3 SPDX-License-Identifier: BSD-2-Clause
5 Copyright (c) 2018-2020 Gavin D. Howard and contributors.
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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 : Disables the prompt in TTY mode. (The prompt is only enabled in TTY mode.
84 See the **TTY MODE** section) This is mostly for those users that do not
85 want a prompt or are not used to having them in dc(1). Most of those users
86 would want to put this option in **DC_ENV_ARGS**.
88 This is a **non-portable extension**.
90 **-x** **--extended-register**
92 : Enables extended register mode. See the *Extended Register Mode* subsection
93 of the **REGISTERS** section for more information.
95 This is a **non-portable extension**.
97 **-e** *expr*, **--expression**=*expr*
99 : Evaluates *expr*. If multiple expressions are given, they are evaluated in
100 order. If files are given as well (see below), the expressions and files are
101 evaluated in the order given. This means that if a file is given before an
102 expression, the file is read in and evaluated first.
104 After processing all expressions and files, dc(1) will exit, unless **-**
105 (**stdin**) was given as an argument at least once to **-f** or **--file**.
107 This is a **non-portable extension**.
109 **-f** *file*, **--file**=*file*
111 : Reads in *file* and evaluates it, line by line, as though it were read
112 through **stdin**. If expressions are also given (see above), the
113 expressions are evaluated in the order given.
115 After processing all expressions and files, dc(1) will exit, unless **-**
116 (**stdin**) was given as an argument at least once to **-f** or **--file**.
117 However, if any other **-e**, **--expression**, **-f**, or **--file**
118 arguments are given after that, bc(1) will give a fatal error and exit.
120 This is a **non-portable extension**.
122 All long options are **non-portable extensions**.
126 Any non-error output is written to **stdout**.
128 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
129 error (see the **EXIT STATUS** section) if it cannot write to **stdout**, so if
130 **stdout** is closed, as in **dc <file> >&-**, it will quit with an error. This
131 is done so that dc(1) can report problems when **stdout** is redirected to a
134 If there are scripts that depend on the behavior of other dc(1) implementations,
135 it is recommended that those scripts be changed to redirect **stdout** to
140 Any error output is written to **stderr**.
142 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
143 error (see the **EXIT STATUS** section) if it cannot write to **stderr**, so if
144 **stderr** is closed, as in **dc <file> 2>&-**, it will quit with an error. This
145 is done so that dc(1) can exit with an error code when **stderr** is redirected
148 If there are scripts that depend on the behavior of other dc(1) implementations,
149 it is recommended that those scripts be changed to redirect **stderr** to
154 Each item in the input source code, either a number (see the **NUMBERS**
155 section) or a command (see the **COMMANDS** section), is processed and executed,
156 in order. Input is processed immediately when entered.
158 **ibase** is a register (see the **REGISTERS** section) that determines how to
159 interpret constant numbers. It is the "input" base, or the number base used for
160 interpreting input numbers. **ibase** is initially **10**. The max allowable
161 value for **ibase** is **16**. The min allowable value for **ibase** is **2**.
162 The max allowable value for **ibase** can be queried in dc(1) programs with the
165 **obase** is a register (see the **REGISTERS** section) that determines how to
166 output results. It is the "output" base, or the number base used for outputting
167 numbers. **obase** is initially **10**. The max allowable value for **obase** is
168 **DC_BASE_MAX** and can be queried with the **U** command. The min allowable
169 value for **obase** is **0**. If **obase** is **0**, values are output in
170 scientific notation, and if **obase** is **1**, values are output in engineering
171 notation. Otherwise, values are output in the specified base.
173 Outputting in scientific and engineering notations are **non-portable
176 The *scale* of an expression is the number of digits in the result of the
177 expression right of the decimal point, and **scale** is a register (see the
178 **REGISTERS** section) that sets the precision of any operations (with
179 exceptions). **scale** is initially **0**. **scale** cannot be negative. The max
180 allowable value for **scale** can be queried in dc(1) programs with the **V**
183 **seed** is a register containing the current seed for the pseudo-random number
184 generator. If the current value of **seed** is queried and stored, then if it is
185 assigned to **seed** later, the pseudo-random number generator is guaranteed to
186 produce the same sequence of pseudo-random numbers that were generated after the
187 value of **seed** was first queried.
