1<!--- 2 3SPDX-License-Identifier: BSD-2-Clause 4 5Copyright (c) 2018-2023 Gavin D. Howard and contributors. 6 7Redistribution and use in source and binary forms, with or without 8modification, are permitted provided that the following conditions are met: 9 10* Redistributions of source code must retain the above copyright notice, this 11 list of conditions and the following disclaimer. 12 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. 16 17THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" 18AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE 21LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 22CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 23SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 24INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 25CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 26ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 27POSSIBILITY OF SUCH DAMAGE. 28 29--> 30 31# Name 32 33dc - arbitrary-precision decimal reverse-Polish notation calculator 34 35# SYNOPSIS 36 37**dc** [**-cChiPRvVx**] [**-\-version**] [**-\-help**] [**-\-digit-clamp**] [**-\-no-digit-clamp**] [**-\-interactive**] [**-\-no-prompt**] [**-\-no-read-prompt**] [**-\-extended-register**] [**-e** *expr*] [**-\-expression**=*expr*...] [**-f** *file*...] [**-\-file**=*file*...] [*file*...] [**-I** *ibase*] [**-\-ibase**=*ibase*] [**-O** *obase*] [**-\-obase**=*obase*] [**-S** *scale*] [**-\-scale**=*scale*] [**-E** *seed*] [**-\-seed**=*seed*] 38 39# DESCRIPTION 40 41dc(1) is an arbitrary-precision calculator. It uses a stack (reverse Polish 42notation) to store numbers and results of computations. Arithmetic operations 43pop arguments off of the stack and push the results. 44 45If no files are given on the command-line, then dc(1) reads from **stdin** (see 46the **STDIN** section). Otherwise, those files are processed, and dc(1) will 47then exit. 48 49If a user wants to set up a standard environment, they can use **DC_ENV_ARGS** 50(see the **ENVIRONMENT VARIABLES** section). For example, if a user wants the 51**scale** always set to **10**, they can set **DC_ENV_ARGS** to **-e 10k**, and 52this dc(1) will always start with a **scale** of **10**. 53 54# OPTIONS 55 56The following are the options that dc(1) accepts. 57 58**-C**, **-\-no-digit-clamp** 59 60: Disables clamping of digits greater than or equal to the current **ibase** 61 when parsing numbers. 62 63 This means that the value added to a number from a digit is always that 64 digit's value multiplied by the value of ibase raised to the power of the 65 digit's position, which starts from 0 at the least significant digit. 66 67 If this and/or the **-c** or **-\-digit-clamp** options are given multiple 68 times, the last one given is used. 69 70 This option overrides the **DC_DIGIT_CLAMP** environment variable (see the 71 **ENVIRONMENT VARIABLES** section) and the default, which can be queried 72 with the **-h** or **-\-help** options. 73 74 This is a **non-portable extension**. 75 76**-c**, **-\-digit-clamp** 77 78: Enables clamping of digits greater than or equal to the current **ibase** 79 when parsing numbers. 80 81 This means that digits that the value added to a number from a digit that is 82 greater than or equal to the ibase is the value of ibase minus 1 all 83 multiplied by the value of ibase raised to the power of the digit's 84 position, which starts from 0 at the least significant digit. 85 86 If this and/or the **-C** or **-\-no-digit-clamp** options are given 87 multiple times, the last one given is used. 88 89 This option overrides the **DC_DIGIT_CLAMP** environment variable (see the 90 **ENVIRONMENT VARIABLES** section) and the default, which can be queried 91 with the **-h** or **-\-help** options. 92 93 This is a **non-portable extension**. 94 95**-E** *seed*, **-\-seed**=*seed* 96 97: Sets the builtin variable **seed** to the value *seed* assuming that *seed* 98 is in base 10. It is a fatal error if *seed* is not a valid number. 99 100 If multiple instances of this option are given, the last is used. 101 102 This is a **non-portable extension**. 103 104**-e** *expr*, **-\-expression**=*expr* 105 106: Evaluates *expr*. If multiple expressions are given, they are evaluated in 107 order. If files are given as well (see below), the expressions and files are 108 evaluated in the order given. This means that if a file is given before an 109 expression, the file is read in and evaluated first. 110 111 If this option is given on the command-line (i.e., not in **DC_ENV_ARGS**, 112 see the **ENVIRONMENT VARIABLES** section), then after processing all 113 expressions and files, dc(1) will exit, unless **-** (**stdin**) was given 114 as an argument at least once to **-f** or **-\-file**, whether on the 115 command-line or in **DC_ENV_ARGS**. However, if any other **-e**, 116 **-\-expression**, **-f**, or **-\-file** arguments are given after **-f-** 117 or equivalent is given, dc(1) will give a fatal error and exit. 118 119 This is a **non-portable extension**. 120 121**-f** *file*, **-\-file**=*file* 122 123: Reads in *file* and evaluates it, line by line, as though it were read 124 through **stdin**. If expressions are also given (see above), the 125 expressions are evaluated in the order given. 126 127 If this option is given on the command-line (i.e., not in **DC_ENV_ARGS**, 128 see the **ENVIRONMENT VARIABLES** section), then after processing all 129 expressions and files, dc(1) will exit, unless **-** (**stdin**) was given 130 as an argument at least once to **-f** or **-\-file**. However, if any other 131 **-e**, **-\-expression**, **-f**, or **-\-file** arguments are given after 132 **-f-** or equivalent is given, dc(1) will give a fatal error and exit. 133 134 This is a **non-portable extension**. 135 136**-h**, **-\-help** 137 138: Prints a usage message and exits. 139 140**-I** *ibase*, **-\-ibase**=*ibase* 141 142: Sets the builtin variable **ibase** to the value *ibase* assuming that 143 *ibase* is in base 10. It is a fatal error if *ibase* is not a valid number. 144 145 If multiple instances of this option are given, the last is used. 146 147 This is a **non-portable extension**. 148 149**-i**, **-\-interactive** 150 151: Forces interactive mode. (See the **INTERACTIVE MODE** section.) 152 153 This is a **non-portable extension**. 154 155**-L**, **-\-no-line-length** 156 157: Disables line length checking and prints numbers without backslashes and 158 newlines. In other words, this option sets **BC_LINE_LENGTH** to **0** (see 159 the **ENVIRONMENT VARIABLES** section). 160 161 This is a **non-portable extension**. 162 163**-O** *obase*, **-\-obase**=*obase* 164 165: Sets the builtin variable **obase** to the value *obase* assuming that 166 *obase* is in base 10. It is a fatal error if *obase* is not a valid number. 167 168 If multiple instances of this option are given, the last is used. 169 170 This is a **non-portable extension**. 171 172**-P**, **-\-no-prompt** 173 174: Disables the prompt in TTY mode. (The prompt is only enabled in TTY mode. 175 See the **TTY MODE** section.) This is mostly for those users that do not 176 want a prompt or are not used to having them in dc(1). Most of those users 177 would want to put this option in **DC_ENV_ARGS**. 