1<!--- 2 3SPDX-License-Identifier: BSD-2-Clause 4 5Copyright (c) 2018-2021 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** [**-hiPRvVx**] [**-\-version**] [**-\-help**] [**-\-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**-h**, **-\-help** 59 60: Prints a usage message and quits. 61 62**-v**, **-V**, **-\-version** 63 64: Print the version information (copyright header) and exit. 65 66**-i**, **-\-interactive** 67 68: Forces interactive mode. (See the **INTERACTIVE MODE** section.) 69 70 This is a **non-portable extension**. 71 72**-L**, **-\-no-line-length** 73 74: Disables line length checking and prints numbers without backslashes and 75 newlines. In other words, this option sets **BC_LINE_LENGTH** to **0** (see 76 the **ENVIRONMENT VARIABLES** section). 77 78 This is a **non-portable extension**. 79 80**-P**, **-\-no-prompt** 81 82: Disables the prompt in TTY mode. (The prompt is only enabled in TTY mode. 83 See the **TTY MODE** section.) This is mostly for those users that do not 84 want a prompt or are not used to having them in dc(1). Most of those users 85 would want to put this option in **DC_ENV_ARGS**. 86 87 These options override the **DC_PROMPT** and **DC_TTY_MODE** environment 88 variables (see the **ENVIRONMENT VARIABLES** section). 89 90 This is a **non-portable extension**. 91 92**-R**, **-\-no-read-prompt** 93 94: Disables the read prompt in TTY mode. (The read prompt is only enabled in 95 TTY mode. See the **TTY MODE** section.) This is mostly for those users that 96 do not want a read prompt or are not used to having them in dc(1). Most of 97 those users would want to put this option in **BC_ENV_ARGS** (see the 98 **ENVIRONMENT VARIABLES** section). This option is also useful in hash bang 99 lines of dc(1) scripts that prompt for user input. 100 101 This option does not disable the regular prompt because the read prompt is 102 only used when the **?** command is used. 103 104 These options *do* override the **DC_PROMPT** and **DC_TTY_MODE** 105 environment variables (see the **ENVIRONMENT VARIABLES** section), but only 106 for the read prompt. 107 108 This is a **non-portable extension**. 109 110**-x** **-\-extended-register** 111 112: Enables extended register mode. See the *Extended Register Mode* subsection 113 of the **REGISTERS** section for more information. 114 115 This is a **non-portable extension**. 116 117**-z**, **-\-leading-zeroes** 118 119: Makes dc(1) print all numbers greater than **-1** and less than **1**, and 120 not equal to **0**, with a leading zero. 121 122 This can be set for individual numbers with the **plz(x)**, plznl(x)**, 123 **pnlz(x)**, and **pnlznl(x)** functions in the extended math library (see 124 the **LIBRARY** section). 125 126 This is a **non-portable extension**. 127 128**-e** *expr*, **-\-expression**=*expr* 129 130: Evaluates *expr*. If multiple expressions are given, they are evaluated in 131 order. If files are given as well (see below), the expressions and files are 132 evaluated in the order given. This means that if a file is given before an 133 expression, the file is read in and evaluated first. 134 135 If this option is given on the command-line (i.e., not in **DC_ENV_ARGS**, 136 see the **ENVIRONMENT VARIABLES** section), then after processing all 137 expressions and files, dc(1) will exit, unless **-** (**stdin**) was given 138 as an argument at least once to **-f** or **-\-file**, whether on the 139 command-line or in **DC_ENV_ARGS**. However, if any other **-e**, 140 **-\-expression**, **-f**, or **-\-file** arguments are given after **-f-** 141 or equivalent is given, dc(1) will give a fatal error and exit. 142 143 This is a **non-portable extension**. 144 145**-f** *file*, **-\-file**=*file* 146 147: Reads in *file* and evaluates it, line by line, as though it were read 148 through **stdin**. If expressions are also given (see above), the 149 expressions are evaluated in the order given. 150 151 If this option is given on the command-line (i.e., not in **DC_ENV_ARGS**, 152 see the **ENVIRONMENT VARIABLES** section), then after processing all 153 expressions and files, dc(1) will exit, unless **-** (**stdin**) was given 154 as an argument at least once to **-f** or **-\-file**. However, if any other 155 **-e**, **-\-expression**, **-f**, or **-\-file** arguments are given after 156 **-f-** or equivalent is given, dc(1) will give a fatal error and exit. 157 158 This is a **non-portable extension**. 159 160**-I** *ibase*, **-\-ibase**=*ibase* 161 162: Sets the builtin variable **ibase** to the value *ibase* assuming that 163 *ibase* is in base 10. It is a fatal error if *ibase* is not a valid number. 164 165 If multiple instances of this option are given, the last is used. 166 167 This is a **non-portable extension**. 168 169**-O** *obase*, **-\-obase**=*obase* 170 171: Sets the builtin variable **obase** to the value *obase* assuming that 172 *obase* is in base 10. It is a fatal error if *obase* is not a valid number. 173 174 If multiple instances of this option are given, the last is used. 175 176 This is a **non-portable extension**. 177 178**-S** *scale*, **-\-scale**=*scale* 179 180: Sets the builtin variable **scale** to the value *scale* assuming that 181 *scale* is in base 10. It is a fatal error if *scale* is not a valid number. 182 183 If multiple instances of this option are given, the last is used. 184 185 This is a **non-portable extension**. 186 187**-E** *seed*, **-\-seed**=*seed* 188 189: Sets the builtin variable **seed** to the value *seed* assuming that *seed* 190 is in base 10. It is a fatal error if *seed* is not a valid number. 191 192 If multiple instances of this option are given, the last is used. 193 194 This is a **non-portable extension**. 195 196All long options are **non-portable extensions**. 197 198# STDIN 199 200If no files are given on the command-line and no files or expressions are given 201by the **-f**, **-\-file**, **-e**, or **-\-expression** options, then dc(1) 202reads from **stdin**. 203 204However, there is a caveat to this. 205 206First, **stdin** is evaluated a line at a time. The only exception to this is if 207a string has been finished, but not ended. This means that, except for escaped 208brackets, all brackets must be balanced before dc(1) parses and executes. 209 210# STDOUT 211 212Any non-error output is written to **stdout**. In addition, if history (see the 213**HISTORY** section) and the prompt (see the **TTY MODE** section) are enabled, 214both are output to **stdout**. 