xref: /freebsd/contrib/bc/manuals/dc/N.1.md (revision c66ec88fed842fbaad62c30d510644ceb7bd2d71)
1<!---
2
3SPDX-License-Identifier: BSD-2-Clause
4
5Copyright (c) 2018-2020 Gavin D. Howard and contributors.
6
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10* Redistributions of source code must retain the above copyright notice, this
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29-->
30
31# Name
32
33dc - arbitrary-precision decimal reverse-Polish notation calculator
34
35# SYNOPSIS
36
37**dc** [**-hiPvVx**] [**--version**] [**--help**] [**--interactive**] [**--no-prompt**] [**--extended-register**] [**-e** *expr*] [**--expression**=*expr*...] [**-f** *file*...] [**-file**=*file*...] [*file*...]
38
39# DESCRIPTION
40
41dc(1) is an arbitrary-precision calculator. It uses a stack (reverse Polish
42notation) to store numbers and results of computations. Arithmetic operations
43pop arguments off of the stack and push the results.
44
45If 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,
47those files are processed, and dc(1) will then exit.
48
49This is different from the dc(1) on OpenBSD and possibly other dc(1)
50implementations, where **-e** (**--expression**) and **-f** (**--file**)
51arguments cause dc(1) to execute them and exit. The reason for this is that this
52dc(1) allows users to set arguments in the environment variable **DC_ENV_ARGS**
53(see the **ENVIRONMENT VARIABLES** section). Any expressions given on the
54command-line should be used to set up a standard environment. For example, if a
55user 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**.
57
58If 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**
60as the last command-line argument or define the environment variable
61**DC_EXPR_EXIT**.
62
63# OPTIONS
64
65The following are the options that dc(1) accepts.
66
67**-h**, **--help**
68
69:   Prints a usage message and quits.
70
71**-v**, **-V**, **--version**
72
73:   Print the version information (copyright header) and exit.
74
75**-i**, **--interactive**
76
77:   Forces interactive mode. (See the **INTERACTIVE MODE** section.)
78
79    This is a **non-portable extension**.
80
81**-P**, **--no-prompt**
82
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**.
87
88    This is a **non-portable extension**.
89
90**-x** **--extended-register**
91
92:   Enables extended register mode. See the *Extended Register Mode* subsection
93    of the **REGISTERS** section for more information.
94
95    This is a **non-portable extension**.
96
97**-e** *expr*, **--expression**=*expr*
98
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.
103
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**.
106
107    This is a **non-portable extension**.
108
109**-f** *file*, **--file**=*file*
110
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.
114
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.
119
120    This is a **non-portable extension**.
121
122All long options are **non-portable extensions**.
123
124# STDOUT
125
126Any non-error output is written to **stdout**.
127
128**Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
129error (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
131is done so that dc(1) can report problems when **stdout** is redirected to a
132file.
133
134If there are scripts that depend on the behavior of other dc(1) implementations,
135it is recommended that those scripts be changed to redirect **stdout** to
136**/dev/null**.
137
138# STDERR
139
140Any error output is written to **stderr**.
141
142**Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
143error (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
145is done so that dc(1) can exit with an error code when **stderr** is redirected
146to a file.
147
148If there are scripts that depend on the behavior of other dc(1) implementations,
149it is recommended that those scripts be changed to redirect **stderr** to
150**/dev/null**.
151
152# SYNTAX
153
154Each item in the input source code, either a number (see the **NUMBERS**
155section) or a command (see the **COMMANDS** section), is processed and executed,
156in order. Input is processed immediately when entered.
157
158**ibase** is a register (see the **REGISTERS** section) that determines how to
159interpret constant numbers. It is the "input" base, or the number base used for
160interpreting input numbers. **ibase** is initially **10**. The max allowable
161value for **ibase** is **16**. The min allowable value for **ibase** is **2**.
162The max allowable value for **ibase** can be queried in dc(1) programs with the
163**T** command.
164
165**obase** is a register (see the **REGISTERS** section) that determines how to
166output results. It is the "output" base, or the number base used for outputting
167numbers. **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
169value for **obase** is **0**. If **obase** is **0**, values are output in
170scientific notation, and if **obase** is **1**, values are output in engineering
171notation. Otherwise, values are output in the specified base.
172
173Outputting in scientific and engineering notations are **non-portable
174extensions**.
