xref: /freebsd/contrib/bc/manuals/dc/EN.1.md (revision c66ec88fed842fbaad62c30d510644ceb7bd2d71)
1<!---
2
3SPDX-License-Identifier: BSD-2-Clause
4
5Copyright (c) 2018-2020 Gavin D. Howard and contributors.
6
7Redistribution and use in source and binary forms, with or without
8modification, are permitted provided that the following conditions are met:
9
10* Redistributions of source code must retain the above copyright notice, this
11  list of conditions and the following disclaimer.
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13* Redistributions in binary form must reproduce the above copyright notice,
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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 **2**. Values are output in the specified base.
170
171The *scale* of an expression is the number of digits in the result of the
172expression right of the decimal point, and **scale** is a register (see the
173**REGISTERS** section) that sets the precision of any operations (with
174exceptions). **scale** is initially **0**. **scale** cannot be negative. The max
175allowable value for **scale** can be queried in dc(1) programs with the **V**
176command.
177
178## Comments
179
180Comments go from **#** until, and not including, the next newline. This is a
181**non-portable extension**.
182
183# NUMBERS
184
185Numbers are strings made up of digits, uppercase letters up to **F**, and at
186most **1** period for a radix. Numbers can have up to **DC_NUM_MAX** digits.
187Uppercase letters are equal to **9** + their position in the alphabet (i.e.,
188**A** equals **10**, or **9+1**). If a digit or letter makes no sense with the
189current value of **ibase**, they are set to the value of the highest valid digit
190in **ibase**.
191
192Single-character numbers (i.e., **A** alone) take the value that they would have
193if they were valid digits, regardless of the value of **ibase**. This means that
194**A** alone always equals decimal **10** and **F** alone always equals decimal
195**15**.
196
197# COMMANDS
198
199The valid commands are listed below.
200
201## Printing
202
203These commands are used for printing.
204
205**p**
206
207:   Prints the value on top of the stack, whether number or string, and prints a
208    newline after.
209
210    This does not alter the stack.
211
212**n**
213
214:   Prints the value on top of the stack, whether number or string, and pops it
215    off of the stack.
216
217**P**
218
219:   Pops a value off the stack.
220
221    If the value is a number, it is truncated and the absolute value of the
222    result is printed as though **obase** is **UCHAR_MAX+1** and each digit is
223    interpreted as an ASCII character, making it a byte stream.
224
225    If the value is a string, it is printed without a trailing newline.
226
227    This is a **non-portable extension**.
228
229**f**
230
231:   Prints the entire contents of the stack, in order from newest to oldest,
232    without altering anything.
233
234    Users should use this command when they get lost.
235
236## Arithmetic
237
238These are the commands used for arithmetic.
239
240**+**
241
242:   The top two values are popped off the stack, added, and the result is pushed
243    onto the stack. The *scale* of the result is equal to the max *scale* of
244    both operands.
245
246**-**
247
248:   The top two values are popped off the stack, subtracted, and the result is
249    pushed onto the stack. The *scale* of the result is equal to the max
250    *scale* of both operands.
251
252**\***
253
254:   The top two values are popped off the stack, multiplied, and the result is
255    pushed onto the stack. If **a** is the *scale* of the first expression and
256    **b** is the *scale* of the second expression, the *scale* of the result
257    is equal to **min(a+b,max(scale,a,b))** where **min()** and **max()** return
258    the obvious values.
259
260**/**
261
262:   The top two values are popped off the stack, divided, and the result is
263    pushed onto the stack. The *scale* of the result is equal to **scale**.
264
265    The first value popped off of the stack must be non-zero.
266
267**%**
268
269:   The top two values are popped off the stack, remaindered, and the result is
270    pushed onto the stack.
271
272    Remaindering is equivalent to 1) Computing **a/b** to current **scale**, and
273    2) Using the result of step 1 to calculate **a-(a/b)\*b** to *scale*
274    **max(scale+scale(b),scale(a))**.
275
276    The first value popped off of the stack must be non-zero.
277
278**~**
279
280:   The top two values are popped off the stack, divided and remaindered, and
281    the results (divided first, remainder second) are pushed onto the stack.
282    This is equivalent to **x y / x y %** except that **x** and **y** are only
283    evaluated once.
284
285    The first value popped off of the stack must be non-zero.
286
287    This is a **non-portable extension**.
288
289**\^**
290
291:   The top two values are popped off the stack, the second is raised to the
292    power of the first, and the result is pushed onto the stack. The *scale* of
293    the result is equal to **scale**.
