3 SPDX-License-Identifier: BSD-2-Clause
5 Copyright (c) 2018-2021 Gavin D. Howard and contributors.
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33 dc - arbitrary-precision decimal 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 If this option is given on the command-line (i.e., not in **DC_ENV_ARGS**,
105 see the **ENVIRONMENT VARIABLES** section), then after processing all
106 expressions and files, dc(1) will exit, unless **-** (**stdin**) was given
107 as an argument at least once to **-f** or **--file**, whether on the
108 command-line or in **DC_ENV_ARGS**. However, if any other **-e**,
109 **--expression**, **-f**, or **--file** arguments are given after **-f-** or
110 equivalent is given, dc(1) will give a fatal error and exit.
112 This is a **non-portable extension**.
114 **-f** *file*, **--file**=*file*
116 : Reads in *file* and evaluates it, line by line, as though it were read
117 through **stdin**. If expressions are also given (see above), the
118 expressions are evaluated in the order given.
120 If this option is given on the command-line (i.e., not in **DC_ENV_ARGS**,
121 see the **ENVIRONMENT VARIABLES** section), then after processing all
122 expressions and files, dc(1) will exit, unless **-** (**stdin**) was given
123 as an argument at least once to **-f** or **--file**. However, if any other
124 **-e**, **--expression**, **-f**, or **--file** arguments are given after
125 **-f-** or equivalent is given, dc(1) will give a fatal error and exit.
127 This is a **non-portable extension**.
129 All long options are **non-portable extensions**.
133 Any non-error output is written to **stdout**. In addition, if history (see the
134 **HISTORY** section) and the prompt (see the **TTY MODE** section) are enabled,
135 both are output to **stdout**.
137 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
138 error (see the **EXIT STATUS** section) if it cannot write to **stdout**, so if
139 **stdout** is closed, as in **dc <file> >&-**, it will quit with an error. This
140 is done so that dc(1) can report problems when **stdout** is redirected to a
143 If there are scripts that depend on the behavior of other dc(1) implementations,
144 it is recommended that those scripts be changed to redirect **stdout** to
149 Any error output is written to **stderr**.
151 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
152 error (see the **EXIT STATUS** section) if it cannot write to **stderr**, so if
153 **stderr** is closed, as in **dc <file> 2>&-**, it will quit with an error. This
154 is done so that dc(1) can exit with an error code when **stderr** is redirected
157 If there are scripts that depend on the behavior of other dc(1) implementations,
158 it is recommended that those scripts be changed to redirect **stderr** to
163 Each item in the input source code, either a number (see the **NUMBERS**
164 section) or a command (see the **COMMANDS** section), is processed and executed,
165 in order. Input is processed immediately when entered.
167 **ibase** is a register (see the **REGISTERS** section) that determines how to
168 interpret constant numbers. It is the "input" base, or the number base used for
169 interpreting input numbers. **ibase** is initially **10**. The max allowable
170 value for **ibase** is **16**. The min allowable value for **ibase** is **2**.
171 The max allowable value for **ibase** can be queried in dc(1) programs with the
174 **obase** is a register (see the **REGISTERS** section) that determines how to
175 output results. It is the "output" base, or the number base used for outputting
176 numbers. **obase** is initially **10**. The max allowable value for **obase** is
177 **DC_BASE_MAX** and can be queried with the **U** command. The min allowable
178 value for **obase** is **2**. Values are output in the specified base.
180 The *scale* of an expression is the number of digits in the result of the
181 expression right of the decimal point, and **scale** is a register (see the
182 **REGISTERS** section) that sets the precision of any operations (with
183 exceptions). **scale** is initially **0**. **scale** cannot be negative. The max
184 allowable value for **scale** can be queried in dc(1) programs with the **V**
189 Comments go from **#** until, and not including, the next newline. This is a
190 **non-portable extension**.
194 Numbers are strings made up of digits, uppercase letters up to **F**, and at
195 most **1** period for a radix. Numbers can have up to **DC_NUM_MAX** digits.