175
176The *scale* of an expression is the number of digits in the result of the
177expression right of the decimal point, and **scale** is a register (see the
178**REGISTERS** section) that sets the precision of any operations (with
179exceptions). **scale** is initially **0**. **scale** cannot be negative. The max
180allowable value for **scale** can be queried in dc(1) programs with the **V**
181command.
182
183**seed** is a register containing the current seed for the pseudo-random number
184generator. If the current value of **seed** is queried and stored, then if it is
185assigned to **seed** later, the pseudo-random number generator is guaranteed to
186produce the same sequence of pseudo-random numbers that were generated after the
187value of **seed** was first queried.
188
189Multiple values assigned to **seed** can produce the same sequence of
190pseudo-random numbers. Likewise, when a value is assigned to **seed**, it is not
191guaranteed that querying **seed** immediately after will return the same value.
192In addition, the value of **seed** will change after any call to the **'**
193command 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
195**W** command.
196
197**Note**: The values returned by the pseudo-random number generator with the
198**'** and **"** commands are guaranteed to **NOT** be cryptographically secure.
199This is a consequence of using a seeded pseudo-random number generator. However,
200they **are** guaranteed to be reproducible with identical **seed** values.
201
202The pseudo-random number generator, **seed**, and all associated operations are
203**non-portable extensions**.
204
205## Comments
206
207Comments go from **#** until, and not including, the next newline. This is a
208**non-portable extension**.
209
210# NUMBERS
211
212Numbers are strings made up of digits, uppercase letters up to **F**, and at
213most **1** period for a radix. Numbers can have up to **DC_NUM_MAX** digits.
214Uppercase 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
216current value of **ibase**, they are set to the value of the highest valid digit
217in **ibase**.
218
219Single-character numbers (i.e., **A** alone) take the value that they would have
220if 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
222**15**.
223
224In addition, dc(1) accepts numbers in scientific notation. These have the form
225**\<number\>e\<integer\>**. The exponent (the portion after the **e**) must be
226an integer. An example is **1.89237e9**, which is equal to **1892370000**.
227Negative exponents are also allowed, so **4.2890e_3** is equal to **0.0042890**.
228
229**WARNING**: Both the number and the exponent in scientific notation are
230interpreted according to the current **ibase**, but the number is still
231multiplied by **10\^exponent** regardless of the current **ibase**. For example,
232if **ibase** is **16** and dc(1) is given the number string **FFeA**, the
233resulting decimal number will be **2550000000000**, and if dc(1) is given the
234number string **10e_4**, the resulting decimal number will be **0.0016**.
235
236Accepting input as scientific notation is a **non-portable extension**.
237
238# COMMANDS
239
240The valid commands are listed below.
241
242## Printing
243
244These commands are used for printing.
245
246Note that both scientific notation and engineering notation are available for
247printing numbers. Scientific notation is activated by assigning **0** to
248**obase** using **0o**, and engineering notation is activated by assigning **1**
249to **obase** using **1o**. To deactivate them, just assign a different value to
250**obase**.
251
252Printing numbers in scientific notation and/or engineering notation is a
253**non-portable extension**.
254
255**p**
256
257:   Prints the value on top of the stack, whether number or string, and prints a
258    newline after.
259
260    This does not alter the stack.
261
262**n**
263
264:   Prints the value on top of the stack, whether number or string, and pops it
265    off of the stack.
266
267**P**
268
269:   Pops a value off the stack.
270
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.
274
275    If the value is a string, it is printed without a trailing newline.
276
277    This is a **non-portable extension**.
278
279**f**
280
281:   Prints the entire contents of the stack, in order from newest to oldest,
282    without altering anything.
283
284    Users should use this command when they get lost.
285
286## Arithmetic
287
288These are the commands used for arithmetic.
289
290**+**
291
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
294    both operands.
295
296**-**
297
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.
301
302**\***
303
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
308    the obvious values.
309
310**/**
311
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**.
314
315    The first value popped off of the stack must be non-zero.
316
317**%**
318
319:   The top two values are popped off the stack, remaindered, and the result is
320    pushed onto the stack.
321
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))**.
325
326    The first value popped off of the stack must be non-zero.
327
328**~**
329
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
333    evaluated once.
334
335    The first value popped off of the stack must be non-zero.
336
337    This is a **non-portable extension**.
338
339**\^**
340
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. The *scale* of
343    the result is equal to **scale**.
344
345    The first value popped off of the stack must be an integer, and if that
346    value is negative, the second value popped off of the stack must be
347    non-zero.
