3 SPDX-License-Identifier: BSD-2-Clause
5 Copyright (c) 2018-2021 Gavin D. Howard and contributors.
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33 dc - arbitrary-precision decimal reverse-Polish notation calculator
37 **dc** [**-hiPvVx**] [**--version**] [**--help**] [**--interactive**] [**--no-prompt**] [**--extended-register**] [**-e** *expr*] [**--expression**=*expr*...] [**-f** *file*...] [**-file**=*file*...] [*file*...]
41 dc(1) is an arbitrary-precision calculator. It uses a stack (reverse Polish
42 notation) to store numbers and results of computations. Arithmetic operations
43 pop arguments off of the stack and push the results.
45 If no files are given on the command-line as extra arguments (i.e., not as
46 **-f** or **--file** arguments), then dc(1) reads from **stdin**. Otherwise,
47 those files are processed, and dc(1) will then exit.
49 This is different from the dc(1) on OpenBSD and possibly other dc(1)
50 implementations, where **-e** (**--expression**) and **-f** (**--file**)
51 arguments cause dc(1) to execute them and exit. The reason for this is that this
52 dc(1) allows users to set arguments in the environment variable **DC_ENV_ARGS**
53 (see the **ENVIRONMENT VARIABLES** section). Any expressions given on the
54 command-line should be used to set up a standard environment. For example, if a
55 user wants the **scale** always set to **10**, they can set **DC_ENV_ARGS** to
56 **-e 10k**, and this dc(1) will always start with a **scale** of **10**.
58 If users want to have dc(1) exit after processing all input from **-e** and
59 **-f** arguments (and their equivalents), then they can just simply add **-e q**
60 as the last command-line argument or define the environment variable
65 The following are the options that dc(1) accepts.
69 : Prints a usage message and quits.
71 **-v**, **-V**, **--version**
73 : Print the version information (copyright header) and exit.
75 **-i**, **--interactive**
77 : Forces interactive mode. (See the **INTERACTIVE MODE** section.)
79 This is a **non-portable extension**.
81 **-P**, **--no-prompt**
83 : Disables the prompt in TTY mode. (The prompt is only enabled in TTY mode.
84 See the **TTY MODE** section) This is mostly for those users that do not
85 want a prompt or are not used to having them in dc(1). Most of those users
86 would want to put this option in **DC_ENV_ARGS**.
88 This is a **non-portable extension**.
90 **-x** **--extended-register**
92 : Enables extended register mode. See the *Extended Register Mode* subsection
93 of the **REGISTERS** section for more information.
95 This is a **non-portable extension**.
97 **-e** *expr*, **--expression**=*expr*
99 : Evaluates *expr*. If multiple expressions are given, they are evaluated in
100 order. If files are given as well (see below), the expressions and files are
101 evaluated in the order given. This means that if a file is given before an
102 expression, the file is read in and evaluated first.
104 After processing all expressions and files, dc(1) will exit, unless **-**
105 (**stdin**) was given as an argument at least once to **-f** or **--file**.
107 This is a **non-portable extension**.
109 **-f** *file*, **--file**=*file*
111 : Reads in *file* and evaluates it, line by line, as though it were read
112 through **stdin**. If expressions are also given (see above), the
113 expressions are evaluated in the order given.
115 After processing all expressions and files, dc(1) will exit, unless **-**
116 (**stdin**) was given as an argument at least once to **-f** or **--file**.
117 However, if any other **-e**, **--expression**, **-f**, or **--file**
118 arguments are given after that, bc(1) will give a fatal error and exit.
120 This is a **non-portable extension**.
122 All long options are **non-portable extensions**.
126 Any non-error output is written to **stdout**.
128 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
129 error (see the **EXIT STATUS** section) if it cannot write to **stdout**, so if
130 **stdout** is closed, as in **dc <file> >&-**, it will quit with an error. This
131 is done so that dc(1) can report problems when **stdout** is redirected to a
134 If there are scripts that depend on the behavior of other dc(1) implementations,
135 it is recommended that those scripts be changed to redirect **stdout** to
140 Any error output is written to **stderr**.
142 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
143 error (see the **EXIT STATUS** section) if it cannot write to **stderr**, so if
144 **stderr** is closed, as in **dc <file> 2>&-**, it will quit with an error. This
145 is done so that dc(1) can exit with an error code when **stderr** is redirected
148 If there are scripts that depend on the behavior of other dc(1) implementations,
149 it is recommended that those scripts be changed to redirect **stderr** to
154 Each item in the input source code, either a number (see the **NUMBERS**
155 section) or a command (see the **COMMANDS** section), is processed and executed,
156 in order. Input is processed immediately when entered.