215 216**Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal 217error (see the **EXIT STATUS** section) if it cannot write to **stdout**, so if 218**stdout** is closed, as in **dc <file> >&-**, it will quit with an error. This 219is done so that dc(1) can report problems when **stdout** is redirected to a 220file. 221 222If there are scripts that depend on the behavior of other dc(1) implementations, 223it is recommended that those scripts be changed to redirect **stdout** to 224**/dev/null**. 225 226# STDERR 227 228Any error output is written to **stderr**. 229 230**Note**: Unlike other dc(1) implementations, this dc(1) will issue a fatal 231error (see the **EXIT STATUS** section) if it cannot write to **stderr**, so if 232**stderr** is closed, as in **dc <file> 2>&-**, it will quit with an error. This 233is done so that dc(1) can exit with an error code when **stderr** is redirected 234to a file. 235 236If there are scripts that depend on the behavior of other dc(1) implementations, 237it is recommended that those scripts be changed to redirect **stderr** to 238**/dev/null**. 239 240# SYNTAX 241 242Each item in the input source code, either a number (see the **NUMBERS** 243section) or a command (see the **COMMANDS** section), is processed and executed, 244in order. Input is processed immediately when entered. 245 246**ibase** is a register (see the **REGISTERS** section) that determines how to 247interpret constant numbers. It is the "input" base, or the number base used for 248interpreting input numbers. **ibase** is initially **10**. The max allowable 249value for **ibase** is **16**. The min allowable value for **ibase** is **2**. 250The max allowable value for **ibase** can be queried in dc(1) programs with the 251**T** command. 252 253**obase** is a register (see the **REGISTERS** section) that determines how to 254output results. It is the "output" base, or the number base used for outputting 255numbers. **obase** is initially **10**. The max allowable value for **obase** is 256**DC_BASE_MAX** and can be queried with the **U** command. The min allowable 257value for **obase** is **0**. If **obase** is **0**, values are output in 258scientific notation, and if **obase** is **1**, values are output in engineering 259notation. Otherwise, values are output in the specified base. 260 261Outputting in scientific and engineering notations are **non-portable 262extensions**. 263 264The *scale* of an expression is the number of digits in the result of the 265expression right of the decimal point, and **scale** is a register (see the 266**REGISTERS** section) that sets the precision of any operations (with 267exceptions). **scale** is initially **0**. **scale** cannot be negative. The max 268allowable value for **scale** can be queried in dc(1) programs with the **V** 269command. 270 271**seed** is a register containing the current seed for the pseudo-random number 272generator. If the current value of **seed** is queried and stored, then if it is 273assigned to **seed** later, the pseudo-random number generator is guaranteed to 274produce the same sequence of pseudo-random numbers that were generated after the 275value of **seed** was first queried. 276 277Multiple values assigned to **seed** can produce the same sequence of 278pseudo-random numbers. Likewise, when a value is assigned to **seed**, it is not 279guaranteed that querying **seed** immediately after will return the same value. 280In addition, the value of **seed** will change after any call to the **'** 281command or the **"** command that does not get receive a value of **0** or 282**1**. The maximum integer returned by the **'** command can be queried with the 283**W** command. 284 285**Note**: The values returned by the pseudo-random number generator with the 286**'** and **"** commands are guaranteed to **NOT** be cryptographically secure. 287This is a consequence of using a seeded pseudo-random number generator. However, 288they *are* guaranteed to be reproducible with identical **seed** values. This 289means that the pseudo-random values from dc(1) should only be used where a 290reproducible stream of pseudo-random numbers is *ESSENTIAL*. In any other case, 291use a non-seeded pseudo-random number generator. 292 293The pseudo-random number generator, **seed**, and all associated operations are 294**non-portable extensions**. 295 296## Comments 297 298Comments go from **#** until, and not including, the next newline. This is a 299**non-portable extension**. 300 301# NUMBERS 302 303Numbers are strings made up of digits, uppercase letters up to **F**, and at 304most **1** period for a radix. Numbers can have up to **DC_NUM_MAX** digits. 305Uppercase letters are equal to **9** + their position in the alphabet (i.e., 306**A** equals **10**, or **9+1**). If a digit or letter makes no sense with the 307current value of **ibase**, they are set to the value of the highest valid digit 308in **ibase**. 309 310Single-character numbers (i.e., **A** alone) take the value that they would have 311if they were valid digits, regardless of the value of **ibase**. This means that 312**A** alone always equals decimal **10** and **F** alone always equals decimal 313**15**. 314 315In addition, dc(1) accepts numbers in scientific notation. These have the form 316**\<number\>e\<integer\>**. The exponent (the portion after the **e**) must be 317an integer. An example is **1.89237e9**, which is equal to **1892370000**. 318Negative exponents are also allowed, so **4.2890e_3** is equal to **0.0042890**. 319 320**WARNING**: Both the number and the exponent in scientific notation are 321interpreted according to the current **ibase**, but the number is still 322multiplied by **10\^exponent** regardless of the current **ibase**. For example, 323if **ibase** is **16** and dc(1) is given the number string **FFeA**, the 324resulting decimal number will be **2550000000000**, and if dc(1) is given the 325number string **10e_4**, the resulting decimal number will be **0.0016**. 326 327Accepting input as scientific notation is a **non-portable extension**. 328 329# COMMANDS 330 331The valid commands are listed below. 332 333## Printing 334 335These commands are used for printing. 336 337Note that both scientific notation and engineering notation are available for 338printing numbers. Scientific notation is activated by assigning **0** to 339**obase** using **0o**, and engineering notation is activated by assigning **1** 340to **obase** using **1o**. To deactivate them, just assign a different value to 341**obase**. 342 343Printing numbers in scientific notation and/or engineering notation is a 344**non-portable extension**. 345 346**p** 347 348: Prints the value on top of the stack, whether number or string, and prints a 349 newline after. 350 351 This does not alter the stack. 