348
349**v**
350
351:   The top value is popped off the stack, its square root is computed, and the
352    result is pushed onto the stack. The *scale* of the result is equal to
353    **scale**.
354
355    The value popped off of the stack must be non-negative.
356
357**\_**
358
359:   If this command *immediately* precedes a number (i.e., no spaces or other
360    commands), then that number is input as a negative number.
361
362    Otherwise, the top value on the stack is popped and copied, and the copy is
363    negated and pushed onto the stack. This behavior without a number is a
364    **non-portable extension**.
365
366**b**
367
368:   The top value is popped off the stack, and if it is zero, it is pushed back
369    onto the stack. Otherwise, its absolute value is pushed onto the stack.
370
371    This is a **non-portable extension**.
372
373**|**
374
375:   The top three values are popped off the stack, a modular exponentiation is
376    computed, and the result is pushed onto the stack.
377
378    The first value popped is used as the reduction modulus and must be an
379    integer and non-zero. The second value popped is used as the exponent and
380    must be an integer and non-negative. The third value popped is the base and
381    must be an integer.
382
383    This is a **non-portable extension**.
384
385**\$**
386
387:   The top value is popped off the stack and copied, and the copy is truncated
388    and pushed onto the stack.
389
390    This is a **non-portable extension**.
391
392**\@**
393
394:   The top two values are popped off the stack, and the precision of the second
395    is set to the value of the first, whether by truncation or extension.
396
397    The first value popped off of the stack must be an integer and non-negative.
398
399    This is a **non-portable extension**.
400
401**H**
402
403:   The top two values are popped off the stack, and the second is shifted left
404    (radix shifted right) to the value of the first.
405
406    The first value popped off of the stack must be an integer and non-negative.
407
408    This is a **non-portable extension**.
409
410**h**
411
412:   The top two values are popped off the stack, and the second is shifted right
413    (radix shifted left) to the value of the first.
414
415    The first value popped off of the stack must be an integer and non-negative.
416
417    This is a **non-portable extension**.
418
419**G**
420
421:   The top two values are popped off of the stack, they are compared, and a
422    **1** is pushed if they are equal, or **0** otherwise.
423
424    This is a **non-portable extension**.
425
426**N**
427
428:   The top value is popped off of the stack, and if it a **0**, a **1** is
429    pushed; otherwise, a **0** is pushed.
430
431    This is a **non-portable extension**.
432
433**(**
434
435:   The top two values are popped off of the stack, they are compared, and a
436    **1** is pushed if the first is less than the second, or **0** otherwise.
437
438    This is a **non-portable extension**.
439
440**{**
441
442:   The top two values are popped off of the stack, they are compared, and a
443    **1** is pushed if the first is less than or equal to the second, or **0**
444    otherwise.
445
446    This is a **non-portable extension**.
447
448**)**
449
450:   The top two values are popped off of the stack, they are compared, and a
451    **1** is pushed if the first is greater than the second, or **0** otherwise.
452
453    This is a **non-portable extension**.
454
455**}**
456
457:   The top two values are popped off of the stack, they are compared, and a
458    **1** is pushed if the first is greater than or equal to the second, or
459    **0** otherwise.
460
461    This is a **non-portable extension**.
462
463**M**
464
465:   The top two values are popped off of the stack. If they are both non-zero, a
466    **1** is pushed onto the stack. If either of them is zero, or both of them
467    are, then a **0** is pushed onto the stack.
468
469    This is like the **&&** operator in bc(1), and it is *not* a short-circuit
470    operator.
471
472    This is a **non-portable extension**.
473
474**m**
475
476:   The top two values are popped off of the stack. If at least one of them is
477    non-zero, a **1** is pushed onto the stack. If both of them are zero, then a
478    **0** is pushed onto the stack.
479
480    This is like the **||** operator in bc(1), and it is *not* a short-circuit
481    operator.
482
483    This is a **non-portable extension**.
484
485## Pseudo-Random Number Generator
486
487dc(1) has a built-in pseudo-random number generator. These commands query the
488pseudo-random number generator. (See Parameters for more information about the
489**seed** value that controls the pseudo-random number generator.)
490
491The pseudo-random number generator is guaranteed to **NOT** be
492cryptographically secure.
493
494**'**
495
496:   Generates an integer between 0 and **DC_RAND_MAX**, inclusive (see the
497    **LIMITS** section).
498
499    The generated integer is made as unbiased as possible, subject to the
500    limitations of the pseudo-random number generator.
