3 SPDX-License-Identifier: BSD-2-Clause
5 Copyright (c) 2018-2020 Gavin D. Howard and contributors.
7 Redistribution and use in source and binary forms, with or without
8 modification, are permitted provided that the following conditions are met:
10 * Redistributions of source code must retain the above copyright notice, this
11 list of conditions and the following disclaimer.
13 * Redistributions in binary form must reproduce the above copyright notice,
14 this list of conditions and the following disclaimer in the documentation
15 and/or other materials provided with the distribution.
17 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
18 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
21 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
22 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
23 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
24 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
25 CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
26 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
27 POSSIBILITY OF SUCH DAMAGE.
33 dc - arbitrary-precision reverse-Polish notation calculator
37 **dc** [**-hiPvVx**] [**--version**] [**--help**] [**--interactive**] [**--no-prompt**] [**--extended-register**] [**-e** *expr*] [**--expression**=*expr*...] [**-f** *file*...] [**-file**=*file*...] [*file*...]
41 dc(1) is an arbitrary-precision calculator. It uses a stack (reverse Polish
42 notation) to store numbers and results of computations. Arithmetic operations
43 pop arguments off of the stack and push the results.
45 If no files are given on the command-line as extra arguments (i.e., not as
46 **-f** or **--file** arguments), then dc(1) reads from **stdin**. Otherwise,
47 those files are processed, and dc(1) will then exit.
49 This is different from the dc(1) on OpenBSD and possibly other dc(1)
50 implementations, where **-e** (**--expression**) and **-f** (**--file**)
51 arguments cause dc(1) to execute them and exit. The reason for this is that this
52 dc(1) allows users to set arguments in the environment variable **DC_ENV_ARGS**
53 (see the **ENVIRONMENT VARIABLES** section). Any expressions given on the
54 command-line should be used to set up a standard environment. For example, if a
55 user wants the **scale** always set to **10**, they can set **DC_ENV_ARGS** to
56 **-e 10k**, and this dc(1) will always start with a **scale** of **10**.
58 If users want to have dc(1) exit after processing all input from **-e** and
59 **-f** arguments (and their equivalents), then they can just simply add **-e q**
60 as the last command-line argument or define the environment variable
65 The following are the options that dc(1) accepts.
69 : Prints a usage message and quits.
71 **-v**, **-V**, **--version**
73 : Print the version information (copyright header) and exit.
75 **-i**, **--interactive**
77 : Forces interactive mode. (See the **INTERACTIVE MODE** section.)
79 This is a **non-portable extension**.
81 **-P**, **--no-prompt**
83 : 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 After processing all expressions and files, dc(1) will exit, unless **-**
102 (**stdin**) was given as an argument at least once to **-f** or **--file**.
104 This is a **non-portable extension**.
106 **-f** *file*, **--file**=*file*
108 : Reads in *file* and evaluates it, line by line, as though it were read
109 through **stdin**. If expressions are also given (see above), the
110 expressions are evaluated in the order given.
112 After processing all expressions and files, dc(1) will exit, unless **-**
113 (**stdin**) was given as an argument at least once to **-f** or **--file**.
114 However, if any other **-e**, **--expression**, **-f**, or **--file**
115 arguments are given after that, bc(1) will give a fatal error and exit.
117 This is a **non-portable extension**.
119 All long options are **non-portable extensions**.
123 Any non-error output is written to **stdout**.
125 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
126 error (see the **EXIT STATUS** section) if it cannot write to **stdout**, so if
127 **stdout** is closed, as in **dc <file> >&-**, it will quit with an error. This
128 is done so that dc(1) can report problems when **stdout** is redirected to a
131 If there are scripts that depend on the behavior of other dc(1) implementations,
132 it is recommended that those scripts be changed to redirect **stdout** to
137 Any error output is written to **stderr**.
139 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
140 error (see the **EXIT STATUS** section) if it cannot write to **stderr**, so if
141 **stderr** is closed, as in **dc <file> 2>&-**, it will quit with an error. This
142 is done so that dc(1) can exit with an error code when **stderr** is redirected
145 If there are scripts that depend on the behavior of other dc(1) implementations,
146 it is recommended that those scripts be changed to redirect **stderr** to
151 Each item in the input source code, either a number (see the **NUMBERS**
152 section) or a command (see the **COMMANDS** section), is processed and executed,
153 in order. Input is processed immediately when entered.
