| 1 | =head1 NAME |
| 2 | |
| 3 | perlfaq - frequently asked questions about Perl ($Date: 2003/01/31 17:37:17 $) |
| 4 | |
| 5 | =head1 DESCRIPTION |
| 6 | |
| 7 | The perlfaq is divided into several documents based on topics. A table |
| 8 | of contents is at the end of this document. |
| 9 | |
| 10 | =head2 Where to get the perlfaq |
| 11 | |
| 12 | Extracts of the perlfaq are posted regularly to |
| 13 | comp.lang.perl.misc. It is available on many web sites: |
| 14 | http://www.perldoc.com/ and http://faq.perl.org/ |
| 15 | |
| 16 | =head2 How to contribute to the perlfaq |
| 17 | |
| 18 | You may mail corrections, additions, and suggestions to |
| 19 | perlfaq-workers@perl.org . This alias should not be used to |
| 20 | I<ask> FAQs. It's for fixing the current FAQ. Send |
| 21 | questions to the comp.lang.perl.misc newsgroup. You can |
| 22 | view the source tree at http://cvs.perl.org/cvsweb/perlfaq/ |
| 23 | (which is outside of the main Perl source tree). The CVS |
| 24 | repository notes all changes to the FAQ. |
| 25 | |
| 26 | =head2 What will happen if you mail your Perl programming problems to the authors |
| 27 | |
| 28 | Your questions will probably go unread, unless they're |
| 29 | suggestions of new questions to add to the FAQ, in which |
| 30 | case they should have gone to the perlfaq-workers@perl.org |
| 31 | instead. |
| 32 | |
| 33 | You should have read section 2 of this faq. There you would |
| 34 | have learned that comp.lang.perl.misc is the appropriate |
| 35 | place to go for free advice. If your question is really |
| 36 | important and you require a prompt and correct answer, you |
| 37 | should hire a consultant. |
| 38 | |
| 39 | =head1 Credits |
| 40 | |
| 41 | The original perlfaq was written by Tom Christiansen, then expanded |
| 42 | by collaboration between Tom and Nathan Torkington. The current |
| 43 | document is maintained by the perlfaq-workers (perlfaq-workers@perl.org). |
| 44 | Several people have contributed answers, corrections, and comments. |
| 45 | |
| 46 | =head1 Author and Copyright Information |
| 47 | |
| 48 | Copyright (c) 1997-2003 Tom Christiansen, Nathan Torkington, and |
| 49 | other contributors noted in the answers. |
| 50 | |
| 51 | All rights reserved. |
| 52 | |
| 53 | =head2 Bundled Distributions |
| 54 | |
| 55 | This documentation is free; you can redistribute it and/or modify it |
| 56 | under the same terms as Perl itself. |
| 57 | |
| 58 | Irrespective of its distribution, all code examples in these files |
| 59 | are hereby placed into the public domain. You are permitted and |
| 60 | encouraged to use this code in your own programs for fun |
| 61 | or for profit as you see fit. A simple comment in the code giving |
| 62 | credit would be courteous but is not required. |
| 63 | |
| 64 | =head2 Disclaimer |
| 65 | |
| 66 | This information is offered in good faith and in the hope that it may |
| 67 | be of use, but is not guaranteed to be correct, up to date, or suitable |
| 68 | for any particular purpose whatsoever. The authors accept no liability |
| 69 | in respect of this information or its use. |
| 70 | |
| 71 | =head1 Table of Contents |
| 72 | |
| 73 | =over 4 |
| 74 | |
| 75 | =item perlfaq - this document |
| 76 | |
| 77 | =item perlfaq1 - General Questions About Perl |
| 78 | |
| 79 | =item perlfaq2 - Obtaining and Learning about Perl |
| 80 | |
| 81 | =item perlfaq3 - Programming Tools |
| 82 | |
| 83 | =item perlfaq4 - Data Manipulation |
| 84 | |
| 85 | =item perlfaq5 - Files and Formats |
| 86 | |
| 87 | =item perlfaq6 - Regular Expressions |
| 88 | |
| 89 | =item perlfaq7 - General Perl Language Issues |
| 90 | |
| 91 | =item perlfaq8 - System Interaction |
| 92 | |
| 93 | =item perlfaq9 - Networking |
| 94 | |
| 95 | |
| 96 | =back |
| 97 | |
| 98 | |
| 99 | =head1 The Questions |
| 100 | |
| 101 | =head2 L<perlfaq1>: General Questions About Perl |
| 102 | |
| 103 | Very general, high-level questions about Perl. |
| 104 | |
| 105 | =over 4 |
| 106 | |
| 107 | =item * |
| 108 | |
| 109 | What is Perl? |
| 110 | |
| 111 | =item * |
| 112 | |
| 113 | Who supports Perl? Who develops it? Why is it free? |
| 114 | |
| 115 | =item * |
| 116 | |
| 117 | Which version of Perl should I use? |
| 118 | |
| 119 | =item * |
| 120 | |
| 121 | What are perl4 and perl5? |
| 122 | |
| 123 | =item * |
| 124 | |
| 125 | What is perl6? |
| 126 | |
| 127 | =item * |
| 128 | |
| 129 | How stable is Perl? |
| 130 | |
| 131 | =item * |
| 132 | |
| 133 | Is Perl difficult to learn? |