158 **ibase** is a register (see the **REGISTERS** section) that determines how to
159 interpret constant numbers. It is the "input" base, or the number base used for
160 interpreting input numbers. **ibase** is initially **10**. The max allowable
161 value for **ibase** is **16**. The min allowable value for **ibase** is **2**.
162 The max allowable value for **ibase** can be queried in dc(1) programs with the
165 **obase** is a register (see the **REGISTERS** section) that determines how to
166 output results. It is the "output" base, or the number base used for outputting
167 numbers. **obase** is initially **10**. The max allowable value for **obase** is
168 **DC_BASE_MAX** and can be queried with the **U** command. The min allowable
169 value for **obase** is **0**. If **obase** is **0**, values are output in
170 scientific notation, and if **obase** is **1**, values are output in engineering
171 notation. Otherwise, values are output in the specified base.
173 Outputting in scientific and engineering notations are **non-portable
176 The *scale* of an expression is the number of digits in the result of the
177 expression right of the decimal point, and **scale** is a register (see the
178 **REGISTERS** section) that sets the precision of any operations (with
179 exceptions). **scale** is initially **0**. **scale** cannot be negative. The max
180 allowable value for **scale** can be queried in dc(1) programs with the **V**
183 **seed** is a register containing the current seed for the pseudo-random number
184 generator. If the current value of **seed** is queried and stored, then if it is
185 assigned to **seed** later, the pseudo-random number generator is guaranteed to
186 produce the same sequence of pseudo-random numbers that were generated after the
187 value of **seed** was first queried.
189 Multiple values assigned to **seed** can produce the same sequence of
190 pseudo-random numbers. Likewise, when a value is assigned to **seed**, it is not
191 guaranteed that querying **seed** immediately after will return the same value.
192 In addition, the value of **seed** will change after any call to the **'**
193 command or the **"** command that does not get receive a value of **0** or
194 **1**. The maximum integer returned by the **'** command can be queried with the
197 **Note**: The values returned by the pseudo-random number generator with the
198 **'** and **"** commands are guaranteed to **NOT** be cryptographically secure.
199 This is a consequence of using a seeded pseudo-random number generator. However,
200 they *are* guaranteed to be reproducible with identical **seed** values. This
201 means that the pseudo-random values from bc(1) should only be used where a
202 reproducible stream of pseudo-random numbers is *ESSENTIAL*. In any other case,
203 use a non-seeded pseudo-random number generator.
205 The pseudo-random number generator, **seed**, and all associated operations are
206 **non-portable extensions**.
210 Comments go from **#** until, and not including, the next newline. This is a
211 **non-portable extension**.
215 Numbers are strings made up of digits, uppercase letters up to **F**, and at
216 most **1** period for a radix. Numbers can have up to **DC_NUM_MAX** digits.
217 Uppercase letters are equal to **9** + their position in the alphabet (i.e.,
218 **A** equals **10**, or **9+1**). If a digit or letter makes no sense with the
219 current value of **ibase**, they are set to the value of the highest valid digit
222 Single-character numbers (i.e., **A** alone) take the value that they would have
223 if they were valid digits, regardless of the value of **ibase**. This means that
224 **A** alone always equals decimal **10** and **F** alone always equals decimal
227 In addition, dc(1) accepts numbers in scientific notation. These have the form
228 **\<number\>e\<integer\>**. The exponent (the portion after the **e**) must be
229 an integer. An example is **1.89237e9**, which is equal to **1892370000**.