155 **ibase** is a register (see the **REGISTERS** section) that determines how to
156 interpret constant numbers. It is the "input" base, or the number base used for
157 interpreting input numbers. **ibase** is initially **10**. The max allowable
158 value for **ibase** is **16**. The min allowable value for **ibase** is **2**.
159 The max allowable value for **ibase** can be queried in dc(1) programs with the
162 **obase** is a register (see the **REGISTERS** section) that determines how to
163 output results. It is the "output" base, or the number base used for outputting
164 numbers. **obase** is initially **10**. The max allowable value for **obase** is
165 **DC_BASE_MAX** and can be queried with the **U** command. The min allowable
166 value for **obase** is **0**. If **obase** is **0**, values are output in
167 scientific notation, and if **obase** is **1**, values are output in engineering
168 notation. Otherwise, values are output in the specified base.
170 Outputting in scientific and engineering notations are **non-portable
173 The *scale* of an expression is the number of digits in the result of the
174 expression right of the decimal point, and **scale** is a register (see the
175 **REGISTERS** section) that sets the precision of any operations (with
176 exceptions). **scale** is initially **0**. **scale** cannot be negative. The max
177 allowable value for **scale** can be queried in dc(1) programs with the **V**
180 **seed** is a register containing the current seed for the pseudo-random number
181 generator. If the current value of **seed** is queried and stored, then if it is
182 assigned to **seed** later, the pseudo-random number generator is guaranteed to
183 produce the same sequence of pseudo-random numbers that were generated after the
184 value of **seed** was first queried.
186 Multiple values assigned to **seed** can produce the same sequence of
187 pseudo-random numbers. Likewise, when a value is assigned to **seed**, it is not
188 guaranteed that querying **seed** immediately after will return the same value.
189 In addition, the value of **seed** will change after any call to the **'**
190 command or the **"** command that does not get receive a value of **0** or
191 **1**. The maximum integer returned by the **'** command can be queried with the
194 **Note**: The values returned by the pseudo-random number generator with the
195 **'** and **"** commands are guaranteed to **NOT** be cryptographically secure.
196 This is a consequence of using a seeded pseudo-random number generator. However,
197 they **are** guaranteed to be reproducible with identical **seed** values.
199 The pseudo-random number generator, **seed**, and all associated operations are
200 **non-portable extensions**.
204 Comments go from **#** until, and not including, the next newline. This is a
205 **non-portable extension**.
209 Numbers are strings made up of digits, uppercase letters up to **F**, and at
210 most **1** period for a radix. Numbers can have up to **DC_NUM_MAX** digits.
211 Uppercase letters are equal to **9** + their position in the alphabet (i.e.,
212 **A** equals **10**, or **9+1**). If a digit or letter makes no sense with the
213 current value of **ibase**, they are set to the value of the highest valid digit
216 Single-character numbers (i.e., **A** alone) take the value that they would have
217 if they were valid digits, regardless of the value of **ibase**. This means that
218 **A** alone always equals decimal **10** and **F** alone always equals decimal
221 In addition, dc(1) accepts numbers in scientific notation. These have the form
222 **\<number\>e\<integer\>**. The power (the portion after the **e**) must be an
223 integer. An example is **1.89237e9**, which is equal to **1892370000**. Negative
224 exponents are also allowed, so **4.2890e_3** is equal to **0.0042890**.
226 **WARNING**: Both the number and the exponent in scientific notation are
227 interpreted according to the current **ibase**, but the number is still
228 multiplied by **10\^exponent** regardless of the current **ibase**. For example,
229 if **ibase** is **16** and dc(1) is given the number string **FFeA**, the
230 resulting decimal number will be **2550000000000**, and if dc(1) is given the
231 number string **10e_4**, the resulting decimal number will be **0.0016**.