| 134 | |
| 135 | =item * |
| 136 | |
| 137 | How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl? |
| 138 | |
| 139 | =item * |
| 140 | |
| 141 | Can I do [task] in Perl? |
| 142 | |
| 143 | =item * |
| 144 | |
| 145 | When shouldn't I program in Perl? |
| 146 | |
| 147 | =item * |
| 148 | |
| 149 | What's the difference between "perl" and "Perl"? |
| 150 | |
| 151 | =item * |
| 152 | |
| 153 | Is it a Perl program or a Perl script? |
| 154 | |
| 155 | =item * |
| 156 | |
| 157 | What is a JAPH? |
| 158 | |
| 159 | =item * |
| 160 | |
| 161 | Where can I get a list of Larry Wall witticisms? |
| 162 | |
| 163 | =item * |
| 164 | |
| 165 | How can I convince my sysadmin/supervisor/employees to use version 5/5.6.1/Perl instead of some other language? |
| 166 | |
| 167 | =back |
| 168 | |
| 169 | |
| 170 | =head2 L<perlfaq2>: Obtaining and Learning about Perl |
| 171 | |
| 172 | Where to find source and documentation for Perl, support, |
| 173 | and related matters. |
| 174 | |
| 175 | =over 4 |
| 176 | |
| 177 | =item * |
| 178 | |
| 179 | What machines support Perl? Where do I get it? |
| 180 | |
| 181 | =item * |
| 182 | |
| 183 | How can I get a binary version of Perl? |
| 184 | |
| 185 | =item * |
| 186 | |
| 187 | I don't have a C compiler on my system. How can I compile perl? |
| 188 | |
| 189 | =item * |
| 190 | |
| 191 | I copied the Perl binary from one machine to another, but scripts don't work. |
| 192 | |
| 193 | =item * |
| 194 | |
| 195 | I grabbed the sources and tried to compile but gdbm/dynamic loading/malloc/linking/... failed. How do I make it work? |
| 196 | |
| 197 | =item * |
| 198 | |
| 199 | What modules and extensions are available for Perl? What is CPAN? What does CPAN/src/... mean? |
| 200 | |
| 201 | =item * |
| 202 | |
| 203 | Is there an ISO or ANSI certified version of Perl? |
| 204 | |
| 205 | =item * |
| 206 | |
| 207 | Where can I get information on Perl? |
| 208 | |
| 209 | =item * |
| 210 | |
| 211 | What are the Perl newsgroups on Usenet? Where do I post questions? |
| 212 | |
| 213 | =item * |
| 214 | |
| 215 | Where should I post source code? |
| 216 | |
| 217 | =item * |
| 218 | |
| 219 | Perl Books |
| 220 | |
| 221 | =item * |
| 222 | |
| 223 | Perl in Magazines |
| 224 | |
| 225 | =item * |
| 226 | |
| 227 | Perl on the Net: FTP and WWW Access |
| 228 | |
| 229 | =item * |
| 230 | |
| 231 | What mailing lists are there for Perl? |
| 232 | |
| 233 | =item * |
| 234 | |
| 235 | Archives of comp.lang.perl.misc |
| 236 | |
| 237 | =item * |
| 238 | |
| 239 | Where can I buy a commercial version of Perl? |
| 240 | |
| 241 | =item * |
| 242 | |
| 243 | Where do I send bug reports? |
| 244 | |
| 245 | =item * |
| 246 | |
| 247 | What is perl.com? Perl Mongers? pm.org? perl.org? cpan.org? |
| 248 | |
| 249 | =back |
| 250 | |
| 251 | |
| 252 | =head2 L<perlfaq3>: Programming Tools |
| 253 | |
| 254 | Programmer tools and programming support. |
| 255 | |
| 256 | =over 4 |
| 257 | |
| 258 | =item * |
| 259 | |
| 260 | How do I do (anything)? |
| 261 | |
| 262 | =item * |
| 263 | |
| 264 | How can I use Perl interactively? |
| 265 | |
| 266 | =item * |
| 267 | |
| 268 | Is there a Perl shell? |
| 269 | |
| 270 | =item * |
| 271 | |
| 272 | How do I find which modules are installed on my system? |
| 273 | |
| 274 | =item * |
| 275 | |
| 276 | How do I debug my Perl programs? |
| 277 | |
| 278 | =item * |
| 279 | |
| 280 | How do I profile my Perl programs? |
| 281 | |
| 282 | =item * |
| 283 | |
| 284 | How do I cross-reference my Perl programs? |
| 285 | |
| 286 | =item * |
| 287 | |
| 288 | Is there a pretty-printer (formatter) for Perl? |
| 289 | |
| 290 | =item * |
| 291 | |
| 292 | Is there a ctags for Perl? |
| 293 | |
| 294 | =item * |
| 295 | |
| 296 | Is there an IDE or Windows Perl Editor? |
| 297 | |
| 298 | =item * |
| 299 | |
| 300 | Where can I get Perl macros for vi? |
| 301 | |
| 302 | =item * |
| 303 | |
| 304 | Where can I get perl-mode for emacs? |
| 305 | |
| 306 | =item * |
| 307 | |
| 308 | How can I use curses with Perl? |
| 309 | |
| 310 | =item * |
| 311 | |
| 312 | How can I use X or Tk with Perl? |
| 313 | |
| 314 | =item * |
| 315 | |
| 316 | How can I generate simple menus without using CGI or Tk? |
| 317 | |
| 318 | =item * |
| 319 | |
| 320 | How can I make my Perl program run faster? |
| 321 | |
| 322 | =item * |
| 323 | |
| 324 | How can I make my Perl program take less memory? |
| 325 | |
| 326 | =item * |
| 327 | |
| 328 | Is it safe to return a reference to local or lexical data? |
