3 SPDX-License-Identifier: BSD-2-Clause
5 Copyright (c) 2018-2020 Gavin D. Howard and contributors.
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8 modification, are permitted provided that the following conditions are met:
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33 dc - arbitrary-precision reverse-Polish notation calculator
37 **dc** [**-hiPvVx**] [**--version**] [**--help**] [**--interactive**] [**--no-prompt**] [**--extended-register**] [**-e** *expr*] [**--expression**=*expr*...] [**-f** *file*...] [**-file**=*file*...] [*file*...]
41 dc(1) is an arbitrary-precision calculator. It uses a stack (reverse Polish
42 notation) to store numbers and results of computations. Arithmetic operations
43 pop arguments off of the stack and push the results.
45 If no files are given on the command-line as extra arguments (i.e., not as
46 **-f** or **--file** arguments), then dc(1) reads from **stdin**. Otherwise,
47 those files are processed, and dc(1) will then exit.
49 This is different from the dc(1) on OpenBSD and possibly other dc(1)
50 implementations, where **-e** (**--expression**) and **-f** (**--file**)
51 arguments cause dc(1) to execute them and exit. The reason for this is that this
52 dc(1) allows users to set arguments in the environment variable **DC_ENV_ARGS**
53 (see the **ENVIRONMENT VARIABLES** section). Any expressions given on the
54 command-line should be used to set up a standard environment. For example, if a
55 user wants the **scale** always set to **10**, they can set **DC_ENV_ARGS** to
56 **-e 10k**, and this dc(1) will always start with a **scale** of **10**.
58 If users want to have dc(1) exit after processing all input from **-e** and
59 **-f** arguments (and their equivalents), then they can just simply add **-e q**
60 as the last command-line argument or define the environment variable
65 The following are the options that dc(1) accepts.
69 : Prints a usage message and quits.
71 **-v**, **-V**, **--version**
73 : Print the version information (copyright header) and exit.
75 **-i**, **--interactive**
77 : Forces interactive mode. (See the **INTERACTIVE MODE** section.)
79 This is a **non-portable extension**.
81 **-P**, **--no-prompt**
83 : This option is a no-op.
85 This is a **non-portable extension**.
87 **-x** **--extended-register**
89 : Enables extended register mode. See the *Extended Register Mode* subsection
90 of the **REGISTERS** section for more information.
92 This is a **non-portable extension**.
94 **-e** *expr*, **--expression**=*expr*
96 : Evaluates *expr*. If multiple expressions are given, they are evaluated in
97 order. If files are given as well (see below), the expressions and files are
98 evaluated in the order given. This means that if a file is given before an
99 expression, the file is read in and evaluated first.
101 After processing all expressions and files, dc(1) will exit, unless **-**
102 (**stdin**) was given as an argument at least once to **-f** or **--file**.
104 This is a **non-portable extension**.
106 **-f** *file*, **--file**=*file*
108 : Reads in *file* and evaluates it, line by line, as though it were read
109 through **stdin**. If expressions are also given (see above), the
110 expressions are evaluated in the order given.
112 After processing all expressions and files, dc(1) will exit, unless **-**
113 (**stdin**) was given as an argument at least once to **-f** or **--file**.
114 However, if any other **-e**, **--expression**, **-f**, or **--file**
115 arguments are given after that, bc(1) will give a fatal error and exit.
117 This is a **non-portable extension**.
119 All long options are **non-portable extensions**.
123 Any non-error output is written to **stdout**.
125 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
126 error (see the **EXIT STATUS** section) if it cannot write to **stdout**, so if
127 **stdout** is closed, as in **dc <file> >&-**, it will quit with an error. This
128 is done so that dc(1) can report problems when **stdout** is redirected to a
131 If there are scripts that depend on the behavior of other dc(1) implementations,
132 it is recommended that those scripts be changed to redirect **stdout** to
137 Any error output is written to **stderr**.
139 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
140 error (see the **EXIT STATUS** section) if it cannot write to **stderr**, so if
141 **stderr** is closed, as in **dc <file> 2>&-**, it will quit with an error. This
142 is done so that dc(1) can exit with an error code when **stderr** is redirected
145 If there are scripts that depend on the behavior of other dc(1) implementations,
146 it is recommended that those scripts be changed to redirect **stderr** to
151 Each item in the input source code, either a number (see the **NUMBERS**
152 section) or a command (see the **COMMANDS** section), is processed and executed,
153 in order. Input is processed immediately when entered.