294
295    The first value popped off of the stack must be an integer, and if that
296    value is negative, the second value popped off of the stack must be
297    non-zero.
298
299**v**
300
301:   The top value is popped off the stack, its square root is computed, and the
302    result is pushed onto the stack. The *scale* of the result is equal to
303    **scale**.
304
305    The value popped off of the stack must be non-negative.
306
307**\_**
308
309:   If this command *immediately* precedes a number (i.e., no spaces or other
310    commands), then that number is input as a negative number.
311
312    Otherwise, the top value on the stack is popped and copied, and the copy is
313    negated and pushed onto the stack. This behavior without a number is a
314    **non-portable extension**.
315
316**b**
317
318:   The top value is popped off the stack, and if it is zero, it is pushed back
319    onto the stack. Otherwise, its absolute value is pushed onto the stack.
320
321    This is a **non-portable extension**.
322
323**|**
324
325:   The top three values are popped off the stack, a modular exponentiation is
326    computed, and the result is pushed onto the stack.
327
328    The first value popped is used as the reduction modulus and must be an
329    integer and non-zero. The second value popped is used as the exponent and
330    must be an integer and non-negative. The third value popped is the base and
331    must be an integer.
332
333    This is a **non-portable extension**.
334
335**G**
336
337:   The top two values are popped off of the stack, they are compared, and a
338    **1** is pushed if they are equal, or **0** otherwise.
339
340    This is a **non-portable extension**.
341
342**N**
343
344:   The top value is popped off of the stack, and if it a **0**, a **1** is
345    pushed; otherwise, a **0** is pushed.
346
347    This is a **non-portable extension**.
348
349**(**
350
351:   The top two values are popped off of the stack, they are compared, and a
352    **1** is pushed if the first is less than the second, or **0** otherwise.
353
354    This is a **non-portable extension**.
355
356**{**
357
358:   The top two values are popped off of the stack, they are compared, and a
359    **1** is pushed if the first is less than or equal to the second, or **0**
360    otherwise.
361
362    This is a **non-portable extension**.
363
364**)**
365
366:   The top two values are popped off of the stack, they are compared, and a
367    **1** is pushed if the first is greater than the second, or **0** otherwise.
368
369    This is a **non-portable extension**.
370
371**}**
372
373:   The top two values are popped off of the stack, they are compared, and a
374    **1** is pushed if the first is greater than or equal to the second, or
375    **0** otherwise.
376
377    This is a **non-portable extension**.
378
379**M**
380
381:   The top two values are popped off of the stack. If they are both non-zero, a
382    **1** is pushed onto the stack. If either of them is zero, or both of them
383    are, then a **0** is pushed onto the stack.
384
385    This is like the **&&** operator in bc(1), and it is *not* a short-circuit
386    operator.
387
388    This is a **non-portable extension**.
389
390**m**
391
392:   The top two values are popped off of the stack. If at least one of them is
393    non-zero, a **1** is pushed onto the stack. If both of them are zero, then a
394    **0** is pushed onto the stack.
395
396    This is like the **||** operator in bc(1), and it is *not* a short-circuit
397    operator.
398
399    This is a **non-portable extension**.
400
401## Stack Control
402
403These commands control the stack.
404
405**c**
406
407:   Removes all items from ("clears") the stack.
408
409**d**
410
411:   Copies the item on top of the stack ("duplicates") and pushes the copy onto
412    the stack.
413
414**r**
415
416:   Swaps ("reverses") the two top items on the stack.
417
418**R**
419
420:   Pops ("removes") the top value from the stack.
421
422## Register Control
423
424These commands control registers (see the **REGISTERS** section).
425
426**s***r*
427
428:   Pops the value off the top of the stack and stores it into register *r*.
429
430**l***r*
431
432:   Copies the value in register *r* and pushes it onto the stack. This does not
433    alter the contents of *r*.
434
435**S***r*
436
437:   Pops the value off the top of the (main) stack and pushes it onto the stack
438    of register *r*. The previous value of the register becomes inaccessible.
439
440**L***r*
441
442:   Pops the value off the top of the stack for register *r* and push it onto
443    the main stack. The previous value in the stack for register *r*, if any, is
444    now accessible via the **l***r* command.
445
446## Parameters
447
448These commands control the values of **ibase**, **obase**, and **scale**. Also
449see the **SYNTAX** section.
450
451**i**
452
453:   Pops the value off of the top of the stack and uses it to set **ibase**,
454    which must be between **2** and **16**, inclusive.