| 329 | |
| 330 | =item * |
| 331 | |
| 332 | How can I free an array or hash so my program shrinks? |
| 333 | |
| 334 | =item * |
| 335 | |
| 336 | How can I make my CGI script more efficient? |
| 337 | |
| 338 | =item * |
| 339 | |
| 340 | How can I hide the source for my Perl program? |
| 341 | |
| 342 | =item * |
| 343 | |
| 344 | How can I compile my Perl program into byte code or C? |
| 345 | |
| 346 | =item * |
| 347 | |
| 348 | How can I compile Perl into Java? |
| 349 | |
| 350 | =item * |
| 351 | |
| 352 | How can I get C<#!perl> to work on [MS-DOS,NT,...]? |
| 353 | |
| 354 | =item * |
| 355 | |
| 356 | Can I write useful Perl programs on the command line? |
| 357 | |
| 358 | =item * |
| 359 | |
| 360 | Why don't Perl one-liners work on my DOS/Mac/VMS system? |
| 361 | |
| 362 | =item * |
| 363 | |
| 364 | Where can I learn about CGI or Web programming in Perl? |
| 365 | |
| 366 | =item * |
| 367 | |
| 368 | Where can I learn about object-oriented Perl programming? |
| 369 | |
| 370 | =item * |
| 371 | |
| 372 | Where can I learn about linking C with Perl? [h2xs, xsubpp] |
| 373 | |
| 374 | =item * |
| 375 | |
| 376 | I've read perlembed, perlguts, etc., but I can't embed perl in |
| 377 | my C program; what am I doing wrong? |
| 378 | |
| 379 | =item * |
| 380 | |
| 381 | When I tried to run my script, I got this message. What does it mean? |
| 382 | |
| 383 | =item * |
| 384 | |
| 385 | What's MakeMaker? |
| 386 | |
| 387 | =back |
| 388 | |
| 389 | |
| 390 | =head2 L<perlfaq4>: Data Manipulation |
| 391 | |
| 392 | Manipulating numbers, dates, strings, arrays, hashes, and |
| 393 | miscellaneous data issues. |
| 394 | |
| 395 | =over 4 |
| 396 | |
| 397 | =item * |
| 398 | |
| 399 | Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)? |
| 400 | |
| 401 | =item * |
| 402 | |
| 403 | Why isn't my octal data interpreted correctly? |
| 404 | |
| 405 | =item * |
| 406 | |
| 407 | Does Perl have a round() function? What about ceil() and floor()? Trig functions? |
| 408 | |
| 409 | =item * |
| 410 | |
| 411 | How do I convert between numeric representations? |
| 412 | |
| 413 | =item * |
| 414 | |
| 415 | Why doesn't & work the way I want it to? |
| 416 | |
| 417 | =item * |
| 418 | |
| 419 | How do I multiply matrices? |
| 420 | |
| 421 | =item * |
| 422 | |
| 423 | How do I perform an operation on a series of integers? |
| 424 | |
| 425 | =item * |
| 426 | |
| 427 | How can I output Roman numerals? |
| 428 | |
| 429 | =item * |
| 430 | |
| 431 | Why aren't my random numbers random? |
| 432 | |
| 433 | =item * |
| 434 | |
| 435 | How do I get a random number between X and Y? |
| 436 | |
| 437 | =item * |
| 438 | |
| 439 | How do I find the day or week of the year? |
| 440 | |
| 441 | =item * |
| 442 | |
| 443 | How do I find the current century or millennium? |
| 444 | |
| 445 | =item * |
| 446 | |
| 447 | How can I compare two dates and find the difference? |
| 448 | |
| 449 | =item * |
| 450 | |
| 451 | How can I take a string and turn it into epoch seconds? |
| 452 | |
| 453 | =item * |
| 454 | |
| 455 | How can I find the Julian Day? |
| 456 | |
| 457 | =item * |
| 458 | |
| 459 | How do I find yesterday's date? |
| 460 | |
| 461 | =item * |
| 462 | |
| 463 | Does Perl have a Year 2000 problem? Is Perl Y2K compliant? |
| 464 | |
| 465 | =item * |
| 466 | |
| 467 | How do I validate input? |
| 468 | |
| 469 | =item * |
| 470 | |
| 471 | How do I unescape a string? |
| 472 | |
| 473 | =item * |
| 474 | |
| 475 | How do I remove consecutive pairs of characters? |
| 476 | |
| 477 | =item * |
| 478 | |
| 479 | How do I expand function calls in a string? |
| 480 | |
| 481 | =item * |
| 482 | |
| 483 | How do I find matching/nesting anything? |
| 484 | |
| 485 | =item * |
| 486 | |
| 487 | How do I reverse a string? |
| 488 | |
| 489 | =item * |
| 490 | |
| 491 | How do I expand tabs in a string? |
| 492 | |
| 493 | =item * |
| 494 | |
| 495 | How do I reformat a paragraph? |
| 496 | |
| 497 | =item * |
| 498 | |
| 499 | How can I access or change N characters of a string? |
| 500 | |
| 501 | =item * |
| 502 | |
| 503 | How do I change the Nth occurrence of something? |
| 504 | |
| 505 | =item * |
| 506 | |
| 507 | How can I count the number of occurrences of a substring within a string? |
| 508 | |
| 509 | =item * |
| 510 | |
| 511 | How do I capitalize all the words on one line? |
| 512 | |
| 513 | =item * |
| 514 | |
| 515 | How can I split a [character] delimited string except when inside [character]? |
