3 SPDX-License-Identifier: BSD-2-Clause
5 Copyright (c) 2018-2021 Gavin D. Howard and contributors.
7 Redistribution and use in source and binary forms, with or without
8 modification, are permitted provided that the following conditions are met:
10 * Redistributions of source code must retain the above copyright notice, this
11 list of conditions and the following disclaimer.
13 * Redistributions in binary form must reproduce the above copyright notice,
14 this list of conditions and the following disclaimer in the documentation
15 and/or other materials provided with the distribution.
17 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
18 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
21 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
22 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
23 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
24 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
25 CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
26 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
27 POSSIBILITY OF SUCH DAMAGE.
33 dc - arbitrary-precision decimal reverse-Polish notation calculator
37 **dc** [**-hiPRvVx**] [**-\-version**] [**-\-help**] [**-\-interactive**] [**-\-no-prompt**] [**-\-no-read-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 **-R**, **-\-no-read-prompt**
89 : This option is a no-op.
91 This is a **non-portable extension**.
93 **-x** **-\-extended-register**
95 : Enables extended register mode. See the *Extended Register Mode* subsection
96 of the **REGISTERS** section for more information.
98 This is a **non-portable extension**.
100 **-e** *expr*, **-\-expression**=*expr*
102 : Evaluates *expr*. If multiple expressions are given, they are evaluated in
103 order. If files are given as well (see below), the expressions and files are
104 evaluated in the order given. This means that if a file is given before an
105 expression, the file is read in and evaluated first.
107 If this option is given on the command-line (i.e., not in **DC_ENV_ARGS**,
108 see the **ENVIRONMENT VARIABLES** section), then after processing all
109 expressions and files, dc(1) will exit, unless **-** (**stdin**) was given
110 as an argument at least once to **-f** or **-\-file**, whether on the
111 command-line or in **DC_ENV_ARGS**. However, if any other **-e**,
112 **-\-expression**, **-f**, or **-\-file** arguments are given after **-f-**
113 or equivalent is given, dc(1) will give a fatal error and exit.
115 This is a **non-portable extension**.
117 **-f** *file*, **-\-file**=*file*
119 : Reads in *file* and evaluates it, line by line, as though it were read
120 through **stdin**. If expressions are also given (see above), the
121 expressions are evaluated in the order given.
123 If this option is given on the command-line (i.e., not in **DC_ENV_ARGS**,
124 see the **ENVIRONMENT VARIABLES** section), then after processing all
125 expressions and files, dc(1) will exit, unless **-** (**stdin**) was given
126 as an argument at least once to **-f** or **-\-file**. However, if any other
127 **-e**, **-\-expression**, **-f**, or **-\-file** arguments are given after
128 **-f-** or equivalent is given, dc(1) will give a fatal error and exit.
130 This is a **non-portable extension**.
132 All long options are **non-portable extensions**.
136 Any non-error output is written to **stdout**. In addition, if history (see the
137 **HISTORY** section) and the prompt (see the **TTY MODE** section) are enabled,
138 both are output to **stdout**.
140 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
141 error (see the **EXIT STATUS** section) if it cannot write to **stdout**, so if
142 **stdout** is closed, as in **dc <file> >&-**, it will quit with an error. This
143 is done so that dc(1) can report problems when **stdout** is redirected to a
146 If there are scripts that depend on the behavior of other dc(1) implementations,
147 it is recommended that those scripts be changed to redirect **stdout** to
152 Any error output is written to **stderr**.
154 **Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal
155 error (see the **EXIT STATUS** section) if it cannot write to **stderr**, so if
156 **stderr** is closed, as in **dc <file> 2>&-**, it will quit with an error. This
157 is done so that dc(1) can exit with an error code when **stderr** is redirected
160 If there are scripts that depend on the behavior of other dc(1) implementations,
161 it is recommended that those scripts be changed to redirect **stderr** to
166 Each item in the input source code, either a number (see the **NUMBERS**
167 section) or a command (see the **COMMANDS** section), is processed and executed,
168 in order. Input is processed immediately when entered.