178 179 These options override the **DC_PROMPT** and **DC_TTY_MODE** environment 180 variables (see the **ENVIRONMENT VARIABLES** section). 181 182 This is a **non-portable extension**. 183 184**-R**, **-\-no-read-prompt** 185 186: Disables the read prompt in TTY mode. (The read prompt is only enabled in 187 TTY mode. See the **TTY MODE** section.) This is mostly for those users that 188 do not want a read prompt or are not used to having them in dc(1). Most of 189 those users would want to put this option in **BC_ENV_ARGS** (see the 190 **ENVIRONMENT VARIABLES** section). This option is also useful in hash bang 191 lines of dc(1) scripts that prompt for user input. 192 193 This option does not disable the regular prompt because the read prompt is 194 only used when the **?** command is used. 195 196 These options *do* override the **DC_PROMPT** and **DC_TTY_MODE** 197 environment variables (see the **ENVIRONMENT VARIABLES** section), but only 198 for the read prompt. 199 200 This is a **non-portable extension**. 201 202**-S** *scale*, **-\-scale**=*scale* 203 204: Sets the builtin variable **scale** to the value *scale* assuming that 205 *scale* is in base 10. It is a fatal error if *scale* is not a valid number. 206 207 If multiple instances of this option are given, the last is used. 208 209 This is a **non-portable extension**. 210 211**-v**, **-V**, **-\-version** 212 213: Print the version information (copyright header) and exits. 214 215**-x** **-\-extended-register** 216 217: Enables extended register mode. See the *Extended Register Mode* subsection 218 of the **REGISTERS** section for more information. 219 220 This is a **non-portable extension**. 221 222**-z**, **-\-leading-zeroes** 223 224: Makes dc(1) print all numbers greater than **-1** and less than **1**, and 225 not equal to **0**, with a leading zero. 226 227 This is a **non-portable extension**. 228 229All long options are **non-portable extensions**. 230 231# STDIN 232 233If no files are given on the command-line and no files or expressions are given 234by the **-f**, **-\-file**, **-e**, or **-\-expression** options, then dc(1) 235reads from **stdin**. 236 237However, there is a caveat to this. 238 239First, **stdin** is evaluated a line at a time. The only exception to this is if 240a string has been finished, but not ended. This means that, except for escaped 241brackets, all brackets must be balanced before dc(1) parses and executes. 242 243# STDOUT 244 245Any non-error output is written to **stdout**. In addition, if history (see the 246**HISTORY** section) and the prompt (see the **TTY MODE** section) are enabled, 247both are output to **stdout**. 248 249**Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal 250error (see the **EXIT STATUS** section) if it cannot write to **stdout**, so if 251**stdout** is closed, as in **dc <file> >&-**, it will quit with an error. This 252is done so that dc(1) can report problems when **stdout** is redirected to a 253file. 254 255If there are scripts that depend on the behavior of other dc(1) implementations, 256it is recommended that those scripts be changed to redirect **stdout** to 257**/dev/null**. 258 259# STDERR 260 261Any error output is written to **stderr**. 262 263**Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal 264error (see the **EXIT STATUS** section) if it cannot write to **stderr**, so if 265**stderr** is closed, as in **dc <file> 2>&-**, it will quit with an error. This 266is done so that dc(1) can exit with an error code when **stderr** is redirected 267to a file. 268 269If there are scripts that depend on the behavior of other dc(1) implementations, 270it is recommended that those scripts be changed to redirect **stderr** to 271**/dev/null**. 272 273# SYNTAX 274 275Each item in the input source code, either a number (see the **NUMBERS** 276section) or a command (see the **COMMANDS** section), is processed and executed, 277in order. Input is processed immediately when entered. 278 279**ibase** is a register (see the **REGISTERS** section) that determines how to 280interpret constant numbers. It is the "input" base, or the number base used for 281interpreting input numbers. **ibase** is initially **10**. The max allowable 282value for **ibase** is **16**. The min allowable value for **ibase** is **2**. 283The max allowable value for **ibase** can be queried in dc(1) programs with the 284**T** command. 285 286**obase** is a register (see the **REGISTERS** section) that determines how to 287output results. It is the "output" base, or the number base used for outputting 288numbers. **obase** is initially **10**. The max allowable value for **obase** is 289**DC_BASE_MAX** and can be queried with the **U** command. The min allowable 290value for **obase** is **0**. If **obase** is **0**, values are output in 291scientific notation, and if **obase** is **1**, values are output in engineering 292notation. Otherwise, values are output in the specified base. 293 294Outputting in scientific and engineering notations are **non-portable 295extensions**. 296 297The *scale* of an expression is the number of digits in the result of the 298expression right of the decimal point, and **scale** is a register (see the 299**REGISTERS** section) that sets the precision of any operations (with 300exceptions). **scale** is initially **0**. **scale** cannot be negative. The max 301allowable value for **scale** can be queried in dc(1) programs with the **V** 302command. 303 304**seed** is a register containing the current seed for the pseudo-random number 305generator. If the current value of **seed** is queried and stored, then if it is 306assigned to **seed** later, the pseudo-random number generator is guaranteed to 307produce the same sequence of pseudo-random numbers that were generated after the 308value of **seed** was first queried. 309 310Multiple values assigned to **seed** can produce the same sequence of 311pseudo-random numbers. Likewise, when a value is assigned to **seed**, it is not 312guaranteed that querying **seed** immediately after will return the same value. 313In addition, the value of **seed** will change after any call to the **'** 314command or the **"** command that does not get receive a value of **0** or 315**1**. The maximum integer returned by the **'** command can be queried with the 316**W** command. 317 318**Note**: The values returned by the pseudo-random number generator with the 319**'** and **"** commands are guaranteed to **NOT** be cryptographically secure. 320This is a consequence of using a seeded pseudo-random number generator. However, 321they *are* guaranteed to be reproducible with identical **seed** values. This 322means that the pseudo-random values from dc(1) should only be used where a 323reproducible stream of pseudo-random numbers is *ESSENTIAL*. In any other case, 324use a non-seeded pseudo-random number generator. 325 326The pseudo-random number generator, **seed**, and all associated operations are 327**non-portable extensions**. 328 329## Comments 330 331Comments go from **#** until, and not including, the next newline. This is a 332**non-portable extension**. 333 334# NUMBERS 335 336Numbers are strings made up of digits, uppercase letters up to **F**, and at 337most **1** period for a radix. Numbers can have up to **DC_NUM_MAX** digits. 338Uppercase letters are equal to **9** plus their position in the alphabet (i.e., 339**A** equals **10**, or **9+1**). 