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 decimal reverse-Polish notation calculator
37 **dc** [**-hiPvVx**] [**--version**] [**--help**] [**--interactive**] [**--no-prompt**] [**--extended-register**] [**-e** *expr*] [**--expression**=*expr*...] [**-f** *file*...] [**-file**=*file*...] [*file*...]
41 dc(1) is an arbitrary-precision calculator. It uses a stack (reverse Polish
42 notation) to store numbers and results of computations. Arithmetic operations
43 pop arguments off of the stack and push the results.
45 If no files are given on the command-line as extra arguments (i.e., not as
46 **-f** or **--file** arguments), then dc(1) reads from **stdin**. Otherwise,
47 those files are processed, and dc(1) will then exit.
49 This is different from the dc(1) on OpenBSD and possibly other dc(1)
50 implementations, where **-e** (**--expression**) and **-f** (**--file**)
51 arguments cause dc(1) to execute them and exit. The reason for this is that this
52 dc(1) allows users to set arguments in the environment variable **DC_ENV_ARGS**
53 (see the **ENVIRONMENT VARIABLES** section). Any expressions given on the
54 command-line should be used to set up a standard environment. For example, if a
55 user wants the **scale** always set to **10**, they can set **DC_ENV_ARGS** to
56 **-e 10k**, and this dc(1) will always start with a **scale** of **10**.
58 If users want to have dc(1) exit after processing all input from **-e** and
59 **-f** arguments (and their equivalents), then they can just simply add **-e q**
60 as the last command-line argument or define the environment variable
65 The following are the options that dc(1) accepts.
69 : Prints a usage message and quits.
71 **-v**, **-V**, **--version**
73 : Print the version information (copyright header) and exit.
75 **-i**, **--interactive**
77 : Forces interactive mode. (See the **INTERACTIVE MODE** section.)
79 This is a **non-portable extension**.
81 **-P**, **--no-prompt**
83 : 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 exponent (the portion after the **e**) must be
223 an integer. An example is **1.89237e9**, which is equal to **1892370000**.
224 Negative 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. The *scale* of
340 the result is equal to **scale**.
342 The first value popped off of the stack must be an integer, and if that
343 value is negative, the second value popped off of the stack must be
348 : The top value is popped off the stack, its square root is computed, and the
349 result is pushed onto the stack. The *scale* of the result is equal to
352 The value popped off of the stack must be non-negative.
356 : If this command *immediately* precedes a number (i.e., no spaces or other
357 commands), then that number is input as a negative number.
359 Otherwise, the top value on the stack is popped and copied, and the copy is
360 negated and pushed onto the stack. This behavior without a number is a
361 **non-portable extension**.
365 : The top value is popped off the stack, and if it is zero, it is pushed back
366 onto the stack. Otherwise, its absolute value is pushed onto the stack.
368 This is a **non-portable extension**.
372 : The top three values are popped off the stack, a modular exponentiation is
373 computed, and the result is pushed onto the stack.
375 The first value popped is used as the reduction modulus and must be an
376 integer and non-zero. The second value popped is used as the exponent and
377 must be an integer and non-negative. The third value popped is the base and
380 This is a **non-portable extension**.
384 : The top value is popped off the stack and copied, and the copy is truncated
385 and pushed onto the stack.
387 This is a **non-portable extension**.
391 : The top two values are popped off the stack, and the precision of the second
392 is set to the value of the first, whether by truncation or extension.
394 The first value popped off of the stack must be an integer and non-negative.
396 This is a **non-portable extension**.
400 : The top two values are popped off the stack, and the second is shifted left
401 (radix shifted right) to the value of the first.
403 The first value popped off of the stack must be an integer and non-negative.
405 This is a **non-portable extension**.
409 : The top two values are popped off the stack, and the second is shifted right
410 (radix shifted left) to the value of the first.
412 The first value popped off of the stack must be an integer and non-negative.
414 This is a **non-portable extension**.
418 : The top two values are popped off of the stack, they are compared, and a
419 **1** is pushed if they are equal, or **0** otherwise.
421 This is a **non-portable extension**.
425 : The top value is popped off of the stack, and if it a **0**, a **1** is
426 pushed; otherwise, a **0** is pushed.
