3 SPDX-License-Identifier: BSD-2-Clause
5 Copyright (c) 2018-2021 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 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 : 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 If this option is given on the command-line (i.e., not in **DC_ENV_ARGS**,
102 see the **ENVIRONMENT VARIABLES** section), then after processing all
103 expressions and files, dc(1) will exit, unless **-** (**stdin**) was given
104 as an argument at least once to **-f** or **--file**, whether on the
105 command-line or in **DC_ENV_ARGS**. However, if any other **-e**,
106 **--expression**, **-f**, or **--file** arguments are given after **-f-** or
107 equivalent is given, dc(1) will give a fatal error and exit.
109 This is a **non-portable extension**.
111 **-f** *file*, **--file**=*file*
113 : Reads in *file* and evaluates it, line by line, as though it were read
114 through **stdin**. If expressions are also given (see above), the
115 expressions are evaluated in the order given.
117 If this option is given on the command-line (i.e., not in **DC_ENV_ARGS**,
118 see the **ENVIRONMENT VARIABLES** section), then after processing all
119 expressions and files, dc(1) will exit, unless **-** (**stdin**) was given
120 as an argument at least once to **-f** or **--file**. However, if any other
121 **-e**, **--expression**, **-f**, or **--file** arguments are given after
122 **-f-** or equivalent is given, dc(1) will give a fatal error and exit.
124 This is a **non-portable extension**.
126 All long options are **non-portable extensions**.
130 Any non-error output is written to **stdout**. In addition, if history (see the
131 **HISTORY** section) and the prompt (see the **TTY MODE** section) are enabled,
132 both are output to **stdout**.
134 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
135 error (see the **EXIT STATUS** section) if it cannot write to **stdout**, so if
136 **stdout** is closed, as in **dc <file> >&-**, it will quit with an error. This
137 is done so that dc(1) can report problems when **stdout** is redirected to a
140 If there are scripts that depend on the behavior of other dc(1) implementations,
141 it is recommended that those scripts be changed to redirect **stdout** to
146 Any error output is written to **stderr**.
148 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
149 error (see the **EXIT STATUS** section) if it cannot write to **stderr**, so if
150 **stderr** is closed, as in **dc <file> 2>&-**, it will quit with an error. This
151 is done so that dc(1) can exit with an error code when **stderr** is redirected
154 If there are scripts that depend on the behavior of other dc(1) implementations,
155 it is recommended that those scripts be changed to redirect **stderr** to
160 Each item in the input source code, either a number (see the **NUMBERS**
161 section) or a command (see the **COMMANDS** section), is processed and executed,
162 in order. Input is processed immediately when entered.
164 **ibase** is a register (see the **REGISTERS** section) that determines how to
165 interpret constant numbers. It is the "input" base, or the number base used for
166 interpreting input numbers. **ibase** is initially **10**. The max allowable
167 value for **ibase** is **16**. The min allowable value for **ibase** is **2**.
168 The max allowable value for **ibase** can be queried in dc(1) programs with the
171 **obase** is a register (see the **REGISTERS** section) that determines how to
172 output results. It is the "output" base, or the number base used for outputting
173 numbers. **obase** is initially **10**. The max allowable value for **obase** is
174 **DC_BASE_MAX** and can be queried with the **U** command. The min allowable
175 value for **obase** is **2**. Values are output in the specified base.
177 The *scale* of an expression is the number of digits in the result of the
178 expression right of the decimal point, and **scale** is a register (see the
179 **REGISTERS** section) that sets the precision of any operations (with
180 exceptions). **scale** is initially **0**. **scale** cannot be negative. The max
181 allowable value for **scale** can be queried in dc(1) programs with the **V**
186 Comments go from **#** until, and not including, the next newline. This is a
187 **non-portable extension**.
191 Numbers are strings made up of digits, uppercase letters up to **F**, and at
192 most **1** period for a radix. Numbers can have up to **DC_NUM_MAX** digits.
