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   1  =head1 NAME
   2  
   3  perlfaq - frequently asked questions about Perl
   4  
   5  =head1 DESCRIPTION
   6  
   7  The perlfaq comprises several documents that answer the most commonly
   8  asked questions about Perl and Perl programming. It's divided by topic
   9  into nine major sections outlined in this document.
  10  
  11  =head2 Where to get the perlfaq
  12  
  13  The perlfaq comes with the standard Perl distribution, so if you have Perl
  14  you should have the perlfaq. You should also have the C<perldoc> tool
  15  that let's you read the L<perlfaq>:
  16  
  17      $ perldoc perlfaq
  18  
  19  Besides your local system, you can find the perlfaq on the web, including
  20  at http://perldoc.perl.org/ .
  21  
  22  The perlfaq is an evolving document and you can read the latest version
  23  at http://faq.perl.org/ . The perlfaq-workers periodically post extracts
  24  of the latest perlfaq to comp.lang.perl.misc.
  25  
  26  You can view the source tree at
  27  https://svn.perl.org/modules/perlfaq/trunk/ (which is outside of the
  28  main Perl source tree).  The SVN repository notes all changes to the FAQ
  29  and holds the latest version of the working documents and may vary
  30  significantly from the version distributed with the latest version of
  31  Perl. Check the repository before sending your corrections.
  32  
  33  =head2 How to contribute to the perlfaq
  34  
  35  You can mail corrections, additions, and suggestions to
  36  C<< <perlfaq-workers AT perl DOT org> >>. The perlfaq volunteers use this
  37  address to coordinate their efforts and track the perlfaq development.
  38  They appreciate your contributions to the FAQ but do not have time to
  39  provide individual help, so don't use this address to ask FAQs.
  40  
  41  The perlfaq server posts extracts of the perlfaq to that newsgroup every
  42  6 hours (or so), and the community of volunteers reviews and updates the
  43  answers. If you'd like to help review and update the answers, check out
  44  comp.lang.perl.misc.
  45  
  46  =head2 What will happen if you mail your Perl programming problems to the authors?
  47  
  48  The perlfaq-workers like to keep all traffic on the perlfaq-workers list
  49  so that everyone can see the work being done (and the work that needs to
  50  be done). The mailing list serves as an official record. If you email the
  51  authors or maintainers directly, you'll probably get a reply asking you
  52  to post to the mailing list. If you don't get a reply, it probably means
  53  that the person never saw the message or didn't have time to deal with
  54  it. Posting to the list allows the volunteers with time to deal with it
  55  when others are busy.
  56  
  57  If you have a question that isn't in the FAQ and you would like help with
  58  it, try the resources in L<perlfaq2>.
  59  
  60  =head1 CREDITS
  61  
  62  Tom Christiansen wrote the original perlfaq then expanded it with the
  63  help of Nat Torkington.  The perlfaq-workers maintain current document
  64  and the denizens of comp.lang.perl.misc regularly review and update the
  65  FAQ. Several people have contributed answers, corrections, and comments,
  66  and the perlfaq notes those contributions wherever appropriate.
  67  
  68  =head1 AUTHOR AND COPYRIGHT
  69  
  70  Tom Christiansen wrote the original version of this document.
  71  brian d foy C<< <bdfoy@cpan.org> >> wrote this version. See the
  72  individual perlfaq documents for additional copyright information.
  73  
  74  This document is available under the same terms as Perl itself. Code
  75  examples in all the perlfaq documents are in the public domain. Use
  76  them as you see fit (and at your own risk with no warranty from anyone).
