📄 perlfaq.pod
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=head1 NAMEperlfaq - frequently asked questions about Perl=head1 DESCRIPTIONThe perlfaq comprises several documents that answer the most commonlyasked questions about Perl and Perl programming. It's divided by topicinto nine major sections outlined in this document.=head2 Where to get the perlfaqThe perlfaq comes with the standard Perl distribution, so if you have Perlyou should have the perlfaq. You should also have the C<perldoc> toolthat let's you read the L<perlfaq>: $ perldoc perlfaqBesides your local system, you can find the perlfaq on the web, includingat http://perldoc.perl.org/ .The perlfaq is an evolving document and you can read the latest versionat http://faq.perl.org/ . The perlfaq-workers periodically post extractsof the latest perlfaq to comp.lang.perl.misc.You can view the source tree athttps://svn.perl.org/modules/perlfaq/trunk/ (which is outside of themain Perl source tree). The SVN repository notes all changes to the FAQand holds the latest version of the working documents and may varysignificantly from the version distributed with the latest version ofPerl. Check the repository before sending your corrections.=head2 How to contribute to the perlfaqYou can mail corrections, additions, and suggestions toC<< <perlfaq-workers AT perl DOT org> >>. The perlfaq volunteers use thisaddress to coordinate their efforts and track the perlfaq development.They appreciate your contributions to the FAQ but do not have time toprovide individual help, so don't use this address to ask FAQs.The perlfaq server posts extracts of the perlfaq to that newsgroup every6 hours (or so), and the community of volunteers reviews and updates theanswers. If you'd like to help review and update the answers, check outcomp.lang.perl.misc.=head2 What will happen if you mail your Perl programming problems to the authors?The perlfaq-workers like to keep all traffic on the perlfaq-workers listso that everyone can see the work being done (and the work that needs tobe done). The mailing list serves as an official record. If you email theauthors or maintainers directly, you'll probably get a reply asking youto post to the mailing list. If you don't get a reply, it probably meansthat the person never saw the message or didn't have time to deal withit. Posting to the list allows the volunteers with time to deal with itwhen others are busy.If you have a question that isn't in the FAQ and you would like help withit, try the resources in L<perlfaq2>.=head1 CREDITSTom Christiansen wrote the original perlfaq then expanded it with thehelp of Nat Torkington. The perlfaq-workers maintain current documentand the denizens of comp.lang.perl.misc regularly review and update theFAQ. Several people have contributed answers, corrections, and comments,and the perlfaq notes those contributions wherever appropriate.=head1 AUTHOR AND COPYRIGHTTom Christiansen wrote the original version of this document.brian d foy C<< <bdfoy@cpan.org> >> wrote this version. See theindividual perlfaq documents for additional copyright information.This document is available under the same terms as Perl itself. Codeexamples in all the perlfaq documents are in the public domain. Usethem as you see fit (and at your own risk with no warranty from anyone).=head1 Table of Contents=over 4=item perlfaq - this document=item perlfaq1 - General Questions About Perl=item perlfaq2 - Obtaining and Learning about Perl=item perlfaq3 - Programming Tools=item perlfaq4 - Data Manipulation=item perlfaq5 - Files and Formats=item perlfaq6 - Regular Expressions=item perlfaq7 - General Perl Language Issues=item perlfaq8 - System Interaction=item perlfaq9 - Networking=back=head1 The Questions=head2 L<perlfaq1>: General Questions About PerlVery general, high-level questions about Perl.=over 4=item *What is Perl?=item *Who supports Perl? Who develops it? Why is it free?=item *Which version of Perl should I use?=item *What are Perl 4, Perl 5, or Perl 6?=item *What was Ponie?=item *What is Perl 6?=item *How stable is Perl?=item *Is Perl difficult to learn?=item *How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl?=item *Can I do [task] in Perl?=item *When shouldn't I program in Perl?=item *What's the difference between "perl" and "Perl"?=item *Is it a Perl program or a Perl script?=item *What is a JAPH?=item *Where can I get a list of Larry Wall witticisms?=item *How can I convince others to use Perl?=back=head2 L<perlfaq2>: Obtaining and Learning about PerlWhere to find source and documentation for Perl, support, and related matters.=over 4=item *What machines support perl? Where do I get it?=item *How can I get a binary version of perl?=item *I don't have a C compiler. How can I build my own Perl interpreter?=item *I copied the perl binary from one machine to another, but scripts don't work.=item *I grabbed the sources and tried to compile but gdbm/dynamic loading/malloc/linking/... failed. How do I make it work?=item *What modules and extensions are available for Perl? What is CPAN? What does CPAN/src/... mean?=item *Is there an ISO or ANSI certified version of Perl?=item *Where can I get information on Perl?=item *What are the Perl newsgroups on Usenet? Where do I post questions?=item *Where should I post source code?=item *Perl Books=item *Which magazines have Perl content?=item *What mailing lists are there for Perl?=item *Where are the archives for comp.lang.perl.misc?=item *Where can I buy a commercial version of perl?=item *Where do I send bug reports?=item *What is perl.com? Perl Mongers? pm.org? perl.org? cpan.org?=back=head2 L<perlfaq3>: Programming ToolsProgrammer tools and programming support.=over 4=item *How do I do (anything)?=item *How can I use Perl interactively?=item *Is there a Perl shell?=item *How do I find which modules are installed on my system?=item *How do I debug my Perl programs?=item *How do I profile my Perl programs?