : Like the above, but will execute register *s* if the comparison fails.
839 If either or both of the values are not numbers, dc(1) will raise an error
840 and reset (see the **RESET** section).
842 This is a **non-portable extension**.
846 : Pops two values off of the stack that must be numbers and compares them. If
847 the first value is not equal to the second, then the contents of register
850 If either or both of the values are not numbers, dc(1) will raise an error
851 and reset (see the **RESET** section).
855 : Like the above, but will execute register *s* if the comparison fails.
857 If either or both of the values are not numbers, dc(1) will raise an error
858 and reset (see the **RESET** section).
860 This is a **non-portable extension**.
864 : Reads a line from the **stdin** and executes it. This is to allow macros to
865 request input from users.
869 : During execution of a macro, this exits the execution of that macro and the
870 execution of the macro that executed it. If there are no macros, or only one
871 macro executing, dc(1) exits.
875 : Pops a value from the stack which must be non-negative and is used the
876 number of macro executions to pop off of the execution stack. If the number
877 of levels to pop is greater than the number of executing macros, dc(1)
882 These commands query status of the stack or its top value.
886 : Pops a value off of the stack.
888 If it is a number, calculates the number of significant decimal digits it
889 has and pushes the result.
891 If it is a string, pushes the number of characters the string has.
895 : Pops a value off of the stack.
897 If it is a number, pushes the *scale* of the value onto the stack.
899 If it is a string, pushes **0**.
903 : Pushes the current stack depth (before execution of this command).
907 These commands manipulate arrays.
911 : Pops the top two values off of the stack. The second value will be stored in
912 the array *r* (see the **REGISTERS** section), indexed by the first value.
916 : Pops the value on top of the stack and uses it as an index into the array
917 *r*. The selected value is then pushed onto the stack.
921 Registers are names that can store strings, numbers, and arrays. (Number/string
922 registers do not interfere with array registers.)
924 Each register is also its own stack, so the current register value is the top of
925 the stack for the register. All registers, when first referenced, have one value
926 (**0**) in their stack.
928 In non-extended register mode, a register name is just the single character that
929 follows any command that needs a register name. The only exception is a newline
930 (**'\\n'**); it is a parse error for a newline to be used as a register name.
932 ## Extended Register Mode
934 Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited
935 amounts of registers, if extended register mode is enabled.
937 If extended register mode is enabled (**-x** or **--extended-register**
938 command-line arguments are given), then normal single character registers are
939 used *unless* the character immediately following a command that needs a
940 register name is a space (according to **isspace()**) and not a newline
943 In that case, the register name is found according to the regex
944 **\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if
945 the next non-space characters do not match that regex.
949 When dc(1) encounters an error or a signal that it has a non-default handler
950 for, it resets. This means that several things happen.
952 First, any macros that are executing are stopped and popped off the stack.
953 The behavior is not unlike that of exceptions in programming languages. Then
954 the execution point is set so that any code waiting to execute (after all
955 macros returned) is skipped.
957 Thus, when dc(1) resets, it skips any remaining code waiting to be executed.
958 Then, if it is interactive mode, and the error was not a fatal error (see the
959 **EXIT STATUS** section), it asks for more input; otherwise, it exits with the
960 appropriate return code.
964 Most dc(1) implementations use **char** types to calculate the value of **1**
965 decimal digit at a time, but that can be slow. This dc(1) does something
968 It uses large integers to calculate more than **1** decimal digit at a time. If
969 built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is
970 **64**, then each integer has **9** decimal digits. If built in an environment
971 where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
972 value (the number of decimal digits per large integer) is called
975 In addition, this dc(1) uses an even larger integer for overflow checking. This
976 integer type depends on the value of **DC_LONG_BIT**, but is always at least
977 twice as large as the integer type used to store digits.
981 The following are the limits on dc(1):
985 : The number of bits in the **long** type in the environment where dc(1) was
986 built. This determines how many decimal digits can be stored in a single
987 large integer (see the **PERFORMANCE** section).
