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 : 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**.
88 This is a **non-portable extension**.
90 **-x** **--extended-register**
92 : Enables extended register mode. See the *Extended Register Mode* subsection
93 of the **REGISTERS** section for more information.
95 This is a **non-portable extension**.
97 **-e** *expr*, **--expression**=*expr*
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.
104 In other dc(1) implementations, this option causes the program to execute
105 the expressions and then exit. This dc(1) does not, unless the
106 **DC_EXPR_EXIT** is defined (see the **ENVIRONMENT VARIABLES** section).
108 This is a **non-portable extension**.
110 **-f** *file*, **--file**=*file*
112 : Reads in *file* and evaluates it, line by line, as though it were read
113 through **stdin**. If expressions are also given (see above), the
114 expressions are evaluated in the order given.
116 In other dc(1) implementations, this option causes the program to execute
117 the files and then exit. This dc(1) does not, unless the
118 **DC_EXPR_EXIT** is defined (see the **ENVIRONMENT VARIABLES** section).
120 This is a **non-portable extension**.
122 All long options are **non-portable extensions**.
126 Any non-error output is written to **stdout**.
128 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
129 error (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
131 is done so that dc(1) can report problems when **stdout** is redirected to a
134 If there are scripts that depend on the behavior of other dc(1) implementations,
135 it is recommended that those scripts be changed to redirect **stdout** to
140 Any error output is written to **stderr**.
142 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
143 error (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
145 is done so that dc(1) can exit with an error code when **stderr** is redirected
148 If there are scripts that depend on the behavior of other dc(1) implementations,
149 it is recommended that those scripts be changed to redirect **stderr** to
154 Each item in the input source code, either a number (see the **NUMBERS**
155 section) or a command (see the **COMMANDS** section), is processed and executed,
156 in order. Input is processed immediately when entered.
158 **ibase** is a register (see the **REGISTERS** section) that determines how to
159 interpret constant numbers. It is the "input" base, or the number base used for
160 interpreting input numbers. **ibase** is initially **10**. The max allowable
161 value for **ibase** is **16**. The min allowable value for **ibase** is **2**.
162 The max allowable value for **ibase** can be queried in dc(1) programs with the
165 **obase** is a register (see the **REGISTERS** section) that determines how to
166 output results. It is the "output" base, or the number base used for outputting
167 numbers. **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
169 value for **obase** is **2**. Values are output in the specified base.
171 The *scale* of an expression is the number of digits in the result of the
172 expression right of the decimal point, and **scale** is a register (see the
173 **REGISTERS** section) that sets the precision of any operations (with
174 exceptions). **scale** is initially **0**. **scale** cannot be negative. The max
175 allowable value for **scale** can be queried in dc(1) programs with the **V**
180 Comments go from **#** until, and not including, the next newline. This is a
181 **non-portable extension**.
185 Numbers are strings made up of digits, uppercase letters up to **F**, and at
186 most **1** period for a radix. Numbers can have up to **DC_NUM_MAX** digits.
187 Uppercase 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
189 current value of **ibase**, they are set to the value of the highest valid digit
192 Single-character numbers (i.e., **A** alone) take the value that they would have
193 if 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
199 The valid commands are listed below.
203 These commands are used for printing.
207 : Prints the value on top of the stack, whether number or string, and prints a
210 This does not alter the stack.
214 : Prints the value on top of the stack, whether number or string, and pops it
219 : Pops a value off the stack.
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.
225 If the value is a string, it is printed without a trailing newline.
227 This is a **non-portable extension**.
231 : Prints the entire contents of the stack, in order from newest to oldest,
232 without altering anything.
234 Users should use this command when they get lost.
238 These are the commands used for arithmetic.
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
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.
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
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**.
265 The first value popped off of the stack must be non-zero.
269 : The top two values are popped off the stack, remaindered, and the result is
270 pushed onto the stack.
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))**.
276 The first value popped off of the stack must be non-zero.
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
285 The first value popped off of the stack must be non-zero.
287 This is a **non-portable extension**.
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.
294 The first value popped off of the stack must be an integer, and if that
295 value is negative, the second value popped off of the stack must be
300 : The top value is popped off the stack, its square root is computed, and the
301 result is pushed onto the stack. The *scale* of the result is equal to
304 The value popped off of the stack must be non-negative.
308 : If this command *immediately* precedes a number (i.e., no spaces or other
309 commands), then that number is input as a negative number.