455
456    If the value on top of the stack has any *scale*, the *scale* is ignored.
457
458**o**
459
460:   Pops the value off of the top of the stack and uses it to set **obase**,
461    which must be between **2** and **DC_BASE_MAX**, inclusive (see the
462    **LIMITS** section).
463
464    If the value on top of the stack has any *scale*, the *scale* is ignored.
465
466**k**
467
468:   Pops the value off of the top of the stack and uses it to set **scale**,
469    which must be non-negative.
470
471    If the value on top of the stack has any *scale*, the *scale* is ignored.
472
473**I**
474
475:   Pushes the current value of **ibase** onto the main stack.
476
477**O**
478
479:   Pushes the current value of **obase** onto the main stack.
480
481**K**
482
483:   Pushes the current value of **scale** onto the main stack.
484
485**T**
486
487:   Pushes the maximum allowable value of **ibase** onto the main stack.
488
489    This is a **non-portable extension**.
490
491**U**
492
493:   Pushes the maximum allowable value of **obase** onto the main stack.
494
495    This is a **non-portable extension**.
496
497**V**
498
499:   Pushes the maximum allowable value of **scale** onto the main stack.
500
501    This is a **non-portable extension**.
502
503## Strings
504
505The following commands control strings.
506
507dc(1) can work with both numbers and strings, and registers (see the
508**REGISTERS** section) can hold both strings and numbers. dc(1) always knows
509whether the contents of a register are a string or a number.
510
511While arithmetic operations have to have numbers, and will print an error if
512given a string, other commands accept strings.
513
514Strings can also be executed as macros. For example, if the string **[1pR]** is
515executed as a macro, then the code **1pR** is executed, meaning that the **1**
516will be printed with a newline after and then popped from the stack.
517
518**\[**_characters_**\]**
519
520:   Makes a string containing *characters* and pushes it onto the stack.
521
522    If there are brackets (**\[** and **\]**) in the string, then they must be
523    balanced. Unbalanced brackets can be escaped using a backslash (**\\**)
524    character.
525
526    If there is a backslash character in the string, the character after it
527    (even another backslash) is put into the string verbatim, but the (first)
528    backslash is not.
529
530**a**
531
532:   The value on top of the stack is popped.
533
534    If it is a number, it is truncated and its absolute value is taken. The
535    result mod **UCHAR_MAX+1** is calculated. If that result is **0**, push an
536    empty string; otherwise, push a one-character string where the character is
537    the result of the mod interpreted as an ASCII character.
538
539    If it is a string, then a new string is made. If the original string is
540    empty, the new string is empty. If it is not, then the first character of
541    the original string is used to create the new string as a one-character
542    string. The new string is then pushed onto the stack.
543
544    This is a **non-portable extension**.
545
546**x**
547
548:   Pops a value off of the top of the stack.
549
550    If it is a number, it is pushed back onto the stack.
551
552    If it is a string, it is executed as a macro.
553
554    This behavior is the norm whenever a macro is executed, whether by this
555    command or by the conditional execution commands below.
556
557**\>***r*
558
559:   Pops two values off of the stack that must be numbers and compares them. If
560    the first value is greater than the second, then the contents of register
561    *r* are executed.
562
563    For example, **0 1>a** will execute the contents of register **a**, and
564    **1 0>a** will not.
565
566    If either or both of the values are not numbers, dc(1) will raise an error
567    and reset (see the **RESET** section).
568
569**>***r***e***s*
570
571:   Like the above, but will execute register *s* if the comparison fails.
572
573    If either or both of the values are not numbers, dc(1) will raise an error
574    and reset (see the **RESET** section).
575
576    This is a **non-portable extension**.
577
578**!\>***r*
579
580:   Pops two values off of the stack that must be numbers and compares them. If
581    the first value is not greater than the second (less than or equal to), then
582    the contents of register *r* are executed.
583
584    If either or both of the values are not numbers, dc(1) will raise an error
585    and reset (see the **RESET** section).
586
587**!\>***r***e***s*
588
589:   Like the above, but will execute register *s* if the comparison fails.
590
591    If either or both of the values are not numbers, dc(1) will raise an error
592    and reset (see the **RESET** section).
593
594    This is a **non-portable extension**.
595
596**\<***r*
597
598:   Pops two values off of the stack that must be numbers and compares them. If
599    the first value is less than the second, then the contents of register *r*
600    are executed.
601
602    If either or both of the values are not numbers, dc(1) will raise an error
603    and reset (see the **RESET** section).