  77  
  78  =head1 Table of Contents
  79  
  80  =over 4
  81  
  82  =item perlfaq  - this document
  83  
  84  =item perlfaq1 - General Questions About Perl
  85  
  86  =item perlfaq2 - Obtaining and Learning about Perl
  87  
  88  =item perlfaq3 - Programming Tools
  89  
  90  =item perlfaq4 - Data Manipulation
  91  
  92  =item perlfaq5 - Files and Formats
  93  
  94  =item perlfaq6 - Regular Expressions
  95  
  96  =item perlfaq7 - General Perl Language Issues
  97  
  98  =item perlfaq8 - System Interaction
  99  
 100  =item perlfaq9 - Networking
 101  
 102  =back
 103  
 104  =head1 The Questions
 105  
 106  =head2 L<perlfaq1>: General Questions About Perl
 107  
 108  Very general, high-level questions about Perl.
 109  
 110  =over 4
 111  
 112  =item *
 113  
 114  What is Perl?
 115  
 116  =item *
 117  
 118  Who supports Perl?  Who develops it?  Why is it free?
 119  
 120  =item *
 121  
 122  Which version of Perl should I use?
 123  
 124  =item *
 125  
 126  What are Perl 4, Perl 5, or Perl 6?
 127  
 128  =item *
 129  
 130  What was Ponie?
 131  
 132  =item *
 133  
 134  What is Perl 6?
 135  
 136  =item *
 137  
 138  How stable is Perl?
 139  
 140  =item *
 141  
 142  Is Perl difficult to learn?
 143  
 144  =item *
 145  
 146  How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl?
 147  
 148  =item *
 149  
 150  Can I do [task] in Perl?
 151  
 152  =item *
 153  
 154  When shouldn't I program in Perl?
 155  
 156  =item *
 157  
 158  What's the difference between "perl" and "Perl"?
 159  
 160  =item *
 161  
 162  Is it a Perl program or a Perl script?
 163  
 164  =item *
 165  
 166  What is a JAPH?
 167  
 168  =item *
 169  
 170  Where can I get a list of Larry Wall witticisms?
 171  
 172  =item *
 173  
 174  How can I convince others to use Perl?
 175  
 176  =back
 177  
 178  
 179  =head2 L<perlfaq2>: Obtaining and Learning about Perl
 180  
 181  Where to find source and documentation for Perl, support, and related matters.
 182  
 183  =over 4
 184  
 185  =item *
 186  
 187  What machines support perl?  Where do I get it?
 188  
 189  =item *
 190  
 191  How can I get a binary version of perl?
 192  
 193  =item *
 194  
 195  I don't have a C compiler. How can I build my own Perl interpreter?
 196  
 197  =item *
 198  
 199  I copied the perl binary from one machine to another, but scripts don't work.
 200  
 201  =item *
 202  
 203  I grabbed the sources and tried to compile but gdbm/dynamic loading/malloc/linking/... failed.  How do I make it work?