230 Negative exponents are also allowed, so **4.2890e_3** is equal to **0.0042890**.
232 **WARNING**: Both the number and the exponent in scientific notation are
233 interpreted according to the current **ibase**, but the number is still
234 multiplied by **10\^exponent** regardless of the current **ibase**. For example,
235 if **ibase** is **16** and dc(1) is given the number string **FFeA**, the
236 resulting decimal number will be **2550000000000**, and if dc(1) is given the
237 number string **10e_4**, the resulting decimal number will be **0.0016**.
239 Accepting input as scientific notation is a **non-portable extension**.
243 The valid commands are listed below.
247 These commands are used for printing.
249 Note that both scientific notation and engineering notation are available for
250 printing numbers. Scientific notation is activated by assigning **0** to
251 **obase** using **0o**, and engineering notation is activated by assigning **1**
252 to **obase** using **1o**. To deactivate them, just assign a different value to
255 Printing numbers in scientific notation and/or engineering notation is a
256 **non-portable extension**.
260 : Prints the value on top of the stack, whether number or string, and prints a
263 This does not alter the stack.
267 : Prints the value on top of the stack, whether number or string, and pops it
272 : Pops a value off the stack.
274 If the value is a number, it is truncated and the absolute value of the
275 result is printed as though **obase** is **UCHAR_MAX+1** and each digit is
276 interpreted as an ASCII character, making it a byte stream.
278 If the value is a string, it is printed without a trailing newline.
280 This is a **non-portable extension**.
284 : Prints the entire contents of the stack, in order from newest to oldest,
285 without altering anything.
287 Users should use this command when they get lost.
291 These are the commands used for arithmetic.
295 : The top two values are popped off the stack, added, and the result is pushed
296 onto the stack. The *scale* of the result is equal to the max *scale* of
301 : The top two values are popped off the stack, subtracted, and the result is
302 pushed onto the stack. The *scale* of the result is equal to the max
303 *scale* of both operands.
307 : The top two values are popped off the stack, multiplied, and the result is
308 pushed onto the stack. If **a** is the *scale* of the first expression and
309 **b** is the *scale* of the second expression, the *scale* of the result
310 is equal to **min(a+b,max(scale,a,b))** where **min()** and **max()** return
315 : The top two values are popped off the stack, divided, and the result is
316 pushed onto the stack. The *scale* of the result is equal to **scale**.
318 The first value popped off of the stack must be non-zero.
322 : The top two values are popped off the stack, remaindered, and the result is
323 pushed onto the stack.
325 Remaindering is equivalent to 1) Computing **a/b** to current **scale**, and
326 2) Using the result of step 1 to calculate **a-(a/b)\*b** to *scale*
327 **max(scale+scale(b),scale(a))**.
329 The first value popped off of the stack must be non-zero.
333 : The top two values are popped off the stack, divided and remaindered, and
334 the results (divided first, remainder second) are pushed onto the stack.
335 This is equivalent to **x y / x y %** except that **x** and **y** are only
338 The first value popped off of the stack must be non-zero.
340 This is a **non-portable extension**.
344 : The top two values are popped off the stack, the second is raised to the
345 power of the first, and the result is pushed onto the stack. The *scale* of
346 the result is equal to **scale**.
348 The first value popped off of the stack must be an integer, and if that
349 value is negative, the second value popped off of the stack must be
354 : The top value is popped off the stack, its square root is computed, and the
355 result is pushed onto the stack. The *scale* of the result is equal to
358 The value popped off of the stack must be non-negative.
362 : If this command *immediately* precedes a number (i.e., no spaces or other
363 commands), then that number is input as a negative number.
365 Otherwise, the top value on the stack is popped and copied, and the copy is
366 negated and pushed onto the stack. This behavior without a number is a
367 **non-portable extension**.
371 : The top value is popped off the stack, and if it is zero, it is pushed back
372 onto the stack. Otherwise, its absolute value is pushed onto the stack.
374 This is a **non-portable extension**.
378 : The top three values are popped off the stack, a modular exponentiation is
379 computed, and the result is pushed onto the stack.
381 The first value popped is used as the reduction modulus and must be an
382 integer and non-zero. The second value popped is used as the exponent and
383 must be an integer and non-negative. The third value popped is the base and
386 This is a **non-portable extension**.
390 : The top value is popped off the stack and copied, and the copy is truncated
391 and pushed onto the stack.