189 Multiple values assigned to **seed** can produce the same sequence of
190 pseudo-random numbers. Likewise, when a value is assigned to **seed**, it is not
191 guaranteed that querying **seed** immediately after will return the same value.
192 In addition, the value of **seed** will change after any call to the **'**
193 command or the **"** command that does not get receive a value of **0** or
194 **1**. The maximum integer returned by the **'** command can be queried with the
197 **Note**: The values returned by the pseudo-random number generator with the
198 **'** and **"** commands are guaranteed to **NOT** be cryptographically secure.
199 This is a consequence of using a seeded pseudo-random number generator. However,
200 they **are** guaranteed to be reproducible with identical **seed** values.
202 The pseudo-random number generator, **seed**, and all associated operations are
203 **non-portable extensions**.
207 Comments go from **#** until, and not including, the next newline. This is a
208 **non-portable extension**.
212 Numbers are strings made up of digits, uppercase letters up to **F**, and at
213 most **1** period for a radix. Numbers can have up to **DC_NUM_MAX** digits.
214 Uppercase letters are equal to **9** + their position in the alphabet (i.e.,
215 **A** equals **10**, or **9+1**). If a digit or letter makes no sense with the
216 current value of **ibase**, they are set to the value of the highest valid digit
219 Single-character numbers (i.e., **A** alone) take the value that they would have
220 if they were valid digits, regardless of the value of **ibase**. This means that
221 **A** alone always equals decimal **10** and **F** alone always equals decimal
224 In addition, dc(1) accepts numbers in scientific notation. These have the form
225 **\<number\>e\<integer\>**. The power (the portion after the **e**) must be an
226 integer. An example is **1.89237e9**, which is equal to **1892370000**. Negative
227 exponents are also allowed, so **4.2890e_3** is equal to **0.0042890**.
229 **WARNING**: Both the number and the exponent in scientific notation are
230 interpreted according to the current **ibase**, but the number is still
231 multiplied by **10\^exponent** regardless of the current **ibase**. For example,
232 if **ibase** is **16** and dc(1) is given the number string **FFeA**, the
233 resulting decimal number will be **2550000000000**, and if dc(1) is given the
234 number string **10e_4**, the resulting decimal number will be **0.0016**.
236 Accepting input as scientific notation is a **non-portable extension**.
240 The valid commands are listed below.
244 These commands are used for printing.
246 Note that both scientific notation and engineering notation are available for
247 printing numbers. Scientific notation is activated by assigning **0** to
248 **obase** using **0o**, and engineering notation is activated by assigning **1**
249 to **obase** using **1o**. To deactivate them, just assign a different value to
252 Printing numbers in scientific notation and/or engineering notation is a
253 **non-portable extension**.
257 : Prints the value on top of the stack, whether number or string, and prints a
260 This does not alter the stack.
264 : Prints the value on top of the stack, whether number or string, and pops it
269 : Pops a value off the stack.
271 If the value is a number, it is truncated and the absolute value of the
272 result is printed as though **obase** is **UCHAR_MAX+1** and each digit is
273 interpreted as an ASCII character, making it a byte stream.
275 If the value is a string, it is printed without a trailing newline.
277 This is a **non-portable extension**.
281 : Prints the entire contents of the stack, in order from newest to oldest,
282 without altering anything.
284 Users should use this command when they get lost.
288 These are the commands used for arithmetic.
292 : The top two values are popped off the stack, added, and the result is pushed
293 onto the stack. The *scale* of the result is equal to the max *scale* of
298 : The top two values are popped off the stack, subtracted, and the result is
299 pushed onto the stack. The *scale* of the result is equal to the max
300 *scale* of both operands.