193 Uppercase letters are equal to **9** + their position in the alphabet (i.e.,
194 **A** equals **10**, or **9+1**). If a digit or letter makes no sense with the
195 current value of **ibase**, they are set to the value of the highest valid digit
198 Single-character numbers (i.e., **A** alone) take the value that they would have
199 if they were valid digits, regardless of the value of **ibase**. This means that
200 **A** alone always equals decimal **10** and **F** alone always equals decimal
205 The valid commands are listed below.
209 These commands are used for printing.
213 : Prints the value on top of the stack, whether number or string, and prints a
216 This does not alter the stack.
220 : Prints the value on top of the stack, whether number or string, and pops it
225 : Pops a value off the stack.
227 If the value is a number, it is truncated and the absolute value of the
228 result is printed as though **obase** is **UCHAR_MAX+1** and each digit is
229 interpreted as an ASCII character, making it a byte stream.
231 If the value is a string, it is printed without a trailing newline.
233 This is a **non-portable extension**.
237 : Prints the entire contents of the stack, in order from newest to oldest,
238 without altering anything.
240 Users should use this command when they get lost.
244 These are the commands used for arithmetic.
248 : The top two values are popped off the stack, added, and the result is pushed
249 onto the stack. The *scale* of the result is equal to the max *scale* of
254 : The top two values are popped off the stack, subtracted, and the result is
255 pushed onto the stack. The *scale* of the result is equal to the max
256 *scale* of both operands.
260 : The top two values are popped off the stack, multiplied, and the result is
261 pushed onto the stack. If **a** is the *scale* of the first expression and
262 **b** is the *scale* of the second expression, the *scale* of the result
263 is equal to **min(a+b,max(scale,a,b))** where **min()** and **max()** return
268 : The top two values are popped off the stack, divided, and the result is
269 pushed onto the stack. The *scale* of the result is equal to **scale**.
271 The first value popped off of the stack must be non-zero.
275 : The top two values are popped off the stack, remaindered, and the result is
276 pushed onto the stack.
278 Remaindering is equivalent to 1) Computing **a/b** to current **scale**, and
279 2) Using the result of step 1 to calculate **a-(a/b)\*b** to *scale*
280 **max(scale+scale(b),scale(a))**.
282 The first value popped off of the stack must be non-zero.
286 : The top two values are popped off the stack, divided and remaindered, and
287 the results (divided first, remainder second) are pushed onto the stack.
288 This is equivalent to **x y / x y %** except that **x** and **y** are only
291 The first value popped off of the stack must be non-zero.
293 This is a **non-portable extension**.
297 : The top two values are popped off the stack, the second is raised to the
298 power of the first, and the result is pushed onto the stack. The *scale* of
299 the result is equal to **scale**.
301 The first value popped off of the stack must be an integer, and if that
302 value is negative, the second value popped off of the stack must be
307 : The top value is popped off the stack, its square root is computed, and the
308 result is pushed onto the stack. The *scale* of the result is equal to
311 The value popped off of the stack must be non-negative.
315 : If this command *immediately* precedes a number (i.e., no spaces or other
316 commands), then that number is input as a negative number.
318 Otherwise, the top value on the stack is popped and copied, and the copy is
319 negated and pushed onto the stack. This behavior without a number is a
320 **non-portable extension**.
324 : The top value is popped off the stack, and if it is zero, it is pushed back
325 onto the stack. Otherwise, its absolute value is pushed onto the stack.
327 This is a **non-portable extension**.
331 : The top three values are popped off the stack, a modular exponentiation is
332 computed, and the result is pushed onto the stack.
334 The first value popped is used as the reduction modulus and must be an
335 integer and non-zero. The second value popped is used as the exponent and
336 must be an integer and non-negative. The third value popped is the base and
339 This is a **non-portable extension**.
343 : The top two values are popped off of the stack, they are compared, and a
344 **1** is pushed if they are equal, or **0** otherwise.
346 This is a **non-portable extension**.
350 : The top value is popped off of the stack, and if it a **0**, a **1** is
351 pushed; otherwise, a **0** is pushed.
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 the second, or **0** otherwise.
360 This is a **non-portable extension**.
364 : The top two values are popped off of the stack, they are compared, and a
365 **1** is pushed if the first is less than or equal to the second, or **0**
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 the second, or **0** otherwise.