604
605**\<***r***e***s*
606
607:   Like the above, but will execute register *s* if the comparison fails.
608
609    If either or both of the values are not numbers, dc(1) will raise an error
610    and reset (see the **RESET** section).
611
612    This is a **non-portable extension**.
613
614**!\<***r*
615
616:   Pops two values off of the stack that must be numbers and compares them. If
617    the first value is not less than the second (greater than or equal to), then
618    the contents of register *r* are executed.
619
620    If either or both of the values are not numbers, dc(1) will raise an error
621    and reset (see the **RESET** section).
622
623**!\<***r***e***s*
624
625:   Like the above, but will execute register *s* if the comparison fails.
626
627    If either or both of the values are not numbers, dc(1) will raise an error
628    and reset (see the **RESET** section).
629
630    This is a **non-portable extension**.
631
632**=***r*
633
634:   Pops two values off of the stack that must be numbers and compares them. If
635    the first value is equal to the second, then the contents of register *r*
636    are executed.
637
638    If either or both of the values are not numbers, dc(1) will raise an error
639    and reset (see the **RESET** section).
640
641**=***r***e***s*
642
643:   Like the above, but will execute register *s* if the comparison fails.
644
645    If either or both of the values are not numbers, dc(1) will raise an error
646    and reset (see the **RESET** section).
647
648    This is a **non-portable extension**.
649
650**!=***r*
651
652:   Pops two values off of the stack that must be numbers and compares them. If
653    the first value is not equal to the second, then the contents of register
654    *r* are executed.
655
656    If either or both of the values are not numbers, dc(1) will raise an error
657    and reset (see the **RESET** section).
658
659**!=***r***e***s*
660
661:   Like the above, but will execute register *s* if the comparison fails.
662
663    If either or both of the values are not numbers, dc(1) will raise an error
664    and reset (see the **RESET** section).
665
666    This is a **non-portable extension**.
667
668**?**
669
670:   Reads a line from the **stdin** and executes it. This is to allow macros to
671    request input from users.
672
673**q**
674
675:   During execution of a macro, this exits the execution of that macro and the
676    execution of the macro that executed it. If there are no macros, or only one
677    macro executing, dc(1) exits.
678
679**Q**
680
681:   Pops a value from the stack which must be non-negative and is used the
682    number of macro executions to pop off of the execution stack. If the number
683    of levels to pop is greater than the number of executing macros, dc(1)
684    exits.
685
686## Status
687
688These commands query status of the stack or its top value.
689
690**Z**
691
692:   Pops a value off of the stack.
693
694    If it is a number, calculates the number of significant decimal digits it
695    has and pushes the result.
696
697    If it is a string, pushes the number of characters the string has.
698
699**X**
700
701:   Pops a value off of the stack.
702
703    If it is a number, pushes the *scale* of the value onto the stack.
704
705    If it is a string, pushes **0**.
706
707**z**
708
709:   Pushes the current stack depth (before execution of this command).
710
711## Arrays
712
713These commands manipulate arrays.
714
715**:***r*
716
717:   Pops the top two values off of the stack. The second value will be stored in
718    the array *r* (see the **REGISTERS** section), indexed by the first value.
719
720**;***r*
721
722:   Pops the value on top of the stack and uses it as an index into the array
723    *r*. The selected value is then pushed onto the stack.
724
725# REGISTERS
726
727Registers are names that can store strings, numbers, and arrays. (Number/string
728registers do not interfere with array registers.)
729
730Each register is also its own stack, so the current register value is the top of
731the stack for the register. All registers, when first referenced, have one value
732(**0**) in their stack.
733
734In non-extended register mode, a register name is just the single character that
735follows any command that needs a register name. The only exception is a newline
736(**'\\n'**); it is a parse error for a newline to be used as a register name.
737
738## Extended Register Mode
739
740Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited
741amounts of registers, if extended register mode is enabled.
742
743If extended register mode is enabled (**-x** or **--extended-register**
744command-line arguments are given), then normal single character registers are
745used *unless* the character immediately following a command that needs a
746register name is a space (according to **isspace()**) and not a newline
747(**'\\n'**).
748
749In that case, the register name is found according to the regex
750**\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if
751the next non-space characters do not match that regex.
752
753# RESET
754
755When dc(1) encounters an error or a signal that it has a non-default handler
756for, it resets. This means that several things happen.
757
758First, any macros that are executing are stopped and popped off the stack.
759The behavior is not unlike that of exceptions in programming languages. Then
760the execution point is set so that any code waiting to execute (after all
761macros returned) is skipped.
