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, then dc(1) reads from **stdin** (see
46 the **STDIN** section). Otherwise, those files are processed, and dc(1) will
49 If a user wants to set up a standard environment, they can use **DC_ENV_ARGS**
50 (see the **ENVIRONMENT VARIABLES** section). For example, if a user wants the
51 **scale** always set to **10**, they can set **DC_ENV_ARGS** to **-e 10k**, and
52 this dc(1) will always start with a **scale** of **10**.
56 The following are the options that dc(1) accepts.
60 : Prints a usage message and quits.
62 **-v**, **-V**, **-\-version**
64 : Print the version information (copyright header) and exit.
66 **-i**, **-\-interactive**
68 : Forces interactive mode. (See the **INTERACTIVE MODE** section.)
70 This is a **non-portable extension**.
72 **-L**, **-\-no-line-length**
74 : Disables line length checking and prints numbers without backslashes and
75 newlines. In other words, this option sets **BC_LINE_LENGTH** to **0** (see
76 the **ENVIRONMENT VARIABLES** section).
78 This is a **non-portable extension**.
80 **-P**, **-\-no-prompt**
82 : Disables the prompt in TTY mode. (The prompt is only enabled in TTY mode.
83 See the **TTY MODE** section.) This is mostly for those users that do not
84 want a prompt or are not used to having them in dc(1). Most of those users
85 would want to put this option in **DC_ENV_ARGS**.
87 These options override the **DC_PROMPT** and **DC_TTY_MODE** environment
88 variables (see the **ENVIRONMENT VARIABLES** section).
90 This is a **non-portable extension**.
92 **-R**, **-\-no-read-prompt**
94 : Disables the read prompt in TTY mode. (The read prompt is only enabled in
95 TTY mode. See the **TTY MODE** section.) This is mostly for those users that
96 do not want a read prompt or are not used to having them in dc(1). Most of
97 those users would want to put this option in **BC_ENV_ARGS** (see the
98 **ENVIRONMENT VARIABLES** section). This option is also useful in hash bang
99 lines of dc(1) scripts that prompt for user input.
101 This option does not disable the regular prompt because the read prompt is
102 only used when the **?** command is used.
104 These options *do* override the **DC_PROMPT** and **DC_TTY_MODE**
105 environment variables (see the **ENVIRONMENT VARIABLES** section), but only
108 This is a **non-portable extension**.
110 **-x** **-\-extended-register**
112 : Enables extended register mode. See the *Extended Register Mode* subsection
113 of the **REGISTERS** section for more information.
115 This is a **non-portable extension**.
117 **-z**, **-\-leading-zeroes**
119 : Makes bc(1) print all numbers greater than **-1** and less than **1**, and
120 not equal to **0**, with a leading zero.
122 This can be set for individual numbers with the **plz(x)**, plznl(x)**,
123 **pnlz(x)**, and **pnlznl(x)** functions in the extended math library (see
124 the **LIBRARY** section).
126 This is a **non-portable extension**.
128 **-e** *expr*, **-\-expression**=*expr*
130 : Evaluates *expr*. If multiple expressions are given, they are evaluated in
131 order. If files are given as well (see below), the expressions and files are
132 evaluated in the order given. This means that if a file is given before an
133 expression, the file is read in and evaluated first.
135 If this option is given on the command-line (i.e., not in **DC_ENV_ARGS**,
136 see the **ENVIRONMENT VARIABLES** section), then after processing all
137 expressions and files, dc(1) will exit, unless **-** (**stdin**) was given
138 as an argument at least once to **-f** or **-\-file**, whether on the
139 command-line or in **DC_ENV_ARGS**. However, if any other **-e**,
140 **-\-expression**, **-f**, or **-\-file** arguments are given after **-f-**
141 or equivalent is given, dc(1) will give a fatal error and exit.
143 This is a **non-portable extension**.
145 **-f** *file*, **-\-file**=*file*
147 : Reads in *file* and evaluates it, line by line, as though it were read
148 through **stdin**. If expressions are also given (see above), the
149 expressions are evaluated in the order given.
151 If this option is given on the command-line (i.e., not in **DC_ENV_ARGS**,
152 see the **ENVIRONMENT VARIABLES** section), then after processing all
153 expressions and files, dc(1) will exit, unless **-** (**stdin**) was given
154 as an argument at least once to **-f** or **-\-file**. However, if any other
155 **-e**, **-\-expression**, **-f**, or **-\-file** arguments are given after
156 **-f-** or equivalent is given, dc(1) will give a fatal error and exit.
158 This is a **non-portable extension**.
160 All long options are **non-portable extensions**.
164 If no files are given on the command-line and no files or expressions are given
165 by the **-f**, **-\-file**, **-e**, or **-\-expression** options, then dc(1)
168 However, there is a caveat to this.
170 First, **stdin** is evaluated a line at a time. The only exception to this is if
171 a string has been finished, but not ended. This means that, except for escaped
172 brackets, all brackets must be balanced before dc(1) parses and executes.
176 Any non-error output is written to **stdout**. In addition, if history (see the
177 **HISTORY** section) and the prompt (see the **TTY MODE** section) are enabled,
178 both are output to **stdout**.
