3 SPDX-License-Identifier: BSD-2-Clause
5 Copyright (c) 2018-2021 Gavin D. Howard and contributors.
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8 modification, are permitted provided that the following conditions are met:
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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 : This option is a no-op.
85 This is a **non-portable extension**.
87 **-x** **--extended-register**
89 : Enables extended register mode. See the *Extended Register Mode* subsection
90 of the **REGISTERS** section for more information.
92 This is a **non-portable extension**.
94 **-e** *expr*, **--expression**=*expr*
96 : Evaluates *expr*. If multiple expressions are given, they are evaluated in
97 order. If files are given as well (see below), the expressions and files are
98 evaluated in the order given. This means that if a file is given before an
99 expression, the file is read in and evaluated first.
101 If this option is given on the command-line (i.e., not in **DC_ENV_ARGS**,
102 see the **ENVIRONMENT VARIABLES** section), then after processing all
103 expressions and files, dc(1) will exit, unless **-** (**stdin**) was given
104 as an argument at least once to **-f** or **--file**, whether on the
105 command-line or in **DC_ENV_ARGS**. However, if any other **-e**,
106 **--expression**, **-f**, or **--file** arguments are given after **-f-** or
107 equivalent is given, dc(1) will give a fatal error and exit.
109 This is a **non-portable extension**.
111 **-f** *file*, **--file**=*file*
113 : Reads in *file* and evaluates it, line by line, as though it were read
114 through **stdin**. If expressions are also given (see above), the
115 expressions are evaluated in the order given.
117 If this option is given on the command-line (i.e., not in **DC_ENV_ARGS**,
118 see the **ENVIRONMENT VARIABLES** section), then after processing all
119 expressions and files, dc(1) will exit, unless **-** (**stdin**) was given
120 as an argument at least once to **-f** or **--file**. However, if any other
121 **-e**, **--expression**, **-f**, or **--file** arguments are given after
122 **-f-** or equivalent is given, dc(1) will give a fatal error and exit.
124 This is a **non-portable extension**.
126 All long options are **non-portable extensions**.
130 Any non-error output is written to **stdout**. In addition, if history (see the
131 **HISTORY** section) and the prompt (see the **TTY MODE** section) are enabled,
132 both are output to **stdout**.
134 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
135 error (see the **EXIT STATUS** section) if it cannot write to **stdout**, so if
136 **stdout** is closed, as in **dc <file> >&-**, it will quit with an error. This
137 is done so that dc(1) can report problems when **stdout** is redirected to a
140 If there are scripts that depend on the behavior of other dc(1) implementations,
141 it is recommended that those scripts be changed to redirect **stdout** to
146 Any error output is written to **stderr**.
148 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
149 error (see the **EXIT STATUS** section) if it cannot write to **stderr**, so if
150 **stderr** is closed, as in **dc <file> 2>&-**, it will quit with an error. This
151 is done so that dc(1) can exit with an error code when **stderr** is redirected
154 If there are scripts that depend on the behavior of other dc(1) implementations,
155 it is recommended that those scripts be changed to redirect **stderr** to
160 Each item in the input source code, either a number (see the **NUMBERS**
161 section) or a command (see the **COMMANDS** section), is processed and executed,
162 in order. Input is processed immediately when entered.
164 **ibase** is a register (see the **REGISTERS** section) that determines how to
165 interpret constant numbers. It is the "input" base, or the number base used for
166 interpreting input numbers. **ibase** is initially **10**. The max allowable
167 value for **ibase** is **16**. The min allowable value for **ibase** is **2**.