196 Uppercase letters are equal to **9** + their position in the alphabet (i.e.,
197 **A** equals **10**, or **9+1**). If a digit or letter makes no sense with the
198 current value of **ibase**, they are set to the value of the highest valid digit
201 Single-character numbers (i.e., **A** alone) take the value that they would have
202 if they were valid digits, regardless of the value of **ibase**. This means that
203 **A** alone always equals decimal **10** and **F** alone always equals decimal
208 The valid commands are listed below.
212 These commands are used for printing.
216 : Prints the value on top of the stack, whether number or string, and prints a
219 This does not alter the stack.
223 : Prints the value on top of the stack, whether number or string, and pops it
228 : Pops a value off the stack.
230 If the value is a number, it is truncated and the absolute value of the
231 result is printed as though **obase** is **UCHAR_MAX+1** and each digit is
232 interpreted as an ASCII character, making it a byte stream.
234 If the value is a string, it is printed without a trailing newline.
236 This is a **non-portable extension**.
240 : Prints the entire contents of the stack, in order from newest to oldest,
241 without altering anything.
243 Users should use this command when they get lost.
247 These are the commands used for arithmetic.
251 : The top two values are popped off the stack, added, and the result is pushed
252 onto the stack. The *scale* of the result is equal to the max *scale* of
257 : The top two values are popped off the stack, subtracted, and the result is
258 pushed onto the stack. The *scale* of the result is equal to the max
259 *scale* of both operands.
263 : The top two values are popped off the stack, multiplied, and the result is
264 pushed onto the stack. If **a** is the *scale* of the first expression and
265 **b** is the *scale* of the second expression, the *scale* of the result
266 is equal to **min(a+b,max(scale,a,b))** where **min()** and **max()** return
271 : The top two values are popped off the stack, divided, and the result is
272 pushed onto the stack. The *scale* of the result is equal to **scale**.
274 The first value popped off of the stack must be non-zero.
278 : The top two values are popped off the stack, remaindered, and the result is
279 pushed onto the stack.
281 Remaindering is equivalent to 1) Computing **a/b** to current **scale**, and
282 2) Using the result of step 1 to calculate **a-(a/b)\*b** to *scale*
283 **max(scale+scale(b),scale(a))**.
285 The first value popped off of the stack must be non-zero.
289 : The top two values are popped off the stack, divided and remaindered, and
290 the results (divided first, remainder second) are pushed onto the stack.
291 This is equivalent to **x y / x y %** except that **x** and **y** are only
294 The first value popped off of the stack must be non-zero.
296 This is a **non-portable extension**.
300 : The top two values are popped off the stack, the second is raised to the
301 power of the first, and the result is pushed onto the stack. The *scale* of
302 the result is equal to **scale**.
304 The first value popped off of the stack must be an integer, and if that
305 value is negative, the second value popped off of the stack must be
310 : The top value is popped off the stack, its square root is computed, and the
311 result is pushed onto the stack. The *scale* of the result is equal to
314 The value popped off of the stack must be non-negative.
318 : If this command *immediately* precedes a number (i.e., no spaces or other
319 commands), then that number is input as a negative number.
321 Otherwise, the top value on the stack is popped and copied, and the copy is
322 negated and pushed onto the stack. This behavior without a number is a
323 **non-portable extension**.
327 : The top value is popped off the stack, and if it is zero, it is pushed back
328 onto the stack. Otherwise, its absolute value is pushed onto the stack.
330 This is a **non-portable extension**.
334 : The top three values are popped off the stack, a modular exponentiation is
335 computed, and the result is pushed onto the stack.
337 The first value popped is used as the reduction modulus and must be an
338 integer and non-zero. The second value popped is used as the exponent and
339 must be an integer and non-negative. The third value popped is the base and
342 This is a **non-portable extension**.
346 : The top two values are popped off of the stack, they are compared, and a
347 **1** is pushed if they are equal, or **0** otherwise.
349 This is a **non-portable extension**.
353 : The top value is popped off of the stack, and if it a **0**, a **1** is
354 pushed; otherwise, a **0** is pushed.
356 This is a **non-portable extension**.
360 : The top two values are popped off of the stack, they are compared, and a
361 **1** is pushed if the first is less than the second, or **0** otherwise.