155 **ibase** is a register (see the **REGISTERS** section) that determines how to
156 interpret constant numbers. It is the "input" base, or the number base used for
157 interpreting input numbers. **ibase** is initially **10**. The max allowable
158 value for **ibase** is **16**. The min allowable value for **ibase** is **2**.
159 The max allowable value for **ibase** can be queried in dc(1) programs with the
162 **obase** is a register (see the **REGISTERS** section) that determines how to
163 output results. It is the "output" base, or the number base used for outputting
164 numbers. **obase** is initially **10**. The max allowable value for **obase** is
165 **DC_BASE_MAX** and can be queried with the **U** command. The min allowable
166 value for **obase** is **2**. Values are output in the specified base.
168 The *scale* of an expression is the number of digits in the result of the
169 expression right of the decimal point, and **scale** is a register (see the
170 **REGISTERS** section) that sets the precision of any operations (with
171 exceptions). **scale** is initially **0**. **scale** cannot be negative. The max
172 allowable value for **scale** can be queried in dc(1) programs with the **V**
177 Comments go from **#** until, and not including, the next newline. This is a
178 **non-portable extension**.
182 Numbers are strings made up of digits, uppercase letters up to **F**, and at
183 most **1** period for a radix. Numbers can have up to **DC_NUM_MAX** digits.
184 Uppercase letters are equal to **9** + their position in the alphabet (i.e.,
185 **A** equals **10**, or **9+1**). If a digit or letter makes no sense with the
186 current value of **ibase**, they are set to the value of the highest valid digit
189 Single-character numbers (i.e., **A** alone) take the value that they would have
190 if they were valid digits, regardless of the value of **ibase**. This means that
191 **A** alone always equals decimal **10** and **F** alone always equals decimal
196 The valid commands are listed below.
200 These commands are used for printing.
204 : Prints the value on top of the stack, whether number or string, and prints a
207 This does not alter the stack.
211 : Prints the value on top of the stack, whether number or string, and pops it
216 : Pops a value off the stack.
218 If the value is a number, it is truncated and the absolute value of the
219 result is printed as though **obase** is **UCHAR_MAX+1** and each digit is
220 interpreted as an ASCII character, making it a byte stream.
222 If the value is a string, it is printed without a trailing newline.
224 This is a **non-portable extension**.
228 : Prints the entire contents of the stack, in order from newest to oldest,
229 without altering anything.
231 Users should use this command when they get lost.
235 These are the commands used for arithmetic.
239 : The top two values are popped off the stack, added, and the result is pushed
240 onto the stack. The *scale* of the result is equal to the max *scale* of
245 : The top two values are popped off the stack, subtracted, and the result is
246 pushed onto the stack. The *scale* of the result is equal to the max
247 *scale* of both operands.
251 : The top two values are popped off the stack, multiplied, and the result is
252 pushed onto the stack. If **a** is the *scale* of the first expression and
253 **b** is the *scale* of the second expression, the *scale* of the result
254 is equal to **min(a+b,max(scale,a,b))** where **min()** and **max()** return
259 : The top two values are popped off the stack, divided, and the result is
260 pushed onto the stack. The *scale* of the result is equal to **scale**.
262 The first value popped off of the stack must be non-zero.
266 : The top two values are popped off the stack, remaindered, and the result is
267 pushed onto the stack.