168 The max allowable value for **ibase** can be queried in dc(1) programs with the
171 **obase** is a register (see the **REGISTERS** section) that determines how to
172 output results. It is the "output" base, or the number base used for outputting
173 numbers. **obase** is initially **10**. The max allowable value for **obase** is
174 **DC_BASE_MAX** and can be queried with the **U** command. The min allowable
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 The *scale* of an expression is the number of digits in the result of the
183 expression right of the decimal point, and **scale** is a register (see the
184 **REGISTERS** section) that sets the precision of any operations (with
185 exceptions). **scale** is initially **0**. **scale** cannot be negative. The max
186 allowable value for **scale** can be queried in dc(1) programs with the **V**
189 **seed** is a register containing the current seed for the pseudo-random number
190 generator. If the current value of **seed** is queried and stored, then if it is
191 assigned to **seed** later, the pseudo-random number generator is guaranteed to
192 produce the same sequence of pseudo-random numbers that were generated after the
193 value of **seed** was first queried.
195 Multiple values assigned to **seed** can produce the same sequence of
196 pseudo-random numbers. Likewise, when a value is assigned to **seed**, it is not
197 guaranteed that querying **seed** immediately after will return the same value.
198 In addition, the value of **seed** will change after any call to the **'**
199 command or the **"** command that does not get receive a value of **0** or
200 **1**. The maximum integer returned by the **'** command can be queried with the
203 **Note**: The values returned by the pseudo-random number generator with the
204 **'** and **"** commands are guaranteed to **NOT** be cryptographically secure.
205 This is a consequence of using a seeded pseudo-random number generator. However,
206 they *are* guaranteed to be reproducible with identical **seed** values. This
207 means that the pseudo-random values from dc(1) should only be used where a
208 reproducible stream of pseudo-random numbers is *ESSENTIAL*. In any other case,
209 use a non-seeded pseudo-random number generator.
211 The pseudo-random number generator, **seed**, and all associated operations are
212 **non-portable extensions**.
216 Comments go from **#** until, and not including, the next newline. This is a
217 **non-portable extension**.
221 Numbers are strings made up of digits, uppercase letters up to **F**, and at
222 most **1** period for a radix. Numbers can have up to **DC_NUM_MAX** digits.
223 Uppercase letters are equal to **9** + their position in the alphabet (i.e.,
224 **A** equals **10**, or **9+1**). If a digit or letter makes no sense with the
225 current value of **ibase**, they are set to the value of the highest valid digit
228 Single-character numbers (i.e., **A** alone) take the value that they would have
229 if they were valid digits, regardless of the value of **ibase**. This means that
230 **A** alone always equals decimal **10** and **F** alone always equals decimal
233 In addition, dc(1) accepts numbers in scientific notation. These have the form
234 **\<number\>e\<integer\>**. The exponent (the portion after the **e**) must be
235 an integer. An example is **1.89237e9**, which is equal to **1892370000**.
236 Negative exponents are also allowed, so **4.2890e_3** is equal to **0.0042890**.
238 **WARNING**: Both the number and the exponent in scientific notation are
239 interpreted according to the current **ibase**, but the number is still
240 multiplied by **10\^exponent** regardless of the current **ibase**. For example,
241 if **ibase** is **16** and dc(1) is given the number string **FFeA**, the
242 resulting decimal number will be **2550000000000**, and if dc(1) is given the
243 number string **10e_4**, the resulting decimal number will be **0.0016**.
245 Accepting input as scientific notation is a **non-portable extension**.
249 The valid commands are listed below.
253 These commands are used for printing.
255 Note that both scientific notation and engineering notation are available for
256 printing numbers. Scientific notation is activated by assigning **0** to
257 **obase** using **0o**, and engineering notation is activated by assigning **1**
258 to **obase** using **1o**. To deactivate them, just assign a different value to
261 Printing numbers in scientific notation and/or engineering notation is a
262 **non-portable extension**.
266 : Prints the value on top of the stack, whether number or string, and prints a
269 This does not alter the stack.
273 : Prints the value on top of the stack, whether number or string, and pops it
278 : Pops a value off the stack.
280 If the value is a number, it is truncated and the absolute value of the
281 result is printed as though **obase** is **UCHAR_MAX+1** and each digit is
282 interpreted as an ASCII character, making it a byte stream.
284 If the value is a string, it is printed without a trailing newline.
286 This is a **non-portable extension**.
290 : Prints the entire contents of the stack, in order from newest to oldest,
291 without altering anything.