233 Accepting input as scientific notation is a **non-portable extension**.
237 The valid commands are listed below.
241 These commands are used for printing.
243 Note that both scientific notation and engineering notation are available for
244 printing numbers. Scientific notation is activated by assigning **0** to
245 **obase** using **0o**, and engineering notation is activated by assigning **1**
246 to **obase** using **1o**. To deactivate them, just assign a different value to
249 Printing numbers in scientific notation and/or engineering notation is a
250 **non-portable extension**.
254 : Prints the value on top of the stack, whether number or string, and prints a
257 This does not alter the stack.
261 : Prints the value on top of the stack, whether number or string, and pops it
266 : Pops a value off the stack.
268 If the value is a number, it is truncated and the absolute value of the
269 result is printed as though **obase** is **UCHAR_MAX+1** and each digit is
270 interpreted as an ASCII character, making it a byte stream.
272 If the value is a string, it is printed without a trailing newline.
274 This is a **non-portable extension**.
278 : Prints the entire contents of the stack, in order from newest to oldest,
279 without altering anything.
281 Users should use this command when they get lost.
285 These are the commands used for arithmetic.
289 : The top two values are popped off the stack, added, and the result is pushed
290 onto the stack. The *scale* of the result is equal to the max *scale* of
295 : The top two values are popped off the stack, subtracted, and the result is
296 pushed onto the stack. The *scale* of the result is equal to the max
297 *scale* of both operands.
301 : The top two values are popped off the stack, multiplied, and the result is
302 pushed onto the stack. If **a** is the *scale* of the first expression and
303 **b** is the *scale* of the second expression, the *scale* of the result
304 is equal to **min(a+b,max(scale,a,b))** where **min()** and **max()** return
309 : The top two values are popped off the stack, divided, and the result is
310 pushed onto the stack. The *scale* of the result is equal to **scale**.
312 The first value popped off of the stack must be non-zero.
316 : The top two values are popped off the stack, remaindered, and the result is
317 pushed onto the stack.
319 Remaindering is equivalent to 1) Computing **a/b** to current **scale**, and
320 2) Using the result of step 1 to calculate **a-(a/b)\*b** to *scale*
321 **max(scale+scale(b),scale(a))**.
323 The first value popped off of the stack must be non-zero.
327 : The top two values are popped off the stack, divided and remaindered, and
328 the results (divided first, remainder second) are pushed onto the stack.
329 This is equivalent to **x y / x y %** except that **x** and **y** are only
332 The first value popped off of the stack must be non-zero.
334 This is a **non-portable extension**.
338 : The top two values are popped off the stack, the second is raised to the
339 power of the first, and the result is pushed onto the stack.
341 The first value popped off of the stack must be an integer, and if that
342 value is negative, the second value popped off of the stack must be
347 : The top value is popped off the stack, its square root is computed, and the
348 result is pushed onto the stack. The *scale* of the result is equal to
351 The value popped off of the stack must be non-negative.
355 : If this command *immediately* precedes a number (i.e., no spaces or other
356 commands), then that number is input as a negative number.
358 Otherwise, the top value on the stack is popped and copied, and the copy is
359 negated and pushed onto the stack. This behavior without a number is a
360 **non-portable extension**.
364 : The top value is popped off the stack, and if it is zero, it is pushed back
365 onto the stack. Otherwise, its absolute value is pushed onto the stack.
367 This is a **non-portable extension**.
371 : The top three values are popped off the stack, a modular exponentiation is
372 computed, and the result is pushed onto the stack.
374 The first value popped is used as the reduction modulus and must be an
375 integer and non-zero. The second value popped is used as the exponent and
376 must be an integer and non-negative. The third value popped is the base and
379 This is a **non-portable extension**.
383 : The top value is popped off the stack and copied, and the copy is truncated
384 and pushed onto the stack.
386 This is a **non-portable extension**.
390 : The top two values are popped off the stack, and the precision of the second
391 is set to the value of the first, whether by truncation or extension.
393 The first value popped off of the stack must be an integer and non-negative.
395 This is a **non-portable extension**.
399 : The top two values are popped off the stack, and the second is shifted left
400 (radix shifted right) to the value of the first.