340 341If a digit or letter makes no sense with the current value of **ibase** (i.e., 342they are greater than or equal to the current value of **ibase**), then the 343behavior depends on the existence of the **-c**/**-\-digit-clamp** or 344**-C**/**-\-no-digit-clamp** options (see the **OPTIONS** section), the 345existence and setting of the **DC_DIGIT_CLAMP** environment variable (see the 346**ENVIRONMENT VARIABLES** section), or the default, which can be queried with 347the **-h**/**-\-help** option. 348 349If clamping is off, then digits or letters that are greater than or equal to the 350current value of **ibase** are not changed. Instead, their given value is 351multiplied by the appropriate power of **ibase** and added into the number. This 352means that, with an **ibase** of **3**, the number **AB** is equal to 353**3\^1\*A+3\^0\*B**, which is **3** times **10** plus **11**, or **41**. 354 355If clamping is on, then digits or letters that are greater than or equal to the 356current value of **ibase** are set to the value of the highest valid digit in 357**ibase** before being multiplied by the appropriate power of **ibase** and 358added into the number. This means that, with an **ibase** of **3**, the number 359**AB** is equal to **3\^1\*2+3\^0\*2**, which is **3** times **2** plus **2**, 360or **8**. 361 362There is one exception to clamping: single-character numbers (i.e., **A** 363alone). Such numbers are never clamped and always take the value they would have 364in the highest possible **ibase**. This means that **A** alone always equals 365decimal **10** and **Z** alone always equals decimal **35**. This behavior is 366mandated by the standard for bc(1) (see the STANDARDS section) and is meant to 367provide an easy way to set the current **ibase** (with the **i** command) 368regardless of the current value of **ibase**. 369 370If clamping is on, and the clamped value of a character is needed, use a leading 371zero, i.e., for **A**, use **0A**. 372 373In addition, dc(1) accepts numbers in scientific notation. These have the form 374**\<number\>e\<integer\>**. The exponent (the portion after the **e**) must be 375an integer. An example is **1.89237e9**, which is equal to **1892370000**. 376Negative exponents are also allowed, so **4.2890e_3** is equal to **0.0042890**. 377 378**WARNING**: Both the number and the exponent in scientific notation are 379interpreted according to the current **ibase**, but the number is still 380multiplied by **10\^exponent** regardless of the current **ibase**. For example, 381if **ibase** is **16** and dc(1) is given the number string **FFeA**, the 382resulting decimal number will be **2550000000000**, and if dc(1) is given the 383number string **10e_4**, the resulting decimal number will be **0.0016**. 384 385Accepting input as scientific notation is a **non-portable extension**. 386 387# COMMANDS 388 389The valid commands are listed below. 390 391## Printing 392 393These commands are used for printing. 394 395Note that both scientific notation and engineering notation are available for 396printing numbers. Scientific notation is activated by assigning **0** to 397**obase** using **0o**, and engineering notation is activated by assigning **1** 398to **obase** using **1o**. To deactivate them, just assign a different value to 399**obase**. 400 401Printing numbers in scientific notation and/or engineering notation is a 402**non-portable extension**. 403 404**p** 405 406: Prints the value on top of the stack, whether number or string, and prints a 407 newline after. 408 409 This does not alter the stack. 410 411**n** 412 413: Prints the value on top of the stack, whether number or string, and pops it 414 off of the stack. 415 416**P** 417 418: Pops a value off the stack. 419 420 If the value is a number, it is truncated and the absolute value of the 421 result is printed as though **obase** is **256** and each digit is 422 interpreted as an 8-bit ASCII character, making it a byte stream. 423 424 If the value is a string, it is printed without a trailing newline. 425 426 This is a **non-portable extension**. 427 428**f** 429 430: Prints the entire contents of the stack, in order from newest to oldest, 431 without altering anything. 432 433 Users should use this command when they get lost. 434 435## Arithmetic 436 437These are the commands used for arithmetic. 438 439**+** 440 441: The top two values are popped off the stack, added, and the result is pushed 442 onto the stack. The *scale* of the result is equal to the max *scale* of 443 both operands. 444 445**-** 446 447: The top two values are popped off the stack, subtracted, and the result is 448 pushed onto the stack. The *scale* of the result is equal to the max 449 *scale* of both operands. 450 451**\*** 452 453: The top two values are popped off the stack, multiplied, and the result is 454 pushed onto the stack. If **a** is the *scale* of the first expression and 455 **b** is the *scale* of the second expression, the *scale* of the result 456 is equal to **min(a+b,max(scale,a,b))** where **min()** and **max()** return 457 the obvious values. 458 459**/** 460 461: The top two values are popped off the stack, divided, and the result is 462 pushed onto the stack. The *scale* of the result is equal to **scale**. 463 464 The first value popped off of the stack must be non-zero. 465 466**%** 467 468: The top two values are popped off the stack, remaindered, and the result is 469 pushed onto the stack. 470 471 Remaindering is equivalent to 1) Computing **a/b** to current **scale**, and 472 2) Using the result of step 1 to calculate **a-(a/b)\*b** to *scale* 473 **max(scale+scale(b),scale(a))**. 474 475 The first value popped off of the stack must be non-zero. 476 477**~** 478 479: The top two values are popped off the stack, divided and remaindered, and 480 the results (divided first, remainder second) are pushed onto the stack. 481 This is equivalent to **x y / x y %** except that **x** and **y** are only 482 evaluated once. 483 484 The first value popped off of the stack must be non-zero. 485 486 This is a **non-portable extension**. 487 488**\^** 489 490: The top two values are popped off the stack, the second is raised to the 491 power of the first, and the result is pushed onto the stack. The *scale* of 492 the result is equal to **scale**. 493 494 The first value popped off of the stack must be an integer, and if that 495 value is negative, the second value popped off of the stack must be 496 non-zero. 497 498**v** 499 500: The top value is popped off the stack, its square root is computed, and the 501 result is pushed onto the stack. The *scale* of the result is equal to 502 **scale**. 503 504 The value popped off of the stack must be non-negative. 505 506**\_** 507 508: If this command *immediately* precedes a number (i.e., no spaces or other 509 commands), then that number is input as a negative number. 510 511 Otherwise, the top value on the stack is popped and copied, and the copy is 512 negated and pushed onto the stack. This behavior without a number is a 513 **non-portable extension**. 514 515**b** 516 517: The top value is popped off the stack, and if it is zero, it is pushed back 518 onto the stack. Otherwise, its absolute value is pushed onto the stack. 