| 516 | |
| 517 | =item * |
| 518 | |
| 519 | How do I strip blank space from the beginning/end of a string? |
| 520 | |
| 521 | =item * |
| 522 | |
| 523 | How do I pad a string with blanks or pad a number with zeroes? |
| 524 | |
| 525 | =item * |
| 526 | |
| 527 | How do I extract selected columns from a string? |
| 528 | |
| 529 | =item * |
| 530 | |
| 531 | How do I find the soundex value of a string? |
| 532 | |
| 533 | =item * |
| 534 | |
| 535 | How can I expand variables in text strings? |
| 536 | |
| 537 | =item * |
| 538 | |
| 539 | What's wrong with always quoting "$vars"? |
| 540 | |
| 541 | =item * |
| 542 | |
| 543 | Why don't my E<lt>E<lt>HERE documents work? |
| 544 | |
| 545 | =item * |
| 546 | |
| 547 | What is the difference between a list and an array? |
| 548 | |
| 549 | =item * |
| 550 | |
| 551 | What is the difference between $array[1] and @array[1]? |
| 552 | |
| 553 | =item * |
| 554 | |
| 555 | How can I remove duplicate elements from a list or array? |
| 556 | |
| 557 | =item * |
| 558 | |
| 559 | How can I tell whether a certain element is contained in a list or array? |
| 560 | |
| 561 | =item * |
| 562 | |
| 563 | How do I compute the difference of two arrays? How do I compute the intersection of two arrays? |
| 564 | |
| 565 | =item * |
| 566 | |
| 567 | How do I test whether two arrays or hashes are equal? |
| 568 | |
| 569 | =item * |
| 570 | |
| 571 | How do I find the first array element for which a condition is true? |
| 572 | |
| 573 | =item * |
| 574 | |
| 575 | How do I handle linked lists? |
| 576 | |
| 577 | =item * |
| 578 | |
| 579 | How do I handle circular lists? |
| 580 | |
| 581 | =item * |
| 582 | |
| 583 | How do I shuffle an array randomly? |
| 584 | |
| 585 | =item * |
| 586 | |
| 587 | How do I process/modify each element of an array? |
| 588 | |
| 589 | =item * |
| 590 | |
| 591 | How do I select a random element from an array? |
| 592 | |
| 593 | =item * |
| 594 | |
| 595 | How do I permute N elements of a list? |
| 596 | |
| 597 | =item * |
| 598 | |
| 599 | How do I sort an array by (anything)? |
| 600 | |
| 601 | =item * |
| 602 | |
| 603 | How do I manipulate arrays of bits? |
| 604 | |
| 605 | =item * |
| 606 | |
| 607 | Why does defined() return true on empty arrays and hashes? |
| 608 | |
| 609 | =item * |
| 610 | |
| 611 | How do I process an entire hash? |
| 612 | |
| 613 | =item * |
| 614 | |
| 615 | What happens if I add or remove keys from a hash while iterating over it? |
| 616 | |
| 617 | =item * |
| 618 | |
| 619 | How do I look up a hash element by value? |
| 620 | |
| 621 | =item * |
| 622 | |
| 623 | How can I know how many entries are in a hash? |
| 624 | |
| 625 | =item * |
| 626 | |
| 627 | How do I sort a hash (optionally by value instead of key)? |
| 628 | |
| 629 | =item * |
| 630 | |
| 631 | How can I always keep my hash sorted? |
| 632 | |
| 633 | =item * |
| 634 | |
| 635 | What's the difference between "delete" and "undef" with hashes? |
| 636 | |
| 637 | =item * |
| 638 | |
| 639 | Why don't my tied hashes make the defined/exists distinction? |
| 640 | |
| 641 | =item * |
| 642 | |
| 643 | How do I reset an each() operation part-way through? |
| 644 | |
| 645 | =item * |
| 646 | |
| 647 | How can I get the unique keys from two hashes? |
| 648 | |
| 649 | =item * |
| 650 | |
| 651 | How can I store a multidimensional array in a DBM file? |
| 652 | |
| 653 | =item * |
| 654 | |
| 655 | How can I make my hash remember the order I put elements into it? |
| 656 | |
| 657 | =item * |
| 658 | |
| 659 | Why does passing a subroutine an undefined element in a hash create it? |
| 660 | |
| 661 | =item * |
| 662 | |
| 663 | How can I make the Perl equivalent of a C structure/C++ class/hash or array of hashes or arrays? |
| 664 | |
| 665 | =item * |
| 666 | |
| 667 | How can I use a reference as a hash key? |
| 668 | |
| 669 | =item * |
| 670 | |
| 671 | How do I handle binary data correctly? |
| 672 | |
| 673 | =item * |
| 674 | |
| 675 | How do I determine whether a scalar is a number/whole/integer/float? |
| 676 | |
| 677 | =item * |
| 678 | |
| 679 | How do I keep persistent data across program calls? |
| 680 | |
| 681 | =item * |
| 682 | |
| 683 | How do I print out or copy a recursive data structure? |
| 684 | |
| 685 | =item * |
| 686 | |
| 687 | How do I define methods for every class/object? |
| 688 | |
| 689 | =item * |
| 690 | |
| 691 | How do I verify a credit card checksum? |
| 692 | |
| 693 | =item * |
| 694 | |