311 Otherwise, the top value on the stack is popped and copied, and the copy is
312 negated and pushed onto the stack. This behavior without a number is a
313 **non-portable extension**.
317 : The top value is popped off the stack, and if it is zero, it is pushed back
318 onto the stack. Otherwise, its absolute value is pushed onto the stack.
320 This is a **non-portable extension**.
324 : The top three values are popped off the stack, a modular exponentiation is
325 computed, and the result is pushed onto the stack.
327 The first value popped is used as the reduction modulus and must be an
328 integer and non-zero. The second value popped is used as the exponent and
329 must be an integer and non-negative. The third value popped is the base and
332 This is a **non-portable extension**.
336 : The top two values are popped off of the stack, they are compared, and a
337 **1** is pushed if they are equal, or **0** otherwise.
339 This is a **non-portable extension**.
343 : The top value is popped off of the stack, and if it a **0**, a **1** is
344 pushed; otherwise, a **0** is pushed.
346 This is a **non-portable extension**.
350 : The top two values are popped off of the stack, they are compared, and a
351 **1** is pushed if the first is less than the second, or **0** otherwise.
353 This is a **non-portable extension**.
357 : The top two values are popped off of the stack, they are compared, and a
358 **1** is pushed if the first is less than or equal to the second, or **0**
361 This is a **non-portable extension**.
365 : The top two values are popped off of the stack, they are compared, and a
366 **1** is pushed if the first is greater than the second, or **0** otherwise.
368 This is a **non-portable extension**.
372 : The top two values are popped off of the stack, they are compared, and a
373 **1** is pushed if the first is greater than or equal to the second, or
376 This is a **non-portable extension**.
380 : The top two values are popped off of the stack. If they are both non-zero, a
381 **1** is pushed onto the stack. If either of them is zero, or both of them
382 are, then a **0** is pushed onto the stack.
384 This is like the **&&** operator in bc(1), and it is *not* a short-circuit
387 This is a **non-portable extension**.
391 : The top two values are popped off of the stack. If at least one of them is
392 non-zero, a **1** is pushed onto the stack. If both of them are zero, then a
393 **0** is pushed onto the stack.
395 This is like the **||** operator in bc(1), and it is *not* a short-circuit
398 This is a **non-portable extension**.
402 These commands control the stack.
406 : Removes all items from ("clears") the stack.
410 : Copies the item on top of the stack ("duplicates") and pushes the copy onto
415 : Swaps ("reverses") the two top items on the stack.
419 : Pops ("removes") the top value from the stack.
423 These commands control registers (see the **REGISTERS** section).
427 : Pops the value off the top of the stack and stores it into register *r*.
431 : Copies the value in register *r* and pushes it onto the stack. This does not
432 alter the contents of *r*.
436 : Pops the value off the top of the (main) stack and pushes it onto the stack
437 of register *r*. The previous value of the register becomes inaccessible.
441 : Pops the value off the top of the stack for register *r* and push it onto
442 the main stack. The previous value in the stack for register *r*, if any, is
443 now accessible via the **l***r* command.
447 These commands control the values of **ibase**, **obase**, and **scale**. Also
448 see the **SYNTAX** section.
452 : Pops the value off of the top of the stack and uses it to set **ibase**,
453 which must be between **2** and **16**, inclusive.
455 If the value on top of the stack has any *scale*, the *scale* is ignored.
459 : Pops the value off of the top of the stack and uses it to set **obase**,
460 which must be between **2** and **DC_BASE_MAX**, inclusive (see the
463 If the value on top of the stack has any *scale*, the *scale* is ignored.
467 : Pops the value off of the top of the stack and uses it to set **scale**,
468 which must be non-negative.
470 If the value on top of the stack has any *scale*, the *scale* is ignored.
474 : Pushes the current value of **ibase** onto the main stack.
478 : Pushes the current value of **obase** onto the main stack.
482 : Pushes the current value of **scale** onto the main stack.
486 : Pushes the maximum allowable value of **ibase** onto the main stack.
488 This is a **non-portable extension**.
492 : Pushes the maximum allowable value of **obase** onto the main stack.
494 This is a **non-portable extension**.
498 : Pushes the maximum allowable value of **scale** onto the main stack.
500 This is a **non-portable extension**.
504 The following commands control strings.
506 dc(1) can work with both numbers and strings, and registers (see the
507 **REGISTERS** section) can hold both strings and numbers. dc(1) always knows
508 whether the contents of a register are a string or a number.
510 While arithmetic operations have to have numbers, and will print an error if
511 given a string, other commands accept strings.