519 520 This is a **non-portable extension**. 521 522**|** 523 524: The top three values are popped off the stack, a modular exponentiation is 525 computed, and the result is pushed onto the stack. 526 527 The first value popped is used as the reduction modulus and must be an 528 integer and non-zero. The second value popped is used as the exponent and 529 must be an integer and non-negative. The third value popped is the base and 530 must be an integer. 531 532 This is a **non-portable extension**. 533 534**\$** 535 536: The top value is popped off the stack and copied, and the copy is truncated 537 and pushed onto the stack. 538 539 This is a **non-portable extension**. 540 541**\@** 542 543: The top two values are popped off the stack, and the precision of the second 544 is set to the value of the first, whether by truncation or extension. 545 546 The first value popped off of the stack must be an integer and non-negative. 547 548 This is a **non-portable extension**. 549 550**H** 551 552: The top two values are popped off the stack, and the second is shifted left 553 (radix shifted right) to the value of the first. 554 555 The first value popped off of the stack must be an integer and non-negative. 556 557 This is a **non-portable extension**. 558 559**h** 560 561: The top two values are popped off the stack, and the second is shifted right 562 (radix shifted left) to the value of the first. 563 564 The first value popped off of the stack must be an integer and non-negative. 565 566 This is a **non-portable extension**. 567 568**G** 569 570: The top two values are popped off of the stack, they are compared, and a 571 **1** is pushed if they are equal, or **0** otherwise. 572 573 This is a **non-portable extension**. 574 575**N** 576 577: The top value is popped off of the stack, and if it a **0**, a **1** is 578 pushed; otherwise, a **0** is pushed. 579 580 This is a **non-portable extension**. 581 582**(** 583 584: The top two values are popped off of the stack, they are compared, and a 585 **1** is pushed if the first is less than the second, or **0** otherwise. 586 587 This is a **non-portable extension**. 588 589**{** 590 591: The top two values are popped off of the stack, they are compared, and a 592 **1** is pushed if the first is less than or equal to the second, or **0** 593 otherwise. 594 595 This is a **non-portable extension**. 596 597**)** 598 599: The top two values are popped off of the stack, they are compared, and a 600 **1** is pushed if the first is greater than the second, or **0** otherwise. 601 602 This is a **non-portable extension**. 603 604**}** 605 606: The top two values are popped off of the stack, they are compared, and a 607 **1** is pushed if the first is greater than or equal to the second, or 608 **0** otherwise. 609 610 This is a **non-portable extension**. 611 612**M** 613 614: The top two values are popped off of the stack. If they are both non-zero, a 615 **1** is pushed onto the stack. If either of them is zero, or both of them 616 are, then a **0** is pushed onto the stack. 617 618 This is like the **&&** operator in bc(1), and it is *not* a short-circuit 619 operator. 620 621 This is a **non-portable extension**. 622 623**m** 624 625: The top two values are popped off of the stack. If at least one of them is 626 non-zero, a **1** is pushed onto the stack. If both of them are zero, then a 627 **0** is pushed onto the stack. 628 629 This is like the **||** operator in bc(1), and it is *not* a short-circuit 630 operator. 631 632 This is a **non-portable extension**. 633 634## Pseudo-Random Number Generator 635 636dc(1) has a built-in pseudo-random number generator. These commands query the 637pseudo-random number generator. (See Parameters for more information about the 638**seed** value that controls the pseudo-random number generator.) 639 640The pseudo-random number generator is guaranteed to **NOT** be 641cryptographically secure. 642 643**'** 644 645: Generates an integer between 0 and **DC_RAND_MAX**, inclusive (see the 646 **LIMITS** section). 647 648 The generated integer is made as unbiased as possible, subject to the 649 limitations of the pseudo-random number generator. 650 651 This is a **non-portable extension**. 652 653**"** 654 655: Pops a value off of the stack, which is used as an **exclusive** upper bound 656 on the integer that will be generated. If the bound is negative or is a 657 non-integer, an error is raised, and dc(1) resets (see the **RESET** 658 section) while **seed** remains unchanged. If the bound is larger than 659 **DC_RAND_MAX**, the higher bound is honored by generating several 660 pseudo-random integers, multiplying them by appropriate powers of 661 **DC_RAND_MAX+1**, and adding them together. Thus, the size of integer that 662 can be generated with this command is unbounded. Using this command will 663 change the value of **seed**, unless the operand is **0** or **1**. In that 664 case, **0** is pushed onto the stack, and **seed** is *not* changed. 665 666 The generated integer is made as unbiased as possible, subject to the 667 limitations of the pseudo-random number generator. 668 669 This is a **non-portable extension**. 670 671## Stack Control 672 673These commands control the stack. 674 675**c** 676 677: Removes all items from ("clears") the stack. 678 679**d** 680 681: Copies the item on top of the stack ("duplicates") and pushes the copy onto 682 the stack. 683 684**r** 685 686: Swaps ("reverses") the two top items on the stack. 687 688**R** 689 690: Pops ("removes") the top value from the stack. 691 692## Register Control 693 694These commands control registers (see the **REGISTERS** section). 695 696**s**_r_ 697 698: Pops the value off the top of the stack and stores it into register *r*. 699 700**l**_r_ 701 702: Copies the value in register *r* and pushes it onto the stack. This does not 703 alter the contents of *r*. 704 705**S**_r_ 706 707: Pops the value off the top of the (main) stack and pushes it onto the stack 708 of register *r*. The previous value of the register becomes inaccessible. 709 710**L**_r_ 711 712: Pops the value off the top of the stack for register *r* and push it onto 713 the main stack. The previous value in the stack for register *r*, if any, is 714 now accessible via the **l**_r_ command. 715 716## Parameters 717 718These commands control the values of **ibase**, **obase**, **scale**, and 719**seed**. Also see the **SYNTAX** section. 720 721**i** 722 723: Pops the value off of the top of the stack and uses it to set **ibase**, 724 which must be between **2** and **16**, inclusive. 725 726 If the value on top of the stack has any *scale*, the *scale* is ignored. 727 728**o** 729 730: Pops the value off of the top of the stack and uses it to set **obase**, 731 which must be between **0** and **DC_BASE_MAX**, inclusive (see the 732 **LIMITS** section and the **NUMBERS** section). 733 734 If the value on top of the stack has any *scale*, the *scale* is ignored. 735 736**k** 737 738: Pops the value off of the top of the stack and uses it to set **scale**, 739 which must be non-negative. 740 741 If the value on top of the stack has any *scale*, the *scale* is ignored. 742 743**j** 744 745: Pops the value off of the top of the stack and uses it to set **seed**. The 746 meaning of **seed** is dependent on the current pseudo-random number 747 generator but is guaranteed to not change except for new major versions. 