402 The first value popped off of the stack must be an integer and non-negative.
404 This is a **non-portable extension**.
408 : The top two values are popped off the stack, and the second is shifted right
409 (radix shifted left) to the value of the first.
411 The first value popped off of the stack must be an integer and non-negative.
413 This is a **non-portable extension**.
417 : The top two values are popped off of the stack, they are compared, and a
418 **1** is pushed if they are equal, or **0** otherwise.
420 This is a **non-portable extension**.
424 : The top value is popped off of the stack, and if it a **0**, a **1** is
425 pushed; otherwise, a **0** is pushed.
427 This is a **non-portable extension**.
431 : The top two values are popped off of the stack, they are compared, and a
432 **1** is pushed if the first is less than the second, or **0** otherwise.
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 or equal to the second, or **0**
442 This is a **non-portable extension**.
446 : The top two values are popped off of the stack, they are compared, and a
447 **1** is pushed if the first is greater than the second, or **0** otherwise.
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 or equal to the second, or
457 This is a **non-portable extension**.
461 : The top two values are popped off of the stack. If they are both non-zero, a
462 **1** is pushed onto the stack. If either of them is zero, or both of them
463 are, then a **0** is pushed onto the stack.
465 This is like the **&&** operator in bc(1), and it is *not* a short-circuit
468 This is a **non-portable extension**.
472 : The top two values are popped off of the stack. If at least one of them is
473 non-zero, a **1** is pushed onto the stack. If both of them are zero, then a
474 **0** is pushed onto the stack.
476 This is like the **||** operator in bc(1), and it is *not* a short-circuit
479 This is a **non-portable extension**.
481 ## Pseudo-Random Number Generator
483 dc(1) has a built-in pseudo-random number generator. These commands query the
484 pseudo-random number generator. (See Parameters for more information about the
485 **seed** value that controls the pseudo-random number generator.)
487 The pseudo-random number generator is guaranteed to **NOT** be
488 cryptographically secure.
492 : Generates an integer between 0 and **DC_RAND_MAX**, inclusive (see the
495 The generated integer is made as unbiased as possible, subject to the
496 limitations of the pseudo-random number generator.
498 This is a **non-portable extension**.
502 : Pops a value off of the stack, which is used as an **exclusive** upper bound
503 on the integer that will be generated. If the bound is negative or is a
504 non-integer, an error is raised, and dc(1) resets (see the **RESET**
505 section) while **seed** remains unchanged. If the bound is larger than
506 **DC_RAND_MAX**, the higher bound is honored by generating several
507 pseudo-random integers, multiplying them by appropriate powers of
508 **DC_RAND_MAX+1**, and adding them together. Thus, the size of integer that
509 can be generated with this command is unbounded. Using this command will
510 change the value of **seed**, unless the operand is **0** or **1**. In that
511 case, **0** is pushed onto the stack, and **seed** is *not* changed.
513 The generated integer is made as unbiased as possible, subject to the
514 limitations of the pseudo-random number generator.
516 This is a **non-portable extension**.
520 These commands control the stack.
524 : Removes all items from ("clears") the stack.
528 : Copies the item on top of the stack ("duplicates") and pushes the copy onto
533 : Swaps ("reverses") the two top items on the stack.
537 : Pops ("removes") the top value from the stack.
541 These commands control registers (see the **REGISTERS** section).
545 : Pops the value off the top of the stack and stores it into register *r*.
549 : Copies the value in register *r* and pushes it onto the stack. This does not
550 alter the contents of *r*.
554 : Pops the value off the top of the (main) stack and pushes it onto the stack
555 of register *r*. The previous value of the register becomes inaccessible.
559 : Pops the value off the top of the stack for register *r* and push it onto
560 the main stack. The previous value in the stack for register *r*, if any, is
561 now accessible via the **l***r* command.
565 These commands control the values of **ibase**, **obase**, **scale**, and
566 **seed**. Also see the **SYNTAX** section.
570 : Pops the value off of the top of the stack and uses it to set **ibase**,
571 which must be between **2** and **16**, inclusive.