762
763Thus, when dc(1) resets, it skips any remaining code waiting to be executed.
764Then, if it is interactive mode, and the error was not a fatal error (see the
765**EXIT STATUS** section), it asks for more input; otherwise, it exits with the
766appropriate return code.
767
768# PERFORMANCE
769
770Most dc(1) implementations use **char** types to calculate the value of **1**
771decimal digit at a time, but that can be slow. This dc(1) does something
772different.
773
774It uses large integers to calculate more than **1** decimal digit at a time. If
775built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is
776**64**, then each integer has **9** decimal digits. If built in an environment
777where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
778value (the number of decimal digits per large integer) is called
779**DC_BASE_DIGS**.
780
781In addition, this dc(1) uses an even larger integer for overflow checking. This
782integer type depends on the value of **DC_LONG_BIT**, but is always at least
783twice as large as the integer type used to store digits.
784
785# LIMITS
786
787The following are the limits on dc(1):
788
789**DC_LONG_BIT**
790
791:   The number of bits in the **long** type in the environment where dc(1) was
792    built. This determines how many decimal digits can be stored in a single
793    large integer (see the **PERFORMANCE** section).
794
795**DC_BASE_DIGS**
796
797:   The number of decimal digits per large integer (see the **PERFORMANCE**
798    section). Depends on **DC_LONG_BIT**.
799
800**DC_BASE_POW**
801
802:   The max decimal number that each large integer can store (see
803    **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**.
804
805**DC_OVERFLOW_MAX**
806
807:   The max number that the overflow type (see the **PERFORMANCE** section) can
808    hold. Depends on **DC_LONG_BIT**.
809
810**DC_BASE_MAX**
811
812:   The maximum output base. Set at **DC_BASE_POW**.
813
814**DC_DIM_MAX**
815
816:   The maximum size of arrays. Set at **SIZE_MAX-1**.
817
818**DC_SCALE_MAX**
819
820:   The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**.
821
822**DC_STRING_MAX**
823
824:   The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**.
825
826**DC_NAME_MAX**
827
828:   The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**.
829
830**DC_NUM_MAX**
831
832:   The maximum length of a number (in decimal digits), which includes digits
833    after the decimal point. Set at **DC_OVERFLOW_MAX-1**.
834
835Exponent
836
837:   The maximum allowable exponent (positive or negative). Set at
838    **DC_OVERFLOW_MAX**.
839
840Number of vars
841
842:   The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
843
844These limits are meant to be effectively non-existent; the limits are so large
845(at least on 64-bit machines) that there should not be any point at which they
846become a problem. In fact, memory should be exhausted before these limits should
847be hit.
848
849# ENVIRONMENT VARIABLES
850
851dc(1) recognizes the following environment variables:
852
853**DC_ENV_ARGS**
854
855:   This is another way to give command-line arguments to dc(1). They should be
856    in the same format as all other command-line arguments. These are always
857    processed first, so any files given in **DC_ENV_ARGS** will be processed
858    before arguments and files given on the command-line. This gives the user
859    the ability to set up "standard" options and files to be used at every
860    invocation. The most useful thing for such files to contain would be useful
861    functions that the user might want every time dc(1) runs. Another use would
862    be to use the **-e** option to set **scale** to a value other than **0**.
863
864    The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments,
865    but it does not understand escape sequences. For example, the string
866    **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string
867    **"/home/gavin/some \"dc\" file.dc"** will include the backslashes.
868
869    The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
870    if you have a file with any number of single quotes in the name, you can use
871    double quotes as the outside quotes, as in **"some 'bc' file.bc"**, and vice
872    versa if you have a file with double quotes. However, handling a file with
873    both kinds of quotes in **DC_ENV_ARGS** is not supported due to the
874    complexity of the parsing, though such files are still supported on the
875    command-line where the parsing is done by the shell.
876
877**DC_LINE_LENGTH**
878
879:   If this environment variable exists and contains an integer that is greater
880    than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output
881    lines to that length, including the backslash newline combo. The default
882    line length is **70**.
883
884**DC_EXPR_EXIT**
885
886:   If this variable exists (no matter the contents), dc(1) will exit
887    immediately after executing expressions and files given by the **-e** and/or
888    **-f** command-line options (and any equivalents).
889
890# EXIT STATUS
891
892dc(1) returns the following exit statuses:
893
894**0**
895
896:   No error.
897
898**1**
899
900:   A math error occurred. This follows standard practice of using **1** for
901    expected errors, since math errors will happen in the process of normal
902    execution.