352 353**n** 354 355: Prints the value on top of the stack, whether number or string, and pops it 356 off of the stack. 357 358**P** 359 360: Pops a value off the stack. 361 362 If the value is a number, it is truncated and the absolute value of the 363 result is printed as though **obase** is **256** and each digit is 364 interpreted as an 8-bit ASCII character, making it a byte stream. 365 366 If the value is a string, it is printed without a trailing newline. 367 368 This is a **non-portable extension**. 369 370**f** 371 372: Prints the entire contents of the stack, in order from newest to oldest, 373 without altering anything. 374 375 Users should use this command when they get lost. 376 377## Arithmetic 378 379These are the commands used for arithmetic. 380 381**+** 382 383: The top two values are popped off the stack, added, and the result is pushed 384 onto the stack. The *scale* of the result is equal to the max *scale* of 385 both operands. 386 387**-** 388 389: The top two values are popped off the stack, subtracted, and the result is 390 pushed onto the stack. The *scale* of the result is equal to the max 391 *scale* of both operands. 392 393**\*** 394 395: The top two values are popped off the stack, multiplied, and the result is 396 pushed onto the stack. If **a** is the *scale* of the first expression and 397 **b** is the *scale* of the second expression, the *scale* of the result 398 is equal to **min(a+b,max(scale,a,b))** where **min()** and **max()** return 399 the obvious values. 400 401**/** 402 403: The top two values are popped off the stack, divided, and the result is 404 pushed onto the stack. The *scale* of the result is equal to **scale**. 405 406 The first value popped off of the stack must be non-zero. 407 408**%** 409 410: The top two values are popped off the stack, remaindered, and the result is 411 pushed onto the stack. 412 413 Remaindering is equivalent to 1) Computing **a/b** to current **scale**, and 414 2) Using the result of step 1 to calculate **a-(a/b)\*b** to *scale* 415 **max(scale+scale(b),scale(a))**. 416 417 The first value popped off of the stack must be non-zero. 418 419**~** 420 421: The top two values are popped off the stack, divided and remaindered, and 422 the results (divided first, remainder second) are pushed onto the stack. 423 This is equivalent to **x y / x y %** except that **x** and **y** are only 424 evaluated once. 425 426 The first value popped off of the stack must be non-zero. 427 428 This is a **non-portable extension**. 429 430**\^** 431 432: The top two values are popped off the stack, the second is raised to the 433 power of the first, and the result is pushed onto the stack. The *scale* of 434 the result is equal to **scale**. 435 436 The first value popped off of the stack must be an integer, and if that 437 value is negative, the second value popped off of the stack must be 438 non-zero. 439 440**v** 441 442: The top value is popped off the stack, its square root is computed, and the 443 result is pushed onto the stack. The *scale* of the result is equal to 444 **scale**. 445 446 The value popped off of the stack must be non-negative. 447 448**\_** 449 450: If this command *immediately* precedes a number (i.e., no spaces or other 451 commands), then that number is input as a negative number. 452 453 Otherwise, the top value on the stack is popped and copied, and the copy is 454 negated and pushed onto the stack. This behavior without a number is a 455 **non-portable extension**. 456 457**b** 458 459: The top value is popped off the stack, and if it is zero, it is pushed back 460 onto the stack. Otherwise, its absolute value is pushed onto the stack. 461 462 This is a **non-portable extension**. 463 464**|** 465 466: The top three values are popped off the stack, a modular exponentiation is 467 computed, and the result is pushed onto the stack. 468 469 The first value popped is used as the reduction modulus and must be an 470 integer and non-zero. The second value popped is used as the exponent and 471 must be an integer and non-negative. The third value popped is the base and 472 must be an integer. 473 474 This is a **non-portable extension**. 475 476**\$** 477 478: The top value is popped off the stack and copied, and the copy is truncated 479 and pushed onto the stack. 480 481 This is a **non-portable extension**. 482 483**\@** 484 485: The top two values are popped off the stack, and the precision of the second 486 is set to the value of the first, whether by truncation or extension. 487 488 The first value popped off of the stack must be an integer and non-negative. 489 490 This is a **non-portable extension**. 491 492**H** 493 494: The top two values are popped off the stack, and the second is shifted left 495 (radix shifted right) to the value of the first. 496 497 The first value popped off of the stack must be an integer and non-negative. 498 499 This is a **non-portable extension**. 500 501**h** 502 503: The top two values are popped off the stack, and the second is shifted right 504 (radix shifted left) to the value of the first. 505 506 The first value popped off of the stack must be an integer and non-negative. 507 508 This is a **non-portable extension**. 509 510**G** 511 512: The top two values are popped off of the stack, they are compared, and a 513 **1** is pushed if they are equal, or **0** otherwise. 514 515 This is a **non-portable extension**. 516 517**N** 518 519: The top value is popped off of the stack, and if it a **0**, a **1** is 520 pushed; otherwise, a **0** is pushed. 521 522 This is a **non-portable extension**. 523 524**(** 525 526: The top two values are popped off of the stack, they are compared, and a 527 **1** is pushed if the first is less than the second, or **0** otherwise. 528 529 This is a **non-portable extension**. 530 531**{** 532 533: The top two values are popped off of the stack, they are compared, and a 534 **1** is pushed if the first is less than or equal to the second, or **0** 535 otherwise. 536 537 This is a **non-portable extension**. 538 539**)** 540 541: The top two values are popped off of the stack, they are compared, and a 542 **1** is pushed if the first is greater than the second, or **0** otherwise. 543 544 This is a **non-portable extension**. 545 546**}** 547 548: The top two values are popped off of the stack, they are compared, and a 549 **1** is pushed if the first is greater than or equal to the second, or 550 **0** otherwise. 551 552 This is a **non-portable extension**. 553 554**M** 555 556: The top two values are popped off of the stack. If they are both non-zero, a 557 **1** is pushed onto the stack. If either of them is zero, or both of them 558 are, then a **0** is pushed onto the stack. 