501
502    This is a **non-portable extension**.
503
504**"**
505
506:   Pops a value off of the stack, which is used as an **exclusive** upper bound
507    on the integer that will be generated. If the bound is negative or is a
508    non-integer, an error is raised, and dc(1) resets (see the **RESET**
509    section) while **seed** remains unchanged. If the bound is larger than
510    **DC_RAND_MAX**, the higher bound is honored by generating several
511    pseudo-random integers, multiplying them by appropriate powers of
512    **DC_RAND_MAX+1**, and adding them together. Thus, the size of integer that
513    can be generated with this command is unbounded. Using this command will
514    change the value of **seed**, unless the operand is **0** or **1**. In that
515    case, **0** is pushed onto the stack, and **seed** is *not* changed.
516
517    The generated integer is made as unbiased as possible, subject to the
518    limitations of the pseudo-random number generator.
519
520    This is a **non-portable extension**.
521
522## Stack Control
523
524These commands control the stack.
525
526**c**
527
528:   Removes all items from ("clears") the stack.
529
530**d**
531
532:   Copies the item on top of the stack ("duplicates") and pushes the copy onto
533    the stack.
534
535**r**
536
537:   Swaps ("reverses") the two top items on the stack.
538
539**R**
540
541:   Pops ("removes") the top value from the stack.
542
543## Register Control
544
545These commands control registers (see the **REGISTERS** section).
546
547**s***r*
548
549:   Pops the value off the top of the stack and stores it into register *r*.
550
551**l***r*
552
553:   Copies the value in register *r* and pushes it onto the stack. This does not
554    alter the contents of *r*.
555
556**S***r*
557
558:   Pops the value off the top of the (main) stack and pushes it onto the stack
559    of register *r*. The previous value of the register becomes inaccessible.
560
561**L***r*
562
563:   Pops the value off the top of the stack for register *r* and push it onto
564    the main stack. The previous value in the stack for register *r*, if any, is
565    now accessible via the **l***r* command.
566
567## Parameters
568
569These commands control the values of **ibase**, **obase**, **scale**, and
570**seed**. Also see the **SYNTAX** section.
571
572**i**
573
574:   Pops the value off of the top of the stack and uses it to set **ibase**,
575    which must be between **2** and **16**, inclusive.
576
577    If the value on top of the stack has any *scale*, the *scale* is ignored.
578
579**o**
580
581:   Pops the value off of the top of the stack and uses it to set **obase**,
582    which must be between **0** and **DC_BASE_MAX**, inclusive (see the
583    **LIMITS** section and the **NUMBERS** section).
584
585    If the value on top of the stack has any *scale*, the *scale* is ignored.
586
587**k**
588
589:   Pops the value off of the top of the stack and uses it to set **scale**,
590    which must be non-negative.
591
592    If the value on top of the stack has any *scale*, the *scale* is ignored.
593
594**j**
595
596:   Pops the value off of the top of the stack and uses it to set **seed**. The
597    meaning of **seed** is dependent on the current pseudo-random number
598    generator but is guaranteed to not change except for new major versions.
599
600    The *scale* and sign of the value may be significant.
601
602    If a previously used **seed** value is used again, the pseudo-random number
603    generator is guaranteed to produce the same sequence of pseudo-random
604    numbers as it did when the **seed** value was previously used.
605
606    The exact value assigned to **seed** is not guaranteed to be returned if the
607    **J** command is used. However, if **seed** *does* return a different value,
608    both values, when assigned to **seed**, are guaranteed to produce the same
609    sequence of pseudo-random numbers. This means that certain values assigned
610    to **seed** will not produce unique sequences of pseudo-random numbers.
611
612    There is no limit to the length (number of significant decimal digits) or
613    *scale* of the value that can be assigned to **seed**.
614
615    This is a **non-portable extension**.
616
617**I**
618
619:   Pushes the current value of **ibase** onto the main stack.
620
621**O**
622
623:   Pushes the current value of **obase** onto the main stack.
624
625**K**
626
627:   Pushes the current value of **scale** onto the main stack.
628
629**J**
630
631:   Pushes the current value of **seed** onto the main stack.
632
633    This is a **non-portable extension**.
634
635**T**
636
637:   Pushes the maximum allowable value of **ibase** onto the main stack.
638
639    This is a **non-portable extension**.
640
641**U**
642
643:   Pushes the maximum allowable value of **obase** onto the main stack.
644
645    This is a **non-portable extension**.
646
647**V**
648
649:   Pushes the maximum allowable value of **scale** onto the main stack.
