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** [**-hiPRvVx**] [**-\-version**] [**-\-help**] [**-\-interactive**] [**-\-no-prompt**] [**-\-no-read-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 **-R**, **-\-no-read-prompt**
89 : This option is a no-op.
91 This is a **non-portable extension**.
93 **-x** **-\-extended-register**
95 : Enables extended register mode. See the *Extended Register Mode* subsection
96 of the **REGISTERS** section for more information.
98 This is a **non-portable extension**.
100 **-e** *expr*, **-\-expression**=*expr*
102 : Evaluates *expr*. If multiple expressions are given, they are evaluated in
103 order. If files are given as well (see below), the expressions and files are
104 evaluated in the order given. This means that if a file is given before an
105 expression, the file is read in and evaluated first.
107 If this option is given on the command-line (i.e., not in **DC_ENV_ARGS**,
108 see the **ENVIRONMENT VARIABLES** section), then after processing all
109 expressions and files, dc(1) will exit, unless **-** (**stdin**) was given
110 as an argument at least once to **-f** or **-\-file**, whether on the
111 command-line or in **DC_ENV_ARGS**. However, if any other **-e**,
112 **-\-expression**, **-f**, or **-\-file** arguments are given after **-f-**
113 or equivalent is given, dc(1) will give a fatal error and exit.
115 This is a **non-portable extension**.
117 **-f** *file*, **-\-file**=*file*
119 : Reads in *file* and evaluates it, line by line, as though it were read
120 through **stdin**. If expressions are also given (see above), the
121 expressions are evaluated in the order given.
123 If this option is given on the command-line (i.e., not in **DC_ENV_ARGS**,
124 see the **ENVIRONMENT VARIABLES** section), then after processing all
125 expressions and files, dc(1) will exit, unless **-** (**stdin**) was given
126 as an argument at least once to **-f** or **-\-file**. However, if any other
127 **-e**, **-\-expression**, **-f**, or **-\-file** arguments are given after
128 **-f-** or equivalent is given, dc(1) will give a fatal error and exit.
130 This is a **non-portable extension**.
132 All long options are **non-portable extensions**.
136 Any non-error output is written to **stdout**. In addition, if history (see the
137 **HISTORY** section) and the prompt (see the **TTY MODE** section) are enabled,
138 both are output to **stdout**.
140 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
141 error (see the **EXIT STATUS** section) if it cannot write to **stdout**, so if
142 **stdout** is closed, as in **dc <file> >&-**, it will quit with an error. This
143 is done so that dc(1) can report problems when **stdout** is redirected to a
146 If there are scripts that depend on the behavior of other dc(1) implementations,
147 it is recommended that those scripts be changed to redirect **stdout** to
152 Any error output is written to **stderr**.
154 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
155 error (see the **EXIT STATUS** section) if it cannot write to **stderr**, so if
156 **stderr** is closed, as in **dc <file> 2>&-**, it will quit with an error. This
157 is done so that dc(1) can exit with an error code when **stderr** is redirected
160 If there are scripts that depend on the behavior of other dc(1) implementations,
161 it is recommended that those scripts be changed to redirect **stderr** to
166 Each item in the input source code, either a number (see the **NUMBERS**
167 section) or a command (see the **COMMANDS** section), is processed and executed,
168 in order. Input is processed immediately when entered.
170 **ibase** is a register (see the **REGISTERS** section) that determines how to
171 interpret constant numbers. It is the "input" base, or the number base used for
172 interpreting input numbers. **ibase** is initially **10**. The max allowable
173 value for **ibase** is **16**. The min allowable value for **ibase** is **2**.
174 The max allowable value for **ibase** can be queried in dc(1) programs with the
177 **obase** is a register (see the **REGISTERS** section) that determines how to
178 output results. It is the "output" base, or the number base used for outputting
179 numbers. **obase** is initially **10**. The max allowable value for **obase** is
180 **DC_BASE_MAX** and can be queried with the **U** command. The min allowable
181 value for **obase** is **0**. If **obase** is **0**, values are output in
182 scientific notation, and if **obase** is **1**, values are output in engineering
183 notation. Otherwise, values are output in the specified base.