304 : The top two values are popped off the stack, multiplied, and the result is
305 pushed onto the stack. If **a** is the *scale* of the first expression and
306 **b** is the *scale* of the second expression, the *scale* of the result
307 is equal to **min(a+b,max(scale,a,b))** where **min()** and **max()** return
312 : The top two values are popped off the stack, divided, and the result is
313 pushed onto the stack. The *scale* of the result is equal to **scale**.
315 The first value popped off of the stack must be non-zero.
319 : The top two values are popped off the stack, remaindered, and the result is
320 pushed onto the stack.
322 Remaindering is equivalent to 1) Computing **a/b** to current **scale**, and
323 2) Using the result of step 1 to calculate **a-(a/b)\*b** to *scale*
324 **max(scale+scale(b),scale(a))**.
326 The first value popped off of the stack must be non-zero.
330 : The top two values are popped off the stack, divided and remaindered, and
331 the results (divided first, remainder second) are pushed onto the stack.
332 This is equivalent to **x y / x y %** except that **x** and **y** are only
335 The first value popped off of the stack must be non-zero.
337 This is a **non-portable extension**.
341 : The top two values are popped off the stack, the second is raised to the
342 power of the first, and the result is pushed onto the stack.
344 The first value popped off of the stack must be an integer, and if that
345 value is negative, the second value popped off of the stack must be
350 : The top value is popped off the stack, its square root is computed, and the
351 result is pushed onto the stack. The *scale* of the result is equal to
354 The value popped off of the stack must be non-negative.
358 : If this command *immediately* precedes a number (i.e., no spaces or other
359 commands), then that number is input as a negative number.
361 Otherwise, the top value on the stack is popped and copied, and the copy is
362 negated and pushed onto the stack. This behavior without a number is a
363 **non-portable extension**.
367 : The top value is popped off the stack, and if it is zero, it is pushed back
368 onto the stack. Otherwise, its absolute value is pushed onto the stack.
370 This is a **non-portable extension**.
374 : The top three values are popped off the stack, a modular exponentiation is
375 computed, and the result is pushed onto the stack.
377 The first value popped is used as the reduction modulus and must be an
378 integer and non-zero. The second value popped is used as the exponent and
379 must be an integer and non-negative. The third value popped is the base and
382 This is a **non-portable extension**.
386 : The top value is popped off the stack and copied, and the copy is truncated
387 and pushed onto the stack.
389 This is a **non-portable extension**.
393 : The top two values are popped off the stack, and the precision of the second
394 is set to the value of the first, whether by truncation or extension.
396 The first value popped off of the stack must be an integer and non-negative.
398 This is a **non-portable extension**.
402 : The top two values are popped off the stack, and the second is shifted left
403 (radix shifted right) to the value of the first.
405 The first value popped off of the stack must be an integer and non-negative.
407 This is a **non-portable extension**.
411 : The top two values are popped off the stack, and the second is shifted right
412 (radix shifted left) to the value of the first.
414 The first value popped off of the stack must be an integer and non-negative.
416 This is a **non-portable extension**.
420 : The top two values are popped off of the stack, they are compared, and a
421 **1** is pushed if they are equal, or **0** otherwise.
423 This is a **non-portable extension**.
427 : The top value is popped off of the stack, and if it a **0**, a **1** is
428 pushed; otherwise, a **0** is pushed.
430 This is a **non-portable extension**.
434 : The top two values are popped off of the stack, they are compared, and a
435 **1** is pushed if the first is less than the second, or **0** otherwise.
437 This is a **non-portable extension**.
441 : The top two values are popped off of the stack, they are compared, and a
442 **1** is pushed if the first is less than or equal to the second, or **0**
445 This is a **non-portable extension**.
449 : The top two values are popped off of the stack, they are compared, and a
450 **1** is pushed if the first is greater than the second, or **0** otherwise.
452 This is a **non-portable extension**.
456 : The top two values are popped off of the stack, they are compared, and a
457 **1** is pushed if the first is greater than or equal to the second, or
460 This is a **non-portable extension**.
464 : The top two values are popped off of the stack. If they are both non-zero, a
465 **1** is pushed onto the stack. If either of them is zero, or both of them
466 are, then a **0** is pushed onto the stack.