363 This is a **non-portable extension**.
367 : The top two values are popped off of the stack, they are compared, and a
368 **1** is pushed if the first is less than or equal to the second, or **0**
371 This is a **non-portable extension**.
375 : The top two values are popped off of the stack, they are compared, and a
376 **1** is pushed if the first is greater than the second, or **0** otherwise.
378 This is a **non-portable extension**.
382 : The top two values are popped off of the stack, they are compared, and a
383 **1** is pushed if the first is greater than or equal to the second, or
386 This is a **non-portable extension**.
390 : The top two values are popped off of the stack. If they are both non-zero, a
391 **1** is pushed onto the stack. If either of them is zero, or both of them
392 are, then a **0** is pushed onto the stack.
394 This is like the **&&** operator in bc(1), and it is *not* a short-circuit
397 This is a **non-portable extension**.
401 : The top two values are popped off of the stack. If at least one of them is
402 non-zero, a **1** is pushed onto the stack. If both of them are zero, then a
403 **0** is pushed onto the stack.
405 This is like the **||** operator in bc(1), and it is *not* a short-circuit
408 This is a **non-portable extension**.
412 These commands control the stack.
416 : Removes all items from ("clears") the stack.
420 : Copies the item on top of the stack ("duplicates") and pushes the copy onto
425 : Swaps ("reverses") the two top items on the stack.
429 : Pops ("removes") the top value from the stack.
433 These commands control registers (see the **REGISTERS** section).
437 : Pops the value off the top of the stack and stores it into register *r*.
441 : Copies the value in register *r* and pushes it onto the stack. This does not
442 alter the contents of *r*.
446 : Pops the value off the top of the (main) stack and pushes it onto the stack
447 of register *r*. The previous value of the register becomes inaccessible.
451 : Pops the value off the top of the stack for register *r* and push it onto
452 the main stack. The previous value in the stack for register *r*, if any, is
453 now accessible via the **l***r* command.
457 These commands control the values of **ibase**, **obase**, and **scale**. Also
458 see the **SYNTAX** section.
462 : Pops the value off of the top of the stack and uses it to set **ibase**,
463 which must be between **2** and **16**, inclusive.
465 If the value on top of the stack has any *scale*, the *scale* is ignored.
469 : Pops the value off of the top of the stack and uses it to set **obase**,
470 which must be between **2** and **DC_BASE_MAX**, inclusive (see the
473 If the value on top of the stack has any *scale*, the *scale* is ignored.
477 : Pops the value off of the top of the stack and uses it to set **scale**,
478 which must be non-negative.
480 If the value on top of the stack has any *scale*, the *scale* is ignored.
484 : Pushes the current value of **ibase** onto the main stack.
488 : Pushes the current value of **obase** onto the main stack.
492 : Pushes the current value of **scale** onto the main stack.
496 : Pushes the maximum allowable value of **ibase** onto the main stack.
498 This is a **non-portable extension**.
502 : Pushes the maximum allowable value of **obase** onto the main stack.
504 This is a **non-portable extension**.
508 : Pushes the maximum allowable value of **scale** onto the main stack.
510 This is a **non-portable extension**.
514 The following commands control strings.
516 dc(1) can work with both numbers and strings, and registers (see the
517 **REGISTERS** section) can hold both strings and numbers. dc(1) always knows
518 whether the contents of a register are a string or a number.
520 While arithmetic operations have to have numbers, and will print an error if
521 given a string, other commands accept strings.
523 Strings can also be executed as macros. For example, if the string **[1pR]** is
524 executed as a macro, then the code **1pR** is executed, meaning that the **1**
525 will be printed with a newline after and then popped from the stack.
527 **\[**_characters_**\]**
529 : Makes a string containing *characters* and pushes it onto the stack.
531 If there are brackets (**\[** and **\]**) in the string, then they must be
532 balanced. Unbalanced brackets can be escaped using a backslash (**\\**)
535 If there is a backslash character in the string, the character after it
536 (even another backslash) is put into the string verbatim, but the (first)
541 : The value on top of the stack is popped.
543 If it is a number, it is truncated and its absolute value is taken. The
544 result mod **UCHAR_MAX+1** is calculated. If that result is **0**, push an
545 empty string; otherwise, push a one-character string where the character is
546 the result of the mod interpreted as an ASCII character.