 204  
 205  =item *
 206  
 207  What modules and extensions are available for Perl?  What is CPAN?  What does CPAN/src/... mean?
 208  
 209  =item *
 210  
 211  Is there an ISO or ANSI certified version of Perl?
 212  
 213  =item *
 214  
 215  Where can I get information on Perl?
 216  
 217  =item *
 218  
 219  What are the Perl newsgroups on Usenet?  Where do I post questions?
 220  
 221  =item *
 222  
 223  Where should I post source code?
 224  
 225  =item *
 226  
 227  Perl Books
 228  
 229  =item *
 230  
 231  Which magazines have Perl content?
 232  
 233  =item *
 234  
 235  What mailing lists are there for Perl?
 236  
 237  =item *
 238  
 239  Where are the archives for comp.lang.perl.misc?
 240  
 241  =item *
 242  
 243  Where can I buy a commercial version of perl?
 244  
 245  =item *
 246  
 247  Where do I send bug reports?
 248  
 249  =item *
 250  
 251  What is perl.com? Perl Mongers? pm.org? perl.org? cpan.org?
 252  
 253  =back
 254  
 255  
 256  =head2 L<perlfaq3>: Programming Tools
 257  
 258  Programmer tools and programming support.
 259  
 260  =over 4
 261  
 262  =item *
 263  
 264  How do I do (anything)?
 265  
 266  =item *
 267  
 268  How can I use Perl interactively?
 269  
 270  =item *
 271  
 272  Is there a Perl shell?
 273  
 274  =item *
 275  
 276  How do I find which modules are installed on my system?
 277  
 278  =item *
 279  
 280  How do I debug my Perl programs?
 281  
 282  =item *
 283  
 284  How do I profile my Perl programs?
 285  
 286  =item *
 287  
 288  How do I cross-reference my Perl programs?
 289  
 290  =item *
 291  
 292  Is there a pretty-printer (formatter) for Perl?
 293  
 294  =item *
 295  
 296  Is there a ctags for Perl?
 297  
 298  =item *
 299  
 300  Is there an IDE or Windows Perl Editor?
 301  
 302  =item *
 303  
 304  Where can I get Perl macros for vi?
 305  
 306  =item *
 307  
 308  Where can I get perl-mode for emacs?
 309  
 310  =item *
 311  
 312  How can I use curses with Perl?
 313  
 314  =item *
 315  
 316  How can I write a GUI (X, Tk, Gtk, etc.) in Perl?
 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 get C<#!perl> to work on [MS-DOS,NT,...]?
 349  
 350  =item *
 351  
 352  Can I write useful Perl programs on the command line?
 353  
 354  =item *
 355  
 356  Why don't Perl one-liners work on my DOS/Mac/VMS system?
 357  
 358  =item *
 359  
 360  Where can I learn about CGI or Web programming in Perl?
 361  
 362  =item *
 363  
 364  Where can I learn about object-oriented Perl programming?
 365  
 366  =item *
 367  
 368  Where can I learn about linking C with Perl?
 369  
 370  =item *
 371  
 372  I've read perlembed, perlguts, etc., but I can't embed perl in my C program; what am I doing wrong?
 373  
 374  =item *
 375  
 376  When I tried to run my script, I got this message. What does it mean?
 377  
 378  =item *
 379  
 380  What's MakeMaker?
 381  
 382  =back
 383  
 384  
 385  =head2 L<perlfaq4>: Data Manipulation
 386  
 387  Manipulating numbers, dates, strings, arrays, hashes, and miscellaneous data issues.
 388  
 389  =over 4
 390  
 391  =item *
 392  
 393  Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?