393 This is a **non-portable extension**.
397 : The top two values are popped off the stack, and the precision of the second
398 is set to the value of the first, whether by truncation or extension.
400 The first value popped off of the stack must be an integer and non-negative.
402 This is a **non-portable extension**.
406 : The top two values are popped off the stack, and the second is shifted left
407 (radix shifted right) to the value of the first.
409 The first value popped off of the stack must be an integer and non-negative.
411 This is a **non-portable extension**.
415 : The top two values are popped off the stack, and the second is shifted right
416 (radix shifted left) to the value of the first.
418 The first value popped off of the stack must be an integer and non-negative.
420 This is a **non-portable extension**.
424 : The top two values are popped off of the stack, they are compared, and a
425 **1** is pushed if they are equal, or **0** otherwise.
427 This is a **non-portable extension**.
431 : The top value is popped off of the stack, and if it a **0**, a **1** is
432 pushed; otherwise, a **0** is pushed.
434 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 the first is less than the second, or **0** otherwise.
441 This is a **non-portable extension**.
445 : The top two values are popped off of the stack, they are compared, and a
446 **1** is pushed if the first is less than or equal to the second, or **0**
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 greater 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 greater than or equal to the second, or
464 This is a **non-portable extension**.
468 : The top two values are popped off of the stack. If they are both non-zero, a
469 **1** is pushed onto the stack. If either of them is zero, or both of them
470 are, then a **0** is pushed onto the stack.
472 This is like the **&&** operator in bc(1), and it is *not* a short-circuit
475 This is a **non-portable extension**.
479 : The top two values are popped off of the stack. If at least one of them is
480 non-zero, a **1** is pushed onto the stack. If both of them are zero, then a
481 **0** is pushed onto the stack.
483 This is like the **||** operator in bc(1), and it is *not* a short-circuit
486 This is a **non-portable extension**.
488 ## Pseudo-Random Number Generator
490 dc(1) has a built-in pseudo-random number generator. These commands query the
491 pseudo-random number generator. (See Parameters for more information about the
492 **seed** value that controls the pseudo-random number generator.)
494 The pseudo-random number generator is guaranteed to **NOT** be
495 cryptographically secure.
499 : Generates an integer between 0 and **DC_RAND_MAX**, inclusive (see the
502 The generated integer is made as unbiased as possible, subject to the
503 limitations of the pseudo-random number generator.
505 This is a **non-portable extension**.
509 : Pops a value off of the stack, which is used as an **exclusive** upper bound
510 on the integer that will be generated. If the bound is negative or is a
511 non-integer, an error is raised, and dc(1) resets (see the **RESET**
512 section) while **seed** remains unchanged. If the bound is larger than
513 **DC_RAND_MAX**, the higher bound is honored by generating several
514 pseudo-random integers, multiplying them by appropriate powers of
515 **DC_RAND_MAX+1**, and adding them together. Thus, the size of integer that
516 can be generated with this command is unbounded. Using this command will
517 change the value of **seed**, unless the operand is **0** or **1**. In that
518 case, **0** is pushed onto the stack, and **seed** is *not* changed.
520 The generated integer is made as unbiased as possible, subject to the
521 limitations of the pseudo-random number generator.
523 This is a **non-portable extension**.
527 These commands control the stack.
531 : Removes all items from ("clears") the stack.
535 : Copies the item on top of the stack ("duplicates") and pushes the copy onto
540 : Swaps ("reverses") the two top items on the stack.
544 : Pops ("removes") the top value from the stack.
548 These commands control registers (see the **REGISTERS** section).
552 : Pops the value off the top of the stack and stores it into register *r*.
556 : Copies the value in register *r* and pushes it onto the stack. This does not
557 alter the contents of *r*.
561 : Pops the value off the top of the (main) stack and pushes it onto the stack
562 of register *r*. The previous value of the register becomes inaccessible.
566 : Pops the value off the top of the stack for register *r* and push it onto
567 the main stack. The previous value in the stack for register *r*, if any, is
568 now accessible via the **l***r* command.
572 These commands control the values of **ibase**, **obase**, **scale**, and
573 **seed**. Also see the **SYNTAX** section.
