=head1 NAME
-perlfaq - frequently asked questions about Perl ($Date: 1999/05/23 20:38:02 $)
+perlfaq - frequently asked questions about Perl ($Date: 2004/10/05 22:15:44 $)
=head1 DESCRIPTION
-This document is structured into the following sections:
+The perlfaq is divided into several documents based on topics. A table
+of contents is at the end of this document.
-=over
+=head2 Where to get the perlfaq
-=item perlfaq: Structural overview of the FAQ.
+Extracts of the perlfaq are posted regularly to
+comp.lang.perl.misc. It is available on many web sites:
+http://www.perldoc.com/ and http://faq.perl.org/
-This document.
+=head2 How to contribute to the perlfaq
+
+You may mail corrections, additions, and suggestions to
+perlfaq-workers@perl.org . 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. You can
+view the source tree at http://cvs.perl.org/cvsweb/perlfaq/
+(which is outside of the main Perl source tree). The CVS
+repository notes all changes to the FAQ.
+
+=head2 What will happen if you mail your Perl programming problems to the authors
+
+Your questions will probably go unread, unless they're
+suggestions of new questions to add to the FAQ, in which
+case they should have gone to the perlfaq-workers@perl.org
+instead.
+
+You should have read section 2 of this faq. There you would
+have learned that comp.lang.perl.misc is the appropriate
+place to go for free advice. If your question is really
+important and you require a prompt and correct answer, you
+should hire a consultant.
+
+=head1 Credits
+
+The original perlfaq was written by Tom Christiansen, then expanded
+by collaboration between Tom and Nathan Torkington. The current
+document is maintained by the perlfaq-workers (perlfaq-workers@perl.org).
+Several people have contributed answers, corrections, and comments.
+
+=head1 Author and Copyright Information
+
+Copyright (c) 1997-2003 Tom Christiansen, Nathan Torkington, and
+other contributors noted in the answers.
+
+All rights reserved.
+
+=head2 Bundled Distributions
+
+This documentation is free; you can redistribute it and/or modify it
+under the same terms as Perl itself.
+
+Irrespective of its distribution, all code examples in these files
+are hereby placed into the public domain. You are permitted and
+encouraged to use this code in your own programs for fun
+or for profit as you see fit. A simple comment in the code giving
+credit would be courteous but is not required.
+
+=head2 Disclaimer
+
+This information is offered in good faith and in the hope that it may
+be of use, but is not guaranteed to be correct, up to date, or suitable
+for any particular purpose whatsoever. The authors accept no liability
+in respect of this information or its use.
+
+=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
-=item L<perlfaq1>: General Questions About Perl
-Very general, high-level information about Perl.
+=back
+
+
+=head1 The Questions
+
+
+=head2 L<perlfaq1>: General Questions About Perl
+
+Very general, high-level questions about Perl.
=over 4
-=item * What is Perl?
+=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 perl4 and perl5?
+
+=item *
+
+What is Ponie?
+
+=item *
+
+What is perl6?
+
+=item *
+
+How stable is Perl?
+
+=item *
+
+Is Perl difficult to learn?
+
+=item *
-=item * Who supports Perl? Who develops it? Why is it free?
+How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl?
-=item * Which version of Perl should I use?
+=item *
-=item * What are perl4 and perl5?
+Can I do [task] in Perl?
-=item * What is perl6?
+=item *
-=item * How stable is Perl?
+When shouldn't I program in Perl?
-=item * Is Perl difficult to learn?
+=item *
-=item * How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl?
+What's the difference between "perl" and "Perl"?
-=item * Can I do [task] in Perl?
+=item *
-=item * When shouldn't I program in Perl?
+Is it a Perl program or a Perl script?
-=item * What's the difference between "perl" and "Perl"?
+=item *
-=item * Is it a Perl program or a Perl script?
+What is a JAPH?
-=item * What is a JAPH?
+=item *
-=item * Where can I get a list of Larry Wall witticisms?
+Where can I get a list of Larry Wall witticisms?
-=item * How can I convince my sysadmin/supervisor/employees to use version (5/5.005/Perl instead of some other language)?
+=item *
+
+How can I convince my sysadmin/supervisor/employees to use version 5/5.6.1/Perl instead of some other language?
=back
-=
item L<perlfaq2>: Obtaining and Learning about Perl
+=
head2 L<perlfaq2>: Obtaining and Learning about Perl
-Where to find source and documentation to Perl, support,
-and related matters.
+Where to find source and documentation for Perl, support, and related matters.
=over 4
-=item * What machines support Perl? Where do I get it?
+=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 on my system. How can I compile perl?
+
+=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 *
-=item * How can I get a binary version of Perl?
+What modules and extensions are available for Perl? What is CPAN? What does CPAN/src/... mean?
-=item * I don't have a C compiler on my system. How can I compile perl?
+=item *
-=item * I copied the Perl binary from one machine to another, but scripts don't work.
+Is there an ISO or ANSI certified version of Perl?
-=item * I grabbed the sources and tried to compile but gdbm/dynamic loading/malloc/linking/... failed. How do I make it work?
+=item *
-=item * What modules and extensions are available for Perl? What is CPAN? What does CPAN/src/... mean?
+Where can I get information on Perl?
-=item * Is there an ISO or ANSI certified version of Perl?
+=item *
-=item * Where can I get information on Perl?
+What are the