185 Outputting in scientific and engineering notations are **non-portable
188 The *scale* of an expression is the number of digits in the result of the
189 expression right of the decimal point, and **scale** is a register (see the
190 **REGISTERS** section) that sets the precision of any operations (with
191 exceptions). **scale** is initially **0**. **scale** cannot be negative. The max
192 allowable value for **scale** can be queried in dc(1) programs with the **V**
195 **seed** is a register containing the current seed for the pseudo-random number
196 generator. If the current value of **seed** is queried and stored, then if it is
197 assigned to **seed** later, the pseudo-random number generator is guaranteed to
198 produce the same sequence of pseudo-random numbers that were generated after the
199 value of **seed** was first queried.
201 Multiple values assigned to **seed** can produce the same sequence of
202 pseudo-random numbers. Likewise, when a value is assigned to **seed**, it is not
203 guaranteed that querying **seed** immediately after will return the same value.
204 In addition, the value of **seed** will change after any call to the **'**
205 command or the **"** command that does not get receive a value of **0** or
206 **1**. The maximum integer returned by the **'** command can be queried with the
209 **Note**: The values returned by the pseudo-random number generator with the
210 **'** and **"** commands are guaranteed to **NOT** be cryptographically secure.
211 This is a consequence of using a seeded pseudo-random number generator. However,
212 they *are* guaranteed to be reproducible with identical **seed** values. This
213 means that the pseudo-random values from dc(1) should only be used where a
214 reproducible stream of pseudo-random numbers is *ESSENTIAL*. In any other case,
215 use a non-seeded pseudo-random number generator.
217 The pseudo-random number generator, **seed**, and all associated operations are
218 **non-portable extensions**.
222 Comments go from **#** until, and not including, the next newline. This is a
223 **non-portable extension**.
227 Numbers are strings made up of digits, uppercase letters up to **F**, and at
228 most **1** period for a radix. Numbers can have up to **DC_NUM_MAX** digits.
229 Uppercase letters are equal to **9** + their position in the alphabet (i.e.,
230 **A** equals **10**, or **9+1**). If a digit or letter makes no sense with the
231 current value of **ibase**, they are set to the value of the highest valid digit
234 Single-character numbers (i.e., **A** alone) take the value that they would have
235 if they were valid digits, regardless of the value of **ibase**. This means that
236 **A** alone always equals decimal **10** and **F** alone always equals decimal
239 In addition, dc(1) accepts numbers in scientific notation. These have the form
240 **\<number\>e\<integer\>**. The exponent (the portion after the **e**) must be
241 an integer. An example is **1.89237e9**, which is equal to **1892370000**.
242 Negative exponents are also allowed, so **4.2890e_3** is equal to **0.0042890**.
244 **WARNING**: Both the number and the exponent in scientific notation are
245 interpreted according to the current **ibase**, but the number is still
246 multiplied by **10\^exponent** regardless of the current **ibase**. For example,
247 if **ibase** is **16** and dc(1) is given the number string **FFeA**, the
248 resulting decimal number will be **2550000000000**, and if dc(1) is given the
249 number string **10e_4**, the resulting decimal number will be **0.0016**.
251 Accepting input as scientific notation is a **non-portable extension**.
255 The valid commands are listed below.
259 These commands are used for printing.
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**.
272 : Prints the value on top of the stack, whether number or string, and prints a
275 This does not alter the stack.
279 : Prints the value on top of the stack, whether number or string, and pops it
284 : Pops a value off the stack.
286 If the value is a number, it is truncated and the absolute value of the
287 result is printed as though **obase** is **UCHAR_MAX+1** and each digit is
288 interpreted as an ASCII character, making it a byte stream.