748 749 The *scale* and sign of the value may be significant. 750 751 If a previously used **seed** value is used again, the pseudo-random number 752 generator is guaranteed to produce the same sequence of pseudo-random 753 numbers as it did when the **seed** value was previously used. 754 755 The exact value assigned to **seed** is not guaranteed to be returned if the 756 **J** command is used. However, if **seed** *does* return a different value, 757 both values, when assigned to **seed**, are guaranteed to produce the same 758 sequence of pseudo-random numbers. This means that certain values assigned 759 to **seed** will not produce unique sequences of pseudo-random numbers. 760 761 There is no limit to the length (number of significant decimal digits) or 762 *scale* of the value that can be assigned to **seed**. 763 764 This is a **non-portable extension**. 765 766**I** 767 768: Pushes the current value of **ibase** onto the main stack. 769 770**O** 771 772: Pushes the current value of **obase** onto the main stack. 773 774**K** 775 776: Pushes the current value of **scale** onto the main stack. 777 778**J** 779 780: Pushes the current value of **seed** onto the main stack. 781 782 This is a **non-portable extension**. 783 784**T** 785 786: Pushes the maximum allowable value of **ibase** onto the main stack. 787 788 This is a **non-portable extension**. 789 790**U** 791 792: Pushes the maximum allowable value of **obase** onto the main stack. 793 794 This is a **non-portable extension**. 795 796**V** 797 798: Pushes the maximum allowable value of **scale** onto the main stack. 799 800 This is a **non-portable extension**. 801 802**W** 803 804: Pushes the maximum (inclusive) integer that can be generated with the **'** 805 pseudo-random number generator command. 806 807 This is a **non-portable extension**. 808 809## Strings 810 811The following commands control strings. 812 813dc(1) can work with both numbers and strings, and registers (see the 814**REGISTERS** section) can hold both strings and numbers. dc(1) always knows 815whether the contents of a register are a string or a number. 816 817While arithmetic operations have to have numbers, and will print an error if 818given a string, other commands accept strings. 819 820Strings can also be executed as macros. For example, if the string **[1pR]** is 821executed as a macro, then the code **1pR** is executed, meaning that the **1** 822will be printed with a newline after and then popped from the stack. 823 824**\[**_characters_**\]** 825 826: Makes a string containing *characters* and pushes it onto the stack. 827 828 If there are brackets (**\[** and **\]**) in the string, then they must be 829 balanced. Unbalanced brackets can be escaped using a backslash (**\\**) 830 character. 831 832 If there is a backslash character in the string, the character after it 833 (even another backslash) is put into the string verbatim, but the (first) 834 backslash is not. 835 836**a** 837 838: The value on top of the stack is popped. 839 840 If it is a number, it is truncated and its absolute value is taken. The 841 result mod **256** is calculated. If that result is **0**, push an empty 842 string; otherwise, push a one-character string where the character is the 843 result of the mod interpreted as an ASCII character. 844 845 If it is a string, then a new string is made. If the original string is 846 empty, the new string is empty. If it is not, then the first character of 847 the original string is used to create the new string as a one-character 848 string. The new string is then pushed onto the stack. 849 850 This is a **non-portable extension**. 851 852**x** 853 854: Pops a value off of the top of the stack. 855 856 If it is a number, it is pushed back onto the stack. 857 858 If it is a string, it is executed as a macro. 859 860 This behavior is the norm whenever a macro is executed, whether by this 861 command or by the conditional execution commands below. 862 863**\>**_r_ 864 865: Pops two values off of the stack that must be numbers and compares them. If 866 the first value is greater than the second, then the contents of register 867 *r* are executed. 868 869 For example, **0 1>a** will execute the contents of register **a**, and 870 **1 0>a** will not. 871 872 If either or both of the values are not numbers, dc(1) will raise an error 873 and reset (see the **RESET** section). 874 875**>**_r_**e**_s_ 876 877: Like the above, but will execute register *s* if the comparison fails. 878 879 If either or both of the values are not numbers, dc(1) will raise an error 880 and reset (see the **RESET** section). 881 882 This is a **non-portable extension**. 883 884**!\>**_r_ 885 886: Pops two values off of the stack that must be numbers and compares them. If 887 the first value is not greater than the second (less than or equal to), then 888 the contents of register *r* are executed. 889 890 If either or both of the values are not numbers, dc(1) will raise an error 891 and reset (see the **RESET** section). 892 893**!\>**_r_**e**_s_ 894 895: Like the above, but will execute register *s* if the comparison fails. 896 897 If either or both of the values are not numbers, dc(1) will raise an error 898 and reset (see the **RESET** section). 899 900 This is a **non-portable extension**. 901 902**\<**_r_ 903 904: Pops two values off of the stack that must be numbers and compares them. If 905 the first value is less than the second, then the contents of register *r* 906 are executed. 907 908 If either or both of the values are not numbers, dc(1) will raise an error 909 and reset (see the **RESET** section). 910 911**\<**_r_**e**_s_ 912 913: Like the above, but will execute register *s* if the comparison fails. 914 915 If either or both of the values are not numbers, dc(1) will raise an error 916 and reset (see the **RESET** section). 917 918 This is a **non-portable extension**. 919 920**!\<**_r_ 921 922: Pops two values off of the stack that must be numbers and compares them. If 923 the first value is not less than the second (greater than or equal to), then 924 the contents of register *r* are executed. 925 926 If either or both of the values are not numbers, dc(1) will raise an error 927 and reset (see the **RESET** section). 928 929**!\<**_r_**e**_s_ 930 931: Like the above, but will execute register *s* if the comparison fails. 932 933 If either or both of the values are not numbers, dc(1) will raise an error 934 and reset (see the **RESET** section). 935 936 This is a **non-portable extension**. 937 938**=**_r_ 939 940: Pops two values off of the stack that must be numbers and compares them. If 941 the first value is equal to the second, then the contents of register *r* 942 are executed. 943 944 If either or both of the values are not numbers, dc(1) will raise an error 945 and reset (see the **RESET** section). 946 947**=**_r_**e**_s_ 948 949: Like the above, but will execute register *s* if the comparison fails. 950 951 If either or both of the values are not numbers, dc(1) will raise an error 952 and reset (see the **RESET** section). 953 954 This is a **non-portable extension**. 955 956**!=**_r_ 957 958: Pops two values off of the stack that must be numbers and compares them. If 959 the first value is not equal to the second, then the contents of register 960 *r* are executed. 