548 If it is a string, then a new string is made. If the original string is
549 empty, the new string is empty. If it is not, then the first character of
550 the original string is used to create the new string as a one-character
551 string. The new string is then pushed onto the stack.
553 This is a **non-portable extension**.
557 : Pops a value off of the top of the stack.
559 If it is a number, it is pushed back onto the stack.
561 If it is a string, it is executed as a macro.
563 This behavior is the norm whenever a macro is executed, whether by this
564 command or by the conditional execution commands below.
568 : Pops two values off of the stack that must be numbers and compares them. If
569 the first value is greater than the second, then the contents of register
572 For example, **0 1>a** will execute the contents of register **a**, and
575 If either or both of the values are not numbers, dc(1) will raise an error
576 and reset (see the **RESET** section).
580 : Like the above, but will execute register *s* if the comparison fails.
582 If either or both of the values are not numbers, dc(1) will raise an error
583 and reset (see the **RESET** section).
585 This is a **non-portable extension**.
589 : Pops two values off of the stack that must be numbers and compares them. If
590 the first value is not greater than the second (less than or equal to), then
591 the contents of register *r* are executed.
593 If either or both of the values are not numbers, dc(1) will raise an error
594 and reset (see the **RESET** section).
598 : Like the above, but will execute register *s* if the comparison fails.
600 If either or both of the values are not numbers, dc(1) will raise an error
601 and reset (see the **RESET** section).
603 This is a **non-portable extension**.
607 : Pops two values off of the stack that must be numbers and compares them. If
608 the first value is less than the second, then the contents of register *r*
611 If either or both of the values are not numbers, dc(1) will raise an error
612 and reset (see the **RESET** section).
616 : Like the above, but will execute register *s* if the comparison fails.
618 If either or both of the values are not numbers, dc(1) will raise an error
619 and reset (see the **RESET** section).
621 This is a **non-portable extension**.
625 : Pops two values off of the stack that must be numbers and compares them. If
626 the first value is not less than the second (greater than or equal to), then
627 the contents of register *r* are executed.
629 If either or both of the values are not numbers, dc(1) will raise an error
630 and reset (see the **RESET** section).
634 : Like the above, but will execute register *s* if the comparison fails.
636 If either or both of the values are not numbers, dc(1) will raise an error
637 and reset (see the **RESET** section).
639 This is a **non-portable extension**.
643 : Pops two values off of the stack that must be numbers and compares them. If
644 the first value is equal to the second, then the contents of register *r*
647 If either or both of the values are not numbers, dc(1) will raise an error
648 and reset (see the **RESET** section).
652 : Like the above, but will execute register *s* if the comparison fails.
654 If either or both of the values are not numbers, dc(1) will raise an error
655 and reset (see the **RESET** section).
657 This is a **non-portable extension**.
661 : Pops two values off of the stack that must be numbers and compares them. If
662 the first value is not equal to the second, then the contents of register
665 If either or both of the values are not numbers, dc(1) will raise an error
666 and reset (see the **RESET** section).
670 : Like the above, but will execute register *s* if the comparison fails.
672 If either or both of the values are not numbers, dc(1) will raise an error
673 and reset (see the **RESET** section).
675 This is a **non-portable extension**.
679 : Reads a line from the **stdin** and executes it. This is to allow macros to
680 request input from users.
684 : During execution of a macro, this exits the execution of that macro and the
685 execution of the macro that executed it. If there are no macros, or only one
686 macro executing, dc(1) exits.
690 : Pops a value from the stack which must be non-negative and is used the
691 number of macro executions to pop off of the execution stack. If the number
692 of levels to pop is greater than the number of executing macros, dc(1)
697 These commands query status of the stack or its top value.
701 : Pops a value off of the stack.
703 If it is a number, calculates the number of significant decimal digits it
704 has and pushes the result.
706 If it is a string, pushes the number of characters the string has.
710 : Pops a value off of the stack.
712 If it is a number, pushes the *scale* of the value onto the stack.
714 If it is a string, pushes **0**.
718 : Pushes the current stack depth (before execution of this command).
722 These commands manipulate arrays.
726 : Pops the top two values off of the stack. The second value will be stored in
727 the array *r* (see the **REGISTERS** section), indexed by the first value.