290 If the value is a string, it is printed without a trailing newline.
292 This is a **non-portable extension**.
296 : Prints the entire contents of the stack, in order from newest to oldest,
297 without altering anything.
299 Users should use this command when they get lost.
303 These are the commands used for arithmetic.
307 : The top two values are popped off the stack, added, and the result is pushed
308 onto the stack. The *scale* of the result is equal to the max *scale* of
313 : The top two values are popped off the stack, subtracted, and the result is
314 pushed onto the stack. The *scale* of the result is equal to the max
315 *scale* of both operands.
319 : The top two values are popped off the stack, multiplied, and the result is
320 pushed onto the stack. If **a** is the *scale* of the first expression and
321 **b** is the *scale* of the second expression, the *scale* of the result
322 is equal to **min(a+b,max(scale,a,b))** where **min()** and **max()** return
327 : The top two values are popped off the stack, divided, and the result is
328 pushed onto the stack. The *scale* of the result is equal to **scale**.
330 The first value popped off of the stack must be non-zero.
334 : The top two values are popped off the stack, remaindered, and the result is
335 pushed onto the stack.
337 Remaindering is equivalent to 1) Computing **a/b** to current **scale**, and
338 2) Using the result of step 1 to calculate **a-(a/b)\*b** to *scale*
339 **max(scale+scale(b),scale(a))**.
341 The first value popped off of the stack must be non-zero.
345 : The top two values are popped off the stack, divided and remaindered, and
346 the results (divided first, remainder second) are pushed onto the stack.
347 This is equivalent to **x y / x y %** except that **x** and **y** are only
350 The first value popped off of the stack must be non-zero.
352 This is a **non-portable extension**.
356 : The top two values are popped off the stack, the second is raised to the
357 power of the first, and the result is pushed onto the stack. The *scale* of
358 the result is equal to **scale**.
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**.
402 : The top value is popped off the stack and copied, and the copy is truncated
403 and pushed onto the stack.
405 This is a **non-portable extension**.
409 : The top two values are popped off the stack, and the precision of the second
410 is set to the value of the first, whether by truncation or extension.
412 The first value popped off of the stack must be an integer and non-negative.
414 This is a **non-portable extension**.
418 : The top two values are popped off the stack, and the second is shifted left
419 (radix shifted right) to the value of the first.
421 The first value popped off of the stack must be an integer and non-negative.
423 This is a **non-portable extension**.
427 : The top two values are popped off the stack, and the second is shifted right
428 (radix shifted left) to the value of the first.
430 The first value popped off of the stack must be an integer and non-negative.
432 This is a **non-portable extension**.
436 : The top two values are popped off of the stack, they are compared, and a
437 **1** is pushed if they are equal, or **0** otherwise.
439 This is a **non-portable extension**.
443 : The top value is popped off of the stack, and if it a **0**, a **1** is
444 pushed; otherwise, a **0** is pushed.
446 This is a **non-portable extension**.
450 : The top two values are popped off of the stack, they are compared, and a
451 **1** is pushed if the first is less than the second, or **0** otherwise.
453 This is a **non-portable extension**.
457 : The top two values are popped off of the stack, they are compared, and a
458 **1** is pushed if the first is less than or equal to the second, or **0**
461 This is a **non-portable extension**.
465 : The top two values are popped off of the stack, they are compared, and a
466 **1** is pushed if the first is greater than the second, or **0** otherwise.
468 This is a **non-portable extension**.
472 : The top two values are popped off of the stack, they are compared, and a
473 **1** is pushed if the first is greater than or equal to the second, or
476 This is a **non-portable extension**.
480 : The top two values are popped off of the stack. If they are both non-zero, a
481 **1** is pushed onto the stack. If either of them is zero, or both of them
482 are, then a **0** is pushed onto the stack.
484 This is like the **&&** operator in bc(1), and it is *not* a short-circuit
487 This is a **non-portable extension**.
491 : The top two values are popped off of the stack. If at least one of them is
492 non-zero, a **1** is pushed onto the stack. If both of them are zero, then a
493 **0** is pushed onto the stack.