573 If the value on top of the stack has any *scale*, the *scale* is ignored.
577 : Pops the value off of the top of the stack and uses it to set **obase**,
578 which must be between **0** and **DC_BASE_MAX**, inclusive (see the
579 **LIMITS** section and the **NUMBERS** section).
581 If the value on top of the stack has any *scale*, the *scale* is ignored.
585 : Pops the value off of the top of the stack and uses it to set **scale**,
586 which must be non-negative.
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 **seed**. The
593 meaning of **seed** is dependent on the current pseudo-random number
594 generator but is guaranteed to not change except for new major versions.
596 The *scale* and sign of the value may be significant.
598 If a previously used **seed** value is used again, the pseudo-random number
599 generator is guaranteed to produce the same sequence of pseudo-random
600 numbers as it did when the **seed** value was previously used.
602 The exact value assigned to **seed** is not guaranteed to be returned if the
603 **J** command is used. However, if **seed** *does* return a different value,
604 both values, when assigned to **seed**, are guaranteed to produce the same
605 sequence of pseudo-random numbers. This means that certain values assigned
606 to **seed** will not produce unique sequences of pseudo-random numbers.
608 There is no limit to the length (number of significant decimal digits) or
609 *scale* of the value that can be assigned to **seed**.
611 This is a **non-portable extension**.
615 : Pushes the current value of **ibase** onto the main stack.
619 : Pushes the current value of **obase** onto the main stack.
623 : Pushes the current value of **scale** onto the main stack.
627 : Pushes the current value of **seed** onto the main stack.
629 This is a **non-portable extension**.
633 : Pushes the maximum allowable value of **ibase** onto the main stack.
635 This is a **non-portable extension**.
639 : Pushes the maximum allowable value of **obase** onto the main stack.
641 This is a **non-portable extension**.
645 : Pushes the maximum allowable value of **scale** onto the main stack.
647 This is a **non-portable extension**.
651 : Pushes the maximum (inclusive) integer that can be generated with the **'**
652 pseudo-random number generator command.
654 This is a **non-portable extension**.
658 The following commands control strings.
660 dc(1) can work with both numbers and strings, and registers (see the
661 **REGISTERS** section) can hold both strings and numbers. dc(1) always knows
662 whether the contents of a register are a string or a number.
664 While arithmetic operations have to have numbers, and will print an error if
665 given a string, other commands accept strings.
667 Strings can also be executed as macros. For example, if the string **[1pR]** is
668 executed as a macro, then the code **1pR** is executed, meaning that the **1**
669 will be printed with a newline after and then popped from the stack.
671 **\[**_characters_**\]**
673 : Makes a string containing *characters* and pushes it onto the stack.
675 If there are brackets (**\[** and **\]**) in the string, then they must be
676 balanced. Unbalanced brackets can be escaped using a backslash (**\\**)
679 If there is a backslash character in the string, the character after it
680 (even another backslash) is put into the string verbatim, but the (first)
685 : The value on top of the stack is popped.
687 If it is a number, it is truncated and its absolute value is taken. The
688 result mod **UCHAR_MAX+1** is calculated. If that result is **0**, push an
689 empty string; otherwise, push a one-character string where the character is
690 the result of the mod interpreted as an ASCII character.
692 If it is a string, then a new string is made. If the original string is
693 empty, the new string is empty. If it is not, then the first character of
694 the original string is used to create the new string as a one-character
695 string. The new string is then pushed onto the stack.
697 This is a **non-portable extension**.
701 : Pops a value off of the top of the stack.
703 If it is a number, it is pushed back onto the stack.
705 If it is a string, it is executed as a macro.
707 This behavior is the norm whenever a macro is executed, whether by this
708 command or by the conditional execution commands below.
712 : Pops two values off of the stack that must be numbers and compares them. If
713 the first value is greater than the second, then the contents of register
716 For example, **0 1>a** will execute the contents of register **a**, and
719 If either or both of the values are not numbers, dc(1) will raise an error
720 and reset (see the **RESET** section).
724 : Like the above, but will execute register *s* if the comparison fails.
726 If either or both of the values are not numbers, dc(1) will raise an error
727 and reset (see the **RESET** section).