559 560 This is like the **&&** operator in bc(1), and it is *not* a short-circuit 561 operator. 562 563 This is a **non-portable extension**. 564 565**m** 566 567: The top two values are popped off of the stack. If at least one of them is 568 non-zero, a **1** is pushed onto the stack. If both of them are zero, then a 569 **0** is pushed onto the stack. 570 571 This is like the **||** operator in bc(1), and it is *not* a short-circuit 572 operator. 573 574 This is a **non-portable extension**. 575 576## Pseudo-Random Number Generator 577 578dc(1) has a built-in pseudo-random number generator. These commands query the 579pseudo-random number generator. (See Parameters for more information about the 580**seed** value that controls the pseudo-random number generator.) 581 582The pseudo-random number generator is guaranteed to **NOT** be 583cryptographically secure. 584 585**'** 586 587: Generates an integer between 0 and **DC_RAND_MAX**, inclusive (see the 588 **LIMITS** section). 589 590 The generated integer is made as unbiased as possible, subject to the 591 limitations of the pseudo-random number generator. 592 593 This is a **non-portable extension**. 594 595**"** 596 597: Pops a value off of the stack, which is used as an **exclusive** upper bound 598 on the integer that will be generated. If the bound is negative or is a 599 non-integer, an error is raised, and dc(1) resets (see the **RESET** 600 section) while **seed** remains unchanged. If the bound is larger than 601 **DC_RAND_MAX**, the higher bound is honored by generating several 602 pseudo-random integers, multiplying them by appropriate powers of 603 **DC_RAND_MAX+1**, and adding them together. Thus, the size of integer that 604 can be generated with this command is unbounded. Using this command will 605 change the value of **seed**, unless the operand is **0** or **1**. In that 606 case, **0** is pushed onto the stack, and **seed** is *not* changed. 607 608 The generated integer is made as unbiased as possible, subject to the 609 limitations of the pseudo-random number generator. 610 611 This is a **non-portable extension**. 612 613## Stack Control 614 615These commands control the stack. 616 617**c** 618 619: Removes all items from ("clears") the stack. 620 621**d** 622 623: Copies the item on top of the stack ("duplicates") and pushes the copy onto 624 the stack. 625 626**r** 627 628: Swaps ("reverses") the two top items on the stack. 629 630**R** 631 632: Pops ("removes") the top value from the stack. 633 634## Register Control 635 636These commands control registers (see the **REGISTERS** section). 637 638**s**_r_ 639 640: Pops the value off the top of the stack and stores it into register *r*. 641 642**l**_r_ 643 644: Copies the value in register *r* and pushes it onto the stack. This does not 645 alter the contents of *r*. 646 647**S**_r_ 648 649: Pops the value off the top of the (main) stack and pushes it onto the stack 650 of register *r*. The previous value of the register becomes inaccessible. 651 652**L**_r_ 653 654: Pops the value off the top of the stack for register *r* and push it onto 655 the main stack. The previous value in the stack for register *r*, if any, is 656 now accessible via the **l**_r_ command. 657 658## Parameters 659 660These commands control the values of **ibase**, **obase**, **scale**, and 661**seed**. Also see the **SYNTAX** section. 662 663**i** 664 665: Pops the value off of the top of the stack and uses it to set **ibase**, 666 which must be between **2** and **16**, inclusive. 667 668 If the value on top of the stack has any *scale*, the *scale* is ignored. 669 670**o** 671 672: Pops the value off of the top of the stack and uses it to set **obase**, 673 which must be between **0** and **DC_BASE_MAX**, inclusive (see the 674 **LIMITS** section and the **NUMBERS** section). 675 676 If the value on top of the stack has any *scale*, the *scale* is ignored. 677 678**k** 679 680: Pops the value off of the top of the stack and uses it to set **scale**, 681 which must be non-negative. 682 683 If the value on top of the stack has any *scale*, the *scale* is ignored. 684 685**j** 686 687: Pops the value off of the top of the stack and uses it to set **seed**. The 688 meaning of **seed** is dependent on the current pseudo-random number 689 generator but is guaranteed to not change except for new major versions. 690 691 The *scale* and sign of the value may be significant. 692 693 If a previously used **seed** value is used again, the pseudo-random number 694 generator is guaranteed to produce the same sequence of pseudo-random 695 numbers as it did when the **seed** value was previously used. 696 697 The exact value assigned to **seed** is not guaranteed to be returned if the 698 **J** command is used. However, if **seed** *does* return a different value, 699 both values, when assigned to **seed**, are guaranteed to produce the same 700 sequence of pseudo-random numbers. This means that certain values assigned 701 to **seed** will not produce unique sequences of pseudo-random numbers. 702 703 There is no limit to the length (number of significant decimal digits) or 704 *scale* of the value that can be assigned to **seed**. 705 706 This is a **non-portable extension**. 707 708**I** 709 710: Pushes the current value of **ibase** onto the main stack. 711 712**O** 713 714: Pushes the current value of **obase** onto the main stack. 715 716**K** 717 718: Pushes the current value of **scale** onto the main stack. 719 720**J** 721 722: Pushes the current value of **seed** onto the main stack. 723 724 This is a **non-portable extension**. 725 726**T** 727 728: Pushes the maximum allowable value of **ibase** onto the main stack. 729 730 This is a **non-portable extension**. 731 732**U** 733 734: Pushes the maximum allowable value of **obase** onto the main stack. 735 736 This is a **non-portable extension**. 737 738**V** 739 740: Pushes the maximum allowable value of **scale** onto the main stack. 741 742 This is a **non-portable extension**. 743 744**W** 745 746: Pushes the maximum (inclusive) integer that can be generated with the **'** 747 pseudo-random number generator command. 748 749 This is a **non-portable extension**. 750 751## Strings 752 753The following commands control strings. 754 755dc(1) can work with both numbers and strings, and registers (see the 756**REGISTERS** section) can hold both strings and numbers. dc(1) always knows 757whether the contents of a register are a string or a number. 758 759While arithmetic operations have to have numbers, and will print an error if 760given a string, other commands accept strings. 