495 This is like the **||** operator in bc(1), and it is *not* a short-circuit
498 This is a **non-portable extension**.
500 ## Pseudo-Random Number Generator
502 dc(1) has a built-in pseudo-random number generator. These commands query the
503 pseudo-random number generator. (See Parameters for more information about the
504 **seed** value that controls the pseudo-random number generator.)
506 The pseudo-random number generator is guaranteed to **NOT** be
507 cryptographically secure.
511 : Generates an integer between 0 and **DC_RAND_MAX**, inclusive (see the
514 The generated integer is made as unbiased as possible, subject to the
515 limitations of the pseudo-random number generator.
517 This is a **non-portable extension**.
521 : Pops a value off of the stack, which is used as an **exclusive** upper bound
522 on the integer that will be generated. If the bound is negative or is a
523 non-integer, an error is raised, and dc(1) resets (see the **RESET**
524 section) while **seed** remains unchanged. If the bound is larger than
525 **DC_RAND_MAX**, the higher bound is honored by generating several
526 pseudo-random integers, multiplying them by appropriate powers of
527 **DC_RAND_MAX+1**, and adding them together. Thus, the size of integer that
528 can be generated with this command is unbounded. Using this command will
529 change the value of **seed**, unless the operand is **0** or **1**. In that
530 case, **0** is pushed onto the stack, and **seed** is *not* changed.
532 The generated integer is made as unbiased as possible, subject to the
533 limitations of the pseudo-random number generator.
535 This is a **non-portable extension**.
539 These commands control the stack.
543 : Removes all items from ("clears") the stack.
547 : Copies the item on top of the stack ("duplicates") and pushes the copy onto
552 : Swaps ("reverses") the two top items on the stack.
556 : Pops ("removes") the top value from the stack.
560 These commands control registers (see the **REGISTERS** section).
564 : Pops the value off the top of the stack and stores it into register *r*.
568 : Copies the value in register *r* and pushes it onto the stack. This does not
569 alter the contents of *r*.
573 : Pops the value off the top of the (main) stack and pushes it onto the stack
574 of register *r*. The previous value of the register becomes inaccessible.
578 : Pops the value off the top of the stack for register *r* and push it onto
579 the main stack. The previous value in the stack for register *r*, if any, is
580 now accessible via the **l**_r_ command.
584 These commands control the values of **ibase**, **obase**, **scale**, and
585 **seed**. Also see the **SYNTAX** section.
589 : Pops the value off of the top of the stack and uses it to set **ibase**,
590 which must be between **2** and **16**, inclusive.
592 If the value on top of the stack has any *scale*, the *scale* is ignored.
596 : Pops the value off of the top of the stack and uses it to set **obase**,
597 which must be between **0** and **DC_BASE_MAX**, inclusive (see the
598 **LIMITS** section and the **NUMBERS** section).
600 If the value on top of the stack has any *scale*, the *scale* is ignored.
604 : Pops the value off of the top of the stack and uses it to set **scale**,
605 which must be non-negative.
607 If the value on top of the stack has any *scale*, the *scale* is ignored.
611 : Pops the value off of the top of the stack and uses it to set **seed**. The
612 meaning of **seed** is dependent on the current pseudo-random number
613 generator but is guaranteed to not change except for new major versions.
615 The *scale* and sign of the value may be significant.
617 If a previously used **seed** value is used again, the pseudo-random number
618 generator is guaranteed to produce the same sequence of pseudo-random
619 numbers as it did when the **seed** value was previously used.
621 The exact value assigned to **seed** is not guaranteed to be returned if the
622 **J** command is used. However, if **seed** *does* return a different value,
623 both values, when assigned to **seed**, are guaranteed to produce the same
624 sequence of pseudo-random numbers. This means that certain values assigned
625 to **seed** will not produce unique sequences of pseudo-random numbers.