513 Strings can also be executed as macros. For example, if the string **[1pR]** is
514 executed as a macro, then the code **1pR** is executed, meaning that the **1**
515 will be printed with a newline after and then popped from the stack.
517 **\[**_characters_**\]**
519 : Makes a string containing *characters* and pushes it onto the stack.
521 If there are brackets (**\[** and **\]**) in the string, then they must be
522 balanced. Unbalanced brackets can be escaped using a backslash (**\\**)
525 If there is a backslash character in the string, the character after it
526 (even another backslash) is put into the string verbatim, but the (first)
531 : The value on top of the stack is popped.
533 If it is a number, it is truncated and its absolute value is taken. The
534 result mod **UCHAR_MAX+1** is calculated. If that result is **0**, push an
535 empty string; otherwise, push a one-character string where the character is
536 the result of the mod interpreted as an ASCII character.
538 If it is a string, then a new string is made. If the original string is
539 empty, the new string is empty. If it is not, then the first character of
540 the original string is used to create the new string as a one-character
541 string. The new string is then pushed onto the stack.
543 This is a **non-portable extension**.
547 : Pops a value off of the top of the stack.
549 If it is a number, it is pushed back onto the stack.
551 If it is a string, it is executed as a macro.
553 This behavior is the norm whenever a macro is executed, whether by this
554 command or by the conditional execution commands below.
558 : Pops two values off of the stack that must be numbers and compares them. If
559 the first value is greater than the second, then the contents of register
562 For example, **0 1>a** will execute the contents of register **a**, and
565 If either or both of the values are not numbers, dc(1) will raise an error
566 and reset (see the **RESET** section).
570 : Like the above, but will execute register *s* if the comparison fails.
572 If either or both of the values are not numbers, dc(1) will raise an error
573 and reset (see the **RESET** section).
575 This is a **non-portable extension**.
579 : Pops two values off of the stack that must be numbers and compares them. If
580 the first value is not greater than the second (less than or equal to), then
581 the contents of register *r* are executed.
583 If either or both of the values are not numbers, dc(1) will raise an error
584 and reset (see the **RESET** section).
588 : Like the above, but will execute register *s* if the comparison fails.
590 If either or both of the values are not numbers, dc(1) will raise an error
591 and reset (see the **RESET** section).
593 This is a **non-portable extension**.
597 : Pops two values off of the stack that must be numbers and compares them. If
598 the first value is less than the second, then the contents of register *r*
601 If either or both of the values are not numbers, dc(1) will raise an error
602 and reset (see the **RESET** section).
606 : Like the above, but will execute register *s* if the comparison fails.
608 If either or both of the values are not numbers, dc(1) will raise an error
609 and reset (see the **RESET** section).
611 This is a **non-portable extension**.
615 : Pops two values off of the stack that must be numbers and compares them. If
616 the first value is not less than the second (greater than or equal to), then
617 the contents of register *r* are executed.
619 If either or both of the values are not numbers, dc(1) will raise an error
620 and reset (see the **RESET** section).
624 : Like the above, but will execute register *s* if the comparison fails.
626 If either or both of the values are not numbers, dc(1) will raise an error
627 and reset (see the **RESET** section).
629 This is a **non-portable extension**.
633 : Pops two values off of the stack that must be numbers and compares them. If
634 the first value is equal to the second, then the contents of register *r*
637 If either or both of the values are not numbers, dc(1) will raise an error
638 and reset (see the **RESET** section).
642 : Like the above, but will execute register *s* if the comparison fails.
644 If either or both of the values are not numbers, dc(1) will raise an error
645 and reset (see the **RESET** section).
647 This is a **non-portable extension**.
651 : Pops two values off of the stack that must be numbers and compares them. If
652 the first value is not equal to the second, then the contents of register
655 If either or both of the values are not numbers, dc(1) will raise an error
656 and reset (see the **RESET** section).
660 : Like the above, but will execute register *s* if the comparison fails.
662 If either or both of the values are not numbers, dc(1) will raise an error
663 and reset (see the **RESET** section).
665 This is a **non-portable extension**.
669 : Reads a line from the **stdin** and executes it. This is to allow macros to
670 request input from users.
674 : During execution of a macro, this exits the execution of that macro and the
675 execution of the macro that executed it. If there are no macros, or only one
676 macro executing, dc(1) exits.