293 Users should use this command when they get lost.
297 These are the commands used for arithmetic.
301 : The top two values are popped off the stack, added, and the result is pushed
302 onto the stack. The *scale* of the result is equal to the max *scale* of
307 : The top two values are popped off the stack, subtracted, and the result is
308 pushed onto the stack. The *scale* of the result is equal to the max
309 *scale* of both operands.
313 : The top two values are popped off the stack, multiplied, and the result is
314 pushed onto the stack. If **a** is the *scale* of the first expression and
315 **b** is the *scale* of the second expression, the *scale* of the result
316 is equal to **min(a+b,max(scale,a,b))** where **min()** and **max()** return
321 : The top two values are popped off the stack, divided, and the result is
322 pushed onto the stack. The *scale* of the result is equal to **scale**.
324 The first value popped off of the stack must be non-zero.
328 : The top two values are popped off the stack, remaindered, and the result is
329 pushed onto the stack.
331 Remaindering is equivalent to 1) Computing **a/b** to current **scale**, and
332 2) Using the result of step 1 to calculate **a-(a/b)\*b** to *scale*
333 **max(scale+scale(b),scale(a))**.
335 The first value popped off of the stack must be non-zero.
339 : The top two values are popped off the stack, divided and remaindered, and
340 the results (divided first, remainder second) are pushed onto the stack.
341 This is equivalent to **x y / x y %** except that **x** and **y** are only
344 The first value popped off of the stack must be non-zero.
346 This is a **non-portable extension**.
350 : The top two values are popped off the stack, the second is raised to the
351 power of the first, and the result is pushed onto the stack. The *scale* of
352 the result is equal to **scale**.
354 The first value popped off of the stack must be an integer, and if that
355 value is negative, the second value popped off of the stack must be
360 : The top value is popped off the stack, its square root is computed, and the
361 result is pushed onto the stack. The *scale* of the result is equal to
364 The value popped off of the stack must be non-negative.
368 : If this command *immediately* precedes a number (i.e., no spaces or other
369 commands), then that number is input as a negative number.
371 Otherwise, the top value on the stack is popped and copied, and the copy is
372 negated and pushed onto the stack. This behavior without a number is a
373 **non-portable extension**.
377 : The top value is popped off the stack, and if it is zero, it is pushed back
378 onto the stack. Otherwise, its absolute value is pushed onto the stack.
380 This is a **non-portable extension**.
384 : The top three values are popped off the stack, a modular exponentiation is
385 computed, and the result is pushed onto the stack.
387 The first value popped is used as the reduction modulus and must be an
388 integer and non-zero. The second value popped is used as the exponent and
389 must be an integer and non-negative. The third value popped is the base and
392 This is a **non-portable extension**.
396 : The top value is popped off the stack and copied, and the copy is truncated
397 and pushed onto the stack.
399 This is a **non-portable extension**.
403 : The top two values are popped off the stack, and the precision of the second
404 is set to the value of the first, whether by truncation or extension.
406 The first value popped off of the stack must be an integer and non-negative.
408 This is a **non-portable extension**.
412 : The top two values are popped off the stack, and the second is shifted left
413 (radix shifted right) to the value of the first.
415 The first value popped off of the stack must be an integer and non-negative.
417 This is a **non-portable extension**.
421 : The top two values are popped off the stack, and the second is shifted right
422 (radix shifted left) to the value of the first.
424 The first value popped off of the stack must be an integer and non-negative.
426 This is a **non-portable extension**.
430 : The top two values are popped off of the stack, they are compared, and a
431 **1** is pushed if they are equal, or **0** otherwise.
433 This is a **non-portable extension**.
437 : The top value is popped off of the stack, and if it a **0**, a **1** is
438 pushed; otherwise, a **0** is pushed.
440 This is a **non-portable extension**.
444 : The top two values are popped off of the stack, they are compared, and a
445 **1** is pushed if the first is less than the second, or **0** otherwise.