| 695 | How do I pack arrays of doubles or floats for XS code? |
| 696 | |
| 697 | =back |
| 698 | |
| 699 | |
| 700 | =head2 L<perlfaq5>: Files and Formats |
| 701 | |
| 702 | I/O and the "f" issues: filehandles, flushing, formats, and footers. |
| 703 | |
| 704 | =over 4 |
| 705 | |
| 706 | =item * |
| 707 | |
| 708 | How do I flush/unbuffer an output filehandle? Why must I do this? |
| 709 | |
| 710 | =item * |
| 711 | |
| 712 | How do I change one line in a file/delete a line in a file/insert a line in the middle of a file/append to the beginning of a file? |
| 713 | |
| 714 | =item * |
| 715 | |
| 716 | How do I count the number of lines in a file? |
| 717 | |
| 718 | =item * |
| 719 | |
| 720 | How can I use Perl's C<-i> option from within a program? |
| 721 | |
| 722 | =item * |
| 723 | |
| 724 | How do I make a temporary file name? |
| 725 | |
| 726 | =item * |
| 727 | |
| 728 | How can I manipulate fixed-record-length files? |
| 729 | |
| 730 | =item * |
| 731 | |
| 732 | How can I make a filehandle local to a subroutine? How do I pass filehandles between subroutines? How do I make an array of filehandles? |
| 733 | |
| 734 | =item * |
| 735 | |
| 736 | How can I use a filehandle indirectly? |
| 737 | |
| 738 | =item * |
| 739 | |
| 740 | How can I set up a footer format to be used with write()? |
| 741 | |
| 742 | =item * |
| 743 | |
| 744 | How can I write() into a string? |
| 745 | |
| 746 | =item * |
| 747 | |
| 748 | How can I output my numbers with commas added? |
| 749 | |
| 750 | =item * |
| 751 | |
| 752 | How can I translate tildes (~) in a filename? |
| 753 | |
| 754 | =item * |
| 755 | |
| 756 | How come when I open a file read-write it wipes it out? |
| 757 | |
| 758 | =item * |
| 759 | |
| 760 | Why do I sometimes get an "Argument list too long" when I use E<lt>*E<gt>? |
| 761 | |
| 762 | =item * |
| 763 | |
| 764 | Is there a leak/bug in glob()? |
| 765 | |
| 766 | =item * |
| 767 | |
| 768 | How can I open a file with a leading ">" or trailing blanks? |
| 769 | |
| 770 | =item * |
| 771 | |
| 772 | How can I reliably rename a file? |
| 773 | |
| 774 | =item * |
| 775 | |
| 776 | How can I lock a file? |
| 777 | |
| 778 | =item * |
| 779 | |
| 780 | Why can't I just open(FH, "E<gt>file.lock")? |
| 781 | |
| 782 | =item * |
| 783 | |
| 784 | I still don't get locking. I just want to increment the number in the file. How can I do this? |
| 785 | |
| 786 | =item * |
| 787 | |
| 788 | All I want to do is append a small amount of text to the end of a file. Do I still have to use locking? |
| 789 | |
| 790 | =item * |
| 791 | |
| 792 | How do I randomly update a binary file? |
| 793 | |
| 794 | =item * |
| 795 | |
| 796 | How do I get a file's timestamp in perl? |
| 797 | |
| 798 | =item * |
| 799 | |
| 800 | How do I set a file's timestamp in perl? |
| 801 | |
| 802 | =item * |
| 803 | |
| 804 | How do I print to more than one file at once? |
| 805 | |
| 806 | =item * |
| 807 | |
| 808 | How can I read in an entire file all at once? |
| 809 | |
| 810 | =item * |
| 811 | |
| 812 | How can I read in a file by paragraphs? |
| 813 | |
| 814 | =item * |
| 815 | |
| 816 | How can I read a single character from a file? From the keyboard? |
| 817 | |
| 818 | =item * |
| 819 | |
| 820 | How can I tell whether there's a character waiting on a filehandle? |
| 821 | |
| 822 | =item * |
| 823 | |
| 824 | How do I do a C<tail -f> in perl? |
| 825 | |
| 826 | =item * |
| 827 | |
| 828 | How do I dup() a filehandle in Perl? |
| 829 | |
| 830 | =item * |
| 831 | |
| 832 | How do I close a file descriptor by number? |
| 833 | |
| 834 | =item * |
| 835 | |
| 836 | Why can't I use "C:\temp\foo" in DOS paths? What doesn't `C:\temp\foo.exe` work? |
| 837 | |
| 838 | =item * |
| 839 | |
| 840 | Why doesn't glob("*.*") get all the files? |
| 841 | |
| 842 | =item * |
| 843 | |
| 844 | Why does Perl let me delete read-only files? Why does C<-i> clobber protected files? Isn't this a bug in Perl? |
| 845 | |
| 846 | =item * |
| 847 | |
| 848 | How do I select a random line from a file? |
| 849 | |
| 850 | =item * |
| 851 | |
| 852 | Why do I get weird spaces when I print an array of lines? |
| 853 | |
| 854 | =back |
| 855 | |
| 856 | |
| 857 | =head2 L<perlfaq6>: Regular Expressions |
| 858 | |
| 859 | Pattern matching and regular expressions. |
| 860 | |
| 861 | =over 4 |
| 862 | |
| 863 | =item * |
| 864 | |
| 865 | How can I hope to use regular expressions without creating illegible and unmaintainable code? |
| 866 | |
| 867 | =item * |
| 868 | |