269 Remaindering is equivalent to 1) Computing **a/b** to current **scale**, and
270 2) Using the result of step 1 to calculate **a-(a/b)\*b** to *scale*
271 **max(scale+scale(b),scale(a))**.
273 The first value popped off of the stack must be non-zero.
277 : The top two values are popped off the stack, divided and remaindered, and
278 the results (divided first, remainder second) are pushed onto the stack.
279 This is equivalent to **x y / x y %** except that **x** and **y** are only
282 The first value popped off of the stack must be non-zero.
284 This is a **non-portable extension**.
288 : The top two values are popped off the stack, the second is raised to the
289 power of the first, and the result is pushed onto the stack.
291 The first value popped off of the stack must be an integer, and if that
292 value is negative, the second value popped off of the stack must be
297 : The top value is popped off the stack, its square root is computed, and the
298 result is pushed onto the stack. The *scale* of the result is equal to
301 The value popped off of the stack must be non-negative.
305 : If this command *immediately* precedes a number (i.e., no spaces or other
306 commands), then that number is input as a negative number.
308 Otherwise, the top value on the stack is popped and copied, and the copy is
309 negated and pushed onto the stack. This behavior without a number is a
310 **non-portable extension**.
314 : The top value is popped off the stack, and if it is zero, it is pushed back
315 onto the stack. Otherwise, its absolute value is pushed onto the stack.
317 This is a **non-portable extension**.
321 : The top three values are popped off the stack, a modular exponentiation is
322 computed, and the result is pushed onto the stack.
324 The first value popped is used as the reduction modulus and must be an
325 integer and non-zero. The second value popped is used as the exponent and
326 must be an integer and non-negative. The third value popped is the base and
329 This is a **non-portable extension**.
333 : The top two values are popped off of the stack, they are compared, and a
334 **1** is pushed if they are equal, or **0** otherwise.
336 This is a **non-portable extension**.
340 : The top value is popped off of the stack, and if it a **0**, a **1** is
341 pushed; otherwise, a **0** is pushed.
343 This is a **non-portable extension**.
347 : The top two values are popped off of the stack, they are compared, and a
348 **1** is pushed if the first is less than the second, or **0** otherwise.
350 This is a **non-portable extension**.
354 : The top two values are popped off of the stack, they are compared, and a
355 **1** is pushed if the first is less than or equal to the second, or **0**
358 This is a **non-portable extension**.
362 : The top two values are popped off of the stack, they are compared, and a
363 **1** is pushed if the first is greater than the second, or **0** otherwise.
365 This is a **non-portable extension**.
369 : The top two values are popped off of the stack, they are compared, and a
370 **1** is pushed if the first is greater than or equal to the second, or
373 This is a **non-portable extension**.
377 : The top two values are popped off of the stack. If they are both non-zero, a
378 **1** is pushed onto the stack. If either of them is zero, or both of them
379 are, then a **0** is pushed onto the stack.
381 This is like the **&&** operator in bc(1), and it is *not* a short-circuit
384 This is a **non-portable extension**.
388 : The top two values are popped off of the stack. If at least one of them is
389 non-zero, a **1** is pushed onto the stack. If both of them are zero, then a
390 **0** is pushed onto the stack.
392 This is like the **||** operator in bc(1), and it is *not* a short-circuit
395 This is a **non-portable extension**.
399 These commands control the stack.
403 : Removes all items from ("clears") the stack.
407 : Copies the item on top of the stack ("duplicates") and pushes the copy onto
412 : Swaps ("reverses") the two top items on the stack.
416 : Pops ("removes") the top value from the stack.
420 These commands control registers (see the **REGISTERS** section).
424 : Pops the value off the top of the stack and stores it into register *r*.
428 : Copies the value in register *r* and pushes it onto the stack. This does not
429 alter the contents of *r*.
433 : Pops the value off the top of the (main) stack and pushes it onto the stack
434 of register *r*. The previous value of the register becomes inaccessible.