180 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
181 error (see the **EXIT STATUS** section) if it cannot write to **stdout**, so if
182 **stdout** is closed, as in **dc <file> >&-**, it will quit with an error. This
183 is done so that dc(1) can report problems when **stdout** is redirected to a
186 If there are scripts that depend on the behavior of other dc(1) implementations,
187 it is recommended that those scripts be changed to redirect **stdout** to
192 Any error output is written to **stderr**.
194 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
195 error (see the **EXIT STATUS** section) if it cannot write to **stderr**, so if
196 **stderr** is closed, as in **dc <file> 2>&-**, it will quit with an error. This
197 is done so that dc(1) can exit with an error code when **stderr** is redirected
200 If there are scripts that depend on the behavior of other dc(1) implementations,
201 it is recommended that those scripts be changed to redirect **stderr** to
206 Each item in the input source code, either a number (see the **NUMBERS**
207 section) or a command (see the **COMMANDS** section), is processed and executed,
208 in order. Input is processed immediately when entered.
210 **ibase** is a register (see the **REGISTERS** section) that determines how to
211 interpret constant numbers. It is the "input" base, or the number base used for
212 interpreting input numbers. **ibase** is initially **10**. The max allowable
213 value for **ibase** is **16**. The min allowable value for **ibase** is **2**.
214 The max allowable value for **ibase** can be queried in dc(1) programs with the
217 **obase** is a register (see the **REGISTERS** section) that determines how to
218 output results. It is the "output" base, or the number base used for outputting
219 numbers. **obase** is initially **10**. The max allowable value for **obase** is
220 **DC_BASE_MAX** and can be queried with the **U** command. The min allowable
221 value for **obase** is **0**. If **obase** is **0**, values are output in
222 scientific notation, and if **obase** is **1**, values are output in engineering
223 notation. Otherwise, values are output in the specified base.
225 Outputting in scientific and engineering notations are **non-portable
228 The *scale* of an expression is the number of digits in the result of the
229 expression right of the decimal point, and **scale** is a register (see the
230 **REGISTERS** section) that sets the precision of any operations (with
231 exceptions). **scale** is initially **0**. **scale** cannot be negative. The max
232 allowable value for **scale** can be queried in dc(1) programs with the **V**
235 **seed** is a register containing the current seed for the pseudo-random number
236 generator. If the current value of **seed** is queried and stored, then if it is
237 assigned to **seed** later, the pseudo-random number generator is guaranteed to
238 produce the same sequence of pseudo-random numbers that were generated after the
239 value of **seed** was first queried.
241 Multiple values assigned to **seed** can produce the same sequence of
242 pseudo-random numbers. Likewise, when a value is assigned to **seed**, it is not
243 guaranteed that querying **seed** immediately after will return the same value.
244 In addition, the value of **seed** will change after any call to the **'**
245 command or the **"** command that does not get receive a value of **0** or
246 **1**. The maximum integer returned by the **'** command can be queried with the
249 **Note**: The values returned by the pseudo-random number generator with the
250 **'** and **"** commands are guaranteed to **NOT** be cryptographically secure.
251 This is a consequence of using a seeded pseudo-random number generator. However,
252 they *are* guaranteed to be reproducible with identical **seed** values. This
253 means that the pseudo-random values from dc(1) should only be used where a
254 reproducible stream of pseudo-random numbers is *ESSENTIAL*. In any other case,
255 use a non-seeded pseudo-random number generator.
257 The pseudo-random number generator, **seed**, and all associated operations are
258 **non-portable extensions**.
262 Comments go from **#** until, and not including, the next newline. This is a
263 **non-portable extension**.
267 Numbers are strings made up of digits, uppercase letters up to **F**, and at
268 most **1** period for a radix. Numbers can have up to **DC_NUM_MAX** digits.
269 Uppercase letters are equal to **9** + their position in the alphabet (i.e.,
270 **A** equals **10**, or **9+1**). If a digit or letter makes no sense with the
271 current value of **ibase**, they are set to the value of the highest valid digit
274 Single-character numbers (i.e., **A** alone) take the value that they would have
275 if they were valid digits, regardless of the value of **ibase**. This means that
276 **A** alone always equals decimal **10** and **F** alone always equals decimal
279 In addition, dc(1) accepts numbers in scientific notation. These have the form
280 **\<number\>e\<integer\>**. The exponent (the portion after the **e**) must be
281 an integer. An example is **1.89237e9**, which is equal to **1892370000**.
282 Negative exponents are also allowed, so **4.2890e_3** is equal to **0.0042890**.
284 **WARNING**: Both the number and the exponent in scientific notation are
285 interpreted according to the current **ibase**, but the number is still
286 multiplied by **10\^exponent** regardless of the current **ibase**. For example,
287 if **ibase** is **16** and dc(1) is given the number string **FFeA**, the
288 resulting decimal number will be **2550000000000**, and if dc(1) is given the
289 number string **10e_4**, the resulting decimal number will be **0.0016**.
291 Accepting input as scientific notation is a **non-portable extension**.
295 The valid commands are listed below.
299 These commands are used for printing.
301 Note that both scientific notation and engineering notation are available for
302 printing numbers. Scientific notation is activated by assigning **0** to
303 **obase** using **0o**, and engineering notation is activated by assigning **1**
304 to **obase** using **1o**. To deactivate them, just assign a different value to
307 Printing numbers in scientific notation and/or engineering notation is a
308 **non-portable extension**.