731 : Pops the value on top of the stack and uses it as an index into the array
732 *r*. The selected value is then pushed onto the stack.
736 Registers are names that can store strings, numbers, and arrays. (Number/string
737 registers do not interfere with array registers.)
739 Each register is also its own stack, so the current register value is the top of
740 the stack for the register. All registers, when first referenced, have one value
741 (**0**) in their stack.
743 In non-extended register mode, a register name is just the single character that
744 follows any command that needs a register name. The only exception is a newline
745 (**'\\n'**); it is a parse error for a newline to be used as a register name.
747 ## Extended Register Mode
749 Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited
750 amounts of registers, if extended register mode is enabled.
752 If extended register mode is enabled (**-x** or **--extended-register**
753 command-line arguments are given), then normal single character registers are
754 used *unless* the character immediately following a command that needs a
755 register name is a space (according to **isspace()**) and not a newline
758 In that case, the register name is found according to the regex
759 **\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if
760 the next non-space characters do not match that regex.
764 When dc(1) encounters an error or a signal that it has a non-default handler
765 for, it resets. This means that several things happen.
767 First, any macros that are executing are stopped and popped off the stack.
768 The behavior is not unlike that of exceptions in programming languages. Then
769 the execution point is set so that any code waiting to execute (after all
770 macros returned) is skipped.
772 Thus, when dc(1) resets, it skips any remaining code waiting to be executed.
773 Then, if it is interactive mode, and the error was not a fatal error (see the
774 **EXIT STATUS** section), it asks for more input; otherwise, it exits with the
775 appropriate return code.
779 Most dc(1) implementations use **char** types to calculate the value of **1**
780 decimal digit at a time, but that can be slow. This dc(1) does something
783 It uses large integers to calculate more than **1** decimal digit at a time. If
784 built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is
785 **64**, then each integer has **9** decimal digits. If built in an environment
786 where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
787 value (the number of decimal digits per large integer) is called
790 In addition, this dc(1) uses an even larger integer for overflow checking. This
791 integer type depends on the value of **DC_LONG_BIT**, but is always at least
792 twice as large as the integer type used to store digits.
796 The following are the limits on dc(1):
800 : The number of bits in the **long** type in the environment where dc(1) was
801 built. This determines how many decimal digits can be stored in a single
802 large integer (see the **PERFORMANCE** section).
806 : The number of decimal digits per large integer (see the **PERFORMANCE**
807 section). Depends on **DC_LONG_BIT**.
811 : The max decimal number that each large integer can store (see
812 **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**.
816 : The max number that the overflow type (see the **PERFORMANCE** section) can
817 hold. Depends on **DC_LONG_BIT**.
821 : The maximum output base. Set at **DC_BASE_POW**.
825 : The maximum size of arrays. Set at **SIZE_MAX-1**.
829 : The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**.
833 : The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**.
837 : The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**.
841 : The maximum length of a number (in decimal digits), which includes digits
842 after the decimal point. Set at **DC_OVERFLOW_MAX-1**.
846 : The maximum allowable exponent (positive or negative). Set at
851 : The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
853 These limits are meant to be effectively non-existent; the limits are so large
854 (at least on 64-bit machines) that there should not be any point at which they
855 become a problem. In fact, memory should be exhausted before these limits should
858 # ENVIRONMENT VARIABLES
860 dc(1) recognizes the following environment variables:
864 : This is another way to give command-line arguments to dc(1). They should be
865 in the same format as all other command-line arguments. These are always
866 processed first, so any files given in **DC_ENV_ARGS** will be processed
867 before arguments and files given on the command-line. This gives the user
868 the ability to set up "standard" options and files to be used at every
869 invocation. The most useful thing for such files to contain would be useful
870 functions that the user might want every time dc(1) runs. Another use would
871 be to use the **-e** option to set **scale** to a value other than **0**.
873 The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments,
874 but it does not understand escape sequences. For example, the string
875 **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string
876 **"/home/gavin/some \"dc\" file.dc"** will include the backslashes.