375 This is a **non-portable extension**.
379 : The top two values are popped off of the stack, they are compared, and a
380 **1** is pushed if the first is greater than or equal to the second, or
383 This is a **non-portable extension**.
387 : The top two values are popped off of the stack. If they are both non-zero, a
388 **1** is pushed onto the stack. If either of them is zero, or both of them
389 are, then a **0** is pushed onto the stack.
391 This is like the **&&** operator in bc(1), and it is *not* a short-circuit
394 This is a **non-portable extension**.
398 : The top two values are popped off of the stack. If at least one of them is
399 non-zero, a **1** is pushed onto the stack. If both of them are zero, then a
400 **0** is pushed onto the stack.
402 This is like the **||** operator in bc(1), and it is *not* a short-circuit
405 This is a **non-portable extension**.
409 These commands control the stack.
413 : Removes all items from ("clears") the stack.
417 : Copies the item on top of the stack ("duplicates") and pushes the copy onto
422 : Swaps ("reverses") the two top items on the stack.
426 : Pops ("removes") the top value from the stack.
430 These commands control registers (see the **REGISTERS** section).
434 : Pops the value off the top of the stack and stores it into register *r*.
438 : Copies the value in register *r* and pushes it onto the stack. This does not
439 alter the contents of *r*.
443 : Pops the value off the top of the (main) stack and pushes it onto the stack
444 of register *r*. The previous value of the register becomes inaccessible.
448 : Pops the value off the top of the stack for register *r* and push it onto
449 the main stack. The previous value in the stack for register *r*, if any, is
450 now accessible via the **l***r* command.
454 These commands control the values of **ibase**, **obase**, and **scale**. Also
455 see the **SYNTAX** section.
459 : Pops the value off of the top of the stack and uses it to set **ibase**,
460 which must be between **2** and **16**, inclusive.
462 If the value on top of the stack has any *scale*, the *scale* is ignored.
466 : Pops the value off of the top of the stack and uses it to set **obase**,
467 which must be between **2** and **DC_BASE_MAX**, inclusive (see the
470 If the value on top of the stack has any *scale*, the *scale* is ignored.
474 : Pops the value off of the top of the stack and uses it to set **scale**,
475 which must be non-negative.
477 If the value on top of the stack has any *scale*, the *scale* is ignored.
481 : Pushes the current value of **ibase** onto the main stack.
485 : Pushes the current value of **obase** onto the main stack.
489 : Pushes the current value of **scale** onto the main stack.
493 : Pushes the maximum allowable value of **ibase** onto the main stack.
495 This is a **non-portable extension**.
499 : Pushes the maximum allowable value of **obase** onto the main stack.
501 This is a **non-portable extension**.
505 : Pushes the maximum allowable value of **scale** onto the main stack.
507 This is a **non-portable extension**.
511 The following commands control strings.
513 dc(1) can work with both numbers and strings, and registers (see the
514 **REGISTERS** section) can hold both strings and numbers. dc(1) always knows
515 whether the contents of a register are a string or a number.
517 While arithmetic operations have to have numbers, and will print an error if
518 given a string, other commands accept strings.
520 Strings can also be executed as macros. For example, if the string **[1pR]** is
521 executed as a macro, then the code **1pR** is executed, meaning that the **1**
522 will be printed with a newline after and then popped from the stack.
524 **\[**_characters_**\]**
526 : Makes a string containing *characters* and pushes it onto the stack.
528 If there are brackets (**\[** and **\]**) in the string, then they must be
529 balanced. Unbalanced brackets can be escaped using a backslash (**\\**)
532 If there is a backslash character in the string, the character after it
533 (even another backslash) is put into the string verbatim, but the (first)
538 : The value on top of the stack is popped.
540 If it is a number, it is truncated and its absolute value is taken. The
541 result mod **UCHAR_MAX+1** is calculated. If that result is **0**, push an
542 empty string; otherwise, push a one-character string where the character is
543 the result of the mod interpreted as an ASCII character.