761 762Strings can also be executed as macros. For example, if the string **[1pR]** is 763executed as a macro, then the code **1pR** is executed, meaning that the **1** 764will be printed with a newline after and then popped from the stack. 765 766**\[**_characters_**\]** 767 768: Makes a string containing *characters* and pushes it onto the stack. 769 770 If there are brackets (**\[** and **\]**) in the string, then they must be 771 balanced. Unbalanced brackets can be escaped using a backslash (**\\**) 772 character. 773 774 If there is a backslash character in the string, the character after it 775 (even another backslash) is put into the string verbatim, but the (first) 776 backslash is not. 777 778**a** 779 780: The value on top of the stack is popped. 781 782 If it is a number, it is truncated and its absolute value is taken. The 783 result mod **256** is calculated. If that result is **0**, push an empty 784 string; otherwise, push a one-character string where the character is the 785 result of the mod interpreted as an ASCII character. 786 787 If it is a string, then a new string is made. If the original string is 788 empty, the new string is empty. If it is not, then the first character of 789 the original string is used to create the new string as a one-character 790 string. The new string is then pushed onto the stack. 791 792 This is a **non-portable extension**. 793 794**x** 795 796: Pops a value off of the top of the stack. 797 798 If it is a number, it is pushed back onto the stack. 799 800 If it is a string, it is executed as a macro. 801 802 This behavior is the norm whenever a macro is executed, whether by this 803 command or by the conditional execution commands below. 804 805**\>**_r_ 806 807: Pops two values off of the stack that must be numbers and compares them. If 808 the first value is greater than the second, then the contents of register 809 *r* are executed. 810 811 For example, **0 1>a** will execute the contents of register **a**, and 812 **1 0>a** will not. 813 814 If either or both of the values are not numbers, dc(1) will raise an error 815 and reset (see the **RESET** section). 816 817**>**_r_**e**_s_ 818 819: Like the above, but will execute register *s* if the comparison fails. 820 821 If either or both of the values are not numbers, dc(1) will raise an error 822 and reset (see the **RESET** section). 823 824 This is a **non-portable extension**. 825 826**!\>**_r_ 827 828: Pops two values off of the stack that must be numbers and compares them. If 829 the first value is not greater than the second (less than or equal to), then 830 the contents of register *r* are executed. 831 832 If either or both of the values are not numbers, dc(1) will raise an error 833 and reset (see the **RESET** section). 834 835**!\>**_r_**e**_s_ 836 837: Like the above, but will execute register *s* if the comparison fails. 838 839 If either or both of the values are not numbers, dc(1) will raise an error 840 and reset (see the **RESET** section). 841 842 This is a **non-portable extension**. 843 844**\<**_r_ 845 846: Pops two values off of the stack that must be numbers and compares them. If 847 the first value is less than the second, then the contents of register *r* 848 are executed. 849 850 If either or both of the values are not numbers, dc(1) will raise an error 851 and reset (see the **RESET** section). 852 853**\<**_r_**e**_s_ 854 855: Like the above, but will execute register *s* if the comparison fails. 856 857 If either or both of the values are not numbers, dc(1) will raise an error 858 and reset (see the **RESET** section). 859 860 This is a **non-portable extension**. 861 862**!\<**_r_ 863 864: Pops two values off of the stack that must be numbers and compares them. If 865 the first value is not less than the second (greater than or equal to), then 866 the contents of register *r* are executed. 867 868 If either or both of the values are not numbers, dc(1) will raise an error 869 and reset (see the **RESET** section). 870 871**!\<**_r_**e**_s_ 872 873: Like the above, but will execute register *s* if the comparison fails. 874 875 If either or both of the values are not numbers, dc(1) will raise an error 876 and reset (see the **RESET** section). 877 878 This is a **non-portable extension**. 879 880**=**_r_ 881 882: Pops two values off of the stack that must be numbers and compares them. If 883 the first value is equal to the second, then the contents of register *r* 884 are executed. 885 886 If either or both of the values are not numbers, dc(1) will raise an error 887 and reset (see the **RESET** section). 888 889**=**_r_**e**_s_ 890 891: Like the above, but will execute register *s* if the comparison fails. 892 893 If either or both of the values are not numbers, dc(1) will raise an error 894 and reset (see the **RESET** section). 895 896 This is a **non-portable extension**. 897 898**!=**_r_ 899 900: Pops two values off of the stack that must be numbers and compares them. If 901 the first value is not equal to the second, then the contents of register 902 *r* are executed. 903 904 If either or both of the values are not numbers, dc(1) will raise an error 905 and reset (see the **RESET** section). 906 907**!=**_r_**e**_s_ 908 909: Like the above, but will execute register *s* if the comparison fails. 910 911 If either or both of the values are not numbers, dc(1) will raise an error 912 and reset (see the **RESET** section). 913 914 This is a **non-portable extension**. 915 916**?** 917 918: Reads a line from the **stdin** and executes it. This is to allow macros to 919 request input from users. 920 921**q** 922 923: During execution of a macro, this exits the execution of that macro and the 924 execution of the macro that executed it. If there are no macros, or only one 925 macro executing, dc(1) exits. 926 927**Q** 928 929: Pops a value from the stack which must be non-negative and is used the 930 number of macro executions to pop off of the execution stack. If the number 931 of levels to pop is greater than the number of executing macros, dc(1) 932 exits. 933 934**,** 935 936: Pushes the depth of the execution stack onto the stack. The execution stack 937 is the stack of string executions. The number that is pushed onto the stack 938 is exactly as many as is needed to make dc(1) exit with the **Q** command, 939 so the sequence **,Q** will make dc(1) exit. 940 941## Status 942 943These commands query status of the stack or its top value. 944 945**Z** 946 947: Pops a value off of the stack. 948 949 If it is a number, calculates the number of significant decimal digits it 950 has and pushes the result. It will push **1** if the argument is **0** with 951 no decimal places. 