 394  
 395  =item *
 396  
 397  Why is int() broken?
 398  
 399  =item *
 400  
 401  Why isn't my octal data interpreted correctly?
 402  
 403  =item *
 404  
 405  Does Perl have a round() function?  What about ceil() and floor()?  Trig functions?
 406  
 407  =item *
 408  
 409  How do I convert between numeric representations/bases/radixes?
 410  
 411  =item *
 412  
 413  Why doesn't & work the way I want it to?
 414  
 415  =item *
 416  
 417  How do I multiply matrices?
 418  
 419  =item *
 420  
 421  How do I perform an operation on a series of integers?
 422  
 423  =item *
 424  
 425  How can I output Roman numerals?
 426  
 427  =item *
 428  
 429  Why aren't my random numbers random?
 430  
 431  =item *
 432  
 433  How do I get a random number between X and Y?
 434  
 435  =item *
 436  
 437  How do I find the day or week of the year?
 438  
 439  =item *
 440  
 441  How do I find the current century or millennium?
 442  
 443  =item *
 444  
 445  How can I compare two dates and find the difference?
 446  
 447  =item *
 448  
 449  How can I take a string and turn it into epoch seconds?
 450  
 451  =item *
 452  
 453  How can I find the Julian Day?
 454  
 455  =item *
 456  
 457  How do I find yesterday's date?
 458  
 459  =item *
 460  
 461  Does Perl have a Year 2000 problem? Is Perl Y2K compliant?
 462  
 463  =item *
 464  
 465  How do I validate input?
 466  
 467  =item *
 468  
 469  How do I unescape a string?
 470  
 471  =item *
 472  
 473  How do I remove consecutive pairs of characters?
 474  
 475  =item *
 476  
 477  How do I expand function calls in a string?
 478  
 479  =item *
 480  
 481  How do I find matching/nesting anything?
 482  
 483  =item *
 484  
 485  How do I reverse a string?
 486  
 487  =item *
 488  
 489  How do I expand tabs in a string?
 490  
 491  =item *
 492  
 493  How do I reformat a paragraph?
 494  
 495  =item *
 496  
 497  How can I access or change N characters of a string?
 498  
 499  =item *
 500  
 501  How do I change the Nth occurrence of something?
 502  
 503  =item *
 504  
 505  How can I count the number of occurrences of a substring within a string?
 506  
 507  =item *
 508  
 509  How do I capitalize all the words on one line?
 510  
 511  =item *
 512  
 513  How can I split a [character] delimited string except when inside [character]?
 514  
 515  =item *
 516  
 517  How do I strip blank space from the beginning/end of a string?
 518  
 519  =item *
 520  
 521  How do I pad a string with blanks or pad a number with zeroes?
 522  
 523  =item *
 524  
 525  How do I extract selected columns from a string?
 526  
 527  =item *
 528  
 529  How do I find the soundex value of a string?
 530  
 531  =item *
 532  
 533  How can I expand variables in text strings?
 534  
 535  =item *
 536  
 537  What's wrong with always quoting "$vars"?
 538  
 539  =item *
 540  
 541  Why don't my E<lt>E<lt>HERE documents work?
 542  
 543  =item *
 544  
 545  What is the difference between a list and an array?
 546  
 547  =item *
 548  
 549  What is the difference between $array[1] and @array[1]?
 550  
 551  =item *
 552  
 553  How can I remove duplicate elements from a list or array?
 554  
 555  =item *
 556  
 557  How can I tell whether a certain element is contained in a list or array?
 558  
 559  =item *
 560  
 561  How do I compute the difference of two arrays?  How do I compute the intersection of two arrays?
 562  
 563  =item *
 564  
 565  How do I test whether two arrays or hashes are equal?
 566  
 567  =item *
 568  
 569  How do I find the first array element for which a condition is true?
 570  
 571  =item *
 572  
 573  How do I handle linked lists?
 574  
 575  =item *
 576  
 577  How do I handle circular lists?
 578  
 579  =item *
 580  
 581  How do I shuffle an array randomly?
 582  
 583  =item *
 584  
 585  How do I process/modify each element of an array?
 586  
 587  =item *
 588  
 589  How do I select a random element from an array?
 590  
 591  =item *
 592  
 593  How do I permute N elements of a list?
 594  
 595  =item *
 596  
 597  How do I sort an array by (anything)?
 598  
 599  =item *
 600  
 601  How do I manipulate arrays of bits?
 602  
 603  =item *
 604  
 605  Why does defined() return true on empty arrays and hashes?
 606  
 607  =item *
 608  
 609  How do I process an entire hash?
 610  
 611  =item *
 612  
 613  What happens if I add or remove keys from a hash while iterating over it?
 614  
 615  =item *
 616  
 617  How do I look up a hash element by value?
 618  
 619  =item *
 620  
 621  How can I know how many entries are in a hash?
 622  
 623  =item *
 624  
 625  How do I sort a hash (optionally by value instead of key)?
 626  
 627  =item *
 628  
 629  How can I always keep my hash sorted?
 630  
 631  =item *
 632  
 633  What's the difference between "delete" and "undef" with hashes?
 634  
 635  =item *
 636  
 637  Why don't my tied hashes make the defined/exists distinction?
 638  
 639  =item *
 640  
 641  How do I reset an each() operation part-way through?
 642  
 643  =item *
 644  
 645  How can I get the unique keys from two hashes?