903
904    Math errors include divide by **0**, taking the square root of a negative
905    number, attempting to convert a negative number to a hardware integer,
906    overflow when converting a number to a hardware integer, and attempting to
907    use a non-integer where an integer is required.
908
909    Converting to a hardware integer happens for the second operand of the power
910    (**\^**) operator.
911
912**2**
913
914:   A parse error occurred.
915
916    Parse errors include unexpected **EOF**, using an invalid character, failing
917    to find the end of a string or comment, and using a token where it is
918    invalid.
919
920**3**
921
922:   A runtime error occurred.
923
924    Runtime errors include assigning an invalid number to **ibase**, **obase**,
925    or **scale**; give a bad expression to a **read()** call, calling **read()**
926    inside of a **read()** call, type errors, and attempting an operation when
927    the stack has too few elements.
928
929**4**
930
931:   A fatal error occurred.
932
933    Fatal errors include memory allocation errors, I/O errors, failing to open
934    files, attempting to use files that do not have only ASCII characters (dc(1)
935    only accepts ASCII characters), attempting to open a directory as a file,
936    and giving invalid command-line options.
937
938The exit status **4** is special; when a fatal error occurs, dc(1) always exits
939and returns **4**, no matter what mode dc(1) is in.
940
941The other statuses will only be returned when dc(1) is not in interactive mode
942(see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the
943**RESET** section) and accepts more input when one of those errors occurs in
944interactive mode. This is also the case when interactive mode is forced by the
945**-i** flag or **--interactive** option.
946
947These exit statuses allow dc(1) to be used in shell scripting with error
948checking, and its normal behavior can be forced by using the **-i** flag or
949**--interactive** option.
950
951# INTERACTIVE MODE
952
953Like bc(1), dc(1) has an interactive mode and a non-interactive mode.
954Interactive mode is turned on automatically when both **stdin** and **stdout**
955are hooked to a terminal, but the **-i** flag and **--interactive** option can
956turn it on in other cases.
957
958In interactive mode, dc(1) attempts to recover from errors (see the **RESET**
959section), and in normal execution, flushes **stdout** as soon as execution is
960done for the current input.
961
962# TTY MODE
963
964If **stdin**, **stdout**, and **stderr** are all connected to a TTY, dc(1) turns
965on "TTY mode."
966
967TTY mode is required for history to be enabled (see the **COMMAND LINE HISTORY**
968section). It is also required to enable special handling for **SIGINT** signals.
969
970The prompt is enabled in TTY mode.
971
972TTY mode is different from interactive mode because interactive mode is required
973in the [bc(1) specification][1], and interactive mode requires only **stdin**
974and **stdout** to be connected to a terminal.
975
976# SIGNAL HANDLING
977
978Sending a **SIGINT** will cause dc(1) to stop execution of the current input. If
979dc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
980**RESET** section). Otherwise, it will clean up and exit.
981
982Note that "current input" can mean one of two things. If dc(1) is processing
983input from **stdin** in TTY mode, it will ask for more input. If dc(1) is
984processing input from a file in TTY mode, it will stop processing the file and
985start processing the next file, if one exists, or ask for input from **stdin**
986if no other file exists.
987
988This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it
989can seem as though dc(1) did not respond to the signal since it will immediately
990start executing the next file. This is by design; most files that users execute
991when interacting with dc(1) have function definitions, which are quick to parse.
992If a file takes a long time to execute, there may be a bug in that file. The
993rest of the files could still be executed without problem, allowing the user to
994continue.
995
996**SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the
997default handler for all other signals. The one exception is **SIGHUP**; in that
998case, when dc(1) is in TTY mode, a **SIGHUP** will cause dc(1) to clean up and
999exit.
1000
1001# COMMAND LINE HISTORY
1002
1003dc(1) supports interactive command-line editing. If dc(1) is in TTY mode (see
1004the **TTY MODE** section), history is enabled. Previous lines can be recalled
1005and edited with the arrow keys.
1006
1007**Note**: tabs are converted to 8 spaces.
1008
1009# SEE ALSO
1010
1011bc(1)
1012
1013# STANDARDS
1014
1015The dc(1) utility operators are compliant with the operators in the bc(1)
1016[IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1] specification.
1017
1018# BUGS
1019
1020None are known. Report bugs at https://git.yzena.com/gavin/bc.
1021
1022# AUTHOR
1023
1024Gavin D. Howard <gavin@yzena.com> and contributors.
1025
1026[1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html
1027