627 There is no limit to the length (number of significant decimal digits) or
628 *scale* of the value that can be assigned to **seed**.
630 This is a **non-portable extension**.
634 : Pushes the current value of **ibase** onto the main stack.
638 : Pushes the current value of **obase** onto the main stack.
642 : Pushes the current value of **scale** onto the main stack.
646 : Pushes the current value of **seed** onto the main stack.
648 This is a **non-portable extension**.
652 : Pushes the maximum allowable value of **ibase** onto the main stack.
654 This is a **non-portable extension**.
658 : Pushes the maximum allowable value of **obase** onto the main stack.
660 This is a **non-portable extension**.
664 : Pushes the maximum allowable value of **scale** onto the main stack.
666 This is a **non-portable extension**.
670 : Pushes the maximum (inclusive) integer that can be generated with the **'**
671 pseudo-random number generator command.
673 This is a **non-portable extension**.
677 The following commands control strings.
679 dc(1) can work with both numbers and strings, and registers (see the
680 **REGISTERS** section) can hold both strings and numbers. dc(1) always knows
681 whether the contents of a register are a string or a number.
683 While arithmetic operations have to have numbers, and will print an error if
684 given a string, other commands accept strings.
686 Strings can also be executed as macros. For example, if the string **[1pR]** is
687 executed as a macro, then the code **1pR** is executed, meaning that the **1**
688 will be printed with a newline after and then popped from the stack.
690 **\[**_characters_**\]**
692 : Makes a string containing *characters* and pushes it onto the stack.
694 If there are brackets (**\[** and **\]**) in the string, then they must be
695 balanced. Unbalanced brackets can be escaped using a backslash (**\\**)
698 If there is a backslash character in the string, the character after it
699 (even another backslash) is put into the string verbatim, but the (first)
704 : The value on top of the stack is popped.
706 If it is a number, it is truncated and its absolute value is taken. The
707 result mod **UCHAR_MAX+1** is calculated. If that result is **0**, push an
708 empty string; otherwise, push a one-character string where the character is
709 the result of the mod interpreted as an ASCII character.
711 If it is a string, then a new string is made. If the original string is
712 empty, the new string is empty. If it is not, then the first character of
713 the original string is used to create the new string as a one-character
714 string. The new string is then pushed onto the stack.
716 This is a **non-portable extension**.
720 : Pops a value off of the top of the stack.
722 If it is a number, it is pushed back onto the stack.
724 If it is a string, it is executed as a macro.
726 This behavior is the norm whenever a macro is executed, whether by this
727 command or by the conditional execution commands below.
731 : Pops two values off of the stack that must be numbers and compares them. If
732 the first value is greater than the second, then the contents of register
735 For example, **0 1>a** will execute the contents of register **a**, and
738 If either or both of the values are not numbers, dc(1) will raise an error
739 and reset (see the **RESET** section).
743 : Like the above, but will execute register *s* if the comparison fails.
745 If either or both of the values are not numbers, dc(1) will raise an error
746 and reset (see the **RESET** section).
748 This is a **non-portable extension**.
752 : Pops two values off of the stack that must be numbers and compares them. If
753 the first value is not greater than the second (less than or equal to), then
754 the contents of register *r* are executed.
756 If either or both of the values are not numbers, dc(1) will raise an error
757 and reset (see the **RESET** section).
761 : Like the above, but will execute register *s* if the comparison fails.
763 If either or both of the values are not numbers, dc(1) will raise an error
764 and reset (see the **RESET** section).
766 This is a **non-portable extension**.
770 : Pops two values off of the stack that must be numbers and compares them. If
771 the first value is less than the second, then the contents of register *r*
774 If either or both of the values are not numbers, dc(1) will raise an error
775 and reset (see the **RESET** section).
779 : Like the above, but will execute register *s* if the comparison fails.
781 If either or both of the values are not numbers, dc(1) will raise an error
782 and reset (see the **RESET** section).