468 This is like the **&&** operator in bc(1), and it is *not* a short-circuit
471 This is a **non-portable extension**.
475 : The top two values are popped off of the stack. If at least one of them is
476 non-zero, a **1** is pushed onto the stack. If both of them are zero, then a
477 **0** is pushed onto the stack.
479 This is like the **||** operator in bc(1), and it is *not* a short-circuit
482 This is a **non-portable extension**.
484 ## Pseudo-Random Number Generator
486 dc(1) has a built-in pseudo-random number generator. These commands query the
487 pseudo-random number generator. (See Parameters for more information about the
488 **seed** value that controls the pseudo-random number generator.)
490 The pseudo-random number generator is guaranteed to **NOT** be
491 cryptographically secure.
495 : Generates an integer between 0 and **DC_RAND_MAX**, inclusive (see the
498 The generated integer is made as unbiased as possible, subject to the
499 limitations of the pseudo-random number generator.
501 This is a **non-portable extension**.
505 : Pops a value off of the stack, which is used as an **exclusive** upper bound
506 on the integer that will be generated. If the bound is negative or is a
507 non-integer, an error is raised, and dc(1) resets (see the **RESET**
508 section) while **seed** remains unchanged. If the bound is larger than
509 **DC_RAND_MAX**, the higher bound is honored by generating several
510 pseudo-random integers, multiplying them by appropriate powers of
511 **DC_RAND_MAX+1**, and adding them together. Thus, the size of integer that
512 can be generated with this command is unbounded. Using this command will
513 change the value of **seed**, unless the operand is **0** or **1**. In that
514 case, **0** is pushed onto the stack, and **seed** is *not* changed.
516 The generated integer is made as unbiased as possible, subject to the
517 limitations of the pseudo-random number generator.
519 This is a **non-portable extension**.
523 These commands control the stack.
527 : Removes all items from ("clears") the stack.
531 : Copies the item on top of the stack ("duplicates") and pushes the copy onto
536 : Swaps ("reverses") the two top items on the stack.
540 : Pops ("removes") the top value from the stack.
544 These commands control registers (see the **REGISTERS** section).
548 : Pops the value off the top of the stack and stores it into register *r*.
552 : Copies the value in register *r* and pushes it onto the stack. This does not
553 alter the contents of *r*.
557 : Pops the value off the top of the (main) stack and pushes it onto the stack
558 of register *r*. The previous value of the register becomes inaccessible.
562 : Pops the value off the top of the stack for register *r* and push it onto
563 the main stack. The previous value in the stack for register *r*, if any, is
564 now accessible via the **l***r* command.
568 These commands control the values of **ibase**, **obase**, **scale**, and
569 **seed**. Also see the **SYNTAX** section.
573 : Pops the value off of the top of the stack and uses it to set **ibase**,
574 which must be between **2** and **16**, inclusive.
576 If the value on top of the stack has any *scale*, the *scale* is ignored.
580 : Pops the value off of the top of the stack and uses it to set **obase**,
581 which must be between **0** and **DC_BASE_MAX**, inclusive (see the
582 **LIMITS** section and the **NUMBERS** section).
584 If the value on top of the stack has any *scale*, the *scale* is ignored.
588 : Pops the value off of the top of the stack and uses it to set **scale**,
589 which must be non-negative.
591 If the value on top of the stack has any *scale*, the *scale* is ignored.
595 : Pops the value off of the top of the stack and uses it to set **seed**. The
596 meaning of **seed** is dependent on the current pseudo-random number
597 generator but is guaranteed to not change except for new major versions.
599 The *scale* and sign of the value may be significant.
601 If a previously used **seed** value is used again, the pseudo-random number
602 generator is guaranteed to produce the same sequence of pseudo-random
603 numbers as it did when the **seed** value was previously used.