170 **ibase** is a register (see the **REGISTERS** section) that determines how to
171 interpret constant numbers. It is the "input" base, or the number base used for
172 interpreting input numbers. **ibase** is initially **10**. The max allowable
173 value for **ibase** is **16**. The min allowable value for **ibase** is **2**.
174 The max allowable value for **ibase** can be queried in dc(1) programs with the
177 **obase** is a register (see the **REGISTERS** section) that determines how to
178 output results. It is the "output" base, or the number base used for outputting
179 numbers. **obase** is initially **10**. The max allowable value for **obase** is
180 **DC_BASE_MAX** and can be queried with the **U** command. The min allowable
181 value for **obase** is **2**. Values are output in the specified base.
183 The *scale* of an expression is the number of digits in the result of the
184 expression right of the decimal point, and **scale** is a register (see the
185 **REGISTERS** section) that sets the precision of any operations (with
186 exceptions). **scale** is initially **0**. **scale** cannot be negative. The max
187 allowable value for **scale** can be queried in dc(1) programs with the **V**
192 Comments go from **#** until, and not including, the next newline. This is a
193 **non-portable extension**.
197 Numbers are strings made up of digits, uppercase letters up to **F**, and at
198 most **1** period for a radix. Numbers can have up to **DC_NUM_MAX** digits.
199 Uppercase letters are equal to **9** + their position in the alphabet (i.e.,
200 **A** equals **10**, or **9+1**). If a digit or letter makes no sense with the
201 current value of **ibase**, they are set to the value of the highest valid digit
204 Single-character numbers (i.e., **A** alone) take the value that they would have
205 if they were valid digits, regardless of the value of **ibase**. This means that
206 **A** alone always equals decimal **10** and **F** alone always equals decimal
211 The valid commands are listed below.
215 These commands are used for printing.
219 : Prints the value on top of the stack, whether number or string, and prints a
222 This does not alter the stack.
226 : Prints the value on top of the stack, whether number or string, and pops it
231 : Pops a value off the stack.
233 If the value is a number, it is truncated and the absolute value of the
234 result is printed as though **obase** is **UCHAR_MAX+1** and each digit is
235 interpreted as an ASCII character, making it a byte stream.
237 If the value is a string, it is printed without a trailing newline.
239 This is a **non-portable extension**.
243 : Prints the entire contents of the stack, in order from newest to oldest,
244 without altering anything.
246 Users should use this command when they get lost.
250 These are the commands used for arithmetic.
254 : The top two values are popped off the stack, added, and the result is pushed
255 onto the stack. The *scale* of the result is equal to the max *scale* of
260 : The top two values are popped off the stack, subtracted, and the result is
261 pushed onto the stack. The *scale* of the result is equal to the max
262 *scale* of both operands.
266 : The top two values are popped off the stack, multiplied, and the result is
267 pushed onto the stack. If **a** is the *scale* of the first expression and
268 **b** is the *scale* of the second expression, the *scale* of the result
269 is equal to **min(a+b,max(scale,a,b))** where **min()** and **max()** return
274 : The top two values are popped off the stack, divided, and the result is
275 pushed onto the stack. The *scale* of the result is equal to **scale**.
277 The first value popped off of the stack must be non-zero.
281 : The top two values are popped off the stack, remaindered, and the result is
282 pushed onto the stack.
284 Remaindering is equivalent to 1) Computing **a/b** to current **scale**, and
285 2) Using the result of step 1 to calculate **a-(a/b)\*b** to *scale*
286 **max(scale+scale(b),scale(a))**.
288 The first value popped off of the stack must be non-zero.
292 : The top two values are popped off the stack, divided and remaindered, and
293 the results (divided first, remainder second) are pushed onto the stack.