=item *How do I cross-reference my Perl programs?=item *Is there a pretty-printer (formatter) for Perl?=item *Is there a ctags for Perl?=item *Is there an IDE or Windows Perl Editor?=item *Where can I get Perl macros for vi?=item *Where can I get perl-mode for emacs?=item *How can I use curses with Perl?=item *How can I write a GUI (X, Tk, Gtk, etc.) in Perl?=item *How can I make my Perl program run faster?=item *How can I make my Perl program take less memory?=item *Is it safe to return a reference to local or lexical data?=item *How can I free an array or hash so my program shrinks?=item *How can I make my CGI script more efficient?=item *How can I hide the source for my Perl program?=item *How can I compile my Perl program into byte code or C?=item *How can I get C<#!perl> to work on [MS-DOS,NT,...]?=item *Can I write useful Perl programs on the command line?=item *Why don't Perl one-liners work on my DOS/Mac/VMS system?=item *Where can I learn about CGI or Web programming in Perl?=item *Where can I learn about object-oriented Perl programming?=item *Where can I learn about linking C with Perl?=item *I've read perlembed, perlguts, etc., but I can't embed perl in my C program; what am I doing wrong?=item *When I tried to run my script, I got this message. What does it mean?=item *What's MakeMaker?=back=head2 L<perlfaq4>: Data ManipulationManipulating numbers, dates, strings, arrays, hashes, and miscellaneous data issues.=over 4=item *Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?=item *Why is int() broken?=item *Why isn't my octal data interpreted correctly?=item *Does Perl have a round() function? What about ceil() and floor()? Trig functions?=item *How do I convert between numeric representations/bases/radixes?=item *Why doesn't & work the way I want it to?=item *How do I multiply matrices?=item *How do I perform an operation on a series of integers?=item *How can I output Roman numerals?=item *Why aren't my random numbers random?=item *How do I get a random number between X and Y?=item *How do I find the day or week of the year?=item *How do I find the current century or millennium?=item *How can I compare two dates and find the difference?=item *How can I take a string and turn it into epoch seconds?=item *How can I find the Julian Day?=item *How do I find yesterday's date?=item *Does Perl have a Year 2000 problem? Is Perl Y2K compliant?=item *How do I validate input?=item *How do I unescape a string?=item *How do I remove consecutive pairs of characters?=item *How do I expand function calls in a string?=item *How do I find matching/nesting anything?=item *How do I reverse a string?=item *How do I expand tabs in a string?=item *How do I reformat a paragraph?=item *How can I access or change N characters of a string?=item *How do I change the Nth occurrence of something?=item *How can I count the number of occurrences of a substring within a string?=item *How do I capitalize all the words on one line?=item *How can I split a [character] delimited string except when inside [character]?=item *How do I strip blank space from the beginning/end of a string?=item *How do I pad a string with blanks or pad a number with zeroes?=item *How do I extract selected columns from a string?=item *How do I find the soundex value of a string?=item *How can I expand variables in text strings?=item *What's wrong with always quoting "$vars"?=item *Why don't my E<lt>E<lt>HERE documents work?=item *What is the difference between a list and an array?=item *What is the difference between $array[1] and @array[1]?=item *How can I remove duplicate elements from a list or array?=item *How can I tell whether a certain element is contained in a list or array?=item *How do I compute the difference of two arrays? How do I compute the intersection of two arrays?=item *How do I test whether two arrays or hashes are equal?=item *How do I find the first array element for which a condition is true?=item *How do I handle linked lists?=item *How do I handle circular lists?=item *How do I shuffle an array randomly?=item *How do I process/modify each element of an array?=item *How do I select a random element from an array?=item *How do I permute N elements of a list?=item *How do I sort an array by (anything)?=item *How do I manipulate arrays of bits?=item *Why does defined() return true on empty arrays and hashes?=item *How do I process an entire hash?=item *What happens if I add or remove keys from a hash while iterating over it?=item *How do I look up a hash element by value?=item *How can I know how many entries are in a hash?=item *How do I sort a hash (optionally by value instead of key)?=item *How can I always keep my hash sorted?=item *What's the difference between "delete" and "undef" with hashes?=item *Why don't my tied hashes make the defined/exists distinction?=item *How do I reset an each() operation part-way through?=item *How can I get the unique keys from two hashes?=item *How can I store a multidimensional array in a DBM file?=item *How can I make my hash remember the order I put elements into it?=item *Why does passing a subroutine an undefined element in a hash create it?=item *How can I make the Perl equivalent of a C structure/C++ class/hash or array of hashes or arrays?=item *How can I use a reference as a hash key?=item *How do I handle binary data correctly?=item *How do I determine whether a scalar is a number/whole/integer/float?=item *How do I keep persistent data across program calls?=item *How do I print out or copy a recursive data structure?=item *How do I define methods for every class/object?=item *How do I verify a credit card checksum?=item *How do I pack arrays of doubles or floats for XS code?=back=head2 L<perlfaq5>: Files and FormatsI/O and the "f" issues: filehandles, flushing, formats, and footers.=over 4=item *How do I flush/unbuffer an output filehandle? Why must I do this?=item *⌨️ 快捷键说明
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