650
651    This is a **non-portable extension**.
652
653**W**
654
655:   Pushes the maximum (inclusive) integer that can be generated with the **'**
656    pseudo-random number generator command.
657
658    This is a **non-portable extension**.
659
660## Strings
661
662The following commands control strings.
663
664dc(1) can work with both numbers and strings, and registers (see the
665**REGISTERS** section) can hold both strings and numbers. dc(1) always knows
666whether the contents of a register are a string or a number.
667
668While arithmetic operations have to have numbers, and will print an error if
669given a string, other commands accept strings.
670
671Strings can also be executed as macros. For example, if the string **[1pR]** is
672executed as a macro, then the code **1pR** is executed, meaning that the **1**
673will be printed with a newline after and then popped from the stack.
674
675**\[**_characters_**\]**
676
677:   Makes a string containing *characters* and pushes it onto the stack.
678
679    If there are brackets (**\[** and **\]**) in the string, then they must be
680    balanced. Unbalanced brackets can be escaped using a backslash (**\\**)
681    character.
682
683    If there is a backslash character in the string, the character after it
684    (even another backslash) is put into the string verbatim, but the (first)
685    backslash is not.
686
687**a**
688
689:   The value on top of the stack is popped.
690
691    If it is a number, it is truncated and its absolute value is taken. The
692    result mod **UCHAR_MAX+1** is calculated. If that result is **0**, push an
693    empty string; otherwise, push a one-character string where the character is
694    the result of the mod interpreted as an ASCII character.
695
696    If it is a string, then a new string is made. If the original string is
697    empty, the new string is empty. If it is not, then the first character of
698    the original string is used to create the new string as a one-character
699    string. The new string is then pushed onto the stack.
700
701    This is a **non-portable extension**.
702
703**x**
704
705:   Pops a value off of the top of the stack.
706
707    If it is a number, it is pushed back onto the stack.
708
709    If it is a string, it is executed as a macro.
710
711    This behavior is the norm whenever a macro is executed, whether by this
712    command or by the conditional execution commands below.
713
714**\>***r*
715
716:   Pops two values off of the stack that must be numbers and compares them. If
717    the first value is greater than the second, then the contents of register
718    *r* are executed.
719
720    For example, **0 1>a** will execute the contents of register **a**, and
721    **1 0>a** will not.
722
723    If either or both of the values are not numbers, dc(1) will raise an error
724    and reset (see the **RESET** section).
725
726**>***r***e***s*
727
728:   Like the above, but will execute register *s* if the comparison fails.
729
730    If either or both of the values are not numbers, dc(1) will raise an error
731    and reset (see the **RESET** section).
732
733    This is a **non-portable extension**.
734
735**!\>***r*
736
737:   Pops two values off of the stack that must be numbers and compares them. If
738    the first value is not greater than the second (less than or equal to), then
739    the contents of register *r* are executed.
740
741    If either or both of the values are not numbers, dc(1) will raise an error
742    and reset (see the **RESET** section).
743
744**!\>***r***e***s*
745
746:   Like the above, but will execute register *s* if the comparison fails.
747
748    If either or both of the values are not numbers, dc(1) will raise an error
749    and reset (see the **RESET** section).
750
751    This is a **non-portable extension**.
752
753**\<***r*
754
755:   Pops two values off of the stack that must be numbers and compares them. If
756    the first value is less than the second, then the contents of register *r*
757    are executed.
758
759    If either or both of the values are not numbers, dc(1) will raise an error
760    and reset (see the **RESET** section).
761
762**\<***r***e***s*
763
764:   Like the above, but will execute register *s* if the comparison fails.
765
766    If either or both of the values are not numbers, dc(1) will raise an error
767    and reset (see the **RESET** section).
768
769    This is a **non-portable extension**.
770
771**!\<***r*
772
773:   Pops two values off of the stack that must be numbers and compares them. If
774    the first value is not less than the second (greater than or equal to), then
775    the contents of register *r* are executed.
776
777    If either or both of the values are not numbers, dc(1) will raise an error
778    and reset (see the **RESET** section).
779
780**!\<***r***e***s*
781
782:   Like the above, but will execute register *s* if the comparison fails.
783
784    If either or both of the values are not numbers, dc(1) will raise an error
785    and reset (see the **RESET** section).
786
787    This is a **non-portable extension**.
788
789**=***r*
790
791:   Pops two values off of the stack that must be numbers and compares them. If
792    the first value is equal to the second, then the contents of register *r*
793    are executed.
