xref: /freebsd/contrib/bc/manuals/dc/N.1.md (revision 9e5787d2284e187abb5b654d924394a65772e004)
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 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 power (the portion after the **e**) must be an
226integer. An example is **1.89237e9**, which is equal to **1892370000**. Negative
227exponents 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.
343
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
346    non-zero.
347
348**v**
349
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
352    **scale**.
353
354    The value popped off of the stack must be non-negative.
355
356**\_**
357
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.
360
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**.
364
365**b**
366
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.
369
370    This is a **non-portable extension**.
371
372**|**
373
374:   The top three values are popped off the stack, a modular exponentiation is
375    computed, and the result is pushed onto the stack.
376
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
380    must be an integer.
381
382    This is a **non-portable extension**.
383
384**\$**
385
386:   The top value is popped off the stack and copied, and the copy is truncated
387    and pushed onto the stack.
388
389    This is a **non-portable extension**.
390
391**\@**
392
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.
395
396    The first value popped off of the stack must be an integer and non-negative.
397
398    This is a **non-portable extension**.
399
400**H**
401
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.
404
405    The first value popped off of the stack must be an integer and non-negative.
406
407    This is a **non-portable extension**.
408
409**h**
410
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.
413
414    The first value popped off of the stack must be an integer and non-negative.
415
416    This is a **non-portable extension**.
417
418**G**
419
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.
422
423    This is a **non-portable extension**.
424
425**N**
426
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.
429
430    This is a **non-portable extension**.
431
432**(**
433
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.
436
437    This is a **non-portable extension**.
438
439**{**
440
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**
443    otherwise.
444
445    This is a **non-portable extension**.
446
447**)**
448
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.
451
452    This is a **non-portable extension**.
453
454**}**
455
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
458    **0** otherwise.
459
460    This is a **non-portable extension**.
461
462**M**
463
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.
467
468    This is like the **&&** operator in bc(1), and it is *not* a short-circuit
469    operator.
470
471    This is a **non-portable extension**.
472
473**m**
474
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.
478
479    This is like the **||** operator in bc(1), and it is *not* a short-circuit
480    operator.
481
482    This is a **non-portable extension**.
483
484## Pseudo-Random Number Generator
485
486dc(1) has a built-in pseudo-random number generator. These commands query the
487pseudo-random number generator. (See Parameters for more information about the
488**seed** value that controls the pseudo-random number generator.)
489
490The pseudo-random number generator is guaranteed to **NOT** be
491cryptographically secure.
492
493**'**
494
495:   Generates an integer between 0 and **DC_RAND_MAX**, inclusive (see the
496    **LIMITS** section).
497
498    The generated integer is made as unbiased as possible, subject to the
499    limitations of the pseudo-random number generator.
500
501    This is a **non-portable extension**.
502
503**"**
504
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.
515
516    The generated integer is made as unbiased as possible, subject to the
517    limitations of the pseudo-random number generator.
518
519    This is a **non-portable extension**.
520
521## Stack Control
522
523These commands control the stack.
524
525**c**
526
527:   Removes all items from ("clears") the stack.
528
529**d**
530
531:   Copies the item on top of the stack ("duplicates") and pushes the copy onto
532    the stack.
533
534**r**
535
536:   Swaps ("reverses") the two top items on the stack.
537
538**R**
539
540:   Pops ("removes") the top value from the stack.
541
542## Register Control
543
544These commands control registers (see the **REGISTERS** section).
545
546**s***r*
547
548:   Pops the value off the top of the stack and stores it into register *r*.
549
550**l***r*
551
552:   Copies the value in register *r* and pushes it onto the stack. This does not
553    alter the contents of *r*.
554
555**S***r*
556
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.
559
560**L***r*
561
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.
565
566## Parameters
567
568These commands control the values of **ibase**, **obase**, **scale**, and
569**seed**. Also see the **SYNTAX** section.
570
571**i**
572
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.
575
576    If the value on top of the stack has any *scale*, the *scale* is ignored.
577
578**o**
579
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).
583
584    If the value on top of the stack has any *scale*, the *scale* is ignored.
585
586**k**
587
588:   Pops the value off of the top of the stack and uses it to set **scale**,
589    which must be non-negative.
590
591    If the value on top of the stack has any *scale*, the *scale* is ignored.
592
593**j**
594
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.
598
599    The *scale* and sign of the value may be significant.
600
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.
604
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.
610
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**.