878 The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
879 if you have a file with any number of single quotes in the name, you can use
880 double quotes as the outside quotes, as in **"some 'dc' file.dc"**, and vice
881 versa if you have a file with double quotes. However, handling a file with
882 both kinds of quotes in **DC_ENV_ARGS** is not supported due to the
883 complexity of the parsing, though such files are still supported on the
884 command-line where the parsing is done by the shell.
888 : If this environment variable exists and contains an integer that is greater
889 than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output
890 lines to that length, including the backslash newline combo. The default
891 line length is **70**.
895 : If this variable exists (no matter the contents), dc(1) will exit
896 immediately after executing expressions and files given by the **-e** and/or
897 **-f** command-line options (and any equivalents).
901 dc(1) returns the following exit statuses:
909 : A math error occurred. This follows standard practice of using **1** for
910 expected errors, since math errors will happen in the process of normal
913 Math errors include divide by **0**, taking the square root of a negative
914 number, attempting to convert a negative number to a hardware integer,
915 overflow when converting a number to a hardware integer, and attempting to
916 use a non-integer where an integer is required.
918 Converting to a hardware integer happens for the second operand of the power
923 : A parse error occurred.
925 Parse errors include unexpected **EOF**, using an invalid character, failing
926 to find the end of a string or comment, and using a token where it is
931 : A runtime error occurred.
933 Runtime errors include assigning an invalid number to **ibase**, **obase**,
934 or **scale**; give a bad expression to a **read()** call, calling **read()**
935 inside of a **read()** call, type errors, and attempting an operation when
936 the stack has too few elements.
940 : A fatal error occurred.
942 Fatal errors include memory allocation errors, I/O errors, failing to open
943 files, attempting to use files that do not have only ASCII characters (dc(1)
944 only accepts ASCII characters), attempting to open a directory as a file,
945 and giving invalid command-line options.
947 The exit status **4** is special; when a fatal error occurs, dc(1) always exits
948 and returns **4**, no matter what mode dc(1) is in.
950 The other statuses will only be returned when dc(1) is not in interactive mode
951 (see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the
952 **RESET** section) and accepts more input when one of those errors occurs in
953 interactive mode. This is also the case when interactive mode is forced by the
954 **-i** flag or **--interactive** option.
956 These exit statuses allow dc(1) to be used in shell scripting with error
957 checking, and its normal behavior can be forced by using the **-i** flag or
958 **--interactive** option.
962 Like bc(1), dc(1) has an interactive mode and a non-interactive mode.
963 Interactive mode is turned on automatically when both **stdin** and **stdout**
964 are hooked to a terminal, but the **-i** flag and **--interactive** option can
965 turn it on in other cases.
967 In interactive mode, dc(1) attempts to recover from errors (see the **RESET**
968 section), and in normal execution, flushes **stdout** as soon as execution is
969 done for the current input.
973 If **stdin**, **stdout**, and **stderr** are all connected to a TTY, dc(1) turns
976 The prompt is enabled in TTY mode.
978 TTY mode is different from interactive mode because interactive mode is required
979 in the [bc(1) specification][1], and interactive mode requires only **stdin**
980 and **stdout** to be connected to a terminal.
984 Sending a **SIGINT** will cause dc(1) to stop execution of the current input. If
985 dc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
986 **RESET** section). Otherwise, it will clean up and exit.
988 Note that "current input" can mean one of two things. If dc(1) is processing
989 input from **stdin** in TTY mode, it will ask for more input. If dc(1) is
990 processing input from a file in TTY mode, it will stop processing the file and
991 start processing the next file, if one exists, or ask for input from **stdin**
992 if no other file exists.
994 This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it
995 can seem as though dc(1) did not respond to the signal since it will immediately
996 start executing the next file. This is by design; most files that users execute
997 when interacting with dc(1) have function definitions, which are quick to parse.
998 If a file takes a long time to execute, there may be a bug in that file. The
999 rest of the files could still be executed without problem, allowing the user to
1002 **SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the
1003 default handler for all other signals.
1011 The dc(1) utility operators are compliant with the operators in the bc(1)
1012 [IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1] specification.
1016 None are known. Report bugs at https://git.yzena.com/gavin/bc.
1020 Gavin D. Howard <gavin@yzena.com> and contributors.
1022 [1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html