447 This is a **non-portable extension**.
451 : The top two values are popped off of the stack, they are compared, and a
452 **1** is pushed if the first is less than or equal to the second, or **0**
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 greater than the second, or **0** otherwise.
462 This is a **non-portable extension**.
466 : The top two values are popped off of the stack, they are compared, and a
467 **1** is pushed if the first is greater than or equal to the second, or
470 This is a **non-portable extension**.
474 : The top two values are popped off of the stack. If they are both non-zero, a
475 **1** is pushed onto the stack. If either of them is zero, or both of them
476 are, then a **0** is pushed onto the stack.
478 This is like the **&&** operator in bc(1), and it is *not* a short-circuit
481 This is a **non-portable extension**.
485 : The top two values are popped off of the stack. If at least one of them is
486 non-zero, a **1** is pushed onto the stack. If both of them are zero, then a
487 **0** is pushed onto the stack.
489 This is like the **||** operator in bc(1), and it is *not* a short-circuit
492 This is a **non-portable extension**.
494 ## Pseudo-Random Number Generator
496 dc(1) has a built-in pseudo-random number generator. These commands query the
497 pseudo-random number generator. (See Parameters for more information about the
498 **seed** value that controls the pseudo-random number generator.)
500 The pseudo-random number generator is guaranteed to **NOT** be
501 cryptographically secure.
505 : Generates an integer between 0 and **DC_RAND_MAX**, inclusive (see the
508 The generated integer is made as unbiased as possible, subject to the
509 limitations of the pseudo-random number generator.
511 This is a **non-portable extension**.
515 : Pops a value off of the stack, which is used as an **exclusive** upper bound
516 on the integer that will be generated. If the bound is negative or is a
517 non-integer, an error is raised, and dc(1) resets (see the **RESET**
518 section) while **seed** remains unchanged. If the bound is larger than
519 **DC_RAND_MAX**, the higher bound is honored by generating several
520 pseudo-random integers, multiplying them by appropriate powers of
521 **DC_RAND_MAX+1**, and adding them together. Thus, the size of integer that
522 can be generated with this command is unbounded. Using this command will
523 change the value of **seed**, unless the operand is **0** or **1**. In that
524 case, **0** is pushed onto the stack, and **seed** is *not* changed.
526 The generated integer is made as unbiased as possible, subject to the
527 limitations of the pseudo-random number generator.
529 This is a **non-portable extension**.
533 These commands control the stack.
537 : Removes all items from ("clears") the stack.
541 : Copies the item on top of the stack ("duplicates") and pushes the copy onto
546 : Swaps ("reverses") the two top items on the stack.
550 : Pops ("removes") the top value from the stack.
554 These commands control registers (see the **REGISTERS** section).
558 : Pops the value off the top of the stack and stores it into register *r*.
562 : Copies the value in register *r* and pushes it onto the stack. This does not
563 alter the contents of *r*.
567 : Pops the value off the top of the (main) stack and pushes it onto the stack
568 of register *r*. The previous value of the register becomes inaccessible.
572 : Pops the value off the top of the stack for register *r* and push it onto
573 the main stack. The previous value in the stack for register *r*, if any, is
574 now accessible via the **l***r* command.
578 These commands control the values of **ibase**, **obase**, **scale**, and
579 **seed**. Also see the **SYNTAX** section.
583 : Pops the value off of the top of the stack and uses it to set **ibase**,
584 which must be between **2** and **16**, inclusive.
586 If the value on top of the stack has any *scale*, the *scale* is ignored.
590 : Pops the value off of the top of the stack and uses it to set **obase**,
591 which must be between **0** and **DC_BASE_MAX**, inclusive (see the
592 **LIMITS** section and the **NUMBERS** section).
594 If the value on top of the stack has any *scale*, the *scale* is ignored.
598 : Pops the value off of the top of the stack and uses it to set **scale**,
599 which must be non-negative.