312 : Prints the value on top of the stack, whether number or string, and prints a
315 This does not alter the stack.
319 : Prints the value on top of the stack, whether number or string, and pops it
324 : Pops a value off the stack.
326 If the value is a number, it is truncated and the absolute value of the
327 result is printed as though **obase** is **256** and each digit is
328 interpreted as an 8-bit ASCII character, making it a byte stream.
330 If the value is a string, it is printed without a trailing newline.
332 This is a **non-portable extension**.
336 : Prints the entire contents of the stack, in order from newest to oldest,
337 without altering anything.
339 Users should use this command when they get lost.
343 These are the commands used for arithmetic.
347 : The top two values are popped off the stack, added, and the result is pushed
348 onto the stack. The *scale* of the result is equal to the max *scale* of
353 : The top two values are popped off the stack, subtracted, and the result is
354 pushed onto the stack. The *scale* of the result is equal to the max
355 *scale* of both operands.
359 : The top two values are popped off the stack, multiplied, and the result is
360 pushed onto the stack. If **a** is the *scale* of the first expression and
361 **b** is the *scale* of the second expression, the *scale* of the result
362 is equal to **min(a+b,max(scale,a,b))** where **min()** and **max()** return
367 : The top two values are popped off the stack, divided, and the result is
368 pushed onto the stack. The *scale* of the result is equal to **scale**.
370 The first value popped off of the stack must be non-zero.
374 : The top two values are popped off the stack, remaindered, and the result is
375 pushed onto the stack.
377 Remaindering is equivalent to 1) Computing **a/b** to current **scale**, and
378 2) Using the result of step 1 to calculate **a-(a/b)\*b** to *scale*
379 **max(scale+scale(b),scale(a))**.
381 The first value popped off of the stack must be non-zero.
385 : The top two values are popped off the stack, divided and remaindered, and
386 the results (divided first, remainder second) are pushed onto the stack.
387 This is equivalent to **x y / x y %** except that **x** and **y** are only
390 The first value popped off of the stack must be non-zero.
392 This is a **non-portable extension**.
396 : The top two values are popped off the stack, the second is raised to the
397 power of the first, and the result is pushed onto the stack. The *scale* of
398 the result is equal to **scale**.
400 The first value popped off of the stack must be an integer, and if that
401 value is negative, the second value popped off of the stack must be
406 : The top value is popped off the stack, its square root is computed, and the
407 result is pushed onto the stack. The *scale* of the result is equal to
410 The value popped off of the stack must be non-negative.
414 : If this command *immediately* precedes a number (i.e., no spaces or other
415 commands), then that number is input as a negative number.
417 Otherwise, the top value on the stack is popped and copied, and the copy is
418 negated and pushed onto the stack. This behavior without a number is a
419 **non-portable extension**.
423 : The top value is popped off the stack, and if it is zero, it is pushed back
424 onto the stack. Otherwise, its absolute value is pushed onto the stack.
426 This is a **non-portable extension**.
430 : The top three values are popped off the stack, a modular exponentiation is
431 computed, and the result is pushed onto the stack.
433 The first value popped is used as the reduction modulus and must be an
434 integer and non-zero. The second value popped is used as the exponent and
435 must be an integer and non-negative. The third value popped is the base and
438 This is a **non-portable extension**.
442 : The top value is popped off the stack and copied, and the copy is truncated
443 and pushed onto the stack.
445 This is a **non-portable extension**.
449 : The top two values are popped off the stack, and the precision of the second
450 is set to the value of the first, whether by truncation or extension.
452 The first value popped off of the stack must be an integer and non-negative.
454 This is a **non-portable extension**.
458 : The top two values are popped off the stack, and the second is shifted left
459 (radix shifted right) to the value of the first.
461 The first value popped off of the stack must be an integer and non-negative.
463 This is a **non-portable extension**.
467 : The top two values are popped off the stack, and the second is shifted right
468 (radix shifted left) to the value of the first.
470 The first value popped off of the stack must be an integer and non-negative.
472 This is a **non-portable extension**.
476 : The top two values are popped off of the stack, they are compared, and a
477 **1** is pushed if they are equal, or **0** otherwise.
479 This is a **non-portable extension**.
483 : The top value is popped off of the stack, and if it a **0**, a **1** is
484 pushed; otherwise, a **0** is pushed.
486 This is a **non-portable extension**.
490 : The top two values are popped off of the stack, they are compared, and a
491 **1** is pushed if the first is less than the second, or **0** otherwise.
493 This is a **non-portable extension**.
497 : The top two values are popped off of the stack, they are compared, and a
498 **1** is pushed if the first is less than or equal to the second, or **0**
501 This is a **non-portable extension**.
505 : The top two values are popped off of the stack, they are compared, and a
506 **1** is pushed if the first is greater than the second, or **0** otherwise.