 646  
 647  =item *
 648  
 649  How can I store a multidimensional array in a DBM file?
 650  
 651  =item *
 652  
 653  How can I make my hash remember the order I put elements into it?
 654  
 655  =item *
 656  
 657  Why does passing a subroutine an undefined element in a hash create it?
 658  
 659  =item *
 660  
 661  How can I make the Perl equivalent of a C structure/C++ class/hash or array of hashes or arrays?
 662  
 663  =item *
 664  
 665  How can I use a reference as a hash key?
 666  
 667  =item *
 668  
 669  How do I handle binary data correctly?
 670  
 671  =item *
 672  
 673  How do I determine whether a scalar is a number/whole/integer/float?
 674  
 675  =item *
 676  
 677  How do I keep persistent data across program calls?
 678  
 679  =item *
 680  
 681  How do I print out or copy a recursive data structure?
 682  
 683  =item *
 684  
 685  How do I define methods for every class/object?
 686  
 687  =item *
 688  
 689  How do I verify a credit card checksum?
 690  
 691  =item *
 692  
 693  How do I pack arrays of doubles or floats for XS code?
 694  
 695  =back
 696  
 697  
 698  =head2 L<perlfaq5>: Files and Formats
 699  
 700  I/O and the "f" issues: filehandles, flushing, formats, and footers.
 701  
 702  =over 4
 703  
 704  =item *
 705  
 706  How do I flush/unbuffer an output filehandle?  Why must I do this?
 707  
 708  =item *
 709  
 710  How do I change, delete, or insert a line in a file, or append to the beginning of a file?
 711  
 712  =item *
 713  
 714  How do I count the number of lines in a file?
 715  
 716  =item *
 717  
 718  How can I use Perl's C<-i> option from within a program?
 719  
 720  =item *
 721  
 722  How can I copy a file?
 723  
 724  =item *
 725  
 726  How do I make a temporary file name?
 727  
 728  =item *
 729  
 730  How can I manipulate fixed-record-length files?
 731  
 732  =item *
 733  
 734  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?
 735  
 736  =item *
 737  
 738  How can I use a filehandle indirectly?
 739  
 740  =item *
 741  
 742  How can I set up a footer format to be used with write()?
 743  
 744  =item *
 745  
 746  How can I write() into a string?
 747  
 748  =item *
 749  
 750  How can I open a filehandle to a string?
 751  
 752  =item *
 753  
 754  How can I output my numbers with commas added?
 755  
 756  =item *
 757  
 758  How can I translate tildes (~) in a filename?
 759  
 760  =item *
 761  
 762  How come when I open a file read-write it wipes it out?
 763  
 764  =item *
 765  
 766  Why do I sometimes get an "Argument list too long" when I use E<lt>*E<gt>?
 767  
 768  =item *
 769  
 770  Is there a leak/bug in glob()?
 771  
 772  =item *
 773  
 774  How can I open a file with a leading ">" or trailing blanks?
 775  
 776  =item *
 777  
 778  How can I reliably rename a file?
 779  
 780  =item *
 781  
 782  How can I lock a file?
 783  
 784  =item *
 785  
 786  Why can't I just open(FH, "E<gt>file.lock")?
 787  
 788  =item *
 789  
 790  I still don't get locking.  I just want to increment the number in the file.  How can I do this?
 791  
 792  =item *
 793  
 794  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?
 795  
 796  =item *
 797  
 798  How do I randomly update a binary file?
 799  
 800  =item *
 801  
 802  How do I get a file's timestamp in perl?
 803  
 804  =item *
 805  
 806  How do I set a file's timestamp in perl?
 807  
 808  =item *
 809  
 810  How do I print to more than one file at once?
 811  
 812  =item *
 813  
 814  How can I read in an entire file all at once?
 815  
 816  =item *
 817  
 818  How can I read in a file by paragraphs?
 819  
 820  =item *
 821  
 822  How can I read a single character from a file?  From the keyboard?
 823  
 824  =item *
 825  
 826  How can I tell whether there's a character waiting on a filehandle?
 827  
 828  =item *
 829  
 830  How do I do a C<tail -f> in perl?
 831  
 832  =item *
 833  
 834  How do I dup() a filehandle in Perl?
 835  
 836  =item *
 837  
 838  How do I close a file descriptor by number?
 839  
 840  =item *
 841  
 842  Why can't I use "C:\temp\foo" in DOS paths?  Why doesn't `C:\temp\foo.exe` work?
 843  
 844  =item *
 845  
 846  Why doesn't glob("*.*") get all the files?
 847  
 848  =item *
 849  
 850  Why does Perl let me delete read-only files?  Why does C<-i> clobber protected files?  Isn't this a bug in Perl?
 851  
 852  =item *
 853  
 854  How do I select a random line from a file?
 855  
 856  =item *
 857  
 858  Why do I get weird spaces when I print an array of lines?
 859  
 860  =back
 861  
 862  
 863  =head2 L<perlfaq6>: Regular Expressions
 864  
 865  This section is surprisingly small because the rest of the FAQ is littered with answers involving regular expressions. For example, decoding a URL and checking whether something is a number are handled with regular expressions, but those answers are found elsewhere in this document (in L<perlfaq9>: "How do I decode or create those %-encodings on the web" and L<perlfaq4>: "How do I determine whether a scalar is a number/whole/integer/float", to be precise).