438 : Pops the value off the top of the stack for register *r* and push it onto
439 the main stack. The previous value in the stack for register *r*, if any, is
440 now accessible via the **l***r* command.
444 These commands control the values of **ibase**, **obase**, and **scale**. Also
445 see the **SYNTAX** section.
449 : Pops the value off of the top of the stack and uses it to set **ibase**,
450 which must be between **2** and **16**, inclusive.
452 If the value on top of the stack has any *scale*, the *scale* is ignored.
456 : Pops the value off of the top of the stack and uses it to set **obase**,
457 which must be between **2** and **DC_BASE_MAX**, inclusive (see the
460 If the value on top of the stack has any *scale*, the *scale* is ignored.
464 : Pops the value off of the top of the stack and uses it to set **scale**,
465 which must be non-negative.
467 If the value on top of the stack has any *scale*, the *scale* is ignored.
471 : Pushes the current value of **ibase** onto the main stack.
475 : Pushes the current value of **obase** onto the main stack.
479 : Pushes the current value of **scale** onto the main stack.
483 : Pushes the maximum allowable value of **ibase** onto the main stack.
485 This is a **non-portable extension**.
489 : Pushes the maximum allowable value of **obase** onto the main stack.
491 This is a **non-portable extension**.
495 : Pushes the maximum allowable value of **scale** onto the main stack.
497 This is a **non-portable extension**.
501 The following commands control strings.
503 dc(1) can work with both numbers and strings, and registers (see the
504 **REGISTERS** section) can hold both strings and numbers. dc(1) always knows
505 whether the contents of a register are a string or a number.
507 While arithmetic operations have to have numbers, and will print an error if
508 given a string, other commands accept strings.
510 Strings can also be executed as macros. For example, if the string **[1pR]** is
511 executed as a macro, then the code **1pR** is executed, meaning that the **1**
512 will be printed with a newline after and then popped from the stack.
514 **\[**_characters_**\]**
516 : Makes a string containing *characters* and pushes it onto the stack.
518 If there are brackets (**\[** and **\]**) in the string, then they must be
519 balanced. Unbalanced brackets can be escaped using a backslash (**\\**)
522 If there is a backslash character in the string, the character after it
523 (even another backslash) is put into the string verbatim, but the (first)
528 : The value on top of the stack is popped.
530 If it is a number, it is truncated and its absolute value is taken. The
531 result mod **UCHAR_MAX+1** is calculated. If that result is **0**, push an
532 empty string; otherwise, push a one-character string where the character is
533 the result of the mod interpreted as an ASCII character.
535 If it is a string, then a new string is made. If the original string is
536 empty, the new string is empty. If it is not, then the first character of
537 the original string is used to create the new string as a one-character
538 string. The new string is then pushed onto the stack.
540 This is a **non-portable extension**.
544 : Pops a value off of the top of the stack.
546 If it is a number, it is pushed back onto the stack.
548 If it is a string, it is executed as a macro.
550 This behavior is the norm whenever a macro is executed, whether by this
551 command or by the conditional execution commands below.
555 : Pops two values off of the stack that must be numbers and compares them. If
556 the first value is greater than the second, then the contents of register
559 For example, **0 1>a** will execute the contents of register **a**, and
562 If either or both of the values are not numbers, dc(1) will raise an error
563 and reset (see the **RESET** section).
567 : Like the above, but will execute register *s* if the comparison fails.
569 If either or both of the values are not numbers, dc(1) will raise an error
570 and reset (see the **RESET** section).
572 This is a **non-portable extension**.
576 : Pops two values off of the stack that must be numbers and compares them. If
577 the first value is not greater than the second (less than or equal to), then
578 the contents of register *r* are executed.
580 If either or both of the values are not numbers, dc(1) will raise an error
581 and reset (see the **RESET** section).
585 : Like the above, but will execute register *s* if the comparison fails.
587 If either or both of the values are not numbers, dc(1) will raise an error
588 and reset (see the **RESET** section).