784 This is a **non-portable extension**.
788 : Pops two values off of the stack that must be numbers and compares them. If
789 the first value is not less than the second (greater than or equal to), then
790 the contents of register *r* are executed.
792 If either or both of the values are not numbers, dc(1) will raise an error
793 and reset (see the **RESET** section).
797 : Like the above, but will execute register *s* if the comparison fails.
799 If either or both of the values are not numbers, dc(1) will raise an error
800 and reset (see the **RESET** section).
802 This is a **non-portable extension**.
806 : Pops two values off of the stack that must be numbers and compares them. If
807 the first value is equal to the second, then the contents of register *r*
810 If either or both of the values are not numbers, dc(1) will raise an error
811 and reset (see the **RESET** section).
815 : Like the above, but will execute register *s* if the comparison fails.
817 If either or both of the values are not numbers, dc(1) will raise an error
818 and reset (see the **RESET** section).
820 This is a **non-portable extension**.
824 : Pops two values off of the stack that must be numbers and compares them. If
825 the first value is not equal to the second, then the contents of register
828 If either or both of the values are not numbers, dc(1) will raise an error
829 and reset (see the **RESET** section).
833 : Like the above, but will execute register *s* if the comparison fails.
835 If either or both of the values are not numbers, dc(1) will raise an error
836 and reset (see the **RESET** section).
838 This is a **non-portable extension**.
842 : Reads a line from the **stdin** and executes it. This is to allow macros to
843 request input from users.
847 : During execution of a macro, this exits the execution of that macro and the
848 execution of the macro that executed it. If there are no macros, or only one
849 macro executing, dc(1) exits.
853 : Pops a value from the stack which must be non-negative and is used the
854 number of macro executions to pop off of the execution stack. If the number
855 of levels to pop is greater than the number of executing macros, dc(1)
860 These commands query status of the stack or its top value.
864 : Pops a value off of the stack.
866 If it is a number, calculates the number of significant decimal digits it
867 has and pushes the result.
869 If it is a string, pushes the number of characters the string has.
873 : Pops a value off of the stack.
875 If it is a number, pushes the *scale* of the value onto the stack.
877 If it is a string, pushes **0**.
881 : Pushes the current stack depth (before execution of this command).
885 These commands manipulate arrays.
889 : Pops the top two values off of the stack. The second value will be stored in
890 the array *r* (see the **REGISTERS** section), indexed by the first value.
894 : Pops the value on top of the stack and uses it as an index into the array
895 *r*. The selected value is then pushed onto the stack.
899 Registers are names that can store strings, numbers, and arrays. (Number/string
900 registers do not interfere with array registers.)
902 Each register is also its own stack, so the current register value is the top of
903 the stack for the register. All registers, when first referenced, have one value
904 (**0**) in their stack.
906 In non-extended register mode, a register name is just the single character that
907 follows any command that needs a register name. The only exception is a newline
908 (**'\\n'**); it is a parse error for a newline to be used as a register name.
910 ## Extended Register Mode
912 Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited
913 amounts of registers, if extended register mode is enabled.
915 If extended register mode is enabled (**-x** or **-\-extended-register**
916 command-line arguments are given), then normal single character registers are
917 used *unless* the character immediately following a command that needs a
918 register name is a space (according to **isspace()**) and not a newline
921 In that case, the register name is found according to the regex
922 **\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if
923 the next non-space characters do not match that regex.
927 When dc(1) encounters an error or a signal that it has a non-default handler
928 for, it resets. This means that several things happen.
930 First, any macros that are executing are stopped and popped off the stack.
931 The behavior is not unlike that of exceptions in programming languages. Then
932 the execution point is set so that any code waiting to execute (after all
933 macros returned) is skipped.
935 Thus, when dc(1) resets, it skips any remaining code waiting to be executed.
936 Then, if it is interactive mode, and the error was not a fatal error (see the
937 **EXIT STATUS** section), it asks for more input; otherwise, it exits with the
938 appropriate return code.