794
795    If either or both of the values are not numbers, dc(1) will raise an error
796    and reset (see the **RESET** section).
797
798**=***r***e***s*
799
800:   Like the above, but will execute register *s* if the comparison fails.
801
802    If either or both of the values are not numbers, dc(1) will raise an error
803    and reset (see the **RESET** section).
804
805    This is a **non-portable extension**.
806
807**!=***r*
808
809:   Pops two values off of the stack that must be numbers and compares them. If
810    the first value is not equal to the second, then the contents of register
811    *r* are executed.
812
813    If either or both of the values are not numbers, dc(1) will raise an error
814    and reset (see the **RESET** section).
815
816**!=***r***e***s*
817
818:   Like the above, but will execute register *s* if the comparison fails.
819
820    If either or both of the values are not numbers, dc(1) will raise an error
821    and reset (see the **RESET** section).
822
823    This is a **non-portable extension**.
824
825**?**
826
827:   Reads a line from the **stdin** and executes it. This is to allow macros to
828    request input from users.
829
830**q**
831
832:   During execution of a macro, this exits the execution of that macro and the
833    execution of the macro that executed it. If there are no macros, or only one
834    macro executing, dc(1) exits.
835
836**Q**
837
838:   Pops a value from the stack which must be non-negative and is used the
839    number of macro executions to pop off of the execution stack. If the number
840    of levels to pop is greater than the number of executing macros, dc(1)
841    exits.
842
843## Status
844
845These commands query status of the stack or its top value.
846
847**Z**
848
849:   Pops a value off of the stack.
850
851    If it is a number, calculates the number of significant decimal digits it
852    has and pushes the result.
853
854    If it is a string, pushes the number of characters the string has.
855
856**X**
857
858:   Pops a value off of the stack.
859
860    If it is a number, pushes the *scale* of the value onto the stack.
861
862    If it is a string, pushes **0**.
863
864**z**
865
866:   Pushes the current stack depth (before execution of this command).
867
868## Arrays
869
870These commands manipulate arrays.
871
872**:***r*
873
874:   Pops the top two values off of the stack. The second value will be stored in
875    the array *r* (see the **REGISTERS** section), indexed by the first value.
876
877**;***r*
878
879:   Pops the value on top of the stack and uses it as an index into the array
880    *r*. The selected value is then pushed onto the stack.
881
882# REGISTERS
883
884Registers are names that can store strings, numbers, and arrays. (Number/string
885registers do not interfere with array registers.)
886
887Each register is also its own stack, so the current register value is the top of
888the stack for the register. All registers, when first referenced, have one value
889(**0**) in their stack.
890
891In non-extended register mode, a register name is just the single character that
892follows any command that needs a register name. The only exception is a newline
893(**'\\n'**); it is a parse error for a newline to be used as a register name.
894
895## Extended Register Mode
896
897Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited
898amounts of registers, if extended register mode is enabled.
899
900If extended register mode is enabled (**-x** or **--extended-register**
901command-line arguments are given), then normal single character registers are
902used *unless* the character immediately following a command that needs a
903register name is a space (according to **isspace()**) and not a newline
904(**'\\n'**).
905
906In that case, the register name is found according to the regex
907**\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if
908the next non-space characters do not match that regex.
909
910# RESET
911
912When dc(1) encounters an error or a signal that it has a non-default handler
913for, it resets. This means that several things happen.
914
915First, any macros that are executing are stopped and popped off the stack.
916The behavior is not unlike that of exceptions in programming languages. Then
917the execution point is set so that any code waiting to execute (after all
918macros returned) is skipped.
919
920Thus, when dc(1) resets, it skips any remaining code waiting to be executed.
921Then, if it is interactive mode, and the error was not a fatal error (see the
922**EXIT STATUS** section), it asks for more input; otherwise, it exits with the
923appropriate return code.
924
925# PERFORMANCE
926
927Most dc(1) implementations use **char** types to calculate the value of **1**
928decimal digit at a time, but that can be slow. This dc(1) does something
929different.
930
931It uses large integers to calculate more than **1** decimal digit at a time. If
932built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is
933**64**, then each integer has **9** decimal digits. If built in an environment
934where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
935value (the number of decimal digits per large integer) is called
936**DC_BASE_DIGS**.
937
938In addition, this dc(1) uses an even larger integer for overflow checking. This
939integer type depends on the value of **DC_LONG_BIT**, but is always at least
940twice as large as the integer type used to store digits.