| 869 | I'm having trouble matching over more than one line. What's wrong? |
| 870 | |
| 871 | =item * |
| 872 | |
| 873 | How can I pull out lines between two patterns that are themselves on different lines? |
| 874 | |
| 875 | =item * |
| 876 | |
| 877 | I put a regular expression into $/ but it didn't work. What's wrong? |
| 878 | |
| 879 | =item * |
| 880 | |
| 881 | How do I substitute case insensitively on the LHS while preserving case on the RHS? |
| 882 | |
| 883 | =item * |
| 884 | |
| 885 | How can I make C<\w> match national character sets? |
| 886 | |
| 887 | =item * |
| 888 | |
| 889 | How can I match a locale-smart version of C</[a-zA-Z]/>? |
| 890 | |
| 891 | =item * |
| 892 | |
| 893 | How can I quote a variable to use in a regex? |
| 894 | |
| 895 | =item * |
| 896 | |
| 897 | What is C</o> really for? |
| 898 | |
| 899 | =item * |
| 900 | |
| 901 | How do I use a regular expression to strip C style comments from a file? |
| 902 | |
| 903 | =item * |
| 904 | |
| 905 | Can I use Perl regular expressions to match balanced text? |
| 906 | |
| 907 | =item * |
| 908 | |
| 909 | What does it mean that regexes are greedy? How can I get around it? |
| 910 | |
| 911 | =item * |
| 912 | |
| 913 | How do I process each word on each line? |
| 914 | |
| 915 | =item * |
| 916 | |
| 917 | How can I print out a word-frequency or line-frequency summary? |
| 918 | |
| 919 | =item * |
| 920 | |
| 921 | How can I do approximate matching? |
| 922 | |
| 923 | =item * |
| 924 | |
| 925 | How do I efficiently match many regular expressions at once? |
| 926 | |
| 927 | =item * |
| 928 | |
| 929 | Why don't word-boundary searches with C<\b> work for me? |
| 930 | |
| 931 | =item * |
| 932 | |
| 933 | Why does using $&, $`, or $' slow my program down? |
| 934 | |
| 935 | =item * |
| 936 | |
| 937 | What good is C<\G> in a regular expression? |
| 938 | |
| 939 | =item * |
| 940 | |
| 941 | Are Perl regexes DFAs or NFAs? Are they POSIX compliant? |
| 942 | |
| 943 | =item * |
| 944 | |
| 945 | What's wrong with using grep or map in a void context? |
| 946 | |
| 947 | =item * |
| 948 | |
| 949 | How can I match strings with multibyte characters? |
| 950 | |
| 951 | =item * |
| 952 | |
| 953 | How do I match a pattern that is supplied by the user? |
| 954 | |
| 955 | =back |
| 956 | |
| 957 | |
| 958 | =head2 L<perlfaq7>: General Perl Language Issues |
| 959 | |
| 960 | General Perl language issues that don't clearly fit into any of the |
| 961 | other sections. |
| 962 | |
| 963 | =over 4 |
| 964 | |
| 965 | =item * |
| 966 | |
| 967 | Can I get a BNF/yacc/RE for the Perl language? |
| 968 | |
| 969 | =item * |
| 970 | |
| 971 | What are all these $@%&* punctuation signs, and how do I know when to use them? |
| 972 | |
| 973 | =item * |
| 974 | |
| 975 | Do I always/never have to quote my strings or use semicolons and commas? |
| 976 | |
| 977 | =item * |
| 978 | |
| 979 | How do I skip some return values? |
| 980 | |
| 981 | =item * |
| 982 | |
| 983 | How do I temporarily block warnings? |
| 984 | |
| 985 | =item * |
| 986 | |
| 987 | What's an extension? |
| 988 | |
| 989 | =item * |
| 990 | |
| 991 | Why do Perl operators have different precedence than C operators? |
| 992 | |
| 993 | =item * |
| 994 | |
| 995 | How do I declare/create a structure? |
| 996 | |
| 997 | =item * |
| 998 | |
| 999 | How do I create a module? |
| 1000 | |
| 1001 | =item * |
| 1002 | |
| 1003 | How do I create a class? |
| 1004 | |
| 1005 | =item * |
| 1006 | |
| 1007 | How can I tell if a variable is tainted? |
| 1008 | |
| 1009 | =item * |
| 1010 | |
| 1011 | What's a closure? |
| 1012 | |
| 1013 | =item * |
| 1014 | |
| 1015 | What is variable suicide and how can I prevent it? |
| 1016 | |
| 1017 | =item * |
| 1018 | |
| 1019 | How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}? |
| 1020 | |
| 1021 | =item * |
| 1022 | |
| 1023 | How do I create a static variable? |
| 1024 | |
| 1025 | =item * |
| 1026 | |
| 1027 | What's the difference between dynamic and lexical (static) scoping? Between local() and my()? |
| 1028 | |
| 1029 | =item * |
| 1030 | |
| 1031 | How can I access a dynamic variable while a similarly named lexical is in scope? |
| 1032 | |
| 1033 | =item * |
| 1034 | |
| 1035 | What's the difference between deep and shallow binding? |
| 1036 | |
| 1037 | =item * |
| 1038 | |
| 1039 | Why doesn't "my($foo) = E<lt>FILEE<gt>;" work right? |
| 1040 | |
| 1041 | =item * |
| 1042 | |
| 1043 | How do I redefine a builtin function, operator, or method? |
| 1044 | |