545 If it is a string, then a new string is made. If the original string is
546 empty, the new string is empty. If it is not, then the first character of
547 the original string is used to create the new string as a one-character
548 string. The new string is then pushed onto the stack.
550 This is a **non-portable extension**.
554 : Pops a value off of the top of the stack.
556 If it is a number, it is pushed back onto the stack.
558 If it is a string, it is executed as a macro.
560 This behavior is the norm whenever a macro is executed, whether by this
561 command or by the conditional execution commands below.
565 : Pops two values off of the stack that must be numbers and compares them. If
566 the first value is greater than the second, then the contents of register
569 For example, **0 1>a** will execute the contents of register **a**, and
572 If either or both of the values are not numbers, dc(1) will raise an error
573 and reset (see the **RESET** section).
577 : Like the above, but will execute register *s* if the comparison fails.
579 If either or both of the values are not numbers, dc(1) will raise an error
580 and reset (see the **RESET** section).
582 This is a **non-portable extension**.
586 : Pops two values off of the stack that must be numbers and compares them. If
587 the first value is not greater than the second (less than or equal to), then
588 the contents of register *r* are executed.
590 If either or both of the values are not numbers, dc(1) will raise an error
591 and reset (see the **RESET** section).
595 : Like the above, but will execute register *s* if the comparison fails.
597 If either or both of the values are not numbers, dc(1) will raise an error
598 and reset (see the **RESET** section).
600 This is a **non-portable extension**.
604 : Pops two values off of the stack that must be numbers and compares them. If
605 the first value is less than the second, then the contents of register *r*
608 If either or both of the values are not numbers, dc(1) will raise an error
609 and reset (see the **RESET** section).
613 : Like the above, but will execute register *s* if the comparison fails.
615 If either or both of the values are not numbers, dc(1) will raise an error
616 and reset (see the **RESET** section).
618 This is a **non-portable extension**.
622 : Pops two values off of the stack that must be numbers and compares them. If
623 the first value is not less than the second (greater than or equal to), then
624 the contents of register *r* are executed.
626 If either or both of the values are not numbers, dc(1) will raise an error
627 and reset (see the **RESET** section).
631 : Like the above, but will execute register *s* if the comparison fails.
633 If either or both of the values are not numbers, dc(1) will raise an error
634 and reset (see the **RESET** section).
636 This is a **non-portable extension**.
640 : Pops two values off of the stack that must be numbers and compares them. If
641 the first value is equal to the second, then the contents of register *r*
644 If either or both of the values are not numbers, dc(1) will raise an error
645 and reset (see the **RESET** section).
649 : Like the above, but will execute register *s* if the comparison fails.
651 If either or both of the values are not numbers, dc(1) will raise an error
652 and reset (see the **RESET** section).
654 This is a **non-portable extension**.
658 : Pops two values off of the stack that must be numbers and compares them. If
659 the first value is not equal to the second, then the contents of register
662 If either or both of the values are not numbers, dc(1) will raise an error
663 and reset (see the **RESET** section).
667 : Like the above, but will execute register *s* if the comparison fails.
669 If either or both of the values are not numbers, dc(1) will raise an error
670 and reset (see the **RESET** section).
672 This is a **non-portable extension**.
676 : Reads a line from the **stdin** and executes it. This is to allow macros to
677 request input from users.
681 : During execution of a macro, this exits the execution of that macro and the
682 execution of the macro that executed it. If there are no macros, or only one
683 macro executing, dc(1) exits.
687 : Pops a value from the stack which must be non-negative and is used the
688 number of macro executions to pop off of the execution stack. If the number
689 of levels to pop is greater than the number of executing macros, dc(1)
694 These commands query status of the stack or its top value.
698 : Pops a value off of the stack.
700 If it is a number, calculates the number of significant decimal digits it
701 has and pushes the result.
703 If it is a string, pushes the number of characters the string has.
707 : Pops a value off of the stack.
709 If it is a number, pushes the *scale* of the value onto the stack.
711 If it is a string, pushes **0**.
715 : Pushes the current stack depth (before execution of this command).