961 962 If either or both of the values are not numbers, dc(1) will raise an error 963 and reset (see the **RESET** section). 964 965**!=**_r_**e**_s_ 966 967: Like the above, but will execute register *s* if the comparison fails. 968 969 If either or both of the values are not numbers, dc(1) will raise an error 970 and reset (see the **RESET** section). 971 972 This is a **non-portable extension**. 973 974**?** 975 976: Reads a line from the **stdin** and executes it. This is to allow macros to 977 request input from users. 978 979**q** 980 981: During execution of a macro, this exits the execution of that macro and the 982 execution of the macro that executed it. If there are no macros, or only one 983 macro executing, dc(1) exits. 984 985**Q** 986 987: Pops a value from the stack which must be non-negative and is used the 988 number of macro executions to pop off of the execution stack. If the number 989 of levels to pop is greater than the number of executing macros, dc(1) 990 exits. 991 992**,** 993 994: Pushes the depth of the execution stack onto the stack. The execution stack 995 is the stack of string executions. The number that is pushed onto the stack 996 is exactly as many as is needed to make dc(1) exit with the **Q** command, 997 so the sequence **,Q** will make dc(1) exit. 998 999 This is a **non-portable extension**. 1000 1001## Status 1002 1003These commands query status of the stack or its top value. 1004 1005**Z** 1006 1007: Pops a value off of the stack. 1008 1009 If it is a number, calculates the number of significant decimal digits it 1010 has and pushes the result. It will push **1** if the argument is **0** with 1011 no decimal places. 1012 1013 If it is a string, pushes the number of characters the string has. 1014 1015**X** 1016 1017: Pops a value off of the stack. 1018 1019 If it is a number, pushes the *scale* of the value onto the stack. 1020 1021 If it is a string, pushes **0**. 1022 1023**u** 1024 1025: Pops one value off of the stack. If the value is a number, this pushes **1** 1026 onto the stack. Otherwise (if it is a string), it pushes **0**. 1027 1028 This is a **non-portable extension**. 1029 1030**t** 1031 1032: Pops one value off of the stack. If the value is a string, this pushes **1** 1033 onto the stack. Otherwise (if it is a number), it pushes **0**. 1034 1035 This is a **non-portable extension**. 1036 1037**z** 1038 1039: Pushes the current depth of the stack (before execution of this command) 1040 onto the stack. 1041 1042**y**_r_ 1043 1044: Pushes the current stack depth of the register *r* onto the main stack. 1045 1046 Because each register has a depth of **1** (with the value **0** in the top 1047 item) when dc(1) starts, dc(1) requires that each register's stack must 1048 always have at least one item; dc(1) will give an error and reset otherwise 1049 (see the **RESET** section). This means that this command will never push 1050 **0**. 1051 1052 This is a **non-portable extension**. 1053 1054## Arrays 1055 1056These commands manipulate arrays. 1057 1058**:**_r_ 1059 1060: Pops the top two values off of the stack. The second value will be stored in 1061 the array *r* (see the **REGISTERS** section), indexed by the first value. 1062 1063**;**_r_ 1064 1065: Pops the value on top of the stack and uses it as an index into the array 1066 *r*. The selected value is then pushed onto the stack. 1067 1068**Y**_r_ 1069 1070: Pushes the length of the array *r* onto the stack. 1071 1072 This is a **non-portable extension**. 1073 1074## Global Settings 1075 1076These commands retrieve global settings. These are the only commands that 1077require multiple specific characters, and all of them begin with the letter 1078**g**. Only the characters below are allowed after the character **g**; any 1079other character produces a parse error (see the **ERRORS** section). 1080 1081**gl** 1082 1083: Pushes the line length set by **DC_LINE_LENGTH** (see the **ENVIRONMENT 1084 VARIABLES** section) onto the stack. 1085 1086**gx** 1087 1088: Pushes **1** onto the stack if extended register mode is on, **0** 1089 otherwise. See the *Extended Register Mode* subsection of the **REGISTERS** 1090 section for more information. 1091 1092**gz** 1093 1094: Pushes **0** onto the stack if the leading zero setting has not been enabled 1095 with the **-z** or **-\-leading-zeroes** options (see the **OPTIONS** 1096 section), non-zero otherwise. 1097 1098# REGISTERS 1099 1100Registers are names that can store strings, numbers, and arrays. (Number/string 1101registers do not interfere with array registers.) 1102 1103Each register is also its own stack, so the current register value is the top of 1104the stack for the register. All registers, when first referenced, have one value 1105(**0**) in their stack, and it is a runtime error to attempt to pop that item 1106off of the register stack. 1107 1108In non-extended register mode, a register name is just the single character that 1109follows any command that needs a register name. The only exceptions are: a 1110newline (**'\\n'**) and a left bracket (**'['**); it is a parse error for a 1111newline or a left bracket to be used as a register name. 1112 1113## Extended Register Mode 1114 1115Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited 1116amounts of registers, if extended register mode is enabled. 1117 1118If extended register mode is enabled (**-x** or **-\-extended-register** 1119command-line arguments are given), then normal single character registers are 1120used *unless* the character immediately following a command that needs a 1121register name is a space (according to **isspace()**) and not a newline 1122(**'\\n'**). 1123 1124In that case, the register name is found according to the regex 1125**\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if 1126the next non-space characters do not match that regex. 1127 1128# RESET 1129 1130When dc(1) encounters an error or a signal that it has a non-default handler 1131for, it resets. This means that several things happen. 1132 1133First, any macros that are executing are stopped and popped off the stack. 1134The behavior is not unlike that of exceptions in programming languages. Then 1135the execution point is set so that any code waiting to execute (after all 1136macros returned) is skipped. 1137 1138Thus, when dc(1) resets, it skips any remaining code waiting to be executed. 1139Then, if it is interactive mode, and the error was not a fatal error (see the 1140**EXIT STATUS** section), it asks for more input; otherwise, it exits with the 1141appropriate return code. 1142 1143# PERFORMANCE 1144 1145Most dc(1) implementations use **char** types to calculate the value of **1** 1146decimal digit at a time, but that can be slow. This dc(1) does something 1147different. 1148 1149It uses large integers to calculate more than **1** decimal digit at a time. If 1150built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is 1151**64**, then each integer has **9** decimal digits. If built in an environment 1152where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This 1153value (the number of decimal digits per large integer) is called 1154**DC_BASE_DIGS**. 