508 This is a **non-portable extension**.
512 : The top two values are popped off of the stack, they are compared, and a
513 **1** is pushed if the first is greater than or equal to the second, or
516 This is a **non-portable extension**.
520 : The top two values are popped off of the stack. If they are both non-zero, a
521 **1** is pushed onto the stack. If either of them is zero, or both of them
522 are, then a **0** is pushed onto the stack.
524 This is like the **&&** operator in bc(1), and it is *not* a short-circuit
527 This is a **non-portable extension**.
531 : The top two values are popped off of the stack. If at least one of them is
532 non-zero, a **1** is pushed onto the stack. If both of them are zero, then a
533 **0** is pushed onto the stack.
535 This is like the **||** operator in bc(1), and it is *not* a short-circuit
538 This is a **non-portable extension**.
540 ## Pseudo-Random Number Generator
542 dc(1) has a built-in pseudo-random number generator. These commands query the
543 pseudo-random number generator. (See Parameters for more information about the
544 **seed** value that controls the pseudo-random number generator.)
546 The pseudo-random number generator is guaranteed to **NOT** be
547 cryptographically secure.
551 : Generates an integer between 0 and **DC_RAND_MAX**, inclusive (see the
554 The generated integer is made as unbiased as possible, subject to the
555 limitations of the pseudo-random number generator.
557 This is a **non-portable extension**.
561 : Pops a value off of the stack, which is used as an **exclusive** upper bound
562 on the integer that will be generated. If the bound is negative or is a
563 non-integer, an error is raised, and dc(1) resets (see the **RESET**
564 section) while **seed** remains unchanged. If the bound is larger than
565 **DC_RAND_MAX**, the higher bound is honored by generating several
566 pseudo-random integers, multiplying them by appropriate powers of
567 **DC_RAND_MAX+1**, and adding them together. Thus, the size of integer that
568 can be generated with this command is unbounded. Using this command will
569 change the value of **seed**, unless the operand is **0** or **1**. In that
570 case, **0** is pushed onto the stack, and **seed** is *not* changed.
572 The generated integer is made as unbiased as possible, subject to the
573 limitations of the pseudo-random number generator.
575 This is a **non-portable extension**.
579 These commands control the stack.
583 : Removes all items from ("clears") the stack.
587 : Copies the item on top of the stack ("duplicates") and pushes the copy onto
592 : Swaps ("reverses") the two top items on the stack.
596 : Pops ("removes") the top value from the stack.
600 These commands control registers (see the **REGISTERS** section).
604 : Pops the value off the top of the stack and stores it into register *r*.
608 : Copies the value in register *r* and pushes it onto the stack. This does not
609 alter the contents of *r*.
613 : Pops the value off the top of the (main) stack and pushes it onto the stack
614 of register *r*. The previous value of the register becomes inaccessible.
618 : Pops the value off the top of the stack for register *r* and push it onto
619 the main stack. The previous value in the stack for register *r*, if any, is
620 now accessible via the **l**_r_ command.
624 These commands control the values of **ibase**, **obase**, **scale**, and
625 **seed**. Also see the **SYNTAX** section.
629 : Pops the value off of the top of the stack and uses it to set **ibase**,
630 which must be between **2** and **16**, inclusive.
632 If the value on top of the stack has any *scale*, the *scale* is ignored.
636 : Pops the value off of the top of the stack and uses it to set **obase**,
637 which must be between **0** and **DC_BASE_MAX**, inclusive (see the
638 **LIMITS** section and the **NUMBERS** section).
640 If the value on top of the stack has any *scale*, the *scale* is ignored.
644 : Pops the value off of the top of the stack and uses it to set **scale**,
645 which must be non-negative.
647 If the value on top of the stack has any *scale*, the *scale* is ignored.
651 : Pops the value off of the top of the stack and uses it to set **seed**. The
652 meaning of **seed** is dependent on the current pseudo-random number
653 generator but is guaranteed to not change except for new major versions.
655 The *scale* and sign of the value may be significant.
657 If a previously used **seed** value is used again, the pseudo-random number
658 generator is guaranteed to produce the same sequence of pseudo-random
659 numbers as it did when the **seed** value was previously used.
661 The exact value assigned to **seed** is not guaranteed to be returned if the
662 **J** command is used. However, if **seed** *does* return a different value,
663 both values, when assigned to **seed**, are guaranteed to produce the same
664 sequence of pseudo-random numbers. This means that certain values assigned
665 to **seed** will not produce unique sequences of pseudo-random numbers.
667 There is no limit to the length (number of significant decimal digits) or
668 *scale* of the value that can be assigned to **seed**.
670 This is a **non-portable extension**.
674 : Pushes the current value of **ibase** onto the main stack.
678 : Pushes the current value of **obase** onto the main stack.
682 : Pushes the current value of **scale** onto the main stack.
686 : Pushes the current value of **seed** onto the main stack.
688 This is a **non-portable extension**.
692 : Pushes the maximum allowable value of **ibase** onto the main stack.
694 This is a **non-portable extension**.
698 : Pushes the maximum allowable value of **obase** onto the main stack.
700 This is a **non-portable extension**.
704 : Pushes the maximum allowable value of **scale** onto the main stack.
706 This is a **non-portable extension**.
710 : Pushes the maximum (inclusive) integer that can be generated with the **'**
711 pseudo-random number generator command.