| 1045 | =item * |
| 1046 | |
| 1047 | What's the difference between calling a function as &foo and foo()? |
| 1048 | |
| 1049 | =item * |
| 1050 | |
| 1051 | How do I create a switch or case statement? |
| 1052 | |
| 1053 | =item * |
| 1054 | |
| 1055 | How can I catch accesses to undefined variables, functions, or methods? |
| 1056 | |
| 1057 | =item * |
| 1058 | |
| 1059 | Why can't a method included in this same file be found? |
| 1060 | |
| 1061 | =item * |
| 1062 | |
| 1063 | How can I find out my current package? |
| 1064 | |
| 1065 | =item * |
| 1066 | |
| 1067 | How can I comment out a large block of perl code? |
| 1068 | |
| 1069 | =item * |
| 1070 | |
| 1071 | How do I clear a package? |
| 1072 | |
| 1073 | =item * |
| 1074 | |
| 1075 | How can I use a variable as a variable name? |
| 1076 | |
| 1077 | =item * |
| 1078 | |
| 1079 | What does "bad interpreter" mean? |
| 1080 | |
| 1081 | =back |
| 1082 | |
| 1083 | |
| 1084 | =head2 L<perlfaq8>: System Interaction |
| 1085 | |
| 1086 | Interprocess communication (IPC), control over the user-interface |
| 1087 | (keyboard, screen and pointing devices). |
| 1088 | |
| 1089 | =over 4 |
| 1090 | |
| 1091 | =item * |
| 1092 | |
| 1093 | How do I find out which operating system I'm running under? |
| 1094 | |
| 1095 | =item * |
| 1096 | |
| 1097 | How come exec() doesn't return? |
| 1098 | |
| 1099 | =item * |
| 1100 | |
| 1101 | How do I do fancy stuff with the keyboard/screen/mouse? |
| 1102 | |
| 1103 | =item * |
| 1104 | |
| 1105 | How do I print something out in color? |
| 1106 | |
| 1107 | =item * |
| 1108 | |
| 1109 | How do I read just one key without waiting for a return key? |
| 1110 | |
| 1111 | =item * |
| 1112 | |
| 1113 | How do I check whether input is ready on the keyboard? |
| 1114 | |
| 1115 | =item * |
| 1116 | |
| 1117 | How do I clear the screen? |
| 1118 | |
| 1119 | =item * |
| 1120 | |
| 1121 | How do I get the screen size? |
| 1122 | |
| 1123 | =item * |
| 1124 | |
| 1125 | How do I ask the user for a password? |
| 1126 | |
| 1127 | =item * |
| 1128 | |
| 1129 | How do I read and write the serial port? |
| 1130 | |
| 1131 | =item * |
| 1132 | |
| 1133 | How do I decode encrypted password files? |
| 1134 | |
| 1135 | =item * |
| 1136 | |
| 1137 | How do I start a process in the background? |
| 1138 | |
| 1139 | =item * |
| 1140 | |
| 1141 | How do I trap control characters/signals? |
| 1142 | |
| 1143 | =item * |
| 1144 | |
| 1145 | How do I modify the shadow password file on a Unix system? |
| 1146 | |
| 1147 | =item * |
| 1148 | |
| 1149 | How do I set the time and date? |
| 1150 | |
| 1151 | =item * |
| 1152 | |
| 1153 | How can I sleep() or alarm() for under a second? |
| 1154 | |
| 1155 | =item * |
| 1156 | |
| 1157 | How can I measure time under a second? |
| 1158 | |
| 1159 | =item * |
| 1160 | |
| 1161 | How can I do an atexit() or setjmp()/longjmp()? (Exception handling) |
| 1162 | |
| 1163 | =item * |
| 1164 | |
| 1165 | Why doesn't my sockets program work under System V (Solaris)? What does the error message "Protocol not supported" mean? |
| 1166 | |
| 1167 | =item * |
| 1168 | |
| 1169 | How can I call my system's unique C functions from Perl? |
| 1170 | |
| 1171 | =item * |
| 1172 | |
| 1173 | Where do I get the include files to do ioctl() or syscall()? |
| 1174 | |
| 1175 | =item * |
| 1176 | |
| 1177 | Why do setuid perl scripts complain about kernel problems? |
| 1178 | |
| 1179 | =item * |
| 1180 | |
| 1181 | How can I open a pipe both to and from a command? |
| 1182 | |
| 1183 | =item * |
| 1184 | |
| 1185 | Why can't I get the output of a command with system()? |
| 1186 | |
| 1187 | =item * |
| 1188 | |
| 1189 | How can I capture STDERR from an external command? |
| 1190 | |
| 1191 | =item * |
| 1192 | |
| 1193 | Why doesn't open() return an error when a pipe open fails? |
| 1194 | |
| 1195 | =item * |
| 1196 | |
| 1197 | What's wrong with using backticks in a void context? |
| 1198 | |
| 1199 | =item * |
| 1200 | |
| 1201 | How can I call backticks without shell processing? |
| 1202 | |
| 1203 | =item * |
| 1204 | |
| 1205 | Why can't my script read from STDIN after I gave it EOF (^D on Unix, ^Z on MS-DOS)? |
| 1206 | |
| 1207 | =item * |
| 1208 | |
| 1209 | How can I convert my shell script to perl? |
| 1210 | |
| 1211 | =item * |
| 1212 | |
| 1213 | Can I use perl to run a telnet or ftp session? |
| 1214 | |
| 1215 | =item * |
| 1216 | |
| 1217 | How can I write expect in Perl? |
| 1218 | |
| 1219 | =item * |
| 1220 | |