952 953 If it is a string, pushes the number of characters the string has. 954 955**X** 956 957: Pops a value off of the stack. 958 959 If it is a number, pushes the *scale* of the value onto the stack. 960 961 If it is a string, pushes **0**. 962 963**z** 964 965: Pushes the current depth of the stack (before execution of this command) 966 onto the stack. 967 968**y**_r_ 969 970: Pushes the current stack depth of the register *r* onto the main stack. 971 972 Because each register has a depth of **1** (with the value **0** in the top 973 item) when dc(1) starts, dc(1) requires that each register's stack must 974 always have at least one item; dc(1) will give an error and reset otherwise 975 (see the **RESET** section). This means that this command will never push 976 **0**. 977 978 This is a **non-portable extension**. 979 980## Arrays 981 982These commands manipulate arrays. 983 984**:**_r_ 985 986: Pops the top two values off of the stack. The second value will be stored in 987 the array *r* (see the **REGISTERS** section), indexed by the first value. 988 989**;**_r_ 990 991: Pops the value on top of the stack and uses it as an index into the array 992 *r*. The selected value is then pushed onto the stack. 993 994**Y**_r_ 995 996: Pushes the length of the array *r* onto the stack. 997 998 This is a **non-portable extension**. 999 1000## Global Settings 1001 1002These commands retrieve global settings. These are the only commands that 1003require multiple specific characters, and all of them begin with the letter 1004**g**. Only the characters below are allowed after the character **g**; any 1005other character produces a parse error (see the **ERRORS** section). 1006 1007**gl** 1008 1009: Pushes the line length set by **DC_LINE_LENGTH** (see the **ENVIRONMENT 1010 VARIABLES** section) onto the stack. 1011 1012**gz** 1013 1014: Pushes **0** onto the stack if the leading zero setting has not been enabled 1015 with the **-z** or **-\-leading-zeroes** options (see the **OPTIONS** 1016 section), non-zero otherwise. 1017 1018# REGISTERS 1019 1020Registers are names that can store strings, numbers, and arrays. (Number/string 1021registers do not interfere with array registers.) 1022 1023Each register is also its own stack, so the current register value is the top of 1024the stack for the register. All registers, when first referenced, have one value 1025(**0**) in their stack, and it is a runtime error to attempt to pop that item 1026off of the register stack. 1027 1028In non-extended register mode, a register name is just the single character that 1029follows any command that needs a register name. The only exceptions are: a 1030newline (**'\\n'**) and a left bracket (**'['**); it is a parse error for a 1031newline or a left bracket to be used as a register name. 1032 1033## Extended Register Mode 1034 1035Unlike most other dc(1) implentations, this dc(1) provides nearly unlimited 1036amounts of registers, if extended register mode is enabled. 1037 1038If extended register mode is enabled (**-x** or **-\-extended-register** 1039command-line arguments are given), then normal single character registers are 1040used *unless* the character immediately following a command that needs a 1041register name is a space (according to **isspace()**) and not a newline 1042(**'\\n'**). 1043 1044In that case, the register name is found according to the regex 1045**\[a-z\]\[a-z0-9\_\]\*** (like bc(1) identifiers), and it is a parse error if 1046the next non-space characters do not match that regex. 1047 1048# RESET 1049 1050When dc(1) encounters an error or a signal that it has a non-default handler 1051for, it resets. This means that several things happen. 1052 1053First, any macros that are executing are stopped and popped off the stack. 1054The behavior is not unlike that of exceptions in programming languages. Then 1055the execution point is set so that any code waiting to execute (after all 1056macros returned) is skipped. 1057 1058Thus, when dc(1) resets, it skips any remaining code waiting to be executed. 1059Then, if it is interactive mode, and the error was not a fatal error (see the 1060**EXIT STATUS** section), it asks for more input; otherwise, it exits with the 1061appropriate return code. 1062 1063# PERFORMANCE 1064 1065Most dc(1) implementations use **char** types to calculate the value of **1** 1066decimal digit at a time, but that can be slow. This dc(1) does something 1067different. 1068 1069It uses large integers to calculate more than **1** decimal digit at a time. If 1070built in a environment where **DC_LONG_BIT** (see the **LIMITS** section) is 1071**64**, then each integer has **9** decimal digits. If built in an environment 1072where **DC_LONG_BIT** is **32** then each integer has **4** decimal digits. This 1073value (the number of decimal digits per large integer) is called 1074**DC_BASE_DIGS**. 1075 1076In addition, this dc(1) uses an even larger integer for overflow checking. This 1077integer type depends on the value of **DC_LONG_BIT**, but is always at least 1078twice as large as the integer type used to store digits. 1079 1080# LIMITS 1081 1082The following are the limits on dc(1): 1083 1084**DC_LONG_BIT** 1085 1086: The number of bits in the **long** type in the environment where dc(1) was 1087 built. This determines how many decimal digits can be stored in a single 1088 large integer (see the **PERFORMANCE** section). 1089 1090**DC_BASE_DIGS** 1091 1092: The number of decimal digits per large integer (see the **PERFORMANCE** 1093 section). Depends on **DC_LONG_BIT**. 1094 1095**DC_BASE_POW** 1096 1097: The max decimal number that each large integer can store (see 1098 **DC_BASE_DIGS**) plus **1**. Depends on **DC_BASE_DIGS**. 1099 1100**DC_OVERFLOW_MAX** 1101 1102: The max number that the overflow type (see the **PERFORMANCE** section) can 1103 hold. Depends on **DC_LONG_BIT**. 1104 1105**DC_BASE_MAX** 1106 1107: The maximum output base. Set at **DC_BASE_POW**. 1108 1109**DC_DIM_MAX** 1110 1111: The maximum size of arrays. Set at **SIZE_MAX-1**. 1112 1113**DC_SCALE_MAX** 1114 1115: The maximum **scale**. Set at **DC_OVERFLOW_MAX-1**. 1116 1117**DC_STRING_MAX** 1118 1119: The maximum length of strings. Set at **DC_OVERFLOW_MAX-1**. 1120 1121**DC_NAME_MAX** 1122 1123: The maximum length of identifiers. Set at **DC_OVERFLOW_MAX-1**. 1124 1125**DC_NUM_MAX** 1126 1127: The maximum length of a number (in decimal digits), which includes digits 1128 after the decimal point. Set at **DC_OVERFLOW_MAX-1**. 1129 1130**DC_RAND_MAX** 1131 1132: The maximum integer (inclusive) returned by the **'** command, if dc(1). Set 1133 at **2\^DC_LONG_BIT-1**. 