680 : Pops a value from the stack which must be non-negative and is used the
681 number of macro executions to pop off of the execution stack. If the number
682 of levels to pop is greater than the number of executing macros, dc(1)
687 These commands query status of the stack or its top value.
691 : Pops a value off of the stack.
693 If it is a number, calculates the number of significant decimal digits it
694 has and pushes the result.
696 If it is a string, pushes the number of characters the string has.
700 : Pops a value off of the stack.
702 If it is a number, pushes the *scale* of the value onto the stack.
704 If it is a string, pushes **0**.
708 : Pushes the current stack depth (before execution of this command).
712 These commands manipulate arrays.
716 : Pops the top two values off of the stack. The second value will be stored in
717 the array *r* (see the **REGISTERS** section), indexed by the first value.
721 : Pops the value on top of the stack and uses it as an index into the array
722 *r*. The selected value is then pushed onto the stack.
726 Registers are names that can store strings, numbers, and arrays. (Number/string
727 registers do not interfere with array registers.)
729 Each register is also its own stack, so the current register value is the top of
730 the stack for the register. All registers, when first referenced, have one value
731 (**0**) in their stack.
733 In non-extended register mode, a register name is just the single character that
734 follows any command that needs a register name. The only exception is a newline
735 (**'\\n'**); it is a parse error for a newline to be used as a register name.
737 ## Extended Register Mode
739 Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited
740 amounts of registers, if extended register mode is enabled.
742 If extended register mode is enabled (**-x** or **--extended-register**
743 command-line arguments are given), then normal single character registers are
744 used *unless* the character immediately following a command that needs a
745 register name is a space (according to **isspace()**) and not a newline
748 In that case, the register name is found according to the regex
749 **\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if
750 the next non-space characters do not match that regex.
754 When dc(1) encounters an error or a signal that it has a non-default handler
755 for, it resets. This means that several things happen.
757 First, any macros that are executing are stopped and popped off the stack.
758 The behavior is not unlike that of exceptions in programming languages. Then
759 the execution point is set so that any code waiting to execute (after all
760 macros returned) is skipped.
762 Thus, when dc(1) resets, it skips any remaining code waiting to be executed.
763 Then, if it is interactive mode, and the error was not a fatal error (see the
764 **EXIT STATUS** section), it asks for more input; otherwise, it exits with the
765 appropriate return code.
769 Most dc(1) implementations use **char** types to calculate the value of **1**
770 decimal digit at a time, but that can be slow. This dc(1) does something
773 It uses large integers to calculate more than **1** decimal digit at a time. If
774 built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is
775 **64**, then each integer has **9** decimal digits. If built in an environment
776 where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
777 value (the number of decimal digits per large integer) is called
780 In addition, this dc(1) uses an even larger integer for overflow checking. This
781 integer type depends on the value of **DC_LONG_BIT**, but is always at least
782 twice as large as the integer type used to store digits.
786 The following are the limits on dc(1):
790 : The number of bits in the **long** type in the environment where dc(1) was
791 built. This determines how many decimal digits can be stored in a single
792 large integer (see the **PERFORMANCE** section).
796 : The number of decimal digits per large integer (see the **PERFORMANCE**
797 section). Depends on **DC_LONG_BIT**.
801 : The max decimal number that each large integer can store (see
802 **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**.
806 : The max number that the overflow type (see the **PERFORMANCE** section) can
807 hold. Depends on **DC_LONG_BIT**.
811 : The maximum output base. Set at **DC_BASE_POW**.
815 : The maximum size of arrays. Set at **SIZE_MAX-1**.
819 : The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**.
823 : The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**.
827 : The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**.
831 : The maximum length of a number (in decimal digits), which includes digits
832 after the decimal point. Set at **DC_OVERFLOW_MAX-1**.
836 : The maximum allowable exponent (positive or negative). Set at
841 : The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
843 These limits are meant to be effectively non-existent; the limits are so large
844 (at least on 64-bit machines) that there should not be any point at which they
845 become a problem. In fact, memory should be exhausted before these limits should
848 # ENVIRONMENT VARIABLES
850 dc(1) recognizes the following environment variables:
854 : This is another way to give command-line arguments to dc(1). They should be
855 in the same format as all other command-line arguments. These are always
856 processed first, so any files given in **DC_ENV_ARGS** will be processed
857 before arguments and files given on the command-line. This gives the user
858 the ability to set up "standard" options and files to be used at every
859 invocation. The most useful thing for such files to contain would be useful
860 functions that the user might want every time dc(1) runs. Another use would
861 be to use the **-e** option to set **scale** to a value other than **0**.