590 This is a **non-portable extension**.
594 : Pops two values off of the stack that must be numbers and compares them. If
595 the first value is less than the second, then the contents of register *r*
598 If either or both of the values are not numbers, dc(1) will raise an error
599 and reset (see the **RESET** section).
603 : Like the above, but will execute register *s* if the comparison fails.
605 If either or both of the values are not numbers, dc(1) will raise an error
606 and reset (see the **RESET** section).
608 This is a **non-portable extension**.
612 : Pops two values off of the stack that must be numbers and compares them. If
613 the first value is not less than the second (greater than or equal to), then
614 the contents of register *r* are executed.
616 If either or both of the values are not numbers, dc(1) will raise an error
617 and reset (see the **RESET** section).
621 : Like the above, but will execute register *s* if the comparison fails.
623 If either or both of the values are not numbers, dc(1) will raise an error
624 and reset (see the **RESET** section).
626 This is a **non-portable extension**.
630 : Pops two values off of the stack that must be numbers and compares them. If
631 the first value is equal to the second, then the contents of register *r*
634 If either or both of the values are not numbers, dc(1) will raise an error
635 and reset (see the **RESET** section).
639 : Like the above, but will execute register *s* if the comparison fails.
641 If either or both of the values are not numbers, dc(1) will raise an error
642 and reset (see the **RESET** section).
644 This is a **non-portable extension**.
648 : Pops two values off of the stack that must be numbers and compares them. If
649 the first value is not equal to the second, then the contents of register
652 If either or both of the values are not numbers, dc(1) will raise an error
653 and reset (see the **RESET** section).
657 : Like the above, but will execute register *s* if the comparison fails.
659 If either or both of the values are not numbers, dc(1) will raise an error
660 and reset (see the **RESET** section).
662 This is a **non-portable extension**.
666 : Reads a line from the **stdin** and executes it. This is to allow macros to
667 request input from users.
671 : During execution of a macro, this exits the execution of that macro and the
672 execution of the macro that executed it. If there are no macros, or only one
673 macro executing, dc(1) exits.
677 : Pops a value from the stack which must be non-negative and is used the
678 number of macro executions to pop off of the execution stack. If the number
679 of levels to pop is greater than the number of executing macros, dc(1)
684 These commands query status of the stack or its top value.
688 : Pops a value off of the stack.
690 If it is a number, calculates the number of significant decimal digits it
691 has and pushes the result.
693 If it is a string, pushes the number of characters the string has.
697 : Pops a value off of the stack.
699 If it is a number, pushes the *scale* of the value onto the stack.
701 If it is a string, pushes **0**.
705 : Pushes the current stack depth (before execution of this command).
709 These commands manipulate arrays.
713 : Pops the top two values off of the stack. The second value will be stored in
714 the array *r* (see the **REGISTERS** section), indexed by the first value.
718 : Pops the value on top of the stack and uses it as an index into the array
719 *r*. The selected value is then pushed onto the stack.
723 Registers are names that can store strings, numbers, and arrays. (Number/string
724 registers do not interfere with array registers.)
726 Each register is also its own stack, so the current register value is the top of
727 the stack for the register. All registers, when first referenced, have one value
728 (**0**) in their stack.
730 In non-extended register mode, a register name is just the single character that
731 follows any command that needs a register name. The only exception is a newline
732 (**'\\n'**); it is a parse error for a newline to be used as a register name.
734 ## Extended Register Mode
736 Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited
737 amounts of registers, if extended register mode is enabled.
739 If extended register mode is enabled (**-x** or **--extended-register**
740 command-line arguments are given), then normal single character registers are
741 used *unless* the character immediately following a command that needs a
742 register name is a space (according to **isspace()**) and not a newline
745 In that case, the register name is found according to the regex
746 **\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if
747 the next non-space characters do not match that regex.
751 When dc(1) encounters an error or a signal that it has a non-default handler
752 for, it resets. This means that several things happen.