605 The exact value assigned to **seed** is not guaranteed to be returned if the
606 **J** command is used. However, if **seed** *does* return a different value,
607 both values, when assigned to **seed**, are guaranteed to produce the same
608 sequence of pseudo-random numbers. This means that certain values assigned
609 to **seed** will not produce unique sequences of pseudo-random numbers.
611 There is no limit to the length (number of significant decimal digits) or
612 *scale* of the value that can be assigned to **seed**.
614 This is a **non-portable extension**.
618 : Pushes the current value of **ibase** onto the main stack.
622 : Pushes the current value of **obase** onto the main stack.
626 : Pushes the current value of **scale** onto the main stack.
630 : Pushes the current value of **seed** onto the main stack.
632 This is a **non-portable extension**.
636 : Pushes the maximum allowable value of **ibase** onto the main stack.
638 This is a **non-portable extension**.
642 : Pushes the maximum allowable value of **obase** onto the main stack.
644 This is a **non-portable extension**.
648 : Pushes the maximum allowable value of **scale** onto the main stack.
650 This is a **non-portable extension**.
654 : Pushes the maximum (inclusive) integer that can be generated with the **'**
655 pseudo-random number generator command.
657 This is a **non-portable extension**.
661 The following commands control strings.
663 dc(1) can work with both numbers and strings, and registers (see the
664 **REGISTERS** section) can hold both strings and numbers. dc(1) always knows
665 whether the contents of a register are a string or a number.
667 While arithmetic operations have to have numbers, and will print an error if
668 given a string, other commands accept strings.
670 Strings can also be executed as macros. For example, if the string **[1pR]** is
671 executed as a macro, then the code **1pR** is executed, meaning that the **1**
672 will be printed with a newline after and then popped from the stack.
674 **\[**_characters_**\]**
676 : Makes a string containing *characters* and pushes it onto the stack.
678 If there are brackets (**\[** and **\]**) in the string, then they must be
679 balanced. Unbalanced brackets can be escaped using a backslash (**\\**)
682 If there is a backslash character in the string, the character after it
683 (even another backslash) is put into the string verbatim, but the (first)
688 : The value on top of the stack is popped.
690 If it is a number, it is truncated and its absolute value is taken. The
691 result mod **UCHAR_MAX+1** is calculated. If that result is **0**, push an
692 empty string; otherwise, push a one-character string where the character is
693 the result of the mod interpreted as an ASCII character.
695 If it is a string, then a new string is made. If the original string is
696 empty, the new string is empty. If it is not, then the first character of
697 the original string is used to create the new string as a one-character
698 string. The new string is then pushed onto the stack.
700 This is a **non-portable extension**.
704 : Pops a value off of the top of the stack.
706 If it is a number, it is pushed back onto the stack.
708 If it is a string, it is executed as a macro.
710 This behavior is the norm whenever a macro is executed, whether by this
711 command or by the conditional execution commands below.
715 : Pops two values off of the stack that must be numbers and compares them. If
716 the first value is greater than the second, then the contents of register
719 For example, **0 1>a** will execute the contents of register **a**, and
722 If either or both of the values are not numbers, dc(1) will raise an error
723 and reset (see the **RESET** section).
727 : Like the above, but will execute register *s* if the comparison fails.
729 If either or both of the values are not numbers, dc(1) will raise an error
730 and reset (see the **RESET** section).
732 This is a **non-portable extension**.
736 : Pops two values off of the stack that must be numbers and compares them. If
737 the first value is not greater than the second (less than or equal to), then
738 the contents of register *r* are executed.
740 If either or both of the values are not numbers, dc(1) will raise an error
741 and reset (see the **RESET** section).
745 : Like the above, but will execute register *s* if the comparison fails.
747 If either or both of the values are not numbers, dc(1) will raise an error
748 and reset (see the **RESET** section).
750 This is a **non-portable extension**.
754 : Pops two values off of the stack that must be numbers and compares them. If
755 the first value is less than the second, then the contents of register *r*
758 If either or both of the values are not numbers, dc(1) will raise an error
759 and reset (see the **RESET** section).
763 : Like the above, but will execute register *s* if the comparison fails.