601 If the value on top of the stack has any *scale*, the *scale* is ignored.
605 : Pops the value off of the top of the stack and uses it to set **seed**. The
606 meaning of **seed** is dependent on the current pseudo-random number
607 generator but is guaranteed to not change except for new major versions.
609 The *scale* and sign of the value may be significant.
611 If a previously used **seed** value is used again, the pseudo-random number
612 generator is guaranteed to produce the same sequence of pseudo-random
613 numbers as it did when the **seed** value was previously used.
615 The exact value assigned to **seed** is not guaranteed to be returned if the
616 **J** command is used. However, if **seed** *does* return a different value,
617 both values, when assigned to **seed**, are guaranteed to produce the same
618 sequence of pseudo-random numbers. This means that certain values assigned
619 to **seed** will not produce unique sequences of pseudo-random numbers.
621 There is no limit to the length (number of significant decimal digits) or
622 *scale* of the value that can be assigned to **seed**.
624 This is a **non-portable extension**.
628 : Pushes the current value of **ibase** onto the main stack.
632 : Pushes the current value of **obase** onto the main stack.
636 : Pushes the current value of **scale** onto the main stack.
640 : Pushes the current value of **seed** onto the main stack.
642 This is a **non-portable extension**.
646 : Pushes the maximum allowable value of **ibase** onto the main stack.
648 This is a **non-portable extension**.
652 : Pushes the maximum allowable value of **obase** onto the main stack.
654 This is a **non-portable extension**.
658 : Pushes the maximum allowable value of **scale** onto the main stack.
660 This is a **non-portable extension**.
664 : Pushes the maximum (inclusive) integer that can be generated with the **'**
665 pseudo-random number generator command.
667 This is a **non-portable extension**.
671 The following commands control strings.
673 dc(1) can work with both numbers and strings, and registers (see the
674 **REGISTERS** section) can hold both strings and numbers. dc(1) always knows
675 whether the contents of a register are a string or a number.
677 While arithmetic operations have to have numbers, and will print an error if
678 given a string, other commands accept strings.
680 Strings can also be executed as macros. For example, if the string **[1pR]** is
681 executed as a macro, then the code **1pR** is executed, meaning that the **1**
682 will be printed with a newline after and then popped from the stack.
684 **\[**_characters_**\]**
686 : Makes a string containing *characters* and pushes it onto the stack.
688 If there are brackets (**\[** and **\]**) in the string, then they must be
689 balanced. Unbalanced brackets can be escaped using a backslash (**\\**)
692 If there is a backslash character in the string, the character after it
693 (even another backslash) is put into the string verbatim, but the (first)
698 : The value on top of the stack is popped.
700 If it is a number, it is truncated and its absolute value is taken. The
701 result mod **UCHAR_MAX+1** is calculated. If that result is **0**, push an
702 empty string; otherwise, push a one-character string where the character is
703 the result of the mod interpreted as an ASCII character.
705 If it is a string, then a new string is made. If the original string is
706 empty, the new string is empty. If it is not, then the first character of
707 the original string is used to create the new string as a one-character
708 string. The new string is then pushed onto the stack.
710 This is a **non-portable extension**.
714 : Pops a value off of the top of the stack.
716 If it is a number, it is pushed back onto the stack.
718 If it is a string, it is executed as a macro.
720 This behavior is the norm whenever a macro is executed, whether by this
721 command or by the conditional execution commands below.
725 : Pops two values off of the stack that must be numbers and compares them. If
726 the first value is greater than the second, then the contents of register
729 For example, **0 1>a** will execute the contents of register **a**, and
732 If either or both of the values are not numbers, dc(1) will raise an error
733 and reset (see the **RESET** section).
737 : Like the above, but will execute register *s* if the comparison fails.
739 If either or both of the values are not numbers, dc(1) will raise an error
740 and reset (see the **RESET** section).
742 This is a **non-portable extension**.
746 : Pops two values off of the stack that must be numbers and compares them. If
747 the first value is not greater than the second (less than or equal to), then
748 the contents of register *r* are executed.
750 If either or both of the values are not numbers, dc(1) will raise an error
751 and reset (see the **RESET** section).