 866  
 867  =over 4
 868  
 869  =item *
 870  
 871  How can I hope to use regular expressions without creating illegible and unmaintainable code?
 872  
 873  =item *
 874  
 875  I'm having trouble matching over more than one line.  What's wrong?
 876  
 877  =item *
 878  
 879  How can I pull out lines between two patterns that are themselves on different lines?
 880  
 881  =item *
 882  
 883  I put a regular expression into $/ but it didn't work. What's wrong?
 884  
 885  =item *
 886  
 887  How do I substitute case insensitively on the LHS while preserving case on the RHS?
 888  
 889  =item *
 890  
 891  How can I make C<\w> match national character sets?
 892  
 893  =item *
 894  
 895  How can I match a locale-smart version of C</[a-zA-Z]/>?
 896  
 897  =item *
 898  
 899  How can I quote a variable to use in a regex?
 900  
 901  =item *
 902  
 903  What is C</o> really for?
 904  
 905  =item *
 906  
 907  How do I use a regular expression to strip C style comments from a file?
 908  
 909  =item *
 910  
 911  Can I use Perl regular expressions to match balanced text?
 912  
 913  =item *
 914  
 915  What does it mean that regexes are greedy?  How can I get around it?
 916  
 917  =item *
 918  
 919  How do I process each word on each line?
 920  
 921  =item *
 922  
 923  How can I print out a word-frequency or line-frequency summary?
 924  
 925  =item *
 926  
 927  How can I do approximate matching?
 928  
 929  =item *
 930  
 931  How do I efficiently match many regular expressions at once?
 932  
 933  =item *
 934  
 935  Why don't word-boundary searches with C<\b> work for me?
 936  
 937  =item *
 938  
 939  Why does using $&, $`, or $' slow my program down?
 940  
 941  =item *
 942  
 943  What good is C<\G> in a regular expression?
 944  
 945  =item *
 946  
 947  Are Perl regexes DFAs or NFAs?  Are they POSIX compliant?
 948  
 949  =item *
 950  
 951  What's wrong with using grep in a void context?
 952  
 953  =item *
 954  
 955  How can I match strings with multibyte characters?
 956  
 957  =item *
 958  
 959  How do I match a regular expression that's in a variable?
 960  
 961  =back
 962  
 963  
 964  =head2 L<perlfaq7>: General Perl Language Issues
 965  
 966  General Perl language issues that don't clearly fit into any of the other sections.
 967  
 968  =over 4
 969  
 970  =item *
 971  
 972  Can I get a BNF/yacc/RE for the Perl language?
 973  
 974  =item *
 975  
 976  What are all these $@%&* punctuation signs, and how do I know when to use them?
 977  
 978  =item *
 979  
 980  Do I always/never have to quote my strings or use semicolons and commas?
 981  
 982  =item *
 983  
 984  How do I skip some return values?
 985  
 986  =item *
 987  
 988  How do I temporarily block warnings?
 989  
 990  =item *
 991  
 992  What's an extension?
 993  
 994  =item *
 995  
 996  Why do Perl operators have different precedence than C operators?
 997  
 998  =item *
 999  
1000  How do I declare/create a structure?
1001  
1002  =item *
1003  
1004  How do I create a module?
1005  
1006  =item *
1007  
1008  How do I adopt or take over a module already on CPAN?
1009  
1010  =item *
1011  
1012  How do I create a class?
1013  
1014  =item *
1015  
1016  How can I tell if a variable is tainted?
1017  
1018  =item *
1019  
1020  What's a closure?
1021  
1022  =item *
1023  
1024  What is variable suicide and how can I prevent it?
1025  
1026  =item *
1027  
1028  How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}?
1029  
1030  =item *
1031  
1032  How do I create a static variable?
1033  
1034  =item *
1035  
1036  What's the difference between dynamic and lexical (static) scoping?  Between local() and my()?
1037  
1038  =item *
1039  
1040  How can I access a dynamic variable while a similarly named lexical is in scope?
1041  
1042  =item *
1043  
1044  What's the difference between deep and shallow binding?
1045  
1046  =item *
1047  
1048  Why doesn't "my($foo) = E<lt>FILEE<gt>;" work right?
1049  
1050  =item *
1051  
1052  How do I redefine a builtin function, operator, or method?
1053  
1054  =item *
1055  