863 The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments,
864 but it does not understand escape sequences. For example, the string
865 **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string
866 **"/home/gavin/some \"dc\" file.dc"** will include the backslashes.
868 The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
869 if you have a file with any number of single quotes in the name, you can use
870 double quotes as the outside quotes, as in **"some 'bc' file.bc"**, and vice
871 versa if you have a file with double quotes. However, handling a file with
872 both kinds of quotes in **DC_ENV_ARGS** is not supported due to the
873 complexity of the parsing, though such files are still supported on the
874 command-line where the parsing is done by the shell.
878 : If this environment variable exists and contains an integer that is greater
879 than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output
880 lines to that length, including the backslash newline combo. The default
881 line length is **70**.
885 : If this variable exists (no matter the contents), dc(1) will exit
886 immediately after executing expressions and files given by the **-e** and/or
887 **-f** command-line options (and any equivalents).
891 dc(1) returns the following exit statuses:
899 : A math error occurred. This follows standard practice of using **1** for
900 expected errors, since math errors will happen in the process of normal
903 Math errors include divide by **0**, taking the square root of a negative
904 number, attempting to convert a negative number to a hardware integer,
905 overflow when converting a number to a hardware integer, and attempting to
906 use a non-integer where an integer is required.
908 Converting to a hardware integer happens for the second operand of the power
913 : A parse error occurred.
915 Parse errors include unexpected **EOF**, using an invalid character, failing
916 to find the end of a string or comment, and using a token where it is
921 : A runtime error occurred.
923 Runtime errors include assigning an invalid number to **ibase**, **obase**,
924 or **scale**; give a bad expression to a **read()** call, calling **read()**
925 inside of a **read()** call, type errors, and attempting an operation when
926 the stack has too few elements.
930 : A fatal error occurred.
932 Fatal errors include memory allocation errors, I/O errors, failing to open
933 files, attempting to use files that do not have only ASCII characters (dc(1)
934 only accepts ASCII characters), attempting to open a directory as a file,
935 and giving invalid command-line options.
937 The exit status **4** is special; when a fatal error occurs, dc(1) always exits
938 and returns **4**, no matter what mode dc(1) is in.
940 The other statuses will only be returned when dc(1) is not in interactive mode
941 (see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the
942 **RESET** section) and accepts more input when one of those errors occurs in
943 interactive mode. This is also the case when interactive mode is forced by the
944 **-i** flag or **--interactive** option.
946 These exit statuses allow dc(1) to be used in shell scripting with error
947 checking, and its normal behavior can be forced by using the **-i** flag or
948 **--interactive** option.
952 Like bc(1), dc(1) has an interactive mode and a non-interactive mode.
953 Interactive mode is turned on automatically when both **stdin** and **stdout**
954 are hooked to a terminal, but the **-i** flag and **--interactive** option can
955 turn it on in other cases.
957 In interactive mode, dc(1) attempts to recover from errors (see the **RESET**
958 section), and in normal execution, flushes **stdout** as soon as execution is
959 done for the current input.
963 If **stdin**, **stdout**, and **stderr** are all connected to a TTY, dc(1) turns
966 The prompt is enabled in TTY mode.
968 TTY mode is different from interactive mode because interactive mode is required
969 in the [bc(1) specification][1], and interactive mode requires only **stdin**
970 and **stdout** to be connected to a terminal.
974 Sending a **SIGINT** will cause dc(1) to stop execution of the current input. If
975 dc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
976 **RESET** section). Otherwise, it will clean up and exit.
978 Note that "current input" can mean one of two things. If dc(1) is processing
979 input from **stdin** in TTY mode, it will ask for more input. If dc(1) is
980 processing input from a file in TTY mode, it will stop processing the file and
981 start processing the next file, if one exists, or ask for input from **stdin**
982 if no other file exists.
984 This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it
985 can seem as though dc(1) did not respond to the signal since it will immediately
986 start executing the next file. This is by design; most files that users execute
987 when interacting with dc(1) have function definitions, which are quick to parse.
988 If a file takes a long time to execute, there may be a bug in that file. The
989 rest of the files could still be executed without problem, allowing the user to
992 **SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the
993 default handler for all other signals.
1001 The dc(1) utility operators are compliant with the operators in the bc(1)
1002 [IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1] specification.
1006 None are known. Report bugs at https://git.yzena.com/gavin/bc.
1010 Gavin D. Howard <yzena.tech@gmail.com> and contributors.
1012 [1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html