713 This is a **non-portable extension**.
717 The following commands control strings.
719 dc(1) can work with both numbers and strings, and registers (see the
720 **REGISTERS** section) can hold both strings and numbers. dc(1) always knows
721 whether the contents of a register are a string or a number.
723 While arithmetic operations have to have numbers, and will print an error if
724 given a string, other commands accept strings.
726 Strings can also be executed as macros. For example, if the string **[1pR]** is
727 executed as a macro, then the code **1pR** is executed, meaning that the **1**
728 will be printed with a newline after and then popped from the stack.
730 **\[**_characters_**\]**
732 : Makes a string containing *characters* and pushes it onto the stack.
734 If there are brackets (**\[** and **\]**) in the string, then they must be
735 balanced. Unbalanced brackets can be escaped using a backslash (**\\**)
738 If there is a backslash character in the string, the character after it
739 (even another backslash) is put into the string verbatim, but the (first)
744 : The value on top of the stack is popped.
746 If it is a number, it is truncated and its absolute value is taken. The
747 result mod **256** is calculated. If that result is **0**, push an empty
748 string; otherwise, push a one-character string where the character is the
749 result of the mod interpreted as an ASCII character.
751 If it is a string, then a new string is made. If the original string is
752 empty, the new string is empty. If it is not, then the first character of
753 the original string is used to create the new string as a one-character
754 string. The new string is then pushed onto the stack.
756 This is a **non-portable extension**.
760 : Pops a value off of the top of the stack.
762 If it is a number, it is pushed back onto the stack.
764 If it is a string, it is executed as a macro.
766 This behavior is the norm whenever a macro is executed, whether by this
767 command or by the conditional execution commands below.
771 : Pops two values off of the stack that must be numbers and compares them. If
772 the first value is greater than the second, then the contents of register
775 For example, **0 1>a** will execute the contents of register **a**, and
778 If either or both of the values are not numbers, dc(1) will raise an error
779 and reset (see the **RESET** section).
783 : Like the above, but will execute register *s* if the comparison fails.
785 If either or both of the values are not numbers, dc(1) will raise an error
786 and reset (see the **RESET** section).
788 This is a **non-portable extension**.
792 : Pops two values off of the stack that must be numbers and compares them. If
793 the first value is not greater than the second (less than or equal to), then
794 the contents of register *r* are executed.
796 If either or both of the values are not numbers, dc(1) will raise an error
797 and reset (see the **RESET** section).
801 : Like the above, but will execute register *s* if the comparison fails.
803 If either or both of the values are not numbers, dc(1) will raise an error
804 and reset (see the **RESET** section).
806 This is a **non-portable extension**.
810 : Pops two values off of the stack that must be numbers and compares them. If
811 the first value is less than the second, then the contents of register *r*
814 If either or both of the values are not numbers, dc(1) will raise an error
815 and reset (see the **RESET** section).
819 : Like the above, but will execute register *s* if the comparison fails.
821 If either or both of the values are not numbers, dc(1) will raise an error
822 and reset (see the **RESET** section).
824 This is a **non-portable extension**.
828 : Pops two values off of the stack that must be numbers and compares them. If
829 the first value is not less than the second (greater than or equal to), then
830 the contents of register *r* are executed.
832 If either or both of the values are not numbers, dc(1) will raise an error
833 and reset (see the **RESET** section).
837 : Like the above, but will execute register *s* if the comparison fails.
839 If either or both of the values are not numbers, dc(1) will raise an error
840 and reset (see the **RESET** section).
842 This is a **non-portable extension**.
846 : Pops two values off of the stack that must be numbers and compares them. If
847 the first value is equal to the second, then the contents of register *r*
850 If either or both of the values are not numbers, dc(1) will raise an error
851 and reset (see the **RESET** section).
855 : Like the above, but will execute register *s* if the comparison fails.
857 If either or both of the values are not numbers, dc(1) will raise an error
858 and reset (see the **RESET** section).
860 This is a **non-portable extension**.
864 : Pops two values off of the stack that must be numbers and compares them. If
865 the first value is not equal to the second, then the contents of register
868 If either or both of the values are not numbers, dc(1) will raise an error
869 and reset (see the **RESET** section).
873 : Like the above, but will execute register *s* if the comparison fails.
875 If either or both of the values are not numbers, dc(1) will raise an error
876 and reset (see the **RESET** section).
878 This is a **non-portable extension**.
882 : Reads a line from the **stdin** and executes it. This is to allow macros to
883 request input from users.
887 : During execution of a macro, this exits the execution of that macro and the
888 execution of the macro that executed it. If there are no macros, or only one
889 macro executing, dc(1) exits.
893 : Pops a value from the stack which must be non-negative and is used the
894 number of macro executions to pop off of the execution stack. If the number
895 of levels to pop is greater than the number of executing macros, dc(1)
900 : Pushes the depth of the execution stack onto the stack. The execution stack
901 is the stack of string executions. The number that is pushed onto the stack
902 is exactly as many as is needed to make dc(1) exit with the **Q** command,
903 so the sequence **,Q** will make dc(1) exit.
907 These commands query status of the stack or its top value.
911 : Pops a value off of the stack.