613
614    This is a **non-portable extension**.
615
616**I**
617
618:   Pushes the current value of **ibase** onto the main stack.
619
620**O**
621
622:   Pushes the current value of **obase** onto the main stack.
623
624**K**
625
626:   Pushes the current value of **scale** onto the main stack.
627
628**J**
629
630:   Pushes the current value of **seed** onto the main stack.
631
632    This is a **non-portable extension**.
633
634**T**
635
636:   Pushes the maximum allowable value of **ibase** onto the main stack.
637
638    This is a **non-portable extension**.
639
640**U**
641
642:   Pushes the maximum allowable value of **obase** onto the main stack.
643
644    This is a **non-portable extension**.
645
646**V**
647
648:   Pushes the maximum allowable value of **scale** onto the main stack.
649
650    This is a **non-portable extension**.
651
652**W**
653
654:   Pushes the maximum (inclusive) integer that can be generated with the **'**
655    pseudo-random number generator command.
656
657    This is a **non-portable extension**.
658
659## Strings
660
661The following commands control strings.
662
663dc(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
665whether the contents of a register are a string or a number.
666
667While arithmetic operations have to have numbers, and will print an error if
668given a string, other commands accept strings.
669
670Strings can also be executed as macros. For example, if the string **[1pR]** is
671executed as a macro, then the code **1pR** is executed, meaning that the **1**
672will be printed with a newline after and then popped from the stack.
673
674**\[**_characters_**\]**
675
676:   Makes a string containing *characters* and pushes it onto the stack.
677
678    If there are brackets (**\[** and **\]**) in the string, then they must be
679    balanced. Unbalanced brackets can be escaped using a backslash (**\\**)
680    character.
681
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)
684    backslash is not.
685
686**a**
687
688:   The value on top of the stack is popped.
689
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.
694
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.
699
700    This is a **non-portable extension**.
701
702**x**
703
704:   Pops a value off of the top of the stack.
705
706    If it is a number, it is pushed back onto the stack.
707
708    If it is a string, it is executed as a macro.
709
710    This behavior is the norm whenever a macro is executed, whether by this
711    command or by the conditional execution commands below.
712
713**\>***r*
714
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
717    *r* are executed.
718
719    For example, **0 1>a** will execute the contents of register **a**, and
720    **1 0>a** will not.
721
722    If either or both of the values are not numbers, dc(1) will raise an error
723    and reset (see the **RESET** section).
724
725**>***r***e***s*
726
727:   Like the above, but will execute register *s* if the comparison fails.
728
729    If either or both of the values are not numbers, dc(1) will raise an error
730    and reset (see the **RESET** section).
731
732    This is a **non-portable extension**.
733
734**!\>***r*
735
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.
739
740    If either or both of the values are not numbers, dc(1) will raise an error
741    and reset (see the **RESET** section).
742
743**!\>***r***e***s*
744
745:   Like the above, but will execute register *s* if the comparison fails.
746
747    If either or both of the values are not numbers, dc(1) will raise an error
748    and reset (see the **RESET** section).
749
750    This is a **non-portable extension**.
751
752**\<***r*
753
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*
756    are executed.
757
758    If either or both of the values are not numbers, dc(1) will raise an error
759    and reset (see the **RESET** section).
760
761**\<***r***e***s*
762
763:   Like the above, but will execute register *s* if the comparison fails.
764
765    If either or both of the values are not numbers, dc(1) will raise an error
766    and reset (see the **RESET** section).
767
768    This is a **non-portable extension**.
769
770**!\<***r*
771
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.
775
776    If either or both of the values are not numbers, dc(1) will raise an error
777    and reset (see the **RESET** section).
778
779**!\<***r***e***s*
780
781:   Like the above, but will execute register *s* if the comparison fails.
782
783    If either or both of the values are not numbers, dc(1) will raise an error
784    and reset (see the **RESET** section).
785
786    This is a **non-portable extension**.
787
788**=***r*
789
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*
792    are executed.
793
794    If either or both of the values are not numbers, dc(1) will raise an error
795    and reset (see the **RESET** section).
796
797**=***r***e***s*
798
799:   Like the above, but will execute register *s* if the comparison fails.
800
801    If either or both of the values are not numbers, dc(1) will raise an error
802    and reset (see the **RESET** section).
803
804    This is a **non-portable extension**.
805
806**!=***r*
807
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
810    *r* are executed.
811
812    If either or both of the values are not numbers, dc(1) will raise an error
813    and reset (see the **RESET** section).