428 This is a **non-portable extension**.
432 : The top two values are popped off of the stack, they are compared, and a
433 **1** is pushed if the first is less than the second, or **0** otherwise.
435 This is a **non-portable extension**.
439 : The top two values are popped off of the stack, they are compared, and a
440 **1** is pushed if the first is less than or equal to the second, or **0**
443 This is a **non-portable extension**.
447 : The top two values are popped off of the stack, they are compared, and a
448 **1** is pushed if the first is greater than the second, or **0** otherwise.
450 This is a **non-portable extension**.
454 : The top two values are popped off of the stack, they are compared, and a
455 **1** is pushed if the first is greater than or equal to the second, or
458 This is a **non-portable extension**.
462 : The top two values are popped off of the stack. If they are both non-zero, a
463 **1** is pushed onto the stack. If either of them is zero, or both of them
464 are, then a **0** is pushed onto the stack.
466 This is like the **&&** operator in bc(1), and it is *not* a short-circuit
469 This is a **non-portable extension**.
473 : The top two values are popped off of the stack. If at least one of them is
474 non-zero, a **1** is pushed onto the stack. If both of them are zero, then a
475 **0** is pushed onto the stack.
477 This is like the **||** operator in bc(1), and it is *not* a short-circuit
480 This is a **non-portable extension**.
482 ## Pseudo-Random Number Generator
484 dc(1) has a built-in pseudo-random number generator. These commands query the
485 pseudo-random number generator. (See Parameters for more information about the
486 **seed** value that controls the pseudo-random number generator.)
488 The pseudo-random number generator is guaranteed to **NOT** be
489 cryptographically secure.
493 : Generates an integer between 0 and **DC_RAND_MAX**, inclusive (see the
496 The generated integer is made as unbiased as possible, subject to the
497 limitations of the pseudo-random number generator.
499 This is a **non-portable extension**.
503 : Pops a value off of the stack, which is used as an **exclusive** upper bound
504 on the integer that will be generated. If the bound is negative or is a
505 non-integer, an error is raised, and dc(1) resets (see the **RESET**
506 section) while **seed** remains unchanged. If the bound is larger than
507 **DC_RAND_MAX**, the higher bound is honored by generating several
508 pseudo-random integers, multiplying them by appropriate powers of
509 **DC_RAND_MAX+1**, and adding them together. Thus, the size of integer that
510 can be generated with this command is unbounded. Using this command will
511 change the value of **seed**, unless the operand is **0** or **1**. In that
512 case, **0** is pushed onto the stack, and **seed** is *not* changed.
514 The generated integer is made as unbiased as possible, subject to the
515 limitations of the pseudo-random number generator.
517 This is a **non-portable extension**.
521 These commands control the stack.
525 : Removes all items from ("clears") the stack.
529 : Copies the item on top of the stack ("duplicates") and pushes the copy onto
534 : Swaps ("reverses") the two top items on the stack.
538 : Pops ("removes") the top value from the stack.
542 These commands control registers (see the **REGISTERS** section).
546 : Pops the value off the top of the stack and stores it into register *r*.
550 : Copies the value in register *r* and pushes it onto the stack. This does not
551 alter the contents of *r*.
555 : Pops the value off the top of the (main) stack and pushes it onto the stack
556 of register *r*. The previous value of the register becomes inaccessible.
560 : Pops the value off the top of the stack for register *r* and push it onto
561 the main stack. The previous value in the stack for register *r*, if any, is
562 now accessible via the **l***r* command.
566 These commands control the values of **ibase**, **obase**, **scale**, and
567 **seed**. Also see the **SYNTAX** section.
571 : Pops the value off of the top of the stack and uses it to set **ibase**,
572 which must be between **2** and **16**, inclusive.
574 If the value on top of the stack has any *scale*, the *scale* is ignored.
578 : Pops the value off of the top of the stack and uses it to set **obase**,
579 which must be between **0** and **DC_BASE_MAX**, inclusive (see the
580 **LIMITS** section and the **NUMBERS** section).
582 If the value on top of the stack has any *scale*, the *scale* is ignored.
586 : Pops the value off of the top of the stack and uses it to set **scale**,
587 which must be non-negative.