294 This is equivalent to **x y / x y %** except that **x** and **y** are only
297 The first value popped off of the stack must be non-zero.
299 This is a **non-portable extension**.
303 : The top two values are popped off the stack, the second is raised to the
304 power of the first, and the result is pushed onto the stack. The *scale* of
305 the result is equal to **scale**.
307 The first value popped off of the stack must be an integer, and if that
308 value is negative, the second value popped off of the stack must be
313 : The top value is popped off the stack, its square root is computed, and the
314 result is pushed onto the stack. The *scale* of the result is equal to
317 The value popped off of the stack must be non-negative.
321 : If this command *immediately* precedes a number (i.e., no spaces or other
322 commands), then that number is input as a negative number.
324 Otherwise, the top value on the stack is popped and copied, and the copy is
325 negated and pushed onto the stack. This behavior without a number is a
326 **non-portable extension**.
330 : The top value is popped off the stack, and if it is zero, it is pushed back
331 onto the stack. Otherwise, its absolute value is pushed onto the stack.
333 This is a **non-portable extension**.
337 : The top three values are popped off the stack, a modular exponentiation is
338 computed, and the result is pushed onto the stack.
340 The first value popped is used as the reduction modulus and must be an
341 integer and non-zero. The second value popped is used as the exponent and
342 must be an integer and non-negative. The third value popped is the base and
345 This is a **non-portable extension**.
349 : The top two values are popped off of the stack, they are compared, and a
350 **1** is pushed if they are equal, or **0** otherwise.
352 This is a **non-portable extension**.
356 : The top value is popped off of the stack, and if it a **0**, a **1** is
357 pushed; otherwise, a **0** is pushed.
359 This is a **non-portable extension**.
363 : The top two values are popped off of the stack, they are compared, and a
364 **1** is pushed if the first is less than the second, or **0** otherwise.
366 This is a **non-portable extension**.
370 : The top two values are popped off of the stack, they are compared, and a
371 **1** is pushed if the first is less than or equal to the second, or **0**
374 This is a **non-portable extension**.
378 : The top two values are popped off of the stack, they are compared, and a
379 **1** is pushed if the first is greater than the second, or **0** otherwise.
381 This is a **non-portable extension**.
385 : The top two values are popped off of the stack, they are compared, and a
386 **1** is pushed if the first is greater than or equal to the second, or
389 This is a **non-portable extension**.
393 : The top two values are popped off of the stack. If they are both non-zero, a
394 **1** is pushed onto the stack. If either of them is zero, or both of them
395 are, then a **0** is pushed onto the stack.
397 This is like the **&&** operator in bc(1), and it is *not* a short-circuit
400 This is a **non-portable extension**.
404 : The top two values are popped off of the stack. If at least one of them is
405 non-zero, a **1** is pushed onto the stack. If both of them are zero, then a
406 **0** is pushed onto the stack.
408 This is like the **||** operator in bc(1), and it is *not* a short-circuit
411 This is a **non-portable extension**.
415 These commands control the stack.
419 : Removes all items from ("clears") the stack.
423 : Copies the item on top of the stack ("duplicates") and pushes the copy onto
428 : Swaps ("reverses") the two top items on the stack.
432 : Pops ("removes") the top value from the stack.
436 These commands control registers (see the **REGISTERS** section).
440 : Pops the value off the top of the stack and stores it into register *r*.
444 : Copies the value in register *r* and pushes it onto the stack. This does not
445 alter the contents of *r*.
449 : Pops the value off the top of the (main) stack and pushes it onto the stack
450 of register *r*. The previous value of the register becomes inaccessible.
454 : Pops the value off the top of the stack for register *r* and push it onto
455 the main stack. The previous value in the stack for register *r*, if any, is
456 now accessible via the **l**_r_ command.
460 These commands control the values of **ibase**, **obase**, and **scale**. Also
461 see the **SYNTAX** section.
465 : Pops the value off of the top of the stack and uses it to set **ibase**,
466 which must be between **2** and **16**, inclusive.