| 1221 | Is there a way to hide perl's command line from programs such as "ps"? |
| 1222 | |
| 1223 | =item * |
| 1224 | |
| 1225 | I {changed directory, modified my environment} in a perl script. How come the change disappeared when I exited the script? How do I get my changes to be visible? |
| 1226 | |
| 1227 | =item * |
| 1228 | |
| 1229 | How do I close a process's filehandle without waiting for it to complete? |
| 1230 | |
| 1231 | =item * |
| 1232 | |
| 1233 | How do I fork a daemon process? |
| 1234 | |
| 1235 | =item * |
| 1236 | |
| 1237 | How do I find out if I'm running interactively or not? |
| 1238 | |
| 1239 | =item * |
| 1240 | |
| 1241 | How do I timeout a slow event? |
| 1242 | |
| 1243 | =item * |
| 1244 | |
| 1245 | How do I set CPU limits? |
| 1246 | |
| 1247 | =item * |
| 1248 | |
| 1249 | How do I avoid zombies on a Unix system? |
| 1250 | |
| 1251 | =item * |
| 1252 | |
| 1253 | How do I use an SQL database? |
| 1254 | |
| 1255 | =item * |
| 1256 | |
| 1257 | How do I make a system() exit on control-C? |
| 1258 | |
| 1259 | =item * |
| 1260 | |
| 1261 | How do I open a file without blocking? |
| 1262 | |
| 1263 | =item * |
| 1264 | |
| 1265 | How do I install a module from CPAN? |
| 1266 | |
| 1267 | =item * |
| 1268 | |
| 1269 | What's the difference between require and use? |
| 1270 | |
| 1271 | =item * |
| 1272 | |
| 1273 | How do I keep my own module/library directory? |
| 1274 | |
| 1275 | =item * |
| 1276 | |
| 1277 | How do I add the directory my program lives in to the module/library search path? |
| 1278 | |
| 1279 | =item * |
| 1280 | |
| 1281 | How do I add a directory to my include path at runtime? |
| 1282 | |
| 1283 | =item * |
| 1284 | |
| 1285 | What is socket.ph and where do I get it? |
| 1286 | |
| 1287 | =back |
| 1288 | |
| 1289 | |
| 1290 | =head2 L<perlfaq9>: Networking |
| 1291 | |
| 1292 | Networking, the internet, and a few on the web. |
| 1293 | |
| 1294 | =over 4 |
| 1295 | |
| 1296 | =item * |
| 1297 | |
| 1298 | What is the correct form of response from a CGI script? |
| 1299 | |
| 1300 | =item * |
| 1301 | |
| 1302 | My CGI script runs from the command line but not the browser. (500 Server Error) |
| 1303 | |
| 1304 | =item * |
| 1305 | |
| 1306 | How can I get better error messages from a CGI program? |
| 1307 | |
| 1308 | =item * |
| 1309 | |
| 1310 | How do I remove HTML from a string? |
| 1311 | |
| 1312 | =item * |
| 1313 | |
| 1314 | How do I extract URLs? |
| 1315 | |
| 1316 | =item * |
| 1317 | |
| 1318 | How do I download a file from the user's machine? How do I open a file on another machine? |
| 1319 | |
| 1320 | =item * |
| 1321 | |
| 1322 | How do I make a pop-up menu in HTML? |
| 1323 | |
| 1324 | =item * |
| 1325 | |
| 1326 | How do I fetch an HTML file? |
| 1327 | |
| 1328 | =item * |
| 1329 | |
| 1330 | How do I automate an HTML form submission? |
| 1331 | |
| 1332 | =item * |
| 1333 | |
| 1334 | How do I decode or create those %-encodings on the web? |
| 1335 | |
| 1336 | =item * |
| 1337 | |
| 1338 | How do I redirect to another page? |
| 1339 | |
| 1340 | =item * |
| 1341 | |
| 1342 | How do I put a password on my web pages? |
| 1343 | |
| 1344 | =item * |
| 1345 | |
| 1346 | How do I edit my .htpasswd and .htgroup files with Perl? |
| 1347 | |
| 1348 | =item * |
| 1349 | |
| 1350 | How do I make sure users can't enter values into a form that cause my CGI script to do bad things? |
| 1351 | |
| 1352 | =item * |
| 1353 | |
| 1354 | How do I parse a mail header? |
| 1355 | |
| 1356 | =item * |
| 1357 | |
| 1358 | How do I decode a CGI form? |
| 1359 | |
| 1360 | =item * |
| 1361 | |
| 1362 | How do I check a valid mail address? |
| 1363 | |
| 1364 | =item * |
| 1365 | |
| 1366 | How do I decode a MIME/BASE64 string? |
| 1367 | |
| 1368 | =item * |
| 1369 | |
| 1370 | How do I return the user's mail address? |
| 1371 | |
| 1372 | =item * |
| 1373 | |
| 1374 | How do I send mail? |
| 1375 | |
| 1376 | =item * |
| 1377 | |
| 1378 | How do I use MIME to make an attachment to a mail message? |
| 1379 | |
| 1380 | =item * |
| 1381 | |
| 1382 | How do I read mail? |
| 1383 | |
| 1384 | =item * |
| 1385 | |
| 1386 | How do I find out my hostname/domainname/IP address? |
| 1387 | |
| 1388 | =item * |
| 1389 | |
| 1390 | How do I fetch a news article or the active newsgroups? |
| 1391 | |
| 1392 | =item * |
| 1393 | |
| 1394 | How do I fetch/put an FTP file? |
| 1395 | |
| 1396 | =item * |
| 1397 | |
| 1398 | How can I do RPC in Perl? |
| 1399 | |
| 1400 | =back |
| 1401 | |
| 1402 | |