589 If the value on top of the stack has any *scale*, the *scale* is ignored.
593 : Pops the value off of the top of the stack and uses it to set **seed**. The
594 meaning of **seed** is dependent on the current pseudo-random number
595 generator but is guaranteed to not change except for new major versions.
597 The *scale* and sign of the value may be significant.
599 If a previously used **seed** value is used again, the pseudo-random number
600 generator is guaranteed to produce the same sequence of pseudo-random
601 numbers as it did when the **seed** value was previously used.
603 The exact value assigned to **seed** is not guaranteed to be returned if the
604 **J** command is used. However, if **seed** *does* return a different value,
605 both values, when assigned to **seed**, are guaranteed to produce the same
606 sequence of pseudo-random numbers. This means that certain values assigned
607 to **seed** will not produce unique sequences of pseudo-random numbers.
609 There is no limit to the length (number of significant decimal digits) or
610 *scale* of the value that can be assigned to **seed**.
612 This is a **non-portable extension**.
616 : Pushes the current value of **ibase** onto the main stack.
620 : Pushes the current value of **obase** onto the main stack.
624 : Pushes the current value of **scale** onto the main stack.
628 : Pushes the current value of **seed** onto the main stack.
630 This is a **non-portable extension**.
634 : Pushes the maximum allowable value of **ibase** onto the main stack.
636 This is a **non-portable extension**.
640 : Pushes the maximum allowable value of **obase** onto the main stack.
642 This is a **non-portable extension**.
646 : Pushes the maximum allowable value of **scale** onto the main stack.
648 This is a **non-portable extension**.
652 : Pushes the maximum (inclusive) integer that can be generated with the **'**
653 pseudo-random number generator command.
655 This is a **non-portable extension**.
659 The following commands control strings.
661 dc(1) can work with both numbers and strings, and registers (see the
662 **REGISTERS** section) can hold both strings and numbers. dc(1) always knows
663 whether the contents of a register are a string or a number.
665 While arithmetic operations have to have numbers, and will print an error if
666 given a string, other commands accept strings.
668 Strings can also be executed as macros. For example, if the string **[1pR]** is
669 executed as a macro, then the code **1pR** is executed, meaning that the **1**
670 will be printed with a newline after and then popped from the stack.
672 **\[**_characters_**\]**
674 : Makes a string containing *characters* and pushes it onto the stack.
676 If there are brackets (**\[** and **\]**) in the string, then they must be
677 balanced. Unbalanced brackets can be escaped using a backslash (**\\**)
680 If there is a backslash character in the string, the character after it
681 (even another backslash) is put into the string verbatim, but the (first)
686 : The value on top of the stack is popped.
688 If it is a number, it is truncated and its absolute value is taken. The
689 result mod **UCHAR_MAX+1** is calculated. If that result is **0**, push an
690 empty string; otherwise, push a one-character string where the character is
691 the result of the mod interpreted as an ASCII character.
693 If it is a string, then a new string is made. If the original string is
694 empty, the new string is empty. If it is not, then the first character of
695 the original string is used to create the new string as a one-character
696 string. The new string is then pushed onto the stack.
698 This is a **non-portable extension**.
702 : Pops a value off of the top of the stack.
704 If it is a number, it is pushed back onto the stack.
706 If it is a string, it is executed as a macro.
708 This behavior is the norm whenever a macro is executed, whether by this
709 command or by the conditional execution commands below.
713 : Pops two values off of the stack that must be numbers and compares them. If
714 the first value is greater than the second, then the contents of register
717 For example, **0 1>a** will execute the contents of register **a**, and
720 If either or both of the values are not numbers, dc(1) will raise an error
721 and reset (see the **RESET** section).
725 : Like the above, but will execute register *s* if the comparison fails.
727 If either or both of the values are not numbers, dc(1) will raise an error
728 and reset (see the **RESET** section).
730 This is a **non-portable extension**.
734 : Pops two values off of the stack that must be numbers and compares them. If
735 the first value is not greater than the second (less than or equal to), then
736 the contents of register *r* are executed.
738 If either or both of the values are not numbers, dc(1) will raise an error
739 and reset (see the **RESET** section).