765 If either or both of the values are not numbers, dc(1) will raise an error
766 and reset (see the **RESET** section).
768 This is a **non-portable extension**.
772 : Pops two values off of the stack that must be numbers and compares them. If
773 the first value is not less than the second (greater than or equal to), then
774 the contents of register *r* are executed.
776 If either or both of the values are not numbers, dc(1) will raise an error
777 and reset (see the **RESET** section).
781 : Like the above, but will execute register *s* if the comparison fails.
783 If either or both of the values are not numbers, dc(1) will raise an error
784 and reset (see the **RESET** section).
786 This is a **non-portable extension**.
790 : Pops two values off of the stack that must be numbers and compares them. If
791 the first value is equal to the second, then the contents of register *r*
794 If either or both of the values are not numbers, dc(1) will raise an error
795 and reset (see the **RESET** section).
799 : Like the above, but will execute register *s* if the comparison fails.
801 If either or both of the values are not numbers, dc(1) will raise an error
802 and reset (see the **RESET** section).
804 This is a **non-portable extension**.
808 : Pops two values off of the stack that must be numbers and compares them. If
809 the first value is not equal to the second, then the contents of register
812 If either or both of the values are not numbers, dc(1) will raise an error
813 and reset (see the **RESET** section).
817 : Like the above, but will execute register *s* if the comparison fails.
819 If either or both of the values are not numbers, dc(1) will raise an error
820 and reset (see the **RESET** section).
822 This is a **non-portable extension**.
826 : Reads a line from the **stdin** and executes it. This is to allow macros to
827 request input from users.
831 : During execution of a macro, this exits the execution of that macro and the
832 execution of the macro that executed it. If there are no macros, or only one
833 macro executing, dc(1) exits.
837 : Pops a value from the stack which must be non-negative and is used the
838 number of macro executions to pop off of the execution stack. If the number
839 of levels to pop is greater than the number of executing macros, dc(1)
844 These commands query status of the stack or its top value.
848 : Pops a value off of the stack.
850 If it is a number, calculates the number of significant decimal digits it
851 has and pushes the result.
853 If it is a string, pushes the number of characters the string has.
857 : Pops a value off of the stack.
859 If it is a number, pushes the *scale* of the value onto the stack.
861 If it is a string, pushes **0**.
865 : Pushes the current stack depth (before execution of this command).
869 These commands manipulate arrays.
873 : Pops the top two values off of the stack. The second value will be stored in
874 the array *r* (see the **REGISTERS** section), indexed by the first value.
878 : Pops the value on top of the stack and uses it as an index into the array
879 *r*. The selected value is then pushed onto the stack.
883 Registers are names that can store strings, numbers, and arrays. (Number/string
884 registers do not interfere with array registers.)
886 Each register is also its own stack, so the current register value is the top of
887 the stack for the register. All registers, when first referenced, have one value
888 (**0**) in their stack.
890 In non-extended register mode, a register name is just the single character that
891 follows any command that needs a register name. The only exception is a newline
892 (**'\\n'**); it is a parse error for a newline to be used as a register name.
894 ## Extended Register Mode
896 Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited
897 amounts of registers, if extended register mode is enabled.
899 If extended register mode is enabled (**-x** or **--extended-register**
900 command-line arguments are given), then normal single character registers are
901 used *unless* the character immediately following a command that needs a
902 register name is a space (according to **isspace()**) and not a newline
905 In that case, the register name is found according to the regex
906 **\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if
907 the next non-space characters do not match that regex.
911 When dc(1) encounters an error or a signal that it has a non-default handler
912 for, it resets. This means that several things happen.
914 First, any macros that are executing are stopped and popped off the stack.
915 The behavior is not unlike that of exceptions in programming languages. Then
916 the execution point is set so that any code waiting to execute (after all
917 macros returned) is skipped.
919 Thus, when dc(1) resets, it skips any remaining code waiting to be executed.
920 Then, if it is interactive mode, and the error was not a fatal error (see the
921 **EXIT STATUS** section), it asks for more input; otherwise, it exits with the
922 appropriate return code.