468 If the value on top of the stack has any *scale*, the *scale* is ignored.
472 : Pops the value off of the top of the stack and uses it to set **obase**,
473 which must be between **2** and **DC_BASE_MAX**, inclusive (see the
476 If the value on top of the stack has any *scale*, the *scale* is ignored.
480 : Pops the value off of the top of the stack and uses it to set **scale**,
481 which must be non-negative.
483 If the value on top of the stack has any *scale*, the *scale* is ignored.
487 : Pushes the current value of **ibase** onto the main stack.
491 : Pushes the current value of **obase** onto the main stack.
495 : Pushes the current value of **scale** onto the main stack.
499 : Pushes the maximum allowable value of **ibase** onto the main stack.
501 This is a **non-portable extension**.
505 : Pushes the maximum allowable value of **obase** onto the main stack.
507 This is a **non-portable extension**.
511 : Pushes the maximum allowable value of **scale** onto the main stack.
513 This is a **non-portable extension**.
517 The following commands control strings.
519 dc(1) can work with both numbers and strings, and registers (see the
520 **REGISTERS** section) can hold both strings and numbers. dc(1) always knows
521 whether the contents of a register are a string or a number.
523 While arithmetic operations have to have numbers, and will print an error if
524 given a string, other commands accept strings.
526 Strings can also be executed as macros. For example, if the string **[1pR]** is
527 executed as a macro, then the code **1pR** is executed, meaning that the **1**
528 will be printed with a newline after and then popped from the stack.
530 **\[**_characters_**\]**
532 : Makes a string containing *characters* and pushes it onto the stack.
534 If there are brackets (**\[** and **\]**) in the string, then they must be
535 balanced. Unbalanced brackets can be escaped using a backslash (**\\**)
538 If there is a backslash character in the string, the character after it
539 (even another backslash) is put into the string verbatim, but the (first)
544 : The value on top of the stack is popped.
546 If it is a number, it is truncated and its absolute value is taken. The
547 result mod **UCHAR_MAX+1** is calculated. If that result is **0**, push an
548 empty string; otherwise, push a one-character string where the character is
549 the result of the mod interpreted as an ASCII character.
551 If it is a string, then a new string is made. If the original string is
552 empty, the new string is empty. If it is not, then the first character of
553 the original string is used to create the new string as a one-character
554 string. The new string is then pushed onto the stack.
556 This is a **non-portable extension**.
560 : Pops a value off of the top of the stack.
562 If it is a number, it is pushed back onto the stack.
564 If it is a string, it is executed as a macro.
566 This behavior is the norm whenever a macro is executed, whether by this
567 command or by the conditional execution commands below.
571 : Pops two values off of the stack that must be numbers and compares them. If
572 the first value is greater than the second, then the contents of register
575 For example, **0 1>a** will execute the contents of register **a**, and
578 If either or both of the values are not numbers, dc(1) will raise an error
579 and reset (see the **RESET** section).
583 : Like the above, but will execute register *s* if the comparison fails.
585 If either or both of the values are not numbers, dc(1) will raise an error
586 and reset (see the **RESET** section).
588 This is a **non-portable extension**.
592 : Pops two values off of the stack that must be numbers and compares them. If
593 the first value is not greater than the second (less than or equal to), then
594 the contents of register *r* are executed.
596 If either or both of the values are not numbers, dc(1) will raise an error
597 and reset (see the **RESET** section).
601 : Like the above, but will execute register *s* if the comparison fails.
603 If either or both of the values are not numbers, dc(1) will raise an error
604 and reset (see the **RESET** section).
606 This is a **non-portable extension**.
610 : Pops two values off of the stack that must be numbers and compares them. If
611 the first value is less than the second, then the contents of register *r*
614 If either or both of the values are not numbers, dc(1) will raise an error
615 and reset (see the **RESET** section).
619 : Like the above, but will execute register *s* if the comparison fails.