1056  What's the difference between calling a function as &foo and foo()?
1057  
1058  =item *
1059  
1060  How do I create a switch or case statement?
1061  
1062  =item *
1063  
1064  How can I catch accesses to undefined variables, functions, or methods?
1065  
1066  =item *
1067  
1068  Why can't a method included in this same file be found?
1069  
1070  =item *
1071  
1072  How can I find out my current package?
1073  
1074  =item *
1075  
1076  How can I comment out a large block of perl code?
1077  
1078  =item *
1079  
1080  How do I clear a package?
1081  
1082  =item *
1083  
1084  How can I use a variable as a variable name?
1085  
1086  =item *
1087  
1088  What does "bad interpreter" mean?
1089  
1090  =back
1091  
1092  
1093  =head2 L<perlfaq8>: System Interaction
1094  
1095  This section of the Perl FAQ covers questions involving operating system interaction. Topics include interprocess communication (IPC), control over the user-interface (keyboard, screen and pointing devices), and most anything else not related to data manipulation. Read the FAQs and documentation specific to the port of perl to your operating system (eg, L<perlvms>, L<perlplan9>, ...). These should contain more detailed information on the vagaries of your perl.
1096  
1097  =over 4
1098  
1099  =item *
1100  
1101  How do I find out which operating system I'm running under?
1102  
1103  =item *
1104  
1105  How come exec() doesn't return?
1106  
1107  =item *
1108  
1109  How do I do fancy stuff with the keyboard/screen/mouse?
1110  
1111  =item *
1112  
1113  How do I print something out in color?
1114  
1115  =item *
1116  
1117  How do I read just one key without waiting for a return key?
1118  
1119  =item *
1120  
1121  How do I check whether input is ready on the keyboard?
1122  
1123  =item *
1124  
1125  How do I clear the screen?
1126  
1127  =item *
1128  
1129  How do I get the screen size?
1130  
1131  =item *
1132  
1133  How do I ask the user for a password?
1134  
1135  =item *
1136  
1137  How do I read and write the serial port?
1138  
1139  =item *
1140  
1141  How do I decode encrypted password files?
1142  
1143  =item *
1144  
1145  How do I start a process in the background?
1146  
1147  =item *
1148  
1149  How do I trap control characters/signals?
1150  
1151  =item *
1152  
1153  How do I modify the shadow password file on a Unix system?
1154  
1155  =item *
1156  
1157  How do I set the time and date?
1158  
1159  =item *
1160  
1161  How can I sleep() or alarm() for under a second?
1162  
1163  =item *
1164  
1165  How can I measure time under a second?
1166  
1167  =item *
1168  
1169  How can I do an atexit() or setjmp()/longjmp()? (Exception handling)
1170  
1171  =item *
1172  
1173  Why doesn't my sockets program work under System V (Solaris)?  What does the error message "Protocol not supported" mean?
1174  
1175  =item *
1176  
1177  How can I call my system's unique C functions from Perl?
1178  
1179  =item *
1180  
1181  Where do I get the include files to do ioctl() or syscall()?
1182  
1183  =item *
1184  
1185  Why do setuid perl scripts complain about kernel problems?
1186  
1187  =item *
1188  
1189  How can I open a pipe both to and from a command?
1190  
1191  =item *
1192  
1193  Why can't I get the output of a command with system()?
1194  
1195  =item *
1196  
1197  How can I capture STDERR from an external command?
1198  
1199  =item *
1200  
1201  Why doesn't open() return an error when a pipe open fails?
1202  
1203  =item *
1204  
1205  What's wrong with using backticks in a void context?
1206  
1207  =item *
1208  
1209  How can I call backticks without shell processing?
1210  
1211  =item *
1212  
1213  Why can't my script read from STDIN after I gave it EOF (^D on Unix, ^Z on MS-DOS)?
1214  
1215  =item *
1216  
1217  How can I convert my shell script to perl?
1218  
1219  =item *
1220  
1221  Can I use perl to run a telnet or ftp session?
1222  
1223  =item *
1224  
1225  How can I write expect in Perl?
1226  
1227  =item *
1228  
1229  Is there a way to hide perl's command line from programs such as "ps"?
1230  
1231  =item *
1232  
1233  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?