991 : The number of decimal digits per large integer (see the **PERFORMANCE**
992 section). Depends on **DC_LONG_BIT**.
996 : The max decimal number that each large integer can store (see
997 **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**.
1001 : The max number that the overflow type (see the **PERFORMANCE** section) can
1002 hold. Depends on **DC_LONG_BIT**.
1006 : The maximum output base. Set at **DC_BASE_POW**.
1010 : The maximum size of arrays. Set at **SIZE_MAX-1**.
1014 : The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**.
1018 : The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**.
1022 : The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**.
1026 : The maximum length of a number (in decimal digits), which includes digits
1027 after the decimal point. Set at **DC_OVERFLOW_MAX-1**.
1029 {{ A H N P HN HP NP HNP }}
1032 : The maximum integer (inclusive) returned by the **'** command, if dc(1). Set
1033 at **2\^DC_LONG_BIT-1**.
1038 : The maximum allowable exponent (positive or negative). Set at
1039 **DC_OVERFLOW_MAX**.
1043 : The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
1045 These limits are meant to be effectively non-existent; the limits are so large
1046 (at least on 64-bit machines) that there should not be any point at which they
1047 become a problem. In fact, memory should be exhausted before these limits should
1050 # ENVIRONMENT VARIABLES
1052 dc(1) recognizes the following environment variables:
1056 : This is another way to give command-line arguments to dc(1). They should be
1057 in the same format as all other command-line arguments. These are always
1058 processed first, so any files given in **DC_ENV_ARGS** will be processed
1059 before arguments and files given on the command-line. This gives the user
1060 the ability to set up "standard" options and files to be used at every
1061 invocation. The most useful thing for such files to contain would be useful
1062 functions that the user might want every time dc(1) runs. Another use would
1063 be to use the **-e** option to set **scale** to a value other than **0**.
1065 The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments,
1066 but it does not understand escape sequences. For example, the string
1067 **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string
1068 **"/home/gavin/some \"dc\" file.dc"** will include the backslashes.
1070 The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
1071 if you have a file with any number of single quotes in the name, you can use
1072 double quotes as the outside quotes, as in **"some 'bc' file.bc"**, and vice
1073 versa if you have a file with double quotes. However, handling a file with
1074 both kinds of quotes in **DC_ENV_ARGS** is not supported due to the
1075 complexity of the parsing, though such files are still supported on the
1076 command-line where the parsing is done by the shell.
1080 : If this environment variable exists and contains an integer that is greater
1081 than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output
1082 lines to that length, including the backslash newline combo. The default
1083 line length is **70**.
1087 : If this variable exists (no matter the contents), dc(1) will exit
1088 immediately after executing expressions and files given by the **-e** and/or
1089 **-f** command-line options (and any equivalents).
1093 dc(1) returns the following exit statuses:
1101 : A math error occurred. This follows standard practice of using **1** for
1102 expected errors, since math errors will happen in the process of normal
1105 Math errors include divide by **0**, taking the square root of a negative
1106 {{ A H N P HN HP NP HNP }}
1107 number, using a negative number as a bound for the pseudo-random number
1108 generator, attempting to convert a negative number to a hardware integer,
1109 overflow when converting a number to a hardware integer, and attempting to
1110 use a non-integer where an integer is required.
1112 Converting to a hardware integer happens for the second operand of the power
1113 (**\^**), places (**\@**), left shift (**H**), and right shift (**h**)
1116 {{ E EH EN EP EHN EHP ENP EHNP }}
1117 number, attempting to convert a negative number to a hardware integer,
1118 overflow when converting a number to a hardware integer, and attempting to
1119 use a non-integer where an integer is required.
1121 Converting to a hardware integer happens for the second operand of the power
1127 : A parse error occurred.
1129 Parse errors include unexpected **EOF**, using an invalid character, failing
1130 to find the end of a string or comment, and using a token where it is
1135 : A runtime error occurred.
1137 Runtime errors include assigning an invalid number to **ibase**, **obase**,
1138 or **scale**; give a bad expression to a **read()** call, calling **read()**
1139 inside of a **read()** call, type errors, and attempting an operation when
1140 the stack has too few elements.