577 : Pops the value off of the top of the stack and uses it to set **ibase**,
578 which must be between **2** and **16**, inclusive.
580 If the value on top of the stack has any *scale*, the *scale* is ignored.
584 : Pops the value off of the top of the stack and uses it to set **obase**,
585 which must be between **0** and **DC_BASE_MAX**, inclusive (see the
586 **LIMITS** section and the **NUMBERS** section).
588 If the value on top of the stack has any *scale*, the *scale* is ignored.
592 : Pops the value off of the top of the stack and uses it to set **scale**,
593 which must be non-negative.
595 If the value on top of the stack has any *scale*, the *scale* is ignored.
599 : Pops the value off of the top of the stack and uses it to set **seed**. The
600 meaning of **seed** is dependent on the current pseudo-random number
601 generator but is guaranteed to not change except for new major versions.
603 The *scale* and sign of the value may be significant.
605 If a previously used **seed** value is used again, the pseudo-random number
606 generator is guaranteed to produce the same sequence of pseudo-random
607 numbers as it did when the **seed** value was previously used.
609 The exact value assigned to **seed** is not guaranteed to be returned if the
610 **J** command is used. However, if **seed** *does* return a different value,
611 both values, when assigned to **seed**, are guaranteed to produce the same
612 sequence of pseudo-random numbers. This means that certain values assigned
613 to **seed** will not produce unique sequences of pseudo-random numbers.
615 There is no limit to the length (number of significant decimal digits) or
616 *scale* of the value that can be assigned to **seed**.
618 This is a **non-portable extension**.
622 : Pushes the current value of **ibase** onto the main stack.
626 : Pushes the current value of **obase** onto the main stack.
630 : Pushes the current value of **scale** onto the main stack.
634 : Pushes the current value of **seed** onto the main stack.
636 This is a **non-portable extension**.
640 : Pushes the maximum allowable value of **ibase** onto the main stack.
642 This is a **non-portable extension**.
646 : Pushes the maximum allowable value of **obase** onto the main stack.
648 This is a **non-portable extension**.
652 : Pushes the maximum allowable value of **scale** onto the main stack.
654 This is a **non-portable extension**.
658 : Pushes the maximum (inclusive) integer that can be generated with the **'**
659 pseudo-random number generator command.
661 This is a **non-portable extension**.
665 The following commands control strings.
667 dc(1) can work with both numbers and strings, and registers (see the
668 **REGISTERS** section) can hold both strings and numbers. dc(1) always knows
669 whether the contents of a register are a string or a number.
671 While arithmetic operations have to have numbers, and will print an error if
672 given a string, other commands accept strings.
674 Strings can also be executed as macros. For example, if the string **[1pR]** is
675 executed as a macro, then the code **1pR** is executed, meaning that the **1**
676 will be printed with a newline after and then popped from the stack.
678 **\[**_characters_**\]**
680 : Makes a string containing *characters* and pushes it onto the stack.
682 If there are brackets (**\[** and **\]**) in the string, then they must be
683 balanced. Unbalanced brackets can be escaped using a backslash (**\\**)
686 If there is a backslash character in the string, the character after it
687 (even another backslash) is put into the string verbatim, but the (first)
692 : The value on top of the stack is popped.
694 If it is a number, it is truncated and its absolute value is taken. The
695 result mod **UCHAR_MAX+1** is calculated. If that result is **0**, push an
696 empty string; otherwise, push a one-character string where the character is
697 the result of the mod interpreted as an ASCII character.
699 If it is a string, then a new string is made. If the original string is
700 empty, the new string is empty. If it is not, then the first character of
701 the original string is used to create the new string as a one-character
702 string. The new string is then pushed onto the stack.
704 This is a **non-portable extension**.
708 : Pops a value off of the top of the stack.
710 If it is a number, it is pushed back onto the stack.
712 If it is a string, it is executed as a macro.
714 This behavior is the norm whenever a macro is executed, whether by this
715 command or by the conditional execution commands below.
719 : Pops two values off of the stack that must be numbers and compares them. If
720 the first value is greater than the second, then the contents of register
723 For example, **0 1>a** will execute the contents of register **a**, and
726 If either or both of the values are not numbers, dc(1) will raise an error
727 and reset (see the **RESET** section).