942 Most dc(1) implementations use **char** types to calculate the value of **1**
943 decimal digit at a time, but that can be slow. This dc(1) does something
946 It uses large integers to calculate more than **1** decimal digit at a time. If
947 built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is
948 **64**, then each integer has **9** decimal digits. If built in an environment
949 where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
950 value (the number of decimal digits per large integer) is called
953 In addition, this dc(1) uses an even larger integer for overflow checking. This
954 integer type depends on the value of **DC_LONG_BIT**, but is always at least
955 twice as large as the integer type used to store digits.
959 The following are the limits on dc(1):
963 : The number of bits in the **long** type in the environment where dc(1) was
964 built. This determines how many decimal digits can be stored in a single
965 large integer (see the **PERFORMANCE** section).
969 : The number of decimal digits per large integer (see the **PERFORMANCE**
970 section). Depends on **DC_LONG_BIT**.
974 : The max decimal number that each large integer can store (see
975 **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**.
979 : The max number that the overflow type (see the **PERFORMANCE** section) can
980 hold. Depends on **DC_LONG_BIT**.
984 : The maximum output base. Set at **DC_BASE_POW**.
988 : The maximum size of arrays. Set at **SIZE_MAX-1**.
992 : The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**.
996 : The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**.
1000 : The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**.
1004 : The maximum length of a number (in decimal digits), which includes digits
1005 after the decimal point. Set at **DC_OVERFLOW_MAX-1**.
1009 : The maximum integer (inclusive) returned by the **'** command, if dc(1). Set
1010 at **2\^DC_LONG_BIT-1**.
1014 : The maximum allowable exponent (positive or negative). Set at
1015 **DC_OVERFLOW_MAX**.
1019 : The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
1021 These limits are meant to be effectively non-existent; the limits are so large
1022 (at least on 64-bit machines) that there should not be any point at which they
1023 become a problem. In fact, memory should be exhausted before these limits should
1026 # ENVIRONMENT VARIABLES
1028 dc(1) recognizes the following environment variables:
1032 : This is another way to give command-line arguments to dc(1). They should be
1033 in the same format as all other command-line arguments. These are always
1034 processed first, so any files given in **DC_ENV_ARGS** will be processed
1035 before arguments and files given on the command-line. This gives the user
1036 the ability to set up "standard" options and files to be used at every
1037 invocation. The most useful thing for such files to contain would be useful
1038 functions that the user might want every time dc(1) runs. Another use would
1039 be to use the **-e** option to set **scale** to a value other than **0**.
1041 The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments,
1042 but it does not understand escape sequences. For example, the string
1043 **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string
1044 **"/home/gavin/some \"dc\" file.dc"** will include the backslashes.
1046 The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
1047 if you have a file with any number of single quotes in the name, you can use
1048 double quotes as the outside quotes, as in **"some 'dc' file.dc"**, and vice
1049 versa if you have a file with double quotes. However, handling a file with
1050 both kinds of quotes in **DC_ENV_ARGS** is not supported due to the
1051 complexity of the parsing, though such files are still supported on the
1052 command-line where the parsing is done by the shell.
1056 : If this environment variable exists and contains an integer that is greater
1057 than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output
1058 lines to that length, including the backslash newline combo. The default
1059 line length is **70**.
1063 : If this variable exists (no matter the contents), dc(1) will exit
1064 immediately after executing expressions and files given by the **-e** and/or
1065 **-f** command-line options (and any equivalents).
1069 dc(1) returns the following exit statuses:
1077 : A math error occurred. This follows standard practice of using **1** for
1078 expected errors, since math errors will happen in the process of normal
1081 Math errors include divide by **0**, taking the square root of a negative
1082 number, using a negative number as a bound for the pseudo-random number
1083 generator, attempting to convert a negative number to a hardware integer,
1084 overflow when converting a number to a hardware integer, and attempting to
1085 use a non-integer where an integer is required.