743 : Like the above, but will execute register *s* if the comparison fails.
745 If either or both of the values are not numbers, dc(1) will raise an error
746 and reset (see the **RESET** section).
748 This is a **non-portable extension**.
752 : Pops two values off of the stack that must be numbers and compares them. If
753 the first value is less than the second, then the contents of register *r*
756 If either or both of the values are not numbers, dc(1) will raise an error
757 and reset (see the **RESET** section).
761 : Like the above, but will execute register *s* if the comparison fails.
763 If either or both of the values are not numbers, dc(1) will raise an error
764 and reset (see the **RESET** section).
766 This is a **non-portable extension**.
770 : Pops two values off of the stack that must be numbers and compares them. If
771 the first value is not less than the second (greater than or equal to), then
772 the contents of register *r* are executed.
774 If either or both of the values are not numbers, dc(1) will raise an error
775 and reset (see the **RESET** section).
779 : Like the above, but will execute register *s* if the comparison fails.
781 If either or both of the values are not numbers, dc(1) will raise an error
782 and reset (see the **RESET** section).
784 This is a **non-portable extension**.
788 : Pops two values off of the stack that must be numbers and compares them. If
789 the first value is equal to the second, then the contents of register *r*
792 If either or both of the values are not numbers, dc(1) will raise an error
793 and reset (see the **RESET** section).
797 : Like the above, but will execute register *s* if the comparison fails.
799 If either or both of the values are not numbers, dc(1) will raise an error
800 and reset (see the **RESET** section).
802 This is a **non-portable extension**.
806 : Pops two values off of the stack that must be numbers and compares them. If
807 the first value is not equal to the second, then the contents of register
810 If either or both of the values are not numbers, dc(1) will raise an error
811 and reset (see the **RESET** section).
815 : Like the above, but will execute register *s* if the comparison fails.
817 If either or both of the values are not numbers, dc(1) will raise an error
818 and reset (see the **RESET** section).
820 This is a **non-portable extension**.
824 : Reads a line from the **stdin** and executes it. This is to allow macros to
825 request input from users.
829 : During execution of a macro, this exits the execution of that macro and the
830 execution of the macro that executed it. If there are no macros, or only one
831 macro executing, dc(1) exits.
835 : Pops a value from the stack which must be non-negative and is used the
836 number of macro executions to pop off of the execution stack. If the number
837 of levels to pop is greater than the number of executing macros, dc(1)
842 These commands query status of the stack or its top value.
846 : Pops a value off of the stack.
848 If it is a number, calculates the number of significant decimal digits it
849 has and pushes the result.
851 If it is a string, pushes the number of characters the string has.
855 : Pops a value off of the stack.
857 If it is a number, pushes the *scale* of the value onto the stack.
859 If it is a string, pushes **0**.
863 : Pushes the current stack depth (before execution of this command).
867 These commands manipulate arrays.
871 : Pops the top two values off of the stack. The second value will be stored in
872 the array *r* (see the **REGISTERS** section), indexed by the first value.
876 : Pops the value on top of the stack and uses it as an index into the array
877 *r*. The selected value is then pushed onto the stack.
881 Registers are names that can store strings, numbers, and arrays. (Number/string
882 registers do not interfere with array registers.)
884 Each register is also its own stack, so the current register value is the top of
885 the stack for the register. All registers, when first referenced, have one value
886 (**0**) in their stack.
888 In non-extended register mode, a register name is just the single character that
889 follows any command that needs a register name. The only exception is a newline
890 (**'\\n'**); it is a parse error for a newline to be used as a register name.
892 ## Extended Register Mode
894 Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited
895 amounts of registers, if extended register mode is enabled.
897 If extended register mode is enabled (**-x** or **--extended-register**
898 command-line arguments are given), then normal single character registers are
899 used *unless* the character immediately following a command that needs a
900 register name is a space (according to **isspace()**) and not a newline
903 In that case, the register name is found according to the regex
904 **\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if
905 the next non-space characters do not match that regex.
909 When dc(1) encounters an error or a signal that it has a non-default handler
910 for, it resets. This means that several things happen.