1144 : A fatal error occurred.
1146 Fatal errors include memory allocation errors, I/O errors, failing to open
1147 files, attempting to use files that do not have only ASCII characters (dc(1)
1148 only accepts ASCII characters), attempting to open a directory as a file,
1149 and giving invalid command-line options.
1151 The exit status **4** is special; when a fatal error occurs, dc(1) always exits
1152 and returns **4**, no matter what mode dc(1) is in.
1154 The other statuses will only be returned when dc(1) is not in interactive mode
1155 (see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the
1156 **RESET** section) and accepts more input when one of those errors occurs in
1157 interactive mode. This is also the case when interactive mode is forced by the
1158 **-i** flag or **--interactive** option.
1160 These exit statuses allow dc(1) to be used in shell scripting with error
1161 checking, and its normal behavior can be forced by using the **-i** flag or
1162 **--interactive** option.
1166 Like bc(1), dc(1) has an interactive mode and a non-interactive mode.
1167 Interactive mode is turned on automatically when both **stdin** and **stdout**
1168 are hooked to a terminal, but the **-i** flag and **--interactive** option can
1169 turn it on in other cases.
1171 In interactive mode, dc(1) attempts to recover from errors (see the **RESET**
1172 section), and in normal execution, flushes **stdout** as soon as execution is
1173 done for the current input.
1177 If **stdin**, **stdout**, and **stderr** are all connected to a TTY, dc(1) turns
1180 {{ A E N P EN EP NP ENP }}
1181 TTY mode is required for history to be enabled (see the **COMMAND LINE HISTORY**
1182 section). It is also required to enable special handling for **SIGINT** signals.
1185 {{ A E H N EH EN HN EHN }}
1186 The prompt is enabled in TTY mode.
1189 TTY mode is different from interactive mode because interactive mode is required
1190 in the [bc(1) specification][1], and interactive mode requires only **stdin**
1191 and **stdout** to be connected to a terminal.
1195 Sending a **SIGINT** will cause dc(1) to stop execution of the current input. If
1196 dc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
1197 **RESET** section). Otherwise, it will clean up and exit.
1199 Note that "current input" can mean one of two things. If dc(1) is processing
1200 input from **stdin** in TTY mode, it will ask for more input. If dc(1) is
1201 processing input from a file in TTY mode, it will stop processing the file and
1202 start processing the next file, if one exists, or ask for input from **stdin**
1203 if no other file exists.
1205 This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it
1206 can seem as though dc(1) did not respond to the signal since it will immediately
1207 start executing the next file. This is by design; most files that users execute
1208 when interacting with dc(1) have function definitions, which are quick to parse.
1209 If a file takes a long time to execute, there may be a bug in that file. The
1210 rest of the files could still be executed without problem, allowing the user to
1213 **SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the
1214 {{ A E N P EN EP NP ENP }}
1215 default handler for all other signals. The one exception is **SIGHUP**; in that
1216 case, when dc(1) is in TTY mode, a **SIGHUP** will cause dc(1) to clean up and
1219 {{ H EH HN HP EHN EHP HNP EHNP }}
1220 default handler for all other signals.
1223 {{ A E N P EN EP NP ENP }}
1224 # COMMAND LINE HISTORY
1226 dc(1) supports interactive command-line editing. If dc(1) is in TTY mode (see
1227 the **TTY MODE** section), history is enabled. Previous lines can be recalled
1228 and edited with the arrow keys.
1230 **Note**: tabs are converted to 8 spaces.
1233 {{ A E H P EH EP HP EHP }}
1236 This dc(1) ships with support for adding error messages for different locales
1237 and thus, supports **LC_MESSAGS**.
1246 The dc(1) utility operators are compliant with the operators in the bc(1)
1247 [IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1] specification.
1251 None are known. Report bugs at https://git.yzena.com/gavin/bc.
1255 Gavin D. Howard <yzena.tech@gmail.com> and contributors.
1257 [1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html