913 If it is a number, calculates the number of significant decimal digits it
914 has and pushes the result. It will push **1** if the argument is **0** with
917 If it is a string, pushes the number of characters the string has.
921 : Pops a value off of the stack.
923 If it is a number, pushes the *scale* of the value onto the stack.
925 If it is a string, pushes **0**.
929 : Pushes the current depth of the stack (before execution of this command)
934 : Pushes the current stack depth of the register *r* onto the main stack.
936 Because each register has a depth of **1** (with the value **0** in the top
937 item) when dc(1) starts, dc(1) requires that each register's stack must
938 always have at least one item; dc(1) will give an error and reset otherwise
939 (see the **RESET** section). This means that this command will never push
942 This is a **non-portable extension**.
946 These commands manipulate arrays.
950 : Pops the top two values off of the stack. The second value will be stored in
951 the array *r* (see the **REGISTERS** section), indexed by the first value.
955 : Pops the value on top of the stack and uses it as an index into the array
956 *r*. The selected value is then pushed onto the stack.
960 : Pushes the length of the array *r* onto the stack.
962 This is a **non-portable extension**.
966 These commands retrieve global settings. These are the only commands that
967 require multiple specific characters, and all of them begin with the letter
968 **g**. Only the characters below are allowed after the character **g**; any
969 other character produces a parse error (see the **ERRORS** section).
973 : Pushes the line length set by **DC_LINE_LENGTH** (see the **ENVIRONMENT
974 VARIABLES** section) onto the stack.
978 : Pushes **0** onto the stack if the leading zero setting has not been enabled
979 with the **-z** or **-\-leading-zeroes** options (see the **OPTIONS**
980 section), non-zero otherwise.
984 Registers are names that can store strings, numbers, and arrays. (Number/string
985 registers do not interfere with array registers.)
987 Each register is also its own stack, so the current register value is the top of
988 the stack for the register. All registers, when first referenced, have one value
989 (**0**) in their stack, and it is a runtime error to attempt to pop that item
990 off of the register stack.
992 In non-extended register mode, a register name is just the single character that
993 follows any command that needs a register name. The only exceptions are: a
994 newline (**'\\n'**) and a left bracket (**'['**); it is a parse error for a
995 newline or a left bracket to be used as a register name.
997 ## Extended Register Mode
999 Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited
1000 amounts of registers, if extended register mode is enabled.
1002 If extended register mode is enabled (**-x** or **-\-extended-register**
1003 command-line arguments are given), then normal single character registers are
1004 used *unless* the character immediately following a command that needs a
1005 register name is a space (according to **isspace()**) and not a newline
1008 In that case, the register name is found according to the regex
1009 **\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if
1010 the next non-space characters do not match that regex.
1014 When dc(1) encounters an error or a signal that it has a non-default handler
1015 for, it resets. This means that several things happen.
1017 First, any macros that are executing are stopped and popped off the stack.
1018 The behavior is not unlike that of exceptions in programming languages. Then
1019 the execution point is set so that any code waiting to execute (after all
1020 macros returned) is skipped.
1022 Thus, when dc(1) resets, it skips any remaining code waiting to be executed.
1023 Then, if it is interactive mode, and the error was not a fatal error (see the
1024 **EXIT STATUS** section), it asks for more input; otherwise, it exits with the
1025 appropriate return code.
1029 Most dc(1) implementations use **char** types to calculate the value of **1**
1030 decimal digit at a time, but that can be slow. This dc(1) does something
1033 It uses large integers to calculate more than **1** decimal digit at a time. If
1034 built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is
1035 **64**, then each integer has **9** decimal digits. If built in an environment
1036 where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
1037 value (the number of decimal digits per large integer) is called
1040 In addition, this dc(1) uses an even larger integer for overflow checking. This
1041 integer type depends on the value of **DC_LONG_BIT**, but is always at least
1042 twice as large as the integer type used to store digits.
1046 The following are the limits on dc(1):
1050 : The number of bits in the **long** type in the environment where dc(1) was
1051 built. This determines how many decimal digits can be stored in a single
1052 large integer (see the **PERFORMANCE** section).
1056 : The number of decimal digits per large integer (see the **PERFORMANCE**
1057 section). Depends on **DC_LONG_BIT**.
1061 : The max decimal number that each large integer can store (see
1062 **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**.
1066 : The max number that the overflow type (see the **PERFORMANCE** section) can
1067 hold. Depends on **DC_LONG_BIT**.
1071 : The maximum output base. Set at **DC_BASE_POW**.
1075 : The maximum size of arrays. Set at **SIZE_MAX-1**.
1079 : The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**.
1083 : The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**.
1087 : The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**.
1091 : The maximum length of a number (in decimal digits), which includes digits
1092 after the decimal point. Set at **DC_OVERFLOW_MAX-1**.
1096 : The maximum integer (inclusive) returned by the **'** command, if dc(1). Set
1097 at **2\^DC_LONG_BIT-1**.
1101 : The maximum allowable exponent (positive or negative). Set at
1102 **DC_OVERFLOW_MAX**.