729 This is a **non-portable extension**.
733 : Pops two values off of the stack that must be numbers and compares them. If
734 the first value is not greater than the second (less than or equal to), then
735 the contents of register *r* are executed.
737 If either or both of the values are not numbers, dc(1) will raise an error
738 and reset (see the **RESET** section).
742 : Like the above, but will execute register *s* if the comparison fails.
744 If either or both of the values are not numbers, dc(1) will raise an error
745 and reset (see the **RESET** section).
747 This is a **non-portable extension**.
751 : Pops two values off of the stack that must be numbers and compares them. If
752 the first value is less than the second, then the contents of register *r*
755 If either or both of the values are not numbers, dc(1) will raise an error
756 and reset (see the **RESET** section).
760 : Like the above, but will execute register *s* if the comparison fails.
762 If either or both of the values are not numbers, dc(1) will raise an error
763 and reset (see the **RESET** section).
765 This is a **non-portable extension**.
769 : Pops two values off of the stack that must be numbers and compares them. If
770 the first value is not less than the second (greater than or equal to), then
771 the contents of register *r* are executed.
773 If either or both of the values are not numbers, dc(1) will raise an error
774 and reset (see the **RESET** section).
778 : Like the above, but will execute register *s* if the comparison fails.
780 If either or both of the values are not numbers, dc(1) will raise an error
781 and reset (see the **RESET** section).
783 This is a **non-portable extension**.
787 : Pops two values off of the stack that must be numbers and compares them. If
788 the first value is equal to the second, then the contents of register *r*
791 If either or both of the values are not numbers, dc(1) will raise an error
792 and reset (see the **RESET** section).
796 : Like the above, but will execute register *s* if the comparison fails.
798 If either or both of the values are not numbers, dc(1) will raise an error
799 and reset (see the **RESET** section).
801 This is a **non-portable extension**.
805 : Pops two values off of the stack that must be numbers and compares them. If
806 the first value is not equal to the second, then the contents of register
809 If either or both of the values are not numbers, dc(1) will raise an error
810 and reset (see the **RESET** section).
814 : Like the above, but will execute register *s* if the comparison fails.
816 If either or both of the values are not numbers, dc(1) will raise an error
817 and reset (see the **RESET** section).
819 This is a **non-portable extension**.
823 : Reads a line from the **stdin** and executes it. This is to allow macros to
824 request input from users.
828 : During execution of a macro, this exits the execution of that macro and the
829 execution of the macro that executed it. If there are no macros, or only one
830 macro executing, dc(1) exits.
834 : Pops a value from the stack which must be non-negative and is used the
835 number of macro executions to pop off of the execution stack. If the number
836 of levels to pop is greater than the number of executing macros, dc(1)
841 These commands query status of the stack or its top value.
845 : Pops a value off of the stack.
847 If it is a number, calculates the number of significant decimal digits it
848 has and pushes the result.
850 If it is a string, pushes the number of characters the string has.
854 : Pops a value off of the stack.
856 If it is a number, pushes the *scale* of the value onto the stack.
858 If it is a string, pushes **0**.
862 : Pushes the current stack depth (before execution of this command).
866 These commands manipulate arrays.
870 : Pops the top two values off of the stack. The second value will be stored in
871 the array *r* (see the **REGISTERS** section), indexed by the first value.
875 : Pops the value on top of the stack and uses it as an index into the array
876 *r*. The selected value is then pushed onto the stack.
880 Registers are names that can store strings, numbers, and arrays. (Number/string
881 registers do not interfere with array registers.)
883 Each register is also its own stack, so the current register value is the top of
884 the stack for the register. All registers, when first referenced, have one value
885 (**0**) in their stack.
887 In non-extended register mode, a register name is just the single character that
888 follows any command that needs a register name. The only exception is a newline
889 (**'\\n'**); it is a parse error for a newline to be used as a register name.
891 ## Extended Register Mode
893 Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited
894 amounts of registers, if extended register mode is enabled.
896 If extended register mode is enabled (**-x** or **--extended-register**
897 command-line arguments are given), then normal single character registers are
898 used *unless* the character immediately following a command that needs a
899 register name is a space (according to **isspace()**) and not a newline
902 In that case, the register name is found according to the regex
903 **\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if
904 the next non-space characters do not match that regex.