814
815**!=***r***e***s*
816
817:   Like the above, but will execute register *s* if the comparison fails.
818
819    If either or both of the values are not numbers, dc(1) will raise an error
820    and reset (see the **RESET** section).
821
822    This is a **non-portable extension**.
823
824**?**
825
826:   Reads a line from the **stdin** and executes it. This is to allow macros to
827    request input from users.
828
829**q**
830
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.
834
835**Q**
836
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)
840    exits.
841
842## Status
843
844These commands query status of the stack or its top value.
845
846**Z**
847
848:   Pops a value off of the stack.
849
850    If it is a number, calculates the number of significant decimal digits it
851    has and pushes the result.
852
853    If it is a string, pushes the number of characters the string has.
854
855**X**
856
857:   Pops a value off of the stack.
858
859    If it is a number, pushes the *scale* of the value onto the stack.
860
861    If it is a string, pushes **0**.
862
863**z**
864
865:   Pushes the current stack depth (before execution of this command).
866
867## Arrays
868
869These commands manipulate arrays.
870
871**:***r*
872
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.
875
876**;***r*
877
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.
880
881# REGISTERS
882
883Registers are names that can store strings, numbers, and arrays. (Number/string
884registers do not interfere with array registers.)
885
886Each register is also its own stack, so the current register value is the top of
887the stack for the register. All registers, when first referenced, have one value
888(**0**) in their stack.
889
890In non-extended register mode, a register name is just the single character that
891follows 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.
893
894## Extended Register Mode
895
896Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited
897amounts of registers, if extended register mode is enabled.
898
899If extended register mode is enabled (**-x** or **--extended-register**
900command-line arguments are given), then normal single character registers are
901used *unless* the character immediately following a command that needs a
902register name is a space (according to **isspace()**) and not a newline
903(**'\\n'**).
904
905In 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
907the next non-space characters do not match that regex.
908
909# RESET
910
911When dc(1) encounters an error or a signal that it has a non-default handler
912for, it resets. This means that several things happen.
913
914First, any macros that are executing are stopped and popped off the stack.
915The behavior is not unlike that of exceptions in programming languages. Then
916the execution point is set so that any code waiting to execute (after all
917macros returned) is skipped.
918
919Thus, when dc(1) resets, it skips any remaining code waiting to be executed.
920Then, 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
922appropriate return code.
923
924# PERFORMANCE
925
926Most dc(1) implementations use **char** types to calculate the value of **1**
927decimal digit at a time, but that can be slow. This dc(1) does something
928different.
929
930It uses large integers to calculate more than **1** decimal digit at a time. If
931built 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
933where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
934value (the number of decimal digits per large integer) is called
935**DC_BASE_DIGS**.
936
937In addition, this dc(1) uses an even larger integer for overflow checking. This
938integer type depends on the value of **DC_LONG_BIT**, but is always at least
939twice as large as the integer type used to store digits.
940
941# LIMITS
942
943The following are the limits on dc(1):
944
945**DC_LONG_BIT**
946
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).
950
951**DC_BASE_DIGS**
952
953:   The number of decimal digits per large integer (see the **PERFORMANCE**
954    section). Depends on **DC_LONG_BIT**.
955
956**DC_BASE_POW**
957
958:   The max decimal number that each large integer can store (see
959    **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**.
960
961**DC_OVERFLOW_MAX**
962
963:   The max number that the overflow type (see the **PERFORMANCE** section) can
964    hold. Depends on **DC_LONG_BIT**.
965
966**DC_BASE_MAX**
967
968:   The maximum output base. Set at **DC_BASE_POW**.
969
970**DC_DIM_MAX**
971
972:   The maximum size of arrays. Set at **SIZE_MAX-1**.
973
974**DC_SCALE_MAX**
975
976:   The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**.
977
978**DC_STRING_MAX**
979
980:   The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**.
981
982**DC_NAME_MAX**
983
984:   The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**.
985
986**DC_NUM_MAX**
987
988:   The maximum length of a number (in decimal digits), which includes digits
989    after the decimal point. Set at **DC_OVERFLOW_MAX-1**.
990
991**DC_RAND_MAX**
992
993:   The maximum integer (inclusive) returned by the **'** command, if dc(1). Set
994    at **2\^DC_LONG_BIT-1**.
995
996Exponent
997
998:   The maximum allowable exponent (positive or negative). Set at
999    **DC_OVERFLOW_MAX**.