941
942# LIMITS
943
944The following are the limits on dc(1):
945
946**DC_LONG_BIT**
947
948:   The number of bits in the **long** type in the environment where dc(1) was
949    built. This determines how many decimal digits can be stored in a single
950    large integer (see the **PERFORMANCE** section).
951
952**DC_BASE_DIGS**
953
954:   The number of decimal digits per large integer (see the **PERFORMANCE**
955    section). Depends on **DC_LONG_BIT**.
956
957**DC_BASE_POW**
958
959:   The max decimal number that each large integer can store (see
960    **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**.
961
962**DC_OVERFLOW_MAX**
963
964:   The max number that the overflow type (see the **PERFORMANCE** section) can
965    hold. Depends on **DC_LONG_BIT**.
966
967**DC_BASE_MAX**
968
969:   The maximum output base. Set at **DC_BASE_POW**.
970
971**DC_DIM_MAX**
972
973:   The maximum size of arrays. Set at **SIZE_MAX-1**.
974
975**DC_SCALE_MAX**
976
977:   The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**.
978
979**DC_STRING_MAX**
980
981:   The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**.
982
983**DC_NAME_MAX**
984
985:   The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**.
986
987**DC_NUM_MAX**
988
989:   The maximum length of a number (in decimal digits), which includes digits
990    after the decimal point. Set at **DC_OVERFLOW_MAX-1**.
991
992**DC_RAND_MAX**
993
994:   The maximum integer (inclusive) returned by the **'** command, if dc(1). Set
995    at **2\^DC_LONG_BIT-1**.
996
997Exponent
998
999:   The maximum allowable exponent (positive or negative). Set at
1000    **DC_OVERFLOW_MAX**.
1001
1002Number of vars
1003
1004:   The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
1005
1006These limits are meant to be effectively non-existent; the limits are so large
1007(at least on 64-bit machines) that there should not be any point at which they
1008become a problem. In fact, memory should be exhausted before these limits should
1009be hit.
1010
1011# ENVIRONMENT VARIABLES
1012
1013dc(1) recognizes the following environment variables:
1014
1015**DC_ENV_ARGS**
1016
1017:   This is another way to give command-line arguments to dc(1). They should be
1018    in the same format as all other command-line arguments. These are always
1019    processed first, so any files given in **DC_ENV_ARGS** will be processed
1020    before arguments and files given on the command-line. This gives the user
1021    the ability to set up "standard" options and files to be used at every
1022    invocation. The most useful thing for such files to contain would be useful
1023    functions that the user might want every time dc(1) runs. Another use would
1024    be to use the **-e** option to set **scale** to a value other than **0**.
1025
1026    The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments,
1027    but it does not understand escape sequences. For example, the string
1028    **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string
1029    **"/home/gavin/some \"dc\" file.dc"** will include the backslashes.
1030
1031    The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
1032    if you have a file with any number of single quotes in the name, you can use
1033    double quotes as the outside quotes, as in **"some 'bc' file.bc"**, and vice
1034    versa if you have a file with double quotes. However, handling a file with
1035    both kinds of quotes in **DC_ENV_ARGS** is not supported due to the
1036    complexity of the parsing, though such files are still supported on the
1037    command-line where the parsing is done by the shell.
1038
1039**DC_LINE_LENGTH**
1040
1041:   If this environment variable exists and contains an integer that is greater
1042    than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output
1043    lines to that length, including the backslash newline combo. The default
1044    line length is **70**.
1045
1046**DC_EXPR_EXIT**
1047
1048:   If this variable exists (no matter the contents), dc(1) will exit
1049    immediately after executing expressions and files given by the **-e** and/or
1050    **-f** command-line options (and any equivalents).
1051
1052# EXIT STATUS
1053
1054dc(1) returns the following exit statuses:
1055
1056**0**
1057
1058:   No error.
1059
1060**1**
1061
1062:   A math error occurred. This follows standard practice of using **1** for
1063    expected errors, since math errors will happen in the process of normal
1064    execution.
1065
1066    Math errors include divide by **0**, taking the square root of a negative
1067    number, using a negative number as a bound for the pseudo-random number
1068    generator, attempting to convert a negative number to a hardware integer,
1069    overflow when converting a number to a hardware integer, and attempting to
1070    use a non-integer where an integer is required.
1071
1072    Converting to a hardware integer happens for the second operand of the power
1073    (**\^**), places (**\@**), left shift (**H**), and right shift (**h**)
1074    operators.