731 : Like the above, but will execute register *s* if the comparison fails.
733 If either or both of the values are not numbers, dc(1) will raise an error
734 and reset (see the **RESET** section).
736 This is a **non-portable extension**.
740 : Pops two values off of the stack that must be numbers and compares them. If
741 the first value is not greater than the second (less than or equal to), then
742 the contents of register *r* are executed.
744 If either or both of the values are not numbers, dc(1) will raise an error
745 and reset (see the **RESET** section).
749 : Like the above, but will execute register *s* if the comparison fails.
751 If either or both of the values are not numbers, dc(1) will raise an error
752 and reset (see the **RESET** section).
754 This is a **non-portable extension**.
758 : Pops two values off of the stack that must be numbers and compares them. If
759 the first value is less than the second, then the contents of register *r*
762 If either or both of the values are not numbers, dc(1) will raise an error
763 and reset (see the **RESET** section).
767 : Like the above, but will execute register *s* if the comparison fails.
769 If either or both of the values are not numbers, dc(1) will raise an error
770 and reset (see the **RESET** section).
772 This is a **non-portable extension**.
776 : Pops two values off of the stack that must be numbers and compares them. If
777 the first value is not less than the second (greater than or equal to), then
778 the contents of register *r* are executed.
780 If either or both of the values are not numbers, dc(1) will raise an error
781 and reset (see the **RESET** section).
785 : Like the above, but will execute register *s* if the comparison fails.
787 If either or both of the values are not numbers, dc(1) will raise an error
788 and reset (see the **RESET** section).
790 This is a **non-portable extension**.
794 : Pops two values off of the stack that must be numbers and compares them. If
795 the first value is equal to the second, then the contents of register *r*
798 If either or both of the values are not numbers, dc(1) will raise an error
799 and reset (see the **RESET** section).
803 : Like the above, but will execute register *s* if the comparison fails.
805 If either or both of the values are not numbers, dc(1) will raise an error
806 and reset (see the **RESET** section).
808 This is a **non-portable extension**.
812 : Pops two values off of the stack that must be numbers and compares them. If
813 the first value is not equal to the second, then the contents of register
816 If either or both of the values are not numbers, dc(1) will raise an error
817 and reset (see the **RESET** section).
821 : Like the above, but will execute register *s* if the comparison fails.
823 If either or both of the values are not numbers, dc(1) will raise an error
824 and reset (see the **RESET** section).
826 This is a **non-portable extension**.
830 : Reads a line from the **stdin** and executes it. This is to allow macros to
831 request input from users.
835 : During execution of a macro, this exits the execution of that macro and the
836 execution of the macro that executed it. If there are no macros, or only one
837 macro executing, dc(1) exits.
841 : Pops a value from the stack which must be non-negative and is used the
842 number of macro executions to pop off of the execution stack. If the number
843 of levels to pop is greater than the number of executing macros, dc(1)
848 These commands query status of the stack or its top value.
852 : Pops a value off of the stack.
854 If it is a number, calculates the number of significant decimal digits it
855 has and pushes the result.
857 If it is a string, pushes the number of characters the string has.
861 : Pops a value off of the stack.
863 If it is a number, pushes the *scale* of the value onto the stack.
865 If it is a string, pushes **0**.
869 : Pushes the current stack depth (before execution of this command).
873 These commands manipulate arrays.
877 : Pops the top two values off of the stack. The second value will be stored in
878 the array *r* (see the **REGISTERS** section), indexed by the first value.
882 : Pops the value on top of the stack and uses it as an index into the array
883 *r*. The selected value is then pushed onto the stack.
887 Registers are names that can store strings, numbers, and arrays. (Number/string
888 registers do not interfere with array registers.)
890 Each register is also its own stack, so the current register value is the top of
891 the stack for the register. All registers, when first referenced, have one value
892 (**0**) in their stack.
894 In non-extended register mode, a register name is just the single character that
895 follows any command that needs a register name. The only exception is a newline
896 (**'\\n'**); it is a parse error for a newline to be used as a register name.