908 When dc(1) encounters an error or a signal that it has a non-default handler
909 for, it resets. This means that several things happen.
911 First, any macros that are executing are stopped and popped off the stack.
912 The behavior is not unlike that of exceptions in programming languages. Then
913 the execution point is set so that any code waiting to execute (after all
914 macros returned) is skipped.
916 Thus, when dc(1) resets, it skips any remaining code waiting to be executed.
917 Then, if it is interactive mode, and the error was not a fatal error (see the
918 **EXIT STATUS** section), it asks for more input; otherwise, it exits with the
919 appropriate return code.
923 Most dc(1) implementations use **char** types to calculate the value of **1**
924 decimal digit at a time, but that can be slow. This dc(1) does something
927 It uses large integers to calculate more than **1** decimal digit at a time. If
928 built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is
929 **64**, then each integer has **9** decimal digits. If built in an environment
930 where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
931 value (the number of decimal digits per large integer) is called
934 In addition, this dc(1) uses an even larger integer for overflow checking. This
935 integer type depends on the value of **DC_LONG_BIT**, but is always at least
936 twice as large as the integer type used to store digits.
940 The following are the limits on dc(1):
944 : The number of bits in the **long** type in the environment where dc(1) was
945 built. This determines how many decimal digits can be stored in a single
946 large integer (see the **PERFORMANCE** section).
950 : The number of decimal digits per large integer (see the **PERFORMANCE**
951 section). Depends on **DC_LONG_BIT**.
955 : The max decimal number that each large integer can store (see
956 **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**.
960 : The max number that the overflow type (see the **PERFORMANCE** section) can
961 hold. Depends on **DC_LONG_BIT**.
965 : The maximum output base. Set at **DC_BASE_POW**.
969 : The maximum size of arrays. Set at **SIZE_MAX-1**.
973 : The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**.
977 : The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**.
981 : The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**.
985 : The maximum length of a number (in decimal digits), which includes digits
986 after the decimal point. Set at **DC_OVERFLOW_MAX-1**.
990 : The maximum integer (inclusive) returned by the **'** command, if dc(1). Set
991 at **2\^DC_LONG_BIT-1**.
995 : The maximum allowable exponent (positive or negative). Set at
1000 : The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
1002 These limits are meant to be effectively non-existent; the limits are so large
1003 (at least on 64-bit machines) that there should not be any point at which they
1004 become a problem. In fact, memory should be exhausted before these limits should
1007 # ENVIRONMENT VARIABLES
1009 dc(1) recognizes the following environment variables:
1013 : This is another way to give command-line arguments to dc(1). They should be
1014 in the same format as all other command-line arguments. These are always
1015 processed first, so any files given in **DC_ENV_ARGS** will be processed
1016 before arguments and files given on the command-line. This gives the user
1017 the ability to set up "standard" options and files to be used at every
1018 invocation. The most useful thing for such files to contain would be useful
1019 functions that the user might want every time dc(1) runs. Another use would
1020 be to use the **-e** option to set **scale** to a value other than **0**.
1022 The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments,
1023 but it does not understand escape sequences. For example, the string
1024 **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string
1025 **"/home/gavin/some \"dc\" file.dc"** will include the backslashes.
1027 The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
1028 if you have a file with any number of single quotes in the name, you can use
1029 double quotes as the outside quotes, as in **"some 'bc' file.bc"**, and vice
1030 versa if you have a file with double quotes. However, handling a file with
1031 both kinds of quotes in **DC_ENV_ARGS** is not supported due to the
1032 complexity of the parsing, though such files are still supported on the
1033 command-line where the parsing is done by the shell.
1037 : If this environment variable exists and contains an integer that is greater
1038 than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output
1039 lines to that length, including the backslash newline combo. The default
1040 line length is **70**.
1044 : If this variable exists (no matter the contents), dc(1) will exit
1045 immediately after executing expressions and files given by the **-e** and/or
1046 **-f** command-line options (and any equivalents).