1155 1156In addition, this dc(1) uses an even larger integer for overflow checking. This 1157integer type depends on the value of **DC_LONG_BIT**, but is always at least 1158twice as large as the integer type used to store digits. 1159 1160# LIMITS 1161 1162The following are the limits on dc(1): 1163 1164**DC_LONG_BIT** 1165 1166: The number of bits in the **long** type in the environment where dc(1) was 1167 built. This determines how many decimal digits can be stored in a single 1168 large integer (see the **PERFORMANCE** section). 1169 1170**DC_BASE_DIGS** 1171 1172: The number of decimal digits per large integer (see the **PERFORMANCE** 1173 section). Depends on **DC_LONG_BIT**. 1174 1175**DC_BASE_POW** 1176 1177: The max decimal number that each large integer can store (see 1178 **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**. 1179 1180**DC_OVERFLOW_MAX** 1181 1182: The max number that the overflow type (see the **PERFORMANCE** section) can 1183 hold. Depends on **DC_LONG_BIT**. 1184 1185**DC_BASE_MAX** 1186 1187: The maximum output base. Set at **DC_BASE_POW**. 1188 1189**DC_DIM_MAX** 1190 1191: The maximum size of arrays. Set at **SIZE_MAX-1**. 1192 1193**DC_SCALE_MAX** 1194 1195: The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**. 1196 1197**DC_STRING_MAX** 1198 1199: The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**. 1200 1201**DC_NAME_MAX** 1202 1203: The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**. 1204 1205**DC_NUM_MAX** 1206 1207: The maximum length of a number (in decimal digits), which includes digits 1208 after the decimal point. Set at **DC_OVERFLOW_MAX-1**. 1209 1210**DC_RAND_MAX** 1211 1212: The maximum integer (inclusive) returned by the **'** command, if dc(1). Set 1213 at **2\^DC_LONG_BIT-1**. 1214 1215Exponent 1216 1217: The maximum allowable exponent (positive or negative). Set at 1218 **DC_OVERFLOW_MAX**. 1219 1220Number of vars 1221 1222: The maximum number of vars/arrays. Set at **SIZE_MAX-1**. 1223 1224These limits are meant to be effectively non-existent; the limits are so large 1225(at least on 64-bit machines) that there should not be any point at which they 1226become a problem. In fact, memory should be exhausted before these limits should 1227be hit. 1228 1229# ENVIRONMENT VARIABLES 1230 1231As **non-portable extensions**, dc(1) recognizes the following environment 1232variables: 1233 1234**DC_ENV_ARGS** 1235 1236: This is another way to give command-line arguments to dc(1). They should be 1237 in the same format as all other command-line arguments. These are always 1238 processed first, so any files given in **DC_ENV_ARGS** will be processed 1239 before arguments and files given on the command-line. This gives the user 1240 the ability to set up "standard" options and files to be used at every 1241 invocation. The most useful thing for such files to contain would be useful 1242 functions that the user might want every time dc(1) runs. Another use would 1243 be to use the **-e** option to set **scale** to a value other than **0**. 1244 1245 The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments, 1246 but it does not understand escape sequences. For example, the string 1247 **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string 1248 **"/home/gavin/some \"dc\" file.dc"** will include the backslashes. 1249 1250 The quote parsing will handle either kind of quotes, **'** or **"**. Thus, 1251 if you have a file with any number of single quotes in the name, you can use 1252 double quotes as the outside quotes, as in **"some 'dc' file.dc"**, and vice 1253 versa if you have a file with double quotes. However, handling a file with 1254 both kinds of quotes in **DC_ENV_ARGS** is not supported due to the 1255 complexity of the parsing, though such files are still supported on the 1256 command-line where the parsing is done by the shell. 1257 1258**DC_LINE_LENGTH** 1259 1260: If this environment variable exists and contains an integer that is greater 1261 than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output 1262 lines to that length, including the backslash newline combo. The default 1263 line length is **70**. 1264 1265 The special value of **0** will disable line length checking and print 1266 numbers without regard to line length and without backslashes and newlines. 1267 1268**DC_SIGINT_RESET** 1269 1270: If dc(1) is not in interactive mode (see the **INTERACTIVE MODE** section), 1271 then this environment variable has no effect because dc(1) exits on 1272 **SIGINT** when not in interactive mode. 1273 1274 However, when dc(1) is in interactive mode, then if this environment 1275 variable exists and contains an integer, a non-zero value makes dc(1) reset 1276 on **SIGINT**, rather than exit, and zero makes dc(1) exit. If this 1277 environment variable exists and is *not* an integer, then dc(1) will exit on 1278 **SIGINT**. 1279 1280 This environment variable overrides the default, which can be queried with 1281 the **-h** or **-\-help** options. 1282 1283**DC_TTY_MODE** 1284 1285: If TTY mode is *not* available (see the **TTY MODE** section), then this 1286 environment variable has no effect. 1287 1288 However, when TTY mode is available, then if this environment variable 1289 exists and contains an integer, then a non-zero value makes dc(1) use TTY 1290 mode, and zero makes dc(1) not use TTY mode. 1291 1292 This environment variable overrides the default, which can be queried with 1293 the **-h** or **-\-help** options. 1294 1295**DC_PROMPT** 1296 1297: If TTY mode is *not* available (see the **TTY MODE** section), then this 1298 environment variable has no effect. 1299 1300 However, when TTY mode is available, then if this environment variable 1301 exists and contains an integer, a non-zero value makes dc(1) use a prompt, 1302 and zero or a non-integer makes dc(1) not use a prompt. If this environment 1303 variable does not exist and **DC_TTY_MODE** does, then the value of the 1304 **DC_TTY_MODE** environment variable is used. 1305 1306 This environment variable and the **DC_TTY_MODE** environment variable 1307 override the default, which can be queried with the **-h** or **-\-help** 1308 options. 1309 1310**DC_EXPR_EXIT** 1311 1312: If any expressions or expression files are given on the command-line with 1313 **-e**, **-\-expression**, **-f**, or **-\-file**, then if this environment 1314 variable exists and contains an integer, a non-zero value makes dc(1) exit 1315 after executing the expressions and expression files, and a zero value makes 1316 dc(1) not exit. 1317 1318 This environment variable overrides the default, which can be queried with 1319 the **-h** or **-\-help** options. 1320 1321**DC_DIGIT_CLAMP** 1322 1323: When parsing numbers and if this environment variable exists and contains an 1324 integer, a non-zero value makes dc(1) clamp digits that are greater than or 1325 equal to the current **ibase** so that all such digits are considered equal 1326 to the **ibase** minus 1, and a zero value disables such clamping so that 1327 those digits are always equal to their value, which is multiplied by the 1328 power of the **ibase**. 1329 1330 This never applies to single-digit numbers, as per the bc(1) standard (see 1331 the **STANDARDS** section). 1332 1333 This environment variable overrides the default, which can be queried with 1334 the **-h** or **-\-help** options. 