754 First, any macros that are executing are stopped and popped off the stack.
755 The behavior is not unlike that of exceptions in programming languages. Then
756 the execution point is set so that any code waiting to execute (after all
757 macros returned) is skipped.
759 Thus, when dc(1) resets, it skips any remaining code waiting to be executed.
760 Then, if it is interactive mode, and the error was not a fatal error (see the
761 **EXIT STATUS** section), it asks for more input; otherwise, it exits with the
762 appropriate return code.
766 Most dc(1) implementations use **char** types to calculate the value of **1**
767 decimal digit at a time, but that can be slow. This dc(1) does something
770 It uses large integers to calculate more than **1** decimal digit at a time. If
771 built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is
772 **64**, then each integer has **9** decimal digits. If built in an environment
773 where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
774 value (the number of decimal digits per large integer) is called
777 In addition, this dc(1) uses an even larger integer for overflow checking. This
778 integer type depends on the value of **DC_LONG_BIT**, but is always at least
779 twice as large as the integer type used to store digits.
783 The following are the limits on dc(1):
787 : The number of bits in the **long** type in the environment where dc(1) was
788 built. This determines how many decimal digits can be stored in a single
789 large integer (see the **PERFORMANCE** section).
793 : The number of decimal digits per large integer (see the **PERFORMANCE**
794 section). Depends on **DC_LONG_BIT**.
798 : The max decimal number that each large integer can store (see
799 **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**.
803 : The max number that the overflow type (see the **PERFORMANCE** section) can
804 hold. Depends on **DC_LONG_BIT**.
808 : The maximum output base. Set at **DC_BASE_POW**.
812 : The maximum size of arrays. Set at **SIZE_MAX-1**.
816 : The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**.
820 : The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**.
824 : The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**.
828 : The maximum length of a number (in decimal digits), which includes digits
829 after the decimal point. Set at **DC_OVERFLOW_MAX-1**.
833 : The maximum allowable exponent (positive or negative). Set at
838 : The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
840 These limits are meant to be effectively non-existent; the limits are so large
841 (at least on 64-bit machines) that there should not be any point at which they
842 become a problem. In fact, memory should be exhausted before these limits should
845 # ENVIRONMENT VARIABLES
847 dc(1) recognizes the following environment variables:
851 : This is another way to give command-line arguments to dc(1). They should be
852 in the same format as all other command-line arguments. These are always
853 processed first, so any files given in **DC_ENV_ARGS** will be processed
854 before arguments and files given on the command-line. This gives the user
855 the ability to set up "standard" options and files to be used at every
856 invocation. The most useful thing for such files to contain would be useful
857 functions that the user might want every time dc(1) runs. Another use would
858 be to use the **-e** option to set **scale** to a value other than **0**.
860 The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments,
861 but it does not understand escape sequences. For example, the string
862 **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string
863 **"/home/gavin/some \"dc\" file.dc"** will include the backslashes.
865 The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
866 if you have a file with any number of single quotes in the name, you can use
867 double quotes as the outside quotes, as in **"some 'bc' file.bc"**, and vice
868 versa if you have a file with double quotes. However, handling a file with
869 both kinds of quotes in **DC_ENV_ARGS** is not supported due to the
870 complexity of the parsing, though such files are still supported on the
871 command-line where the parsing is done by the shell.
875 : If this environment variable exists and contains an integer that is greater
876 than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output
877 lines to that length, including the backslash newline combo. The default
878 line length is **70**.
882 : If this variable exists (no matter the contents), dc(1) will exit
883 immediately after executing expressions and files given by the **-e** and/or
884 **-f** command-line options (and any equivalents).
888 dc(1) returns the following exit statuses:
896 : A math error occurred. This follows standard practice of using **1** for
897 expected errors, since math errors will happen in the process of normal
900 Math errors include divide by **0**, taking the square root of a negative
901 number, attempting to convert a negative number to a hardware integer,
902 overflow when converting a number to a hardware integer, and attempting to
903 use a non-integer where an integer is required.
