📄 perlfaq.pod
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=item *How can I read a single character from a file? From the keyboard?=item *How can I tell whether there's a character waiting on a filehandle?=item *How do I do a C<tail -f> in perl?=item *How do I dup() a filehandle in Perl?=item *How do I close a file descriptor by number?=item *Why can't I use "C:\temp\foo" in DOS paths? What doesn't `C:\temp\foo.exe` work?=item *Why doesn't glob("*.*") get all the files?=item *Why does Perl let me delete read-only files? Why does C<-i> clobber protected files? Isn't this a bug in Perl?=item *How do I select a random line from a file?=item *Why do I get weird spaces when I print an array of lines?=back=head2 L<perlfaq6>: RegexpsPattern matching and regular expressions.=over 4=item *How can I hope to use regular expressions without creating illegible and unmaintainable code?=item *I'm having trouble matching over more than one line. What's wrong?=item *How can I pull out lines between two patterns that are themselves on different lines?=item *I put a regular expression into $/ but it didn't work. What's wrong?=item *How do I substitute case insensitively on the LHS while preserving case on the RHS?=item *How can I make C<\w> match national character sets?=item *How can I match a locale-smart version of C</[a-zA-Z]/>?=item *How can I quote a variable to use in a regex?=item *What is C</o> really for?=item *How do I use a regular expression to strip C style comments from a file?=item *Can I use Perl regular expressions to match balanced text?=item *What does it mean that regexes are greedy? How can I get around it?=item *How do I process each word on each line?=item *How can I print out a word-frequency or line-frequency summary?=item *How can I do approximate matching?=item *How do I efficiently match many regular expressions at once?=item *Why don't word-boundary searches with C<\b> work for me?=item *Why does using $&, $`, or $' slow my program down?=item *What good is C<\G> in a regular expression?=item *Are Perl regexes DFAs or NFAs? Are they POSIX compliant?=item *What's wrong with using grep or map in a void context?=item *How can I match strings with multibyte characters?=item *How do I match a pattern that is supplied by the user?=back=head2 L<perlfaq7>: General Perl Language IssuesGeneral Perl language issues that don't clearly fit into any of theother sections.=over 4=item *Can I get a BNF/yacc/RE for the Perl language?=item *What are all these $@%&* punctuation signs, and how do I know when to use them?=item *Do I always/never have to quote my strings or use semicolons and commas?=item *How do I skip some return values?=item *How do I temporarily block warnings?=item *What's an extension?=item *Why do Perl operators have different precedence than C operators?=item *How do I declare/create a structure?=item *How do I create a module?=item *How do I create a class?=item *How can I tell if a variable is tainted?=item *What's a closure?=item *What is variable suicide and how can I prevent it?=item *How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}?=item *How do I create a static variable?=item *What's the difference between dynamic and lexical (static) scoping? Between local() and my()?=item *How can I access a dynamic variable while a similarly named lexical is in scope?=item *What's the difference between deep and shallow binding?=item *Why doesn't "my($foo) = <FILE>;" work right?=item *How do I redefine a builtin function, operator, or method?=item *What's the difference between calling a function as &foo and foo()?=item *How do I create a switch or case statement?=item *How can I catch accesses to undefined variables/functions/methods?=item *Why can't a method included in this same file be found?=item *How can I find out my current package?=item *How can I comment out a large block of perl code?=item *How do I clear a package?=item *How can I use a variable as a variable name?=back=head2 L<perlfaq8>: System InteractionInterprocess communication (IPC), control over the user-interface(keyboard, screen and pointing devices).=over 4=item *How do I find out which operating system I'm running under?=item *How come exec() doesn't return?=item *How do I do fancy stuff with the keyboard/screen/mouse?=item *How do I print something out in color?=item *How do I read just one key without waiting for a return key?=item *How do I check whether input is ready on the keyboard?=item *How do I clear the screen?=item *How do I get the screen size?=item *How do I ask the user for a password?=item *How do I read and write the serial port?=item *How do I decode encrypted password files?=item *How do I start a process in the background?=item *How do I trap control characters/signals?=item *How do I modify the shadow password file on a Unix system?=item *How do I set the time and date?=item *How can I sleep() or alarm() for under a second?=item *How can I measure time under a second?=item *How can I do an atexit() or setjmp()/longjmp()? (Exception handling)=item *Why doesn't my sockets program work under System V (Solaris)? What does the error message "Protocol not supported" mean?=item *How can I call my system's unique C functions from Perl?=item *Where do I get the include files to do ioctl() or syscall()?=item *Why do setuid perl scripts complain about kernel problems?=item *How can I open a pipe both to and from a command?=item *Why can't I get the output of a command with system()?=item *How can I capture STDERR from an external command?=item *Why doesn't open() return an error when a pipe open fails?=item *What's wrong with using backticks in a void context?=item *How can I call backticks without shell processing?=item *Why can't my script read from STDIN after I gave it EOF (^D on Unix, ^Z on MS-DOS)?=item *How can I convert my shell script to perl?=item *Can I use perl to run a telnet or ftp session?=item *How can I write expect in Perl?=item *Is there a way to hide perl's command line from programs such as "ps"?=item *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?=item *How do I close a process's filehandle without waiting for it to complete?=item *How do I fork a daemon process?=item *How do I find out if I'm running interactively or not?=item *How do I timeout a slow event?=item *How do I set CPU limits?=item *How do I avoid zombies on a Unix system?