755 : Like the above, but will execute register *s* if the comparison fails.
757 If either or both of the values are not numbers, dc(1) will raise an error
758 and reset (see the **RESET** section).
760 This is a **non-portable extension**.
764 : Pops two values off of the stack that must be numbers and compares them. If
765 the first value is less than the second, then the contents of register *r*
768 If either or both of the values are not numbers, dc(1) will raise an error
769 and reset (see the **RESET** section).
773 : Like the above, but will execute register *s* if the comparison fails.
775 If either or both of the values are not numbers, dc(1) will raise an error
776 and reset (see the **RESET** section).
778 This is a **non-portable extension**.
782 : Pops two values off of the stack that must be numbers and compares them. If
783 the first value is not less than the second (greater than or equal to), then
784 the contents of register *r* are executed.
786 If either or both of the values are not numbers, dc(1) will raise an error
787 and reset (see the **RESET** section).
791 : Like the above, but will execute register *s* if the comparison fails.
793 If either or both of the values are not numbers, dc(1) will raise an error
794 and reset (see the **RESET** section).
796 This is a **non-portable extension**.
800 : Pops two values off of the stack that must be numbers and compares them. If
801 the first value is equal to the second, then the contents of register *r*
804 If either or both of the values are not numbers, dc(1) will raise an error
805 and reset (see the **RESET** section).
809 : Like the above, but will execute register *s* if the comparison fails.
811 If either or both of the values are not numbers, dc(1) will raise an error
812 and reset (see the **RESET** section).
814 This is a **non-portable extension**.
818 : Pops two values off of the stack that must be numbers and compares them. If
819 the first value is not equal to the second, then the contents of register
822 If either or both of the values are not numbers, dc(1) will raise an error
823 and reset (see the **RESET** section).
827 : Like the above, but will execute register *s* if the comparison fails.
829 If either or both of the values are not numbers, dc(1) will raise an error
830 and reset (see the **RESET** section).
832 This is a **non-portable extension**.
836 : Reads a line from the **stdin** and executes it. This is to allow macros to
837 request input from users.
841 : During execution of a macro, this exits the execution of that macro and the
842 execution of the macro that executed it. If there are no macros, or only one
843 macro executing, dc(1) exits.
847 : Pops a value from the stack which must be non-negative and is used the
848 number of macro executions to pop off of the execution stack. If the number
849 of levels to pop is greater than the number of executing macros, dc(1)
854 These commands query status of the stack or its top value.
858 : Pops a value off of the stack.
860 If it is a number, calculates the number of significant decimal digits it
861 has and pushes the result.
863 If it is a string, pushes the number of characters the string has.
867 : Pops a value off of the stack.
869 If it is a number, pushes the *scale* of the value onto the stack.
871 If it is a string, pushes **0**.
875 : Pushes the current stack depth (before execution of this command).
879 These commands manipulate arrays.
883 : Pops the top two values off of the stack. The second value will be stored in
884 the array *r* (see the **REGISTERS** section), indexed by the first value.
888 : Pops the value on top of the stack and uses it as an index into the array
889 *r*. The selected value is then pushed onto the stack.
893 Registers are names that can store strings, numbers, and arrays. (Number/string
894 registers do not interfere with array registers.)
896 Each register is also its own stack, so the current register value is the top of
897 the stack for the register. All registers, when first referenced, have one value
898 (**0**) in their stack.
900 In non-extended register mode, a register name is just the single character that
901 follows any command that needs a register name. The only exception is a newline
902 (**'\\n'**); it is a parse error for a newline to be used as a register name.
904 ## Extended Register Mode
906 Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited
907 amounts of registers, if extended register mode is enabled.
909 If extended register mode is enabled (**-x** or **--extended-register**
910 command-line arguments are given), then normal single character registers are
911 used *unless* the character immediately following a command that needs a
912 register name is a space (according to **isspace()**) and not a newline
915 In that case, the register name is found according to the regex
916 **\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if
917 the next non-space characters do not match that regex.