1106 : The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
1108 These limits are meant to be effectively non-existent; the limits are so large
1109 (at least on 64-bit machines) that there should not be any point at which they
1110 become a problem. In fact, memory should be exhausted before these limits should
1113 # ENVIRONMENT VARIABLES
1115 dc(1) recognizes the following environment variables:
1119 : This is another way to give command-line arguments to dc(1). They should be
1120 in the same format as all other command-line arguments. These are always
1121 processed first, so any files given in **DC_ENV_ARGS** will be processed
1122 before arguments and files given on the command-line. This gives the user
1123 the ability to set up "standard" options and files to be used at every
1124 invocation. The most useful thing for such files to contain would be useful
1125 functions that the user might want every time dc(1) runs. Another use would
1126 be to use the **-e** option to set **scale** to a value other than **0**.
1128 The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments,
1129 but it does not understand escape sequences. For example, the string
1130 **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string
1131 **"/home/gavin/some \"dc\" file.dc"** will include the backslashes.
1133 The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
1134 if you have a file with any number of single quotes in the name, you can use
1135 double quotes as the outside quotes, as in **"some 'dc' file.dc"**, and vice
1136 versa if you have a file with double quotes. However, handling a file with
1137 both kinds of quotes in **DC_ENV_ARGS** is not supported due to the
1138 complexity of the parsing, though such files are still supported on the
1139 command-line where the parsing is done by the shell.
1143 : If this environment variable exists and contains an integer that is greater
1144 than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output
1145 lines to that length, including the backslash newline combo. The default
1146 line length is **70**.
1148 The special value of **0** will disable line length checking and print
1149 numbers without regard to line length and without backslashes and newlines.
1153 : If dc(1) is not in interactive mode (see the **INTERACTIVE MODE** section),
1154 then this environment variable has no effect because dc(1) exits on
1155 **SIGINT** when not in interactive mode.
1157 However, when dc(1) is in interactive mode, then if this environment
1158 variable exists and contains an integer, a non-zero value makes dc(1) reset
1159 on **SIGINT**, rather than exit, and zero makes dc(1) exit. If this
1160 environment variable exists and is *not* an integer, then dc(1) will exit on
1163 This environment variable overrides the default, which can be queried with
1164 the **-h** or **-\-help** options.
1168 : If TTY mode is *not* available (see the **TTY MODE** section), then this
1169 environment variable has no effect.
1171 However, when TTY mode is available, then if this environment variable
1172 exists and contains an integer, then a non-zero value makes dc(1) use TTY
1173 mode, and zero makes dc(1) not use TTY mode.
1175 This environment variable overrides the default, which can be queried with
1176 the **-h** or **-\-help** options.
1180 : If TTY mode is *not* available (see the **TTY MODE** section), then this
1181 environment variable has no effect.
1183 However, when TTY mode is available, then if this environment variable
1184 exists and contains an integer, a non-zero value makes dc(1) use a prompt,
1185 and zero or a non-integer makes dc(1) not use a prompt. If this environment
1186 variable does not exist and **DC_TTY_MODE** does, then the value of the
1187 **DC_TTY_MODE** environment variable is used.
1189 This environment variable and the **DC_TTY_MODE** environment variable
1190 override the default, which can be queried with the **-h** or **-\-help**
1195 dc(1) returns the following exit statuses:
1203 : A math error occurred. This follows standard practice of using **1** for
1204 expected errors, since math errors will happen in the process of normal
1207 Math errors include divide by **0**, taking the square root of a negative
1208 number, using a negative number as a bound for the pseudo-random number
1209 generator, attempting to convert a negative number to a hardware integer,
1210 overflow when converting a number to a hardware integer, overflow when
1211 calculating the size of a number, and attempting to use a non-integer where
1212 an integer is required.
1214 Converting to a hardware integer happens for the second operand of the power
1215 (**\^**), places (**\@**), left shift (**H**), and right shift (**h**)
1220 : A parse error occurred.
1222 Parse errors include unexpected **EOF**, using an invalid character, failing
1223 to find the end of a string or comment, and using a token where it is
1228 : A runtime error occurred.
1230 Runtime errors include assigning an invalid number to any global (**ibase**,
1231 **obase**, or **scale**), giving a bad expression to a **read()** call,
1232 calling **read()** inside of a **read()** call, type errors (including
1233 attempting to execute a number), and attempting an operation when the stack
1234 has too few elements.
1238 : A fatal error occurred.
1240 Fatal errors include memory allocation errors, I/O errors, failing to open
1241 files, attempting to use files that do not have only ASCII characters (dc(1)
1242 only accepts ASCII characters), attempting to open a directory as a file,
1243 and giving invalid command-line options.
1245 The exit status **4** is special; when a fatal error occurs, dc(1) always exits
1246 and returns **4**, no matter what mode dc(1) is in.
1248 The other statuses will only be returned when dc(1) is not in interactive mode
1249 (see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the
1250 **RESET** section) and accepts more input when one of those errors occurs in
1251 interactive mode. This is also the case when interactive mode is forced by the
1252 **-i** flag or **-\-interactive** option.
1254 These exit statuses allow dc(1) to be used in shell scripting with error
1255 checking, and its normal behavior can be forced by using the **-i** flag or
1256 **-\-interactive** option.