719 These commands manipulate arrays.
723 : Pops the top two values off of the stack. The second value will be stored in
724 the array *r* (see the **REGISTERS** section), indexed by the first value.
728 : Pops the value on top of the stack and uses it as an index into the array
729 *r*. The selected value is then pushed onto the stack.
733 Registers are names that can store strings, numbers, and arrays. (Number/string
734 registers do not interfere with array registers.)
736 Each register is also its own stack, so the current register value is the top of
737 the stack for the register. All registers, when first referenced, have one value
738 (**0**) in their stack.
740 In non-extended register mode, a register name is just the single character that
741 follows any command that needs a register name. The only exception is a newline
742 (**'\\n'**); it is a parse error for a newline to be used as a register name.
744 ## Extended Register Mode
746 Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited
747 amounts of registers, if extended register mode is enabled.
749 If extended register mode is enabled (**-x** or **--extended-register**
750 command-line arguments are given), then normal single character registers are
751 used *unless* the character immediately following a command that needs a
752 register name is a space (according to **isspace()**) and not a newline
755 In that case, the register name is found according to the regex
756 **\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if
757 the next non-space characters do not match that regex.
761 When dc(1) encounters an error or a signal that it has a non-default handler
762 for, it resets. This means that several things happen.
764 First, any macros that are executing are stopped and popped off the stack.
765 The behavior is not unlike that of exceptions in programming languages. Then
766 the execution point is set so that any code waiting to execute (after all
767 macros returned) is skipped.
769 Thus, when dc(1) resets, it skips any remaining code waiting to be executed.
770 Then, if it is interactive mode, and the error was not a fatal error (see the
771 **EXIT STATUS** section), it asks for more input; otherwise, it exits with the
772 appropriate return code.
776 Most dc(1) implementations use **char** types to calculate the value of **1**
777 decimal digit at a time, but that can be slow. This dc(1) does something
780 It uses large integers to calculate more than **1** decimal digit at a time. If
781 built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is
782 **64**, then each integer has **9** decimal digits. If built in an environment
783 where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
784 value (the number of decimal digits per large integer) is called
787 In addition, this dc(1) uses an even larger integer for overflow checking. This
788 integer type depends on the value of **DC_LONG_BIT**, but is always at least
789 twice as large as the integer type used to store digits.
793 The following are the limits on dc(1):
797 : The number of bits in the **long** type in the environment where dc(1) was
798 built. This determines how many decimal digits can be stored in a single
799 large integer (see the **PERFORMANCE** section).
803 : The number of decimal digits per large integer (see the **PERFORMANCE**
804 section). Depends on **DC_LONG_BIT**.
808 : The max decimal number that each large integer can store (see
809 **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**.
813 : The max number that the overflow type (see the **PERFORMANCE** section) can
814 hold. Depends on **DC_LONG_BIT**.
818 : The maximum output base. Set at **DC_BASE_POW**.
822 : The maximum size of arrays. Set at **SIZE_MAX-1**.
826 : The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**.
830 : The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**.
834 : The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**.
838 : The maximum length of a number (in decimal digits), which includes digits
839 after the decimal point. Set at **DC_OVERFLOW_MAX-1**.
843 : The maximum allowable exponent (positive or negative). Set at
848 : The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
850 These limits are meant to be effectively non-existent; the limits are so large
851 (at least on 64-bit machines) that there should not be any point at which they
852 become a problem. In fact, memory should be exhausted before these limits should
855 # ENVIRONMENT VARIABLES
857 dc(1) recognizes the following environment variables:
861 : This is another way to give command-line arguments to dc(1). They should be
862 in the same format as all other command-line arguments. These are always
863 processed first, so any files given in **DC_ENV_ARGS** will be processed
864 before arguments and files given on the command-line. This gives the user
865 the ability to set up "standard" options and files to be used at every
866 invocation. The most useful thing for such files to contain would be useful
867 functions that the user might want every time dc(1) runs. Another use would
868 be to use the **-e** option to set **scale** to a value other than **0**.
870 The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments,
871 but it does not understand escape sequences. For example, the string
872 **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string
873 **"/home/gavin/some \"dc\" file.dc"** will include the backslashes.