926 Most dc(1) implementations use **char** types to calculate the value of **1**
927 decimal digit at a time, but that can be slow. This dc(1) does something
930 It uses large integers to calculate more than **1** decimal digit at a time. If
931 built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is
932 **64**, then each integer has **9** decimal digits. If built in an environment
933 where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
934 value (the number of decimal digits per large integer) is called
937 In addition, this dc(1) uses an even larger integer for overflow checking. This
938 integer type depends on the value of **DC_LONG_BIT**, but is always at least
939 twice as large as the integer type used to store digits.
943 The following are the limits on dc(1):
947 : The number of bits in the **long** type in the environment where dc(1) was
948 built. This determines how many decimal digits can be stored in a single
949 large integer (see the **PERFORMANCE** section).
953 : The number of decimal digits per large integer (see the **PERFORMANCE**
954 section). Depends on **DC_LONG_BIT**.
958 : The max decimal number that each large integer can store (see
959 **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**.
963 : The max number that the overflow type (see the **PERFORMANCE** section) can
964 hold. Depends on **DC_LONG_BIT**.
968 : The maximum output base. Set at **DC_BASE_POW**.
972 : The maximum size of arrays. Set at **SIZE_MAX-1**.
976 : The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**.
980 : The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**.
984 : The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**.
988 : The maximum length of a number (in decimal digits), which includes digits
989 after the decimal point. Set at **DC_OVERFLOW_MAX-1**.
993 : The maximum integer (inclusive) returned by the **'** command, if dc(1). Set
994 at **2\^DC_LONG_BIT-1**.
998 : The maximum allowable exponent (positive or negative). Set at
1003 : The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
1005 These limits are meant to be effectively non-existent; the limits are so large
1006 (at least on 64-bit machines) that there should not be any point at which they
1007 become a problem. In fact, memory should be exhausted before these limits should
1010 # ENVIRONMENT VARIABLES
1012 dc(1) recognizes the following environment variables:
1016 : This is another way to give command-line arguments to dc(1). They should be
1017 in the same format as all other command-line arguments. These are always
1018 processed first, so any files given in **DC_ENV_ARGS** will be processed
1019 before arguments and files given on the command-line. This gives the user
1020 the ability to set up "standard" options and files to be used at every
1021 invocation. The most useful thing for such files to contain would be useful
1022 functions that the user might want every time dc(1) runs. Another use would
1023 be to use the **-e** option to set **scale** to a value other than **0**.
1025 The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments,
1026 but it does not understand escape sequences. For example, the string
1027 **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string
1028 **"/home/gavin/some \"dc\" file.dc"** will include the backslashes.
1030 The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
1031 if you have a file with any number of single quotes in the name, you can use
1032 double quotes as the outside quotes, as in **"some 'bc' file.bc"**, and vice
1033 versa if you have a file with double quotes. However, handling a file with
1034 both kinds of quotes in **DC_ENV_ARGS** is not supported due to the
1035 complexity of the parsing, though such files are still supported on the
1036 command-line where the parsing is done by the shell.
1040 : If this environment variable exists and contains an integer that is greater
1041 than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output
1042 lines to that length, including the backslash newline combo. The default
1043 line length is **70**.
1047 : If this variable exists (no matter the contents), dc(1) will exit
1048 immediately after executing expressions and files given by the **-e** and/or
1049 **-f** command-line options (and any equivalents).
1053 dc(1) returns the following exit statuses:
1061 : A math error occurred. This follows standard practice of using **1** for
1062 expected errors, since math errors will happen in the process of normal
1065 Math errors include divide by **0**, taking the square root of a negative
1066 number, using a negative number as a bound for the pseudo-random number
1067 generator, attempting to convert a negative number to a hardware integer,
1068 overflow when converting a number to a hardware integer, and attempting to
1069 use a non-integer where an integer is required.
1071 Converting to a hardware integer happens for the second operand of the power
1072 (**\^**), places (**\@**), left shift (**H**), and right shift (**h**)
1077 : A parse error occurred.