921 When dc(1) encounters an error or a signal that it has a non-default handler
922 for, it resets. This means that several things happen.
924 First, any macros that are executing are stopped and popped off the stack.
925 The behavior is not unlike that of exceptions in programming languages. Then
926 the execution point is set so that any code waiting to execute (after all
927 macros returned) is skipped.
929 Thus, when dc(1) resets, it skips any remaining code waiting to be executed.
930 Then, if it is interactive mode, and the error was not a fatal error (see the
931 **EXIT STATUS** section), it asks for more input; otherwise, it exits with the
932 appropriate return code.
936 Most dc(1) implementations use **char** types to calculate the value of **1**
937 decimal digit at a time, but that can be slow. This dc(1) does something
940 It uses large integers to calculate more than **1** decimal digit at a time. If
941 built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is
942 **64**, then each integer has **9** decimal digits. If built in an environment
943 where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
944 value (the number of decimal digits per large integer) is called
947 In addition, this dc(1) uses an even larger integer for overflow checking. This
948 integer type depends on the value of **DC_LONG_BIT**, but is always at least
949 twice as large as the integer type used to store digits.
953 The following are the limits on dc(1):
957 : The number of bits in the **long** type in the environment where dc(1) was
958 built. This determines how many decimal digits can be stored in a single
959 large integer (see the **PERFORMANCE** section).
963 : The number of decimal digits per large integer (see the **PERFORMANCE**
964 section). Depends on **DC_LONG_BIT**.
968 : The max decimal number that each large integer can store (see
969 **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**.
973 : The max number that the overflow type (see the **PERFORMANCE** section) can
974 hold. Depends on **DC_LONG_BIT**.
978 : The maximum output base. Set at **DC_BASE_POW**.
982 : The maximum size of arrays. Set at **SIZE_MAX-1**.
986 : The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**.
990 : The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**.
994 : The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**.
998 : The maximum length of a number (in decimal digits), which includes digits
999 after the decimal point. Set at **DC_OVERFLOW_MAX-1**.
1003 : The maximum integer (inclusive) returned by the **'** command, if dc(1). Set
1004 at **2\^DC_LONG_BIT-1**.
1008 : The maximum allowable exponent (positive or negative). Set at
1009 **DC_OVERFLOW_MAX**.
1013 : The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
1015 These limits are meant to be effectively non-existent; the limits are so large
1016 (at least on 64-bit machines) that there should not be any point at which they
1017 become a problem. In fact, memory should be exhausted before these limits should
1020 # ENVIRONMENT VARIABLES
1022 dc(1) recognizes the following environment variables:
1026 : This is another way to give command-line arguments to dc(1). They should be
1027 in the same format as all other command-line arguments. These are always
1028 processed first, so any files given in **DC_ENV_ARGS** will be processed
1029 before arguments and files given on the command-line. This gives the user
1030 the ability to set up "standard" options and files to be used at every
1031 invocation. The most useful thing for such files to contain would be useful
1032 functions that the user might want every time dc(1) runs. Another use would
1033 be to use the **-e** option to set **scale** to a value other than **0**.
1035 The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments,
1036 but it does not understand escape sequences. For example, the string
1037 **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string
1038 **"/home/gavin/some \"dc\" file.dc"** will include the backslashes.
1040 The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
1041 if you have a file with any number of single quotes in the name, you can use
1042 double quotes as the outside quotes, as in **"some 'dc' file.dc"**, and vice
1043 versa if you have a file with double quotes. However, handling a file with
1044 both kinds of quotes in **DC_ENV_ARGS** is not supported due to the
1045 complexity of the parsing, though such files are still supported on the
1046 command-line where the parsing is done by the shell.
1050 : If this environment variable exists and contains an integer that is greater
1051 than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output
1052 lines to that length, including the backslash newline combo. The default
1053 line length is **70**.
1057 : If this variable exists (no matter the contents), dc(1) will exit
1058 immediately after executing expressions and files given by the **-e** and/or
1059 **-f** command-line options (and any equivalents).
