📄 perlfaq.pod
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How do I change, delete, or insert a line in a file, or append to the beginning of a file?=item *How do I count the number of lines in a file?=item *How can I use Perl's C<-i> option from within a program?=item *How can I copy a file?=item *How do I make a temporary file name?=item *How can I manipulate fixed-record-length files?=item *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?=item *How can I use a filehandle indirectly?=item *How can I set up a footer format to be used with write()?=item *How can I write() into a string?=item *How can I open a filehandle to a string?=item *How can I output my numbers with commas added?=item *How can I translate tildes (~) in a filename?=item *How come when I open a file read-write it wipes it out?=item *Why do I sometimes get an "Argument list too long" when I use E<lt>*E<gt>?=item *Is there a leak/bug in glob()?=item *How can I open a file with a leading ">" or trailing blanks?=item *How can I reliably rename a file?=item *How can I lock a file?=item *Why can't I just open(FH, "E<gt>file.lock")?=item *I still don't get locking. I just want to increment the number in the file. How can I do this?=item *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?=item *How do I randomly update a binary file?=item *How do I get a file's timestamp in perl?=item *How do I set a file's timestamp in perl?=item *How do I print to more than one file at once?=item *How can I read in an entire file all at once?=item *How can I read in a file by paragraphs?=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? Why 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>: Regular ExpressionsThis 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).=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 in a void context?=item *How can I match strings with multibyte characters?=item *How do I match a regular expression that's in a variable?=back=head2 L<perlfaq7>: General Perl Language IssuesGeneral Perl language issues that don't clearly fit into any of the other sections.=over 4=item *Can I get a BNF/yacc/RE for the Perl language?=item *What are all these $@%&* punctuation signs, and how do I know when to use them?=item *Do I always/never have to quote my strings or use semicolons and commas?=item *How do I skip some return values?=item *How do I temporarily block warnings?=item *What's an extension?=item *Why do Perl operators have different precedence than C operators?=item *How do I declare/create a structure?=item *How do I create a module?=item *How do I adopt or take over a module already on CPAN?=item *How do I create a class?=item *How can I tell if a variable is tainted?=item *What's a closure?=item *What is variable suicide and how can I prevent it?=item *How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}?=item *How do I create a static variable?=item *What's the difference between dynamic and lexical (static) scoping? Between local() and my()?=item *How can I access a dynamic variable while a similarly named lexical is in scope?=item *What's the difference between deep and shallow binding?=item *Why doesn't "my($foo) = E<lt>FILEE<gt>;" 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, or 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?=item *What does "bad interpreter" mean?=back=head2 L<perlfaq8>: System InteractionThis 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.=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 tell the difference between errors from the shell and perl?=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 (@INC) 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 *What is the correct form of response from a CGI script?=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 an HTML pop-up menu with Perl?=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 use MIME to make an attachment to a mail message?=item *How do I read mail?=item *How do I find out my hostname, domainname, or 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⌨️ 快捷键说明
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