912 First, any macros that are executing are stopped and popped off the stack.
913 The behavior is not unlike that of exceptions in programming languages. Then
914 the execution point is set so that any code waiting to execute (after all
915 macros returned) is skipped.
917 Thus, when dc(1) resets, it skips any remaining code waiting to be executed.
918 Then, if it is interactive mode, and the error was not a fatal error (see the
919 **EXIT STATUS** section), it asks for more input; otherwise, it exits with the
920 appropriate return code.
924 Most dc(1) implementations use **char** types to calculate the value of **1**
925 decimal digit at a time, but that can be slow. This dc(1) does something
928 It uses large integers to calculate more than **1** decimal digit at a time. If
929 built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is
930 **64**, then each integer has **9** decimal digits. If built in an environment
931 where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
932 value (the number of decimal digits per large integer) is called
935 In addition, this dc(1) uses an even larger integer for overflow checking. This
936 integer type depends on the value of **DC_LONG_BIT**, but is always at least
937 twice as large as the integer type used to store digits.
941 The following are the limits on dc(1):
945 : The number of bits in the **long** type in the environment where dc(1) was
946 built. This determines how many decimal digits can be stored in a single
947 large integer (see the **PERFORMANCE** section).
951 : The number of decimal digits per large integer (see the **PERFORMANCE**
952 section). Depends on **DC_LONG_BIT**.
956 : The max decimal number that each large integer can store (see
957 **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**.
961 : The max number that the overflow type (see the **PERFORMANCE** section) can
962 hold. Depends on **DC_LONG_BIT**.
966 : The maximum output base. Set at **DC_BASE_POW**.
970 : The maximum size of arrays. Set at **SIZE_MAX-1**.
974 : The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**.
978 : The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**.
982 : The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**.
986 : The maximum length of a number (in decimal digits), which includes digits
987 after the decimal point. Set at **DC_OVERFLOW_MAX-1**.
991 : The maximum integer (inclusive) returned by the **'** command, if dc(1). Set
992 at **2\^DC_LONG_BIT-1**.
996 : The maximum allowable exponent (positive or negative). Set at
1001 : The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
1003 These limits are meant to be effectively non-existent; the limits are so large
1004 (at least on 64-bit machines) that there should not be any point at which they
1005 become a problem. In fact, memory should be exhausted before these limits should
1008 # ENVIRONMENT VARIABLES
1010 dc(1) recognizes the following environment variables:
1014 : This is another way to give command-line arguments to dc(1). They should be
1015 in the same format as all other command-line arguments. These are always
1016 processed first, so any files given in **DC_ENV_ARGS** will be processed
1017 before arguments and files given on the command-line. This gives the user
1018 the ability to set up "standard" options and files to be used at every
1019 invocation. The most useful thing for such files to contain would be useful
1020 functions that the user might want every time dc(1) runs. Another use would
1021 be to use the **-e** option to set **scale** to a value other than **0**.
1023 The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments,
1024 but it does not understand escape sequences. For example, the string
1025 **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string
1026 **"/home/gavin/some \"dc\" file.dc"** will include the backslashes.
1028 The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
1029 if you have a file with any number of single quotes in the name, you can use
1030 double quotes as the outside quotes, as in **"some 'bc' file.bc"**, and vice
1031 versa if you have a file with double quotes. However, handling a file with
1032 both kinds of quotes in **DC_ENV_ARGS** is not supported due to the
1033 complexity of the parsing, though such files are still supported on the
1034 command-line where the parsing is done by the shell.
1038 : If this environment variable exists and contains an integer that is greater
1039 than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output
1040 lines to that length, including the backslash newline combo. The default
1041 line length is **70**.
1045 : If this variable exists (no matter the contents), dc(1) will exit
1046 immediately after executing expressions and files given by the **-e** and/or
1047 **-f** command-line options (and any equivalents).
1051 dc(1) returns the following exit statuses:
1059 : A math error occurred. This follows standard practice of using **1** for
1060 expected errors, since math errors will happen in the process of normal
1063 Math errors include divide by **0**, taking the square root of a negative
1064 number, using a negative number as a bound for the pseudo-random number
1065 generator, attempting to convert a negative number to a hardware integer,
1066 overflow when converting a number to a hardware integer, and attempting to
1067 use a non-integer where an integer is required.