875 The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
876 if you have a file with any number of single quotes in the name, you can use
877 double quotes as the outside quotes, as in **"some 'dc' file.dc"**, and vice
878 versa if you have a file with double quotes. However, handling a file with
879 both kinds of quotes in **DC_ENV_ARGS** is not supported due to the
880 complexity of the parsing, though such files are still supported on the
881 command-line where the parsing is done by the shell.
885 : If this environment variable exists and contains an integer that is greater
886 than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output
887 lines to that length, including the backslash newline combo. The default
888 line length is **70**.
892 : If this variable exists (no matter the contents), dc(1) will exit
893 immediately after executing expressions and files given by the **-e** and/or
894 **-f** command-line options (and any equivalents).
898 dc(1) returns the following exit statuses:
906 : A math error occurred. This follows standard practice of using **1** for
907 expected errors, since math errors will happen in the process of normal
910 Math errors include divide by **0**, taking the square root of a negative
911 number, attempting to convert a negative number to a hardware integer,
912 overflow when converting a number to a hardware integer, and attempting to
913 use a non-integer where an integer is required.
915 Converting to a hardware integer happens for the second operand of the power
920 : A parse error occurred.
922 Parse errors include unexpected **EOF**, using an invalid character, failing
923 to find the end of a string or comment, and using a token where it is
928 : A runtime error occurred.
930 Runtime errors include assigning an invalid number to **ibase**, **obase**,
931 or **scale**; give a bad expression to a **read()** call, calling **read()**
932 inside of a **read()** call, type errors, and attempting an operation when
933 the stack has too few elements.
937 : A fatal error occurred.
939 Fatal errors include memory allocation errors, I/O errors, failing to open
940 files, attempting to use files that do not have only ASCII characters (dc(1)
941 only accepts ASCII characters), attempting to open a directory as a file,
942 and giving invalid command-line options.
944 The exit status **4** is special; when a fatal error occurs, dc(1) always exits
945 and returns **4**, no matter what mode dc(1) is in.
947 The other statuses will only be returned when dc(1) is not in interactive mode
948 (see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the
949 **RESET** section) and accepts more input when one of those errors occurs in
950 interactive mode. This is also the case when interactive mode is forced by the
951 **-i** flag or **--interactive** option.
953 These exit statuses allow dc(1) to be used in shell scripting with error
954 checking, and its normal behavior can be forced by using the **-i** flag or
955 **--interactive** option.
959 Like bc(1), dc(1) has an interactive mode and a non-interactive mode.
960 Interactive mode is turned on automatically when both **stdin** and **stdout**
961 are hooked to a terminal, but the **-i** flag and **--interactive** option can
962 turn it on in other cases.
964 In interactive mode, dc(1) attempts to recover from errors (see the **RESET**
965 section), and in normal execution, flushes **stdout** as soon as execution is
966 done for the current input.
970 If **stdin**, **stdout**, and **stderr** are all connected to a TTY, dc(1) turns
973 TTY mode is different from interactive mode because interactive mode is required
974 in the [bc(1) specification][1], and interactive mode requires only **stdin**
975 and **stdout** to be connected to a terminal.
979 Sending a **SIGINT** will cause dc(1) to stop execution of the current input. If
980 dc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
981 **RESET** section). Otherwise, it will clean up and exit.
983 Note that "current input" can mean one of two things. If dc(1) is processing
984 input from **stdin** in TTY mode, it will ask for more input. If dc(1) is
985 processing input from a file in TTY mode, it will stop processing the file and
986 start processing the next file, if one exists, or ask for input from **stdin**
987 if no other file exists.
989 This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it
990 can seem as though dc(1) did not respond to the signal since it will immediately
991 start executing the next file. This is by design; most files that users execute
992 when interacting with dc(1) have function definitions, which are quick to parse.
993 If a file takes a long time to execute, there may be a bug in that file. The
994 rest of the files could still be executed without problem, allowing the user to
997 **SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the
998 default handler for all other signals.
1002 This dc(1) ships with support for adding error messages for different locales
1003 and thus, supports **LC_MESSAGS**.
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