621 If either or both of the values are not numbers, dc(1) will raise an error
622 and reset (see the **RESET** section).
624 This is a **non-portable extension**.
628 : Pops two values off of the stack that must be numbers and compares them. If
629 the first value is not less than the second (greater than or equal to), then
630 the contents of register *r* are executed.
632 If either or both of the values are not numbers, dc(1) will raise an error
633 and reset (see the **RESET** section).
637 : Like the above, but will execute register *s* if the comparison fails.
639 If either or both of the values are not numbers, dc(1) will raise an error
640 and reset (see the **RESET** section).
642 This is a **non-portable extension**.
646 : Pops two values off of the stack that must be numbers and compares them. If
647 the first value is equal to the second, then the contents of register *r*
650 If either or both of the values are not numbers, dc(1) will raise an error
651 and reset (see the **RESET** section).
655 : Like the above, but will execute register *s* if the comparison fails.
657 If either or both of the values are not numbers, dc(1) will raise an error
658 and reset (see the **RESET** section).
660 This is a **non-portable extension**.
664 : Pops two values off of the stack that must be numbers and compares them. If
665 the first value is not equal to the second, then the contents of register
668 If either or both of the values are not numbers, dc(1) will raise an error
669 and reset (see the **RESET** section).
673 : Like the above, but will execute register *s* if the comparison fails.
675 If either or both of the values are not numbers, dc(1) will raise an error
676 and reset (see the **RESET** section).
678 This is a **non-portable extension**.
682 : Reads a line from the **stdin** and executes it. This is to allow macros to
683 request input from users.
687 : During execution of a macro, this exits the execution of that macro and the
688 execution of the macro that executed it. If there are no macros, or only one
689 macro executing, dc(1) exits.
693 : Pops a value from the stack which must be non-negative and is used the
694 number of macro executions to pop off of the execution stack. If the number
695 of levels to pop is greater than the number of executing macros, dc(1)
700 These commands query status of the stack or its top value.
704 : Pops a value off of the stack.
706 If it is a number, calculates the number of significant decimal digits it
707 has and pushes the result.
709 If it is a string, pushes the number of characters the string has.
713 : Pops a value off of the stack.
715 If it is a number, pushes the *scale* of the value onto the stack.
717 If it is a string, pushes **0**.
721 : Pushes the current stack depth (before execution of this command).
725 These commands manipulate arrays.
729 : Pops the top two values off of the stack. The second value will be stored in
730 the array *r* (see the **REGISTERS** section), indexed by the first value.
734 : Pops the value on top of the stack and uses it as an index into the array
735 *r*. The selected value is then pushed onto the stack.
739 Registers are names that can store strings, numbers, and arrays. (Number/string
740 registers do not interfere with array registers.)
742 Each register is also its own stack, so the current register value is the top of
743 the stack for the register. All registers, when first referenced, have one value
744 (**0**) in their stack.
746 In non-extended register mode, a register name is just the single character that
747 follows any command that needs a register name. The only exception is a newline
748 (**'\\n'**); it is a parse error for a newline to be used as a register name.
750 ## Extended Register Mode
752 Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited
753 amounts of registers, if extended register mode is enabled.
755 If extended register mode is enabled (**-x** or **-\-extended-register**
756 command-line arguments are given), then normal single character registers are
757 used *unless* the character immediately following a command that needs a
758 register name is a space (according to **isspace()**) and not a newline
761 In that case, the register name is found according to the regex
762 **\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if
763 the next non-space characters do not match that regex.
767 When dc(1) encounters an error or a signal that it has a non-default handler
768 for, it resets. This means that several things happen.
770 First, any macros that are executing are stopped and popped off the stack.
771 The behavior is not unlike that of exceptions in programming languages. Then
772 the execution point is set so that any code waiting to execute (after all
773 macros returned) is skipped.
775 Thus, when dc(1) resets, it skips any remaining code waiting to be executed.
776 Then, if it is interactive mode, and the error was not a fatal error (see the
777 **EXIT STATUS** section), it asks for more input; otherwise, it exits with the
778 appropriate return code.