905 Converting to a hardware integer happens for the second operand of the power
910 : A parse error occurred.
912 Parse errors include unexpected **EOF**, using an invalid character, failing
913 to find the end of a string or comment, and using a token where it is
918 : A runtime error occurred.
920 Runtime errors include assigning an invalid number to **ibase**, **obase**,
921 or **scale**; give a bad expression to a **read()** call, calling **read()**
922 inside of a **read()** call, type errors, and attempting an operation when
923 the stack has too few elements.
927 : A fatal error occurred.
929 Fatal errors include memory allocation errors, I/O errors, failing to open
930 files, attempting to use files that do not have only ASCII characters (dc(1)
931 only accepts ASCII characters), attempting to open a directory as a file,
932 and giving invalid command-line options.
934 The exit status **4** is special; when a fatal error occurs, dc(1) always exits
935 and returns **4**, no matter what mode dc(1) is in.
937 The other statuses will only be returned when dc(1) is not in interactive mode
938 (see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the
939 **RESET** section) and accepts more input when one of those errors occurs in
940 interactive mode. This is also the case when interactive mode is forced by the
941 **-i** flag or **--interactive** option.
943 These exit statuses allow dc(1) to be used in shell scripting with error
944 checking, and its normal behavior can be forced by using the **-i** flag or
945 **--interactive** option.
949 Like bc(1), dc(1) has an interactive mode and a non-interactive mode.
950 Interactive mode is turned on automatically when both **stdin** and **stdout**
951 are hooked to a terminal, but the **-i** flag and **--interactive** option can
952 turn it on in other cases.
954 In interactive mode, dc(1) attempts to recover from errors (see the **RESET**
955 section), and in normal execution, flushes **stdout** as soon as execution is
956 done for the current input.
960 If **stdin**, **stdout**, and **stderr** are all connected to a TTY, dc(1) turns
963 TTY mode is required for history to be enabled (see the **COMMAND LINE HISTORY**
964 section). It is also required to enable special handling for **SIGINT** signals.
966 TTY mode is different from interactive mode because interactive mode is required
967 in the [bc(1) specification][1], and interactive mode requires only **stdin**
968 and **stdout** to be connected to a terminal.
972 Sending a **SIGINT** will cause dc(1) to stop execution of the current input. If
973 dc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
974 **RESET** section). Otherwise, it will clean up and exit.
976 Note that "current input" can mean one of two things. If dc(1) is processing
977 input from **stdin** in TTY mode, it will ask for more input. If dc(1) is
978 processing input from a file in TTY mode, it will stop processing the file and
979 start processing the next file, if one exists, or ask for input from **stdin**
980 if no other file exists.
982 This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it
983 can seem as though dc(1) did not respond to the signal since it will immediately
984 start executing the next file. This is by design; most files that users execute
985 when interacting with dc(1) have function definitions, which are quick to parse.
986 If a file takes a long time to execute, there may be a bug in that file. The
987 rest of the files could still be executed without problem, allowing the user to
990 **SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the
991 default handler for all other signals. The one exception is **SIGHUP**; in that
992 case, when dc(1) is in TTY mode, a **SIGHUP** will cause dc(1) to clean up and
995 # COMMAND LINE HISTORY
997 dc(1) supports interactive command-line editing. If dc(1) is in TTY mode (see
998 the **TTY MODE** section), history is enabled. Previous lines can be recalled
999 and edited with the arrow keys.
1001 **Note**: tabs are converted to 8 spaces.
1005 This dc(1) ships with support for adding error messages for different locales
1006 and thus, supports **LC_MESSAGS**.
1014 The dc(1) utility operators are compliant with the operators in the bc(1)
1015 [IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1] specification.
1019 None are known. Report bugs at https://git.yzena.com/gavin/bc.
1023 Gavin D. Howard <yzena.tech@gmail.com> and contributors.
1025 [1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html