1134 1135Exponent 1136 1137: The maximum allowable exponent (positive or negative). Set at 1138 **DC_OVERFLOW_MAX**. 1139 1140Number of vars 1141 1142: The maximum number of vars/arrays. Set at **SIZE_MAX-1**. 1143 1144These limits are meant to be effectively non-existent; the limits are so large 1145(at least on 64-bit machines) that there should not be any point at which they 1146become a problem. In fact, memory should be exhausted before these limits should 1147be hit. 1148 1149# ENVIRONMENT VARIABLES 1150 1151dc(1) recognizes the following environment variables: 1152 1153**DC_ENV_ARGS** 1154 1155: This is another way to give command-line arguments to dc(1). They should be 1156 in the same format as all other command-line arguments. These are always 1157 processed first, so any files given in **DC_ENV_ARGS** will be processed 1158 before arguments and files given on the command-line. This gives the user 1159 the ability to set up "standard" options and files to be used at every 1160 invocation. The most useful thing for such files to contain would be useful 1161 functions that the user might want every time dc(1) runs. Another use would 1162 be to use the **-e** option to set **scale** to a value other than **0**. 1163 1164 The code that parses **DC_ENV_ARGS** will correctly handle quoted arguments, 1165 but it does not understand escape sequences. For example, the string 1166 **"/home/gavin/some dc file.dc"** will be correctly parsed, but the string 1167 **"/home/gavin/some \"dc\" file.dc"** will include the backslashes. 1168 1169 The quote parsing will handle either kind of quotes, **'** or **"**. Thus, 1170 if you have a file with any number of single quotes in the name, you can use 1171 double quotes as the outside quotes, as in **"some 'dc' file.dc"**, and vice 1172 versa if you have a file with double quotes. However, handling a file with 1173 both kinds of quotes in **DC_ENV_ARGS** is not supported due to the 1174 complexity of the parsing, though such files are still supported on the 1175 command-line where the parsing is done by the shell. 1176 1177**DC_LINE_LENGTH** 1178 1179: If this environment variable exists and contains an integer that is greater 1180 than **1** and is less than **UINT16_MAX** (**2\^16-1**), dc(1) will output 1181 lines to that length, including the backslash newline combo. The default 1182 line length is **70**. 1183 1184 The special value of **0** will disable line length checking and print 1185 numbers without regard to line length and without backslashes and newlines. 1186 1187**DC_SIGINT_RESET** 1188 1189: If dc(1) is not in interactive mode (see the **INTERACTIVE MODE** section), 1190 then this environment variable has no effect because dc(1) exits on 1191 **SIGINT** when not in interactive mode. 1192 1193 However, when dc(1) is in interactive mode, then if this environment 1194 variable exists and contains an integer, a non-zero value makes dc(1) reset 1195 on **SIGINT**, rather than exit, and zero makes dc(1) exit. If this 1196 environment variable exists and is *not* an integer, then dc(1) will exit on 1197 **SIGINT**. 1198 1199 This environment variable overrides the default, which can be queried with 1200 the **-h** or **-\-help** options. 1201 1202**DC_TTY_MODE** 1203 1204: If TTY mode is *not* available (see the **TTY MODE** section), then this 1205 environment variable has no effect. 1206 1207 However, when TTY mode is available, then if this environment variable 1208 exists and contains an integer, then a non-zero value makes dc(1) use TTY 1209 mode, and zero makes dc(1) not use TTY mode. 1210 1211 This environment variable overrides the default, which can be queried with 1212 the **-h** or **-\-help** options. 1213 1214**DC_PROMPT** 1215 1216: If TTY mode is *not* available (see the **TTY MODE** section), then this 1217 environment variable has no effect. 1218 1219 However, when TTY mode is available, then if this environment variable 1220 exists and contains an integer, a non-zero value makes dc(1) use a prompt, 1221 and zero or a non-integer makes dc(1) not use a prompt. If this environment 1222 variable does not exist and **DC_TTY_MODE** does, then the value of the 1223 **DC_TTY_MODE** environment variable is used. 1224 1225 This environment variable and the **DC_TTY_MODE** environment variable 1226 override the default, which can be queried with the **-h** or **-\-help** 1227 options. 1228 1229**DC_EXPR_EXIT** 1230 1231: If any expressions or expression files are given on the command-line with 1232 **-e**, **-\-expression**, **-f**, or **-\-file**, then if this environment 1233 variable exists and contains an integer, a non-zero value makes dc(1) exit 1234 after executing the expressions and expression files, and a zero value makes 1235 dc(1) not exit. 1236 1237 This environment variable overrides the default, which can be queried with 1238 the **-h** or **-\-help** options. 1239 1240# EXIT STATUS 1241 1242dc(1) returns the following exit statuses: 1243 1244**0** 1245 1246: No error. 1247 1248**1** 1249 1250: A math error occurred. This follows standard practice of using **1** for 1251 expected errors, since math errors will happen in the process of normal 1252 execution. 1253 1254 Math errors include divide by **0**, taking the square root of a negative 1255 number, using a negative number as a bound for the pseudo-random number 1256 generator, attempting to convert a negative number to a hardware integer, 1257 overflow when converting a number to a hardware integer, overflow when 1258 calculating the size of a number, and attempting to use a non-integer where 1259 an integer is required. 1260 1261 Converting to a hardware integer happens for the second operand of the power 1262 (**\^**), places (**\@**), left shift (**H**), and right shift (**h**) 1263 operators. 1264 1265**2** 1266 1267: A parse error occurred. 1268 1269 Parse errors include unexpected **EOF**, using an invalid character, failing 1270 to find the end of a string or comment, and using a token where it is 1271 invalid. 1272 1273**3** 1274 1275: A runtime error occurred. 1276 1277 Runtime errors include assigning an invalid number to any global (**ibase**, 1278 **obase**, or **scale**), giving a bad expression to a **read()** call, 1279 calling **read()** inside of a **read()** call, type errors (including 1280 attempting to execute a number), and attempting an operation when the stack 1281 has too few elements. 1282 1283**4** 1284 1285: A fatal error occurred. 1286 1287 Fatal errors include memory allocation errors, I/O errors, failing to open 1288 files, attempting to use files that do not have only ASCII characters (dc(1) 1289 only accepts ASCII characters), attempting to open a directory as a file, 1290 and giving invalid command-line options. 