782 Most dc(1) implementations use **char** types to calculate the value of **1**
783 decimal digit at a time, but that can be slow. This dc(1) does something
786 It uses large integers to calculate more than **1** decimal digit at a time. If
787 built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is
788 **64**, then each integer has **9** decimal digits. If built in an environment
789 where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This
790 value (the number of decimal digits per large integer) is called
793 In addition, this dc(1) uses an even larger integer for overflow checking. This
794 integer type depends on the value of **DC_LONG_BIT**, but is always at least
795 twice as large as the integer type used to store digits.
799 The following are the limits on dc(1):
803 : The number of bits in the **long** type in the environment where dc(1) was
804 built. This determines how many decimal digits can be stored in a single
805 large integer (see the **PERFORMANCE** section).
809 : The number of decimal digits per large integer (see the **PERFORMANCE**
810 section). Depends on **DC_LONG_BIT**.
814 : The max decimal number that each large integer can store (see
815 **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**.
819 : The max number that the overflow type (see the **PERFORMANCE** section) can
820 hold. Depends on **DC_LONG_BIT**.
824 : The maximum output base. Set at **DC_BASE_POW**.
828 : The maximum size of arrays. Set at **SIZE_MAX-1**.
832 : The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**.
836 : The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**.
840 : The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**.
844 : The maximum length of a number (in decimal digits), which includes digits
845 after the decimal point. Set at **DC_OVERFLOW_MAX-1**.
849 : The maximum allowable exponent (positive or negative). Set at
854 : The maximum number of vars/arrays. Set at **SIZE_MAX-1**.
856 These limits are meant to be effectively non-existent; the limits are so large
857 (at least on 64-bit machines) that there should not be any point at which they
858 become a problem. In fact, memory should be exhausted before these limits should
861 # ENVIRONMENT VARIABLES
863 dc(1) recognizes the following environment variables:
867 : This is another way to give command-line arguments to dc(1). They should be
868 in the same format as all other command-line arguments. These are always
869 processed first, so any files given in **DC_ENV_ARGS** will be processed
870 before arguments and files given on the command-line. This gives the user
871 the ability to set up "standard" options and files to be used at every
872 invocation. The most useful thing for such files to contain would be useful
873 functions that the user might want every time dc(1) runs. Another use would
874 be to use the **-e** option to set **scale** to a value other than **0**.
876 The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments,
877 but it does not understand escape sequences. For example, the string
878 **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string
879 **"/home/gavin/some \"dc\" file.dc"** will include the backslashes.
881 The quote parsing will handle either kind of quotes, **'** or **"**. Thus,
882 if you have a file with any number of single quotes in the name, you can use
883 double quotes as the outside quotes, as in **"some 'dc' file.dc"**, and vice
884 versa if you have a file with double quotes. However, handling a file with
885 both kinds of quotes in **DC_ENV_ARGS** is not supported due to the
886 complexity of the parsing, though such files are still supported on the
887 command-line where the parsing is done by the shell.
891 : If this environment variable exists and contains an integer that is greater
892 than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output
893 lines to that length, including the backslash newline combo. The default
894 line length is **70**.
898 : If this variable exists (no matter the contents), dc(1) will exit
899 immediately after executing expressions and files given by the **-e** and/or
900 **-f** command-line options (and any equivalents).
904 dc(1) returns the following exit statuses:
912 : A math error occurred. This follows standard practice of using **1** for
913 expected errors, since math errors will happen in the process of normal
916 Math errors include divide by **0**, taking the square root of a negative
917 number, attempting to convert a negative number to a hardware integer,
918 overflow when converting a number to a hardware integer, and attempting to
919 use a non-integer where an integer is required.
921 Converting to a hardware integer happens for the second operand of the power
926 : A parse error occurred.