1087 Converting to a hardware integer happens for the second operand of the power
1088 (**\^**), places (**\@**), left shift (**H**), and right shift (**h**)
1093 : A parse error occurred.
1095 Parse errors include unexpected **EOF**, using an invalid character, failing
1096 to find the end of a string or comment, and using a token where it is
1101 : A runtime error occurred.
1103 Runtime errors include assigning an invalid number to **ibase**, **obase**,
1104 or **scale**; give a bad expression to a **read()** call, calling **read()**
1105 inside of a **read()** call, type errors, and attempting an operation when
1106 the stack has too few elements.
1110 : A fatal error occurred.
1112 Fatal errors include memory allocation errors, I/O errors, failing to open
1113 files, attempting to use files that do not have only ASCII characters (dc(1)
1114 only accepts ASCII characters), attempting to open a directory as a file,
1115 and giving invalid command-line options.
1117 The exit status **4** is special; when a fatal error occurs, dc(1) always exits
1118 and returns **4**, no matter what mode dc(1) is in.
1120 The other statuses will only be returned when dc(1) is not in interactive mode
1121 (see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the
1122 **RESET** section) and accepts more input when one of those errors occurs in
1123 interactive mode. This is also the case when interactive mode is forced by the
1124 **-i** flag or **-\-interactive** option.
1126 These exit statuses allow dc(1) to be used in shell scripting with error
1127 checking, and its normal behavior can be forced by using the **-i** flag or
1128 **-\-interactive** option.
1132 Like bc(1), dc(1) has an interactive mode and a non-interactive mode.
1133 Interactive mode is turned on automatically when both **stdin** and **stdout**
1134 are hooked to a terminal, but the **-i** flag and **-\-interactive** option can
1135 turn it on in other cases.
1137 In interactive mode, dc(1) attempts to recover from errors (see the **RESET**
1138 section), and in normal execution, flushes **stdout** as soon as execution is
1139 done for the current input.
1143 If **stdin**, **stdout**, and **stderr** are all connected to a TTY, dc(1) turns
1146 TTY mode is required for history to be enabled (see the **COMMAND LINE HISTORY**
1147 section). It is also required to enable special handling for **SIGINT** signals.
1149 TTY mode is different from interactive mode because interactive mode is required
1150 in the [bc(1) specification][1], and interactive mode requires only **stdin**
1151 and **stdout** to be connected to a terminal.
1155 Sending a **SIGINT** will cause dc(1) to stop execution of the current input. If
1156 dc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
1157 **RESET** section). Otherwise, it will clean up and exit.
1159 Note that "current input" can mean one of two things. If dc(1) is processing
1160 input from **stdin** in TTY mode, it will ask for more input. If dc(1) is
1161 processing input from a file in TTY mode, it will stop processing the file and
1162 start processing the next file, if one exists, or ask for input from **stdin**
1163 if no other file exists.
1165 This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it
1166 can seem as though dc(1) did not respond to the signal since it will immediately
1167 start executing the next file. This is by design; most files that users execute
1168 when interacting with dc(1) have function definitions, which are quick to parse.
1169 If a file takes a long time to execute, there may be a bug in that file. The
1170 rest of the files could still be executed without problem, allowing the user to
1173 **SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the
1174 default handler for all other signals. The one exception is **SIGHUP**; in that
1175 case, when dc(1) is in TTY mode, a **SIGHUP** will cause dc(1) to clean up and
1178 # COMMAND LINE HISTORY
1180 dc(1) supports interactive command-line editing. If dc(1) is in TTY mode (see
1181 the **TTY MODE** section), history is enabled. Previous lines can be recalled
1182 and edited with the arrow keys.
1184 **Note**: tabs are converted to 8 spaces.
1192 The dc(1) utility operators are compliant with the operators in the bc(1)
1193 [IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1] specification.
1197 None are known. Report bugs at https://git.yzena.com/gavin/bc.
1201 Gavin D. Howard <gavin@yzena.com> and contributors.
1203 [1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html