1234  
1235  =item *
1236  
1237  How do I close a process's filehandle without waiting for it to complete?
1238  
1239  =item *
1240  
1241  How do I fork a daemon process?
1242  
1243  =item *
1244  
1245  How do I find out if I'm running interactively or not?
1246  
1247  =item *
1248  
1249  How do I timeout a slow event?
1250  
1251  =item *
1252  
1253  How do I set CPU limits?
1254  
1255  =item *
1256  
1257  How do I avoid zombies on a Unix system?
1258  
1259  =item *
1260  
1261  How do I use an SQL database?
1262  
1263  =item *
1264  
1265  How do I make a system() exit on control-C?
1266  
1267  =item *
1268  
1269  How do I open a file without blocking?
1270  
1271  =item *
1272  
1273  How do I tell the difference between errors from the shell and perl?
1274  
1275  =item *
1276  
1277  How do I install a module from CPAN?
1278  
1279  =item *
1280  
1281  What's the difference between require and use?
1282  
1283  =item *
1284  
1285  How do I keep my own module/library directory?
1286  
1287  =item *
1288  
1289  How do I add the directory my program lives in to the module/library search path?
1290  
1291  =item *
1292  
1293  How do I add a directory to my include path (@INC) at runtime?
1294  
1295  =item *
1296  
1297  What is socket.ph and where do I get it?
1298  
1299  =back
1300  
1301  
1302  =head2 L<perlfaq9>: Networking
1303  
1304  Networking, the internet, and a few on the web.
1305  
1306  =over 4
1307  
1308  =item *
1309  
1310  What is the correct form of response from a CGI script?
1311  
1312  =item *
1313  
1314  My CGI script runs from the command line but not the browser.  (500 Server Error)
1315  
1316  =item *
1317  
1318  How can I get better error messages from a CGI program?
1319  
1320  =item *
1321  
1322  How do I remove HTML from a string?
1323  
1324  =item *
1325  
1326  How do I extract URLs?
1327  
1328  =item *
1329  
1330  How do I download a file from the user's machine?  How do I open a file on another machine?
1331  
1332  =item *
1333  
1334  How do I make an HTML pop-up menu with Perl?
1335  
1336  =item *
1337  
1338  How do I fetch an HTML file?
1339  
1340  =item *
1341  
1342  How do I automate an HTML form submission?
1343  
1344  =item *
1345  
1346  How do I decode or create those %-encodings on the web?
1347  
1348  =item *
1349  
1350  How do I redirect to another page?
1351  
1352  =item *
1353  
1354  How do I put a password on my web pages?
1355  
1356  =item *
1357  
1358  How do I edit my .htpasswd and .htgroup files with Perl?
1359  
1360  =item *
1361  
1362  How do I make sure users can't enter values into a form that cause my CGI script to do bad things?
1363  
1364  =item *
1365  
1366  How do I parse a mail header?
1367  
1368  =item *
1369  
1370  How do I decode a CGI form?
1371  
1372  =item *
1373  
1374  How do I check a valid mail address?
1375  
1376  =item *
1377  
1378  How do I decode a MIME/BASE64 string?
1379  
1380  =item *
1381  
1382  How do I return the user's mail address?
1383  
1384  =item *
1385  
1386  How do I send mail?
1387  
1388  =item *
1389  
1390  How do I use MIME to make an attachment to a mail message?
1391  
1392  =item *
1393  
1394  How do I read mail?
1395  
1396  =item *
1397  
1398  How do I find out my hostname, domainname, or IP address?
1399  
1400  =item *
1401  
1402  How do I fetch a news article or the active newsgroups?
1403  
1404  =item *
1405  
1406  How do I fetch/put an FTP file?
1407  
1408  =item *
1409  
1410  How can I do RPC in Perl?
1411  
1412  =back
1413  
1414