1291 1292The exit status **4** is special; when a fatal error occurs, dc(1) always exits 1293and returns **4**, no matter what mode dc(1) is in. 1294 1295The other statuses will only be returned when dc(1) is not in interactive mode 1296(see the **INTERACTIVE MODE** section), since dc(1) resets its state (see the 1297**RESET** section) and accepts more input when one of those errors occurs in 1298interactive mode. This is also the case when interactive mode is forced by the 1299**-i** flag or **-\-interactive** option. 1300 1301These exit statuses allow dc(1) to be used in shell scripting with error 1302checking, and its normal behavior can be forced by using the **-i** flag or 1303**-\-interactive** option. 1304 1305# INTERACTIVE MODE 1306 1307Like bc(1), dc(1) has an interactive mode and a non-interactive mode. 1308Interactive mode is turned on automatically when both **stdin** and **stdout** 1309are hooked to a terminal, but the **-i** flag and **-\-interactive** option can 1310turn it on in other situations. 1311 1312In interactive mode, dc(1) attempts to recover from errors (see the **RESET** 1313section), and in normal execution, flushes **stdout** as soon as execution is 1314done for the current input. dc(1) may also reset on **SIGINT** instead of exit, 1315depending on the contents of, or default for, the **DC_SIGINT_RESET** 1316environment variable (see the **ENVIRONMENT VARIABLES** section). 1317 1318# TTY MODE 1319 1320If **stdin**, **stdout**, and **stderr** are all connected to a TTY, then "TTY 1321mode" is considered to be available, and thus, dc(1) can turn on TTY mode, 1322subject to some settings. 1323 1324If there is the environment variable **DC_TTY_MODE** in the environment (see the 1325**ENVIRONMENT VARIABLES** section), then if that environment variable contains a 1326non-zero integer, dc(1) will turn on TTY mode when **stdin**, **stdout**, and 1327**stderr** are all connected to a TTY. If the **DC_TTY_MODE** environment 1328variable exists but is *not* a non-zero integer, then dc(1) will not turn TTY 1329mode on. 1330 1331If the environment variable **DC_TTY_MODE** does *not* exist, the default 1332setting is used. The default setting can be queried with the **-h** or 1333**-\-help** options. 1334 1335TTY mode is different from interactive mode because interactive mode is required 1336in the bc(1) specification at 1337https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html , and 1338interactive mode requires only **stdin** and **stdout** to be connected to a 1339terminal. 1340 1341## Command-Line History 1342 1343Command-line history is only enabled if TTY mode is, i.e., that **stdin**, 1344**stdout**, and **stderr** are connected to a TTY and the **DC_TTY_MODE** 1345environment variable (see the **ENVIRONMENT VARIABLES** section) and its default 1346do not disable TTY mode. See the **COMMAND LINE HISTORY** section for more 1347information. 1348 1349## Prompt 1350 1351If TTY mode is available, then a prompt can be enabled. Like TTY mode itself, it 1352can be turned on or off with an environment variable: **DC_PROMPT** (see the 1353**ENVIRONMENT VARIABLES** section). 1354 1355If the environment variable **DC_PROMPT** exists and is a non-zero integer, then 1356the prompt is turned on when **stdin**, **stdout**, and **stderr** are connected 1357to a TTY and the **-P** and **-\-no-prompt** options were not used. The read 1358prompt will be turned on under the same conditions, except that the **-R** and 1359**-\-no-read-prompt** options must also not be used. 1360 1361However, if **DC_PROMPT** does not exist, the prompt can be enabled or disabled 1362with the **DC_TTY_MODE** environment variable, the **-P** and **-\-no-prompt** 1363options, and the **-R** and **-\-no-read-prompt** options. See the **ENVIRONMENT 1364VARIABLES** and **OPTIONS** sections for more details. 1365 1366# SIGNAL HANDLING 1367 1368Sending a **SIGINT** will cause dc(1) to do one of two things. 1369 1370If dc(1) is not in interactive mode (see the **INTERACTIVE MODE** section), or 1371the **DC_SIGINT_RESET** environment variable (see the **ENVIRONMENT VARIABLES** 1372section), or its default, is either not an integer or it is zero, dc(1) will 1373exit. 1374 1375However, if dc(1) is in interactive mode, and the **DC_SIGINT_RESET** or its 1376default is an integer and non-zero, then dc(1) will stop executing the current 1377input and reset (see the **RESET** section) upon receiving a **SIGINT**. 1378 1379Note that "current input" can mean one of two things. If dc(1) is processing 1380input from **stdin** in interactive mode, it will ask for more input. If dc(1) 1381is processing input from a file in interactive mode, it will stop processing the 1382file and start processing the next file, if one exists, or ask for input from 1383**stdin** if no other file exists. 1384 1385This means that if a **SIGINT** is sent to dc(1) as it is executing a file, it 1386can seem as though dc(1) did not respond to the signal since it will immediately 1387start executing the next file. This is by design; most files that users execute 1388when interacting with dc(1) have function definitions, which are quick to parse. 1389If a file takes a long time to execute, there may be a bug in that file. The 1390rest of the files could still be executed without problem, allowing the user to 1391continue. 1392 1393**SIGTERM** and **SIGQUIT** cause dc(1) to clean up and exit, and it uses the 1394default handler for all other signals. The one exception is **SIGHUP**; in that 1395case, and only when dc(1) is in TTY mode (see the **TTY MODE** section), a 1396**SIGHUP** will cause dc(1) to clean up and exit. 1397 1398# COMMAND LINE HISTORY 1399 1400dc(1) supports interactive command-line editing. 1401 1402If dc(1) can be in TTY mode (see the **TTY MODE** section), history can be 1403enabled. This means that command-line history can only be enabled when 1404**stdin**, **stdout**, and **stderr** are all connected to a TTY. 1405 1406Like TTY mode itself, it can be turned on or off with the environment variable 1407**DC_TTY_MODE** (see the **ENVIRONMENT VARIABLES** section). 1408 1409**Note**: tabs are converted to 8 spaces. 1410 1411# SEE ALSO 1412 1413bc(1) 1414 1415# STANDARDS 1416 1417The dc(1) utility operators are compliant with the operators in the IEEE Std 14181003.1-2017 (“POSIX.1-2017”) specification at 1419https://pubs.opengroup.org/onlinepubs/9699919799/utilities/bc.html for bc(1). 1420 1421# BUGS 1422 1423None are known. Report bugs at https://git.yzena.com/gavin/bc. 1424 1425# AUTHOR 1426 1427Gavin D. Howard <gavin@yzena.com> and contributors. 1428