1050 dc(1) returns the following exit statuses:
1058 : A math error occurred. This follows standard practice of using **1** for
1059 expected errors, since math errors will happen in the process of normal
1062 Math errors include divide by **0**, taking the square root of a negative
1063 number, using a negative number as a bound for the pseudo-random number
1064 generator, attempting to convert a negative number to a hardware integer,
1065 overflow when converting a number to a hardware integer, and attempting to
1066 use a non-integer where an integer is required.
1068 Converting to a hardware integer happens for the second operand of the power
1069 (**\^**), places (**\@**), left shift (**H**), and right shift (**h**)
1074 : A parse error occurred.
1076 Parse errors include unexpected **EOF**, using an invalid character, failing
1077 to find the end of a string or comment, and using a token where it is
1082 : A runtime error occurred.
1084 Runtime errors include assigning an invalid number to **ibase**, **obase**,
1085 or **scale**; give a bad expression to a **read()** call, calling **read()**
1086 inside of a **read()** call, type errors, and attempting an operation when
1087 the stack has too few elements.
1091 : A fatal error occurred.
1093 Fatal errors include memory allocation errors, I/O errors, failing to open
1094 files, attempting to use files that do not have only ASCII characters (dc(1)
1095 only accepts ASCII characters), attempting to open a directory as a file,
1096 and giving invalid command-line options.
1098 The exit status **4** is special; when a fatal error occurs, dc(1) always exits
1099 and returns **4**, no matter what mode dc(1) is in.
1101 The other statuses will only be returned when dc(1) is not in interactive mode
1102 (see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the
1103 **RESET** section) and accepts more input when one of those errors occurs in
1104 interactive mode. This is also the case when interactive mode is forced by the
1105 **-i** flag or **--interactive** option.
1107 These exit statuses allow dc(1) to be used in shell scripting with error
1108 checking, and its normal behavior can be forced by using the **-i** flag or
1109 **--interactive** option.
1113 Like bc(1), dc(1) has an interactive mode and a non-interactive mode.
1114 Interactive mode is turned on automatically when both **stdin** and **stdout**
1115 are hooked to a terminal, but the **-i** flag and **--interactive** option can
1116 turn it on in other cases.
1118 In interactive mode, dc(1) attempts to recover from errors (see the **RESET**
1119 section), and in normal execution, flushes **stdout** as soon as execution is
1120 done for the current input.
1124 If **stdin**, **stdout**, and **stderr** are all connected to a TTY, dc(1) turns
1127 TTY mode is required for history to be enabled (see the **COMMAND LINE HISTORY**
1128 section). It is also required to enable special handling for **SIGINT** signals.
1130 TTY mode is different from interactive mode because interactive mode is required
1131 in the [bc(1) specification][1], and interactive mode requires only **stdin**
1132 and **stdout** to be connected to a terminal.
1136 Sending a **SIGINT** will cause dc(1) to stop execution of the current input. If
1137 dc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
1138 **RESET** section). Otherwise, it will clean up and exit.
1140 Note that "current input" can mean one of two things. If dc(1) is processing
1141 input from **stdin** in TTY mode, it will ask for more input. If dc(1) is
1142 processing input from a file in TTY mode, it will stop processing the file and
1143 start processing the next file, if one exists, or ask for input from **stdin**
1144 if no other file exists.
1146 This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it
1147 can seem as though dc(1) did not respond to the signal since it will immediately
1148 start executing the next file. This is by design; most files that users execute
1149 when interacting with dc(1) have function definitions, which are quick to parse.
1150 If a file takes a long time to execute, there may be a bug in that file. The
1151 rest of the files could still be executed without problem, allowing the user to
1154 **SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the
1155 default handler for all other signals. The one exception is **SIGHUP**; in that
1156 case, when dc(1) is in TTY mode, a **SIGHUP** will cause dc(1) to clean up and
1159 # COMMAND LINE HISTORY
1161 dc(1) supports interactive command-line editing. If dc(1) is in TTY mode (see
1162 the **TTY MODE** section), history is enabled. Previous lines can be recalled
1163 and edited with the arrow keys.
1165 **Note**: tabs are converted to 8 spaces.
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 <yzena.tech@gmail.com> and contributors.
1189 [1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html