1075
1076**2**
1077
1078:   A parse error occurred.
1079
1080    Parse errors include unexpected **EOF**, using an invalid character, failing
1081    to find the end of a string or comment, and using a token where it is
1082    invalid.
1083
1084**3**
1085
1086:   A runtime error occurred.
1087
1088    Runtime errors include assigning an invalid number to **ibase**, **obase**,
1089    or **scale**; give a bad expression to a **read()** call, calling **read()**
1090    inside of a **read()** call, type errors, and attempting an operation when
1091    the stack has too few elements.
1092
1093**4**
1094
1095:   A fatal error occurred.
1096
1097    Fatal errors include memory allocation errors, I/O errors, failing to open
1098    files, attempting to use files that do not have only ASCII characters (dc(1)
1099    only accepts ASCII characters), attempting to open a directory as a file,
1100    and giving invalid command-line options.
1101
1102The exit status **4** is special; when a fatal error occurs, dc(1) always exits
1103and returns **4**, no matter what mode dc(1) is in.
1104
1105The other statuses will only be returned when dc(1) is not in interactive mode
1106(see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the
1107**RESET** section) and accepts more input when one of those errors occurs in
1108interactive mode. This is also the case when interactive mode is forced by the
1109**-i** flag or **--interactive** option.
1110
1111These exit statuses allow dc(1) to be used in shell scripting with error
1112checking, and its normal behavior can be forced by using the **-i** flag or
1113**--interactive** option.
1114
1115# INTERACTIVE MODE
1116
1117Like bc(1), dc(1) has an interactive mode and a non-interactive mode.
1118Interactive mode is turned on automatically when both **stdin** and **stdout**
1119are hooked to a terminal, but the **-i** flag and **--interactive** option can
1120turn it on in other cases.
1121
1122In interactive mode, dc(1) attempts to recover from errors (see the **RESET**
1123section), and in normal execution, flushes **stdout** as soon as execution is
1124done for the current input.
1125
1126# TTY MODE
1127
1128If **stdin**, **stdout**, and **stderr** are all connected to a TTY, dc(1) turns
1129on "TTY mode."
1130
1131TTY mode is required for history to be enabled (see the **COMMAND LINE HISTORY**
1132section). It is also required to enable special handling for **SIGINT** signals.
1133
1134The prompt is enabled in TTY mode.
1135
1136TTY mode is different from interactive mode because interactive mode is required
1137in the [bc(1) specification][1], and interactive mode requires only **stdin**
1138and **stdout** to be connected to a terminal.
1139
1140# SIGNAL HANDLING
1141
1142Sending a **SIGINT** will cause dc(1) to stop execution of the current input. If
1143dc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
1144**RESET** section). Otherwise, it will clean up and exit.
1145
1146Note that "current input" can mean one of two things. If dc(1) is processing
1147input from **stdin** in TTY mode, it will ask for more input. If dc(1) is
1148processing input from a file in TTY mode, it will stop processing the file and
1149start processing the next file, if one exists, or ask for input from **stdin**
1150if no other file exists.
1151
1152This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it
1153can seem as though dc(1) did not respond to the signal since it will immediately
1154start executing the next file. This is by design; most files that users execute
1155when interacting with dc(1) have function definitions, which are quick to parse.
1156If a file takes a long time to execute, there may be a bug in that file. The
1157rest of the files could still be executed without problem, allowing the user to
1158continue.
1159
1160**SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the
1161default handler for all other signals. The one exception is **SIGHUP**; in that
1162case, when dc(1) is in TTY mode, a **SIGHUP** will cause dc(1) to clean up and
1163exit.
1164
1165# COMMAND LINE HISTORY
1166
1167dc(1) supports interactive command-line editing. If dc(1) is in TTY mode (see
1168the **TTY MODE** section), history is enabled. Previous lines can be recalled
1169and edited with the arrow keys.
1170
1171**Note**: tabs are converted to 8 spaces.
1172
1173# SEE ALSO
1174
1175bc(1)
1176
1177# STANDARDS
1178
1179The dc(1) utility operators are compliant with the operators in the bc(1)
1180[IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1] specification.
1181
1182# BUGS
1183
1184None are known. Report bugs at https://git.yzena.com/gavin/bc.
1185
1186# AUTHOR
1187
1188Gavin D. Howard <gavin@yzena.com> and contributors.
1189
1190[1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html
1191