928 Parse errors include unexpected **EOF**, using an invalid character, failing
929 to find the end of a string or comment, and using a token where it is
934 : A runtime error occurred.
936 Runtime errors include assigning an invalid number to **ibase**, **obase**,
937 or **scale**; give a bad expression to a **read()** call, calling **read()**
938 inside of a **read()** call, type errors, and attempting an operation when
939 the stack has too few elements.
943 : A fatal error occurred.
945 Fatal errors include memory allocation errors, I/O errors, failing to open
946 files, attempting to use files that do not have only ASCII characters (dc(1)
947 only accepts ASCII characters), attempting to open a directory as a file,
948 and giving invalid command-line options.
950 The exit status **4** is special; when a fatal error occurs, dc(1) always exits
951 and returns **4**, no matter what mode dc(1) is in.
953 The other statuses will only be returned when dc(1) is not in interactive mode
954 (see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the
955 **RESET** section) and accepts more input when one of those errors occurs in
956 interactive mode. This is also the case when interactive mode is forced by the
957 **-i** flag or **-\-interactive** option.
959 These exit statuses allow dc(1) to be used in shell scripting with error
960 checking, and its normal behavior can be forced by using the **-i** flag or
961 **-\-interactive** option.
965 Like bc(1), dc(1) has an interactive mode and a non-interactive mode.
966 Interactive mode is turned on automatically when both **stdin** and **stdout**
967 are hooked to a terminal, but the **-i** flag and **-\-interactive** option can
968 turn it on in other cases.
970 In interactive mode, dc(1) attempts to recover from errors (see the **RESET**
971 section), and in normal execution, flushes **stdout** as soon as execution is
972 done for the current input.
976 If **stdin**, **stdout**, and **stderr** are all connected to a TTY, dc(1) turns
979 TTY mode is required for history to be enabled (see the **COMMAND LINE HISTORY**
980 section). It is also required to enable special handling for **SIGINT** signals.
982 TTY mode is different from interactive mode because interactive mode is required
983 in the [bc(1) specification][1], and interactive mode requires only **stdin**
984 and **stdout** to be connected to a terminal.
988 Sending a **SIGINT** will cause dc(1) to stop execution of the current input. If
989 dc(1) is in TTY mode (see the **TTY MODE** section), it will reset (see the
990 **RESET** section). Otherwise, it will clean up and exit.
992 Note that "current input" can mean one of two things. If dc(1) is processing
993 input from **stdin** in TTY mode, it will ask for more input. If dc(1) is
994 processing input from a file in TTY mode, it will stop processing the file and
995 start processing the next file, if one exists, or ask for input from **stdin**
996 if no other file exists.
998 This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it
999 can seem as though dc(1) did not respond to the signal since it will immediately
1000 start executing the next file. This is by design; most files that users execute
1001 when interacting with dc(1) have function definitions, which are quick to parse.
1002 If a file takes a long time to execute, there may be a bug in that file. The
1003 rest of the files could still be executed without problem, allowing the user to
1006 **SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the
1007 default handler for all other signals. The one exception is **SIGHUP**; in that
1008 case, when dc(1) is in TTY mode, a **SIGHUP** will cause dc(1) to clean up and
1011 # COMMAND LINE HISTORY
1013 dc(1) supports interactive command-line editing. If dc(1) is in TTY mode (see
1014 the **TTY MODE** section), history is enabled. Previous lines can be recalled
1015 and edited with the arrow keys.
1017 **Note**: tabs are converted to 8 spaces.
1021 This dc(1) ships with support for adding error messages for different locales
1022 and thus, supports **LC_MESSAGS**.
1030 The dc(1) utility operators are compliant with the operators in the bc(1)
1031 [IEEE Std 1003.1-2017 (“POSIX.1-2017”)][1] specification.
1035 None are known. Report bugs at https://git.yzena.com/gavin/bc.
1039 Gavin D. Howard <gavin@yzena.com> and contributors.
1041 [1]: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html