1069 Converting to a hardware integer happens for the second operand of the power
1070 (**\^**), places (**\@**), left shift (**H**), and right shift (**h**)
1075 : A parse error occurred.
1077 Parse errors include unexpected **EOF**, using an invalid character, failing
1078 to find the end of a string or comment, and using a token where it is
1083 : A runtime error occurred.
1085 Runtime errors include assigning an invalid number to **ibase**, **obase**,
1086 or **scale**; give a bad expression to a **read()** call, calling **read()**
1087 inside of a **read()** call, type errors, and attempting an operation when
1088 the stack has too few elements.
1092 : A fatal error occurred.
1094 Fatal errors include memory allocation errors, I/O errors, failing to open
1095 files, attempting to use files that do not have only ASCII characters (dc(1)
1096 only accepts ASCII characters), attempting to open a directory as a file,
1097 and giving invalid command-line options.
1099 The exit status **4** is special; when a fatal error occurs, dc(1) always exits
1100 and returns **4**, no matter what mode dc(1) is in.
1102 The other statuses will only be returned when dc(1) is not in interactive mode
1103 (see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the
1104 **RESET** section) and accepts more input when one of those errors occurs in
1105 interactive mode. This is also the case when interactive mode is forced by the
1106 **-i** flag or **--interactive** option.
1108 These exit statuses allow dc(1) to be used in shell scripting with error
1109 checking, and its normal behavior can be forced by using the **-i** flag or
1110 **--interactive** option.
1114 Like bc(1), dc(1) has an interactive mode and a non-interactive mode.
1115 Interactive mode is turned on automatically when both **stdin** and **stdout**
1116 are hooked to a terminal, but the **-i** flag and **--interactive** option can
1117 turn it on in other cases.
1119 In interactive mode, dc(1) attempts to recover from errors (see the **RESET**
1120 section), and in normal execution, flushes **stdout** as soon as execution is
1121 done for the current input.
1125 If **stdin**, **stdout**, and **stderr** are all connected to a TTY, dc(1) turns
1128 TTY mode is required for history to be enabled (see the **COMMAND LINE HISTORY**
1129 section). It is also required to enable special handling for **SIGINT** signals.
1131 TTY mode is different from interactive mode because interactive mode is required
1132 in the [bc(1) specification][1], and interactive mode requires only **stdin**
1133 and **stdout** to be connected to a terminal.
1137 Sending a **SIGINT** will cause dc(1) to stop execution of the current input. If
1138 dc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
1139 **RESET** section). Otherwise, it will clean up and exit.
1141 Note that "current input" can mean one of two things. If dc(1) is processing
1142 input from **stdin** in TTY mode, it will ask for more input. If dc(1) is
1143 processing input from a file in TTY mode, it will stop processing the file and
1144 start processing the next file, if one exists, or ask for input from **stdin**
1145 if no other file exists.
1147 This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it
1148 can seem as though dc(1) did not respond to the signal since it will immediately
1149 start executing the next file. This is by design; most files that users execute
1150 when interacting with dc(1) have function definitions, which are quick to parse.
1151 If a file takes a long time to execute, there may be a bug in that file. The
1152 rest of the files could still be executed without problem, allowing the user to
1155 **SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the
1156 default handler for all other signals. The one exception is **SIGHUP**; in that
1157 case, when dc(1) is in TTY mode, a **SIGHUP** will cause dc(1) to clean up and
1160 # COMMAND LINE HISTORY
1162 dc(1) supports interactive command-line editing. If dc(1) is in TTY mode (see
1163 the **TTY MODE** section), history is enabled. Previous lines can be recalled
1164 and edited with the arrow keys.
1166 **Note**: tabs are converted to 8 spaces.
1170 This dc(1) ships with support for adding error messages for different locales
1171 and thus, supports **LC_MESSAGS**.
1179 The dc(1) utility operators are compliant with the operators in the bc(1)
1180 [IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1] specification.
1184 None are known. Report bugs at https://git.yzena.com/gavin/bc.
1188 Gavin D. Howard <gavin@yzena.com> and contributors.
1190 [1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html