1000
1001Number of vars
1002
1003:   The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
1004
1005These 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
1007become a problem. In fact, memory should be exhausted before these limits should
1008be hit.
1009
1010# ENVIRONMENT VARIABLES
1011
1012dc(1) recognizes the following environment variables:
1013
1014**DC_ENV_ARGS**
1015
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**.
1024
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.
1029
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.
1037
1038**DC_LINE_LENGTH**
1039
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**.
1044
1045**DC_EXPR_EXIT**
1046
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).
1050
1051# EXIT STATUS
1052
1053dc(1) returns the following exit statuses:
1054
1055**0**
1056
1057:   No error.
1058
1059**1**
1060
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
1063    execution.
1064
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.
1070
1071    Converting to a hardware integer happens for the second operand of the power
1072    (**\^**), places (**\@**), left shift (**H**), and right shift (**h**)
1073    operators.
1074
1075**2**
1076
1077:   A parse error occurred.
1078
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
1081    invalid.
1082
1083**3**
1084
1085:   A runtime error occurred.
1086
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.
1091
1092**4**
1093
1094:   A fatal error occurred.
1095
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.
1100
1101The exit status **4** is special; when a fatal error occurs, dc(1) always exits
1102and returns **4**, no matter what mode dc(1) is in.
1103
1104The 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
1107interactive mode. This is also the case when interactive mode is forced by the
1108**-i** flag or **--interactive** option.
1109
1110These exit statuses allow dc(1) to be used in shell scripting with error
1111checking, and its normal behavior can be forced by using the **-i** flag or
1112**--interactive** option.
1113
1114# INTERACTIVE MODE
1115
1116Like bc(1), dc(1) has an interactive mode and a non-interactive mode.
1117Interactive mode is turned on automatically when both **stdin** and **stdout**
1118are hooked to a terminal, but the **-i** flag and **--interactive** option can
1119turn it on in other cases.
1120
1121In interactive mode, dc(1) attempts to recover from errors (see the **RESET**
1122section), and in normal execution, flushes **stdout** as soon as execution is
1123done for the current input.
1124
1125# TTY MODE
1126
1127If **stdin**, **stdout**, and **stderr** are all connected to a TTY, dc(1) turns
1128on "TTY mode."
1129
1130TTY mode is required for history to be enabled (see the **COMMAND LINE HISTORY**
1131section). It is also required to enable special handling for **SIGINT** signals.
1132
1133The prompt is enabled in TTY mode.
1134
1135TTY mode is different from interactive mode because interactive mode is required
1136in the [bc(1) specification][1], and interactive mode requires only **stdin**
1137and **stdout** to be connected to a terminal.
1138
1139# SIGNAL HANDLING
1140
1141Sending a **SIGINT** will cause dc(1) to stop execution of the current input. If
1142dc(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.
1144
1145Note that "current input" can mean one of two things. If dc(1) is processing
1146input from **stdin** in TTY mode, it will ask for more input. If dc(1) is
1147processing input from a file in TTY mode, it will stop processing the file and
1148start processing the next file, if one exists, or ask for input from **stdin**
1149if no other file exists.
1150
1151This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it
1152can seem as though dc(1) did not respond to the signal since it will immediately
1153start executing the next file. This is by design; most files that users execute
1154when interacting with dc(1) have function definitions, which are quick to parse.
1155If a file takes a long time to execute, there may be a bug in that file. The
1156rest of the files could still be executed without problem, allowing the user to
1157continue.
1158
1159**SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the
1160default handler for all other signals. The one exception is **SIGHUP**; in that
1161case, when dc(1) is in TTY mode, a **SIGHUP** will cause dc(1) to clean up and
1162exit.
1163
1164# COMMAND LINE HISTORY
1165
1166dc(1) supports interactive command-line editing. If dc(1) is in TTY mode (see
1167the **TTY MODE** section), history is enabled. Previous lines can be recalled
1168and edited with the arrow keys.
1169
1170**Note**: tabs are converted to 8 spaces.
1171
1172# SEE ALSO
1173
1174bc(1)
1175
1176# STANDARDS
1177
1178The dc(1) utility operators are compliant with the operators in the bc(1)
1179[IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1] specification.
1180
1181# BUGS
1182
1183None are known. Report bugs at https://git.yzena.com/gavin/bc.
1184
1185# AUTHOR
1186
1187Gavin D. Howard <yzena.tech@gmail.com> and contributors.
1188
1189[1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html
1190