1063 dc(1) returns the following exit statuses:
1071 : A math error occurred. This follows standard practice of using **1** for
1072 expected errors, since math errors will happen in the process of normal
1075 Math errors include divide by **0**, taking the square root of a negative
1076 number, using a negative number as a bound for the pseudo-random number
1077 generator, attempting to convert a negative number to a hardware integer,
1078 overflow when converting a number to a hardware integer, and attempting to
1079 use a non-integer where an integer is required.
1081 Converting to a hardware integer happens for the second operand of the power
1082 (**\^**), places (**\@**), left shift (**H**), and right shift (**h**)
1087 : A parse error occurred.
1089 Parse errors include unexpected **EOF**, using an invalid character, failing
1090 to find the end of a string or comment, and using a token where it is
1095 : A runtime error occurred.
1097 Runtime errors include assigning an invalid number to **ibase**, **obase**,
1098 or **scale**; give a bad expression to a **read()** call, calling **read()**
1099 inside of a **read()** call, type errors, and attempting an operation when
1100 the stack has too few elements.
1104 : A fatal error occurred.
1106 Fatal errors include memory allocation errors, I/O errors, failing to open
1107 files, attempting to use files that do not have only ASCII characters (dc(1)
1108 only accepts ASCII characters), attempting to open a directory as a file,
1109 and giving invalid command-line options.
1111 The exit status **4** is special; when a fatal error occurs, dc(1) always exits
1112 and returns **4**, no matter what mode dc(1) is in.
1114 The other statuses will only be returned when dc(1) is not in interactive mode
1115 (see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the
1116 **RESET** section) and accepts more input when one of those errors occurs in
1117 interactive mode. This is also the case when interactive mode is forced by the
1118 **-i** flag or **--interactive** option.
1120 These exit statuses allow dc(1) to be used in shell scripting with error
1121 checking, and its normal behavior can be forced by using the **-i** flag or
1122 **--interactive** option.
1126 Like bc(1), dc(1) has an interactive mode and a non-interactive mode.
1127 Interactive mode is turned on automatically when both **stdin** and **stdout**
1128 are hooked to a terminal, but the **-i** flag and **--interactive** option can
1129 turn it on in other cases.
1131 In interactive mode, dc(1) attempts to recover from errors (see the **RESET**
1132 section), and in normal execution, flushes **stdout** as soon as execution is
1133 done for the current input.
1137 If **stdin**, **stdout**, and **stderr** are all connected to a TTY, dc(1) turns
1140 TTY mode is different from interactive mode because interactive mode is required
1141 in the [bc(1) specification][1], and interactive mode requires only **stdin**
1142 and **stdout** to be connected to a terminal.
1146 Sending a **SIGINT** will cause dc(1) to stop execution of the current input. If
1147 dc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
1148 **RESET** section). Otherwise, it will clean up and exit.
1150 Note that "current input" can mean one of two things. If dc(1) is processing
1151 input from **stdin** in TTY mode, it will ask for more input. If dc(1) is
1152 processing input from a file in TTY mode, it will stop processing the file and
1153 start processing the next file, if one exists, or ask for input from **stdin**
1154 if no other file exists.
1156 This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it
1157 can seem as though dc(1) did not respond to the signal since it will immediately
1158 start executing the next file. This is by design; most files that users execute
1159 when interacting with dc(1) have function definitions, which are quick to parse.
1160 If a file takes a long time to execute, there may be a bug in that file. The
1161 rest of the files could still be executed without problem, allowing the user to
1164 **SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the
1165 default handler for all other signals.
1169 This dc(1) ships with support for adding error messages for different locales
1170 and thus, supports **LC_MESSAGS**.
1178 The dc(1) utility operators are compliant with the operators in the bc(1)
1179 [IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1] specification.
1183 None are known. Report bugs at https://git.yzena.com/gavin/bc.
1187 Gavin D. Howard <gavin@yzena.com> and contributors.
1189 [1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html