=item *How do I use an SQL database?=item *How do I make a system() exit on control-C?=item *How do I open a file without blocking?=item *How do I install a module from CPAN?=item *What's the difference between require and use?=item *How do I keep my own module/library directory?=item *How do I add the directory my program lives in to the module/library search path?=item *How do I add a directory to my include path at runtime?=item *What is socket.ph and where do I get it?=back=head2 L<perlfaq9>: NetworkingNetworking, the Internet, and a few on the web.=over 4=item *My CGI script runs from the command line but not the browser. (500 Server Error)=item *How can I get better error messages from a CGI program?=item *How do I remove HTML from a string?=item *How do I extract URLs?=item *How do I download a file from the user's machine? How do I open a file on another machine?=item *How do I make a pop-up menu in HTML?=item *How do I fetch an HTML file?=item *How do I automate an HTML form submission?=item *How do I decode or create those %-encodings on the web?=item *How do I redirect to another page?=item *How do I put a password on my web pages?=item *How do I edit my .htpasswd and .htgroup files with Perl?=item *How do I make sure users can't enter values into a form that cause my CGI script to do bad things?=item *How do I parse a mail header?=item *How do I decode a CGI form?=item *How do I check a valid mail address?=item *How do I decode a MIME/BASE64 string?=item *How do I return the user's mail address?=item *How do I send mail?=item *How do I read mail?=item *How do I find out my hostname/domainname/IP address?=item *How do I fetch a news article or the active newsgroups?=item *How do I fetch/put an FTP file?=item *How can I do RPC in Perl?=back=head1 About the perlfaq documents=head2 Where to get the perlfaqThis document is posted regularly to comp.lang.perl.announce andseveral other related newsgroups. It is available in a variety offormats from CPAN in the /CPAN/doc/FAQs/FAQ/ directory or on the webat http://www.perl.com/perl/faq/ .=head2 How to contribute to the perlfaqYou may mail corrections, additions, and suggestions toperlfaq-suggestions@perl.com . This alias should not be used to I<ask> FAQs. It's for fixing the current FAQ.Send questions to the comp.lang.perl.misc newsgroup.=head2 What will happen if you mail your Perl programming problems to the authorsYour questions will probably go unread, unless they're suggestions ofnew questions to add to the FAQ, in which case they should have goneto the perlfaq-suggestions@perl.com instead.You should have read section 2 of this faq. There you would havelearned that comp.lang.perl.misc is the appropriate place to go forfree advice. If your question is really important and you require aprompt and correct answer, you should hire a consultant.=head1 CreditsWhen I first began the Perl FAQ in the late 80s, I never realized itwould have grown to over a hundred pages, nor that Perl would ever becomeso popular and widespread. This document could not have been writtenwithout the tremendous help provided by Larry Wall and the rest of thePerl Porters.=head1 Author and Copyright InformationCopyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.All rights reserved.=head2 Bundled DistributionsWhen included as part of the Standard Version of Perl or as part ofits complete documentation whether printed or otherwise, this workmay be distributed only under the terms of Perl's Artistic License.Any distribution of this file or derivatives thereof I<outside>of that package requires that special arrangements be made withcopyright holder.Irrespective of its distribution, all code examples in these filesare hereby placed into the public domain. You are permitted andencouraged to use this code in your own programs for funor for profit as you see fit. A simple comment in the code givingcredit would be courteous but is not required.=head2 DisclaimerThis information is offered in good faith and in the hope that it maybe of use, but is not guaranteed to be correct, up to date, or suitablefor any particular purpose whatsoever. The authors accept no liabilityin respect of this information or its use.=head1 Changes=over 4=item 1/November/2000A few grammatical fixes and updates implemented by John Borwick.=item 23/May/99Extensive updates from the net in preparation for 5.6 release.=item 13/April/99More minor touch-ups. Added new question at the endof perlfaq7 on variable names within variables.=item 7/January/99Small touchups here and there. Added all questions in this document as a sort of table of contents.=item 22/June/98Significant changes throughout in preparation for the 5.005release.=item 24/April/97Style and whitespace changes from Chip, new question on reading onecharacter at a time from a terminal using POSIX from Tom.=item 23/April/97Added http://www.oasis.leo.org/perl/ to L<perlfaq2>. Style fix toL<perlfaq3>. Added floating point precision, fixed complex numberarithmetic, cross-references, caveat for Text::Wrap, alternativeanswer for initial capitalizing, fixed incorrect regexp, added exampleof Tie::IxHash to L<perlfaq4>. Added example of passing and storingfilehandles, added commify to L<perlfaq5>. Restored variable suicide,and added mass commenting to L<perlfaq7>. Added Net::Telnet, fixedbackticks, added reader/writer pair to telnet question, added FindBin,grouped module questions together in L<perlfaq8>. Expanded caveatsfor the simple URL extractor, gave LWP example, added CGI securityquestion, expanded on the mail address answer in L<perlfaq9>.=item 25/March/97Added more info to the binary distribution section of L<perlfaq2>.Added Net::Telnet to L<perlfaq6>. Fixed typos in L<perlfaq8>. Addedmail sending example to L<perlfaq9>. Added Merlyn's columns toL<perlfaq2>.=item 18/March/97Added the DATE to the NAME section, indicating which sections havechanged.Mentioned SIGPIPE and L<perlipc> in the forking open answer inL<perlfaq8>.Fixed description of a regular expression in L<perlfaq4>.=item 17/March/97 VersionVarious typos fixed throughout.Added new question on Perl BNF on L<perlfaq7>.=item Initial Release: 11/March/97This is the initial release of version 3 of the FAQ; consequently therehave been no changes since its initial release.=back⌨️ 快捷键说明
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