1079 Parse errors include unexpected **EOF**, using an invalid character, failing
1080 to find the end of a string or comment, and using a token where it is
1085 : A runtime error occurred.
1087 Runtime errors include assigning an invalid number to **ibase**, **obase**,
1088 or **scale**; give a bad expression to a **read()** call, calling **read()**
1089 inside of a **read()** call, type errors, and attempting an operation when
1090 the stack has too few elements.
1094 : A fatal error occurred.
1096 Fatal errors include memory allocation errors, I/O errors, failing to open
1097 files, attempting to use files that do not have only ASCII characters (dc(1)
1098 only accepts ASCII characters), attempting to open a directory as a file,
1099 and giving invalid command-line options.
1101 The exit status **4** is special; when a fatal error occurs, dc(1) always exits
1102 and returns **4**, no matter what mode dc(1) is in.
1104 The other statuses will only be returned when dc(1) is not in interactive mode
1105 (see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the
1106 **RESET** section) and accepts more input when one of those errors occurs in
1107 interactive mode. This is also the case when interactive mode is forced by the
1108 **-i** flag or **--interactive** option.
1110 These exit statuses allow dc(1) to be used in shell scripting with error
1111 checking, and its normal behavior can be forced by using the **-i** flag or
1112 **--interactive** option.
1116 Like bc(1), dc(1) has an interactive mode and a non-interactive mode.
1117 Interactive mode is turned on automatically when both **stdin** and **stdout**
1118 are hooked to a terminal, but the **-i** flag and **--interactive** option can
1119 turn it on in other cases.
1121 In interactive mode, dc(1) attempts to recover from errors (see the **RESET**
1122 section), and in normal execution, flushes **stdout** as soon as execution is
1123 done for the current input.
1127 If **stdin**, **stdout**, and **stderr** are all connected to a TTY, dc(1) turns
1130 TTY mode is required for history to be enabled (see the **COMMAND LINE HISTORY**
1131 section). It is also required to enable special handling for **SIGINT** signals.
1133 The prompt is enabled in TTY mode.
1135 TTY mode is different from interactive mode because interactive mode is required
1136 in the [bc(1) specification][1], and interactive mode requires only **stdin**
1137 and **stdout** to be connected to a terminal.
1141 Sending a **SIGINT** will cause dc(1) to stop execution of the current input. If
1142 dc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
1143 **RESET** section). Otherwise, it will clean up and exit.
1145 Note that "current input" can mean one of two things. If dc(1) is processing
1146 input from **stdin** in TTY mode, it will ask for more input. If dc(1) is
1147 processing input from a file in TTY mode, it will stop processing the file and
1148 start processing the next file, if one exists, or ask for input from **stdin**
1149 if no other file exists.
1151 This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it
1152 can seem as though dc(1) did not respond to the signal since it will immediately
1153 start executing the next file. This is by design; most files that users execute
1154 when interacting with dc(1) have function definitions, which are quick to parse.
1155 If a file takes a long time to execute, there may be a bug in that file. The
1156 rest of the files could still be executed without problem, allowing the user to
1159 **SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the
1160 default handler for all other signals. The one exception is **SIGHUP**; in that
1161 case, when dc(1) is in TTY mode, a **SIGHUP** will cause dc(1) to clean up and
1164 # COMMAND LINE HISTORY
1166 dc(1) supports interactive command-line editing. If dc(1) is in TTY mode (see
1167 the **TTY MODE** section), history is enabled. Previous lines can be recalled
1168 and edited with the arrow keys.
1170 **Note**: tabs are converted to 8 spaces.
1174 This dc(1) ships with support for adding error messages for different locales
1175 and thus, supports **LC_MESSAGS**.
1183 The dc(1) utility operators are compliant with the operators in the bc(1)
1184 [IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1] specification.
1188 None are known. Report bugs at https://git.yzena.com/gavin/bc.
1192 Gavin D. Howard <yzena.tech@gmail.com> and contributors.
1194 [1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html