1335 1336# EXIT STATUS 1337 1338dc(1) returns the following exit statuses: 1339 1340**0** 1341 1342: No error. 1343 1344**1** 1345 1346: A math error occurred. This follows standard practice of using **1** for 1347 expected errors, since math errors will happen in the process of normal 1348 execution. 1349 1350 Math errors include divide by **0**, taking the square root of a negative 1351 number, using a negative number as a bound for the pseudo-random number 1352 generator, attempting to convert a negative number to a hardware integer, 1353 overflow when converting a number to a hardware integer, overflow when 1354 calculating the size of a number, and attempting to use a non-integer where 1355 an integer is required. 1356 1357 Converting to a hardware integer happens for the second operand of the power 1358 (**\^**), places (**\@**), left shift (**H**), and right shift (**h**) 1359 operators. 1360 1361**2** 1362 1363: A parse error occurred. 1364 1365 Parse errors include unexpected **EOF**, using an invalid character, failing 1366 to find the end of a string or comment, and using a token where it is 1367 invalid. 1368 1369**3** 1370 1371: A runtime error occurred. 1372 1373 Runtime errors include assigning an invalid number to any global (**ibase**, 1374 **obase**, or **scale**), giving a bad expression to a **read()** call, 1375 calling **read()** inside of a **read()** call, type errors (including 1376 attempting to execute a number), and attempting an operation when the stack 1377 has too few elements. 1378 1379**4** 1380 1381: A fatal error occurred. 1382 1383 Fatal errors include memory allocation errors, I/O errors, failing to open 1384 files, attempting to use files that do not have only ASCII characters (dc(1) 1385 only accepts ASCII characters), attempting to open a directory as a file, 1386 and giving invalid command-line options. 1387 1388The exit status **4** is special; when a fatal error occurs, dc(1) always exits 1389and returns **4**, no matter what mode dc(1) is in. 1390 1391The other statuses will only be returned when dc(1) is not in interactive mode 1392(see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the 1393**RESET** section) and accepts more input when one of those errors occurs in 1394interactive mode. This is also the case when interactive mode is forced by the 1395**-i** flag or **-\-interactive** option. 1396 1397These exit statuses allow dc(1) to be used in shell scripting with error 1398checking, and its normal behavior can be forced by using the **-i** flag or 1399**-\-interactive** option. 1400 1401# INTERACTIVE MODE 1402 1403Like bc(1), dc(1) has an interactive mode and a non-interactive mode. 1404Interactive mode is turned on automatically when both **stdin** and **stdout** 1405are hooked to a terminal, but the **-i** flag and **-\-interactive** option can 1406turn it on in other situations. 1407 1408In interactive mode, dc(1) attempts to recover from errors (see the **RESET** 1409section), and in normal execution, flushes **stdout** as soon as execution is 1410done for the current input. dc(1) may also reset on **SIGINT** instead of exit, 1411depending on the contents of, or default for, the **DC_SIGINT_RESET** 1412environment variable (see the **ENVIRONMENT VARIABLES** section). 1413 1414# TTY MODE 1415 1416If **stdin**, **stdout**, and **stderr** are all connected to a TTY, then "TTY 1417mode" is considered to be available, and thus, dc(1) can turn on TTY mode, 1418subject to some settings. 1419 1420If there is the environment variable **DC_TTY_MODE** in the environment (see the 1421**ENVIRONMENT VARIABLES** section), then if that environment variable contains a 1422non-zero integer, dc(1) will turn on TTY mode when **stdin**, **stdout**, and 1423**stderr** are all connected to a TTY. If the **DC_TTY_MODE** environment 1424variable exists but is *not* a non-zero integer, then dc(1) will not turn TTY 1425mode on. 1426 1427If the environment variable **DC_TTY_MODE** does *not* exist, the default 1428setting is used. The default setting can be queried with the **-h** or 1429**-\-help** options. 1430 1431TTY mode is different from interactive mode because interactive mode is required 1432in the bc(1) specification (see the **STANDARDS** section), and interactive mode 1433requires only **stdin** and **stdout** to be connected to a terminal. 1434 1435## Prompt 1436 1437If TTY mode is available, then a prompt can be enabled. Like TTY mode itself, it 1438can be turned on or off with an environment variable: **DC_PROMPT** (see the 1439**ENVIRONMENT VARIABLES** section). 1440 1441If the environment variable **DC_PROMPT** exists and is a non-zero integer, then 1442the prompt is turned on when **stdin**, **stdout**, and **stderr** are connected 1443to a TTY and the **-P** and **-\-no-prompt** options were not used. The read 1444prompt will be turned on under the same conditions, except that the **-R** and 1445**-\-no-read-prompt** options must also not be used. 1446 1447However, if **DC_PROMPT** does not exist, the prompt can be enabled or disabled 1448with the **DC_TTY_MODE** environment variable, the **-P** and **-\-no-prompt** 1449options, and the **-R** and **-\-no-read-prompt** options. See the **ENVIRONMENT 1450VARIABLES** and **OPTIONS** sections for more details. 1451 1452# SIGNAL HANDLING 1453 1454Sending a **SIGINT** will cause dc(1) to do one of two things. 1455 1456If dc(1) is not in interactive mode (see the **INTERACTIVE MODE** section), or 1457the **DC_SIGINT_RESET** environment variable (see the **ENVIRONMENT VARIABLES** 1458section), or its default, is either not an integer or it is zero, dc(1) will 1459exit. 1460 1461However, if dc(1) is in interactive mode, and the **DC_SIGINT_RESET** or its 1462default is an integer and non-zero, then dc(1) will stop executing the current 1463input and reset (see the **RESET** section) upon receiving a **SIGINT**. 1464 1465Note that "current input" can mean one of two things. If dc(1) is processing 1466input from **stdin** in interactive mode, it will ask for more input. If dc(1) 1467is processing input from a file in interactive mode, it will stop processing the 1468file and start processing the next file, if one exists, or ask for input from 1469**stdin** if no other file exists. 1470 1471This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it 1472can seem as though dc(1) did not respond to the signal since it will immediately 1473start executing the next file. This is by design; most files that users execute 1474when interacting with dc(1) have function definitions, which are quick to parse. 1475If a file takes a long time to execute, there may be a bug in that file. The 1476rest of the files could still be executed without problem, allowing the user to 1477continue. 1478 1479**SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the 1480default handler for all other signals. 1481 1482# SEE ALSO 1483 1484bc(1) 1485 1486# STANDARDS 1487 1488The dc(1) utility operators and some behavior are compliant with the operators 1489in the IEEE Std 1003.1-2017 (“POSIX.1-2017”) bc(1) specification at 1490https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html . 1491 1492# BUGS 1493 1494None are known. Report bugs at https://git.gavinhoward.com/gavin/bc . 1495 1496# AUTHOR 1497 1498Gavin D. Howard <gavin@gavinhoward.com> and contributors. 1499