1260 Like bc(1), dc(1) has an interactive mode and a non-interactive mode.
1261 Interactive mode is turned on automatically when both **stdin** and **stdout**
1262 are hooked to a terminal, but the **-i** flag and **-\-interactive** option can
1263 turn it on in other situations.
1265 In interactive mode, dc(1) attempts to recover from errors (see the **RESET**
1266 section), and in normal execution, flushes **stdout** as soon as execution is
1267 done for the current input. dc(1) may also reset on **SIGINT** instead of exit,
1268 depending on the contents of, or default for, the **DC_SIGINT_RESET**
1269 environment variable (see the **ENVIRONMENT VARIABLES** section).
1273 If **stdin**, **stdout**, and **stderr** are all connected to a TTY, then "TTY
1274 mode" is considered to be available, and thus, dc(1) can turn on TTY mode,
1275 subject to some settings.
1277 If there is the environment variable **DC_TTY_MODE** in the environment (see the
1278 **ENVIRONMENT VARIABLES** section), then if that environment variable contains a
1279 non-zero integer, dc(1) will turn on TTY mode when **stdin**, **stdout**, and
1280 **stderr** are all connected to a TTY. If the **DC_TTY_MODE** environment
1281 variable exists but is *not* a non-zero integer, then dc(1) will not turn TTY
1284 If the environment variable **DC_TTY_MODE** does *not* exist, the default
1285 setting is used. The default setting can be queried with the **-h** or
1286 **-\-help** options.
1288 TTY mode is different from interactive mode because interactive mode is required
1289 in the [bc(1) specification][1], and interactive mode requires only **stdin**
1290 and **stdout** to be connected to a terminal.
1292 ## Command-Line History
1294 Command-line history is only enabled if TTY mode is, i.e., that **stdin**,
1295 **stdout**, and **stderr** are connected to a TTY and the **DC_TTY_MODE**
1296 environment variable (see the **ENVIRONMENT VARIABLES** section) and its default
1297 do not disable TTY mode. See the **COMMAND LINE HISTORY** section for more
1302 If TTY mode is available, then a prompt can be enabled. Like TTY mode itself, it
1303 can be turned on or off with an environment variable: **DC_PROMPT** (see the
1304 **ENVIRONMENT VARIABLES** section).
1306 If the environment variable **DC_PROMPT** exists and is a non-zero integer, then
1307 the prompt is turned on when **stdin**, **stdout**, and **stderr** are connected
1308 to a TTY and the **-P** and **-\-no-prompt** options were not used. The read
1309 prompt will be turned on under the same conditions, except that the **-R** and
1310 **-\-no-read-prompt** options must also not be used.
1312 However, if **DC_PROMPT** does not exist, the prompt can be enabled or disabled
1313 with the **DC_TTY_MODE** environment variable, the **-P** and **-\-no-prompt**
1314 options, and the **-R** and **-\-no-read-prompt** options. See the **ENVIRONMENT
1315 VARIABLES** and **OPTIONS** sections for more details.
1319 Sending a **SIGINT** will cause dc(1) to do one of two things.
1321 If dc(1) is not in interactive mode (see the **INTERACTIVE MODE** section), or
1322 the **DC_SIGINT_RESET** environment variable (see the **ENVIRONMENT VARIABLES**
1323 section), or its default, is either not an integer or it is zero, dc(1) will
1326 However, if dc(1) is in interactive mode, and the **DC_SIGINT_RESET** or its
1327 default is an integer and non-zero, then dc(1) will stop executing the current
1328 input and reset (see the **RESET** section) upon receiving a **SIGINT**.
1330 Note that "current input" can mean one of two things. If dc(1) is processing
1331 input from **stdin** in interactive mode, it will ask for more input. If dc(1)
1332 is processing input from a file in interactive mode, it will stop processing the
1333 file and start processing the next file, if one exists, or ask for input from
1334 **stdin** if no other file exists.
1336 This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it
1337 can seem as though dc(1) did not respond to the signal since it will immediately
1338 start executing the next file. This is by design; most files that users execute
1339 when interacting with dc(1) have function definitions, which are quick to parse.
1340 If a file takes a long time to execute, there may be a bug in that file. The
1341 rest of the files could still be executed without problem, allowing the user to
1344 **SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the
1345 default handler for all other signals. The one exception is **SIGHUP**; in that
1346 case, and only when dc(1) is in TTY mode (see the **TTY MODE** section), a
1347 **SIGHUP** will cause dc(1) to clean up and exit.
1349 # COMMAND LINE HISTORY
1351 dc(1) supports interactive command-line editing.
1353 If dc(1) can be in TTY mode (see the **TTY MODE** section), history can be
1354 enabled. This means that command-line history can only be enabled when
1355 **stdin**, **stdout**, and **stderr** are all connected to a TTY.
1357 Like TTY mode itself, it can be turned on or off with the environment variable
1358 **DC_TTY_MODE** (see the **ENVIRONMENT VARIABLES** section).
1360 **Note**: tabs are converted to 8 spaces.
1368 The dc(1) utility operators are compliant with the operators in the bc(1)
1369 [IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1] specification.
1373 None are known. Report bugs at https://git.yzena.com/gavin/bc.
1377 Gavin D. Howard <gavin@yzena.com> and contributors.
1379 [1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html