898 ## Extended Register Mode
900 Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited
901 amounts of registers, if extended register mode is enabled.
903 If extended register mode is enabled (**-x** or **--extended-register**
904 command-line arguments are given), then normal single character registers are
905 used *unless* the character immediately following a command that needs a
906 register name is a space (according to **isspace()**) and not a newline
909 In that case, the register name is found according to the regex
910 **\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if
911 the next non-space characters do not match that regex.
915 When dc(1) encounters an error or a signal that it has a non-default handler
916 for, it resets. This means that several things happen.
918 First, any macros that are executing are stopped and popped off the stack.
919 The behavior is not unlike that of exceptions in programming languages. Then
920 the execution point is set so that any code waiting to execute (after all
921 macros returned) is skipped.
923 Thus, when dc(1) resets, it skips any remaining code waiting to be executed.
924 Then, if it is interactive mode, and the error was not a fatal error (see the
925 **EXIT STATUS** section), it asks for more input; otherwise, it exits with the
926 appropriate return code.
930 Most dc(1) implementations use **char** types to calculate the value of **1**
931 decimal digit at a time, but that can be slow. This dc(1) does something
934 It uses large integers to calculate more than **1** decimal digit at a time. If
935 built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is
936 **64**, then each integer has **9** decimal digits. If built in an environment
937 where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
938 value (the number of decimal digits per large integer) is called
941 In addition, this dc(1) uses an even larger integer for overflow checking. This
942 integer type depends on the value of **DC_LONG_BIT**, but is always at least
943 twice as large as the integer type used to store digits.
947 The following are the limits on dc(1):
951 : The number of bits in the **long** type in the environment where dc(1) was
952 built. This determines how many decimal digits can be stored in a single
953 large integer (see the **PERFORMANCE** section).
957 : The number of decimal digits per large integer (see the **PERFORMANCE**
958 section). Depends on **DC_LONG_BIT**.
962 : The max decimal number that each large integer can store (see
963 **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**.
967 : The max number that the overflow type (see the **PERFORMANCE** section) can
968 hold. Depends on **DC_LONG_BIT**.
972 : The maximum output base. Set at **DC_BASE_POW**.
976 : The maximum size of arrays. Set at **SIZE_MAX-1**.
980 : The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**.
984 : The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**.
988 : The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**.
992 : The maximum length of a number (in decimal digits), which includes digits
993 after the decimal point. Set at **DC_OVERFLOW_MAX-1**.
997 : The maximum integer (inclusive) returned by the **'** command, if dc(1). Set
998 at **2\^DC_LONG_BIT-1**.
1002 : The maximum allowable exponent (positive or negative). Set at
1003 **DC_OVERFLOW_MAX**.
1007 : The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
1009 These limits are meant to be effectively non-existent; the limits are so large
1010 (at least on 64-bit machines) that there should not be any point at which they
1011 become a problem. In fact, memory should be exhausted before these limits should
1014 # ENVIRONMENT VARIABLES
1016 dc(1) recognizes the following environment variables:
1020 : This is another way to give command-line arguments to dc(1). They should be
1021 in the same format as all other command-line arguments. These are always
1022 processed first, so any files given in **DC_ENV_ARGS** will be processed
1023 before arguments and files given on the command-line. This gives the user
1024 the ability to set up "standard" options and files to be used at every
1025 invocation. The most useful thing for such files to contain would be useful
1026 functions that the user might want every time dc(1) runs. Another use would
1027 be to use the **-e** option to set **scale** to a value other than **0**.
1029 The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments,
1030 but it does not understand escape sequences. For example, the string
1031 **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string
1032 **"/home/gavin/some \"dc\" file.dc"** will include the backslashes.
1034 The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
1035 if you have a file with any number of single quotes in the name, you can use
1036 double quotes as the outside quotes, as in **"some 'bc' file.bc"**, and vice
1037 versa if you have a file with double quotes. However, handling a file with
1038 both kinds of quotes in **DC_ENV_ARGS** is not supported due to the
1039 complexity of the parsing, though such files are still supported on the
1040 command-line where the parsing is done by the shell.
1044 : If this environment variable exists and contains an integer that is greater
1045 than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output
1046 lines to that length, including the backslash newline combo. The default
1047 line length is **70**.
1051 : If this variable exists (no matter the contents), dc(1) will exit
1052 immediately after executing expressions and files given by the **-e** and/or
1053 **-f** command-line options (and any equivalents).
1057 dc(1) returns the following exit statuses:
1065 : A math error occurred. This follows standard practice of using **1** for
1066 expected errors, since math errors will happen in the process of normal
1069 Math errors include divide by **0**, taking the square root of a negative
1070 number, using a negative number as a bound for the pseudo-random number
1071 generator, attempting to convert a negative number to a hardware integer,
1072 overflow when converting a number to a hardware integer, and attempting to
1073 use a non-integer where an integer is required.
1075 Converting to a hardware integer happens for the second operand of the power
1076 (**\^**), places (**\@**), left shift (**H**), and right shift (**h**)
1081 : A parse error occurred.
1083 Parse errors include unexpected **EOF**, using an invalid character, failing
1084 to find the end of a string or comment, and using a token where it is
1089 : A runtime error occurred.
1091 Runtime errors include assigning an invalid number to **ibase**, **obase**,
1092 or **scale**; give a bad expression to a **read()** call, calling **read()**
1093 inside of a **read()** call, type errors, and attempting an operation when
1094 the stack has too few elements.
1098 : A fatal error occurred.
1100 Fatal errors include memory allocation errors, I/O errors, failing to open
1101 files, attempting to use files that do not have only ASCII characters (dc(1)
1102 only accepts ASCII characters), attempting to open a directory as a file,
1103 and giving invalid command-line options.
1105 The exit status **4** is special; when a fatal error occurs, dc(1) always exits
1106 and returns **4**, no matter what mode dc(1) is in.
1108 The other statuses will only be returned when dc(1) is not in interactive mode
1109 (see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the
1110 **RESET** section) and accepts more input when one of those errors occurs in
1111 interactive mode. This is also the case when interactive mode is forced by the
1112 **-i** flag or **--interactive** option.
1114 These exit statuses allow dc(1) to be used in shell scripting with error
1115 checking, and its normal behavior can be forced by using the **-i** flag or
1116 **--interactive** option.
1120 Like bc(1), dc(1) has an interactive mode and a non-interactive mode.
1121 Interactive mode is turned on automatically when both **stdin** and **stdout**
1122 are hooked to a terminal, but the **-i** flag and **--interactive** option can
1123 turn it on in other cases.
1125 In interactive mode, dc(1) attempts to recover from errors (see the **RESET**
1126 section), and in normal execution, flushes **stdout** as soon as execution is
1127 done for the current input.
1131 If **stdin**, **stdout**, and **stderr** are all connected to a TTY, dc(1) turns
1134 The prompt is enabled in TTY mode.
1136 TTY mode is different from interactive mode because interactive mode is required
1137 in the [bc(1) specification][1], and interactive mode requires only **stdin**
1138 and **stdout** to be connected to a terminal.
1142 Sending a **SIGINT** will cause dc(1) to stop execution of the current input. If
1143 dc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
1144 **RESET** section). Otherwise, it will clean up and exit.
1146 Note that "current input" can mean one of two things. If dc(1) is processing
1147 input from **stdin** in TTY mode, it will ask for more input. If dc(1) is
1148 processing input from a file in TTY mode, it will stop processing the file and
1149 start processing the next file, if one exists, or ask for input from **stdin**
1150 if no other file exists.
1152 This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it
1153 can seem as though dc(1) did not respond to the signal since it will immediately
1154 start executing the next file. This is by design; most files that users execute
1155 when interacting with dc(1) have function definitions, which are quick to parse.
1156 If a file takes a long time to execute, there may be a bug in that file. The
1157 rest of the files could still be executed without problem, allowing the user to
1160 **SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the
1161 default handler for all other signals.
1169 The dc(1) utility operators are compliant with the operators in the bc(1)
1170 [IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1] specification.
1174 None are known. Report bugs at https://git.yzena.com/gavin/bc.
1178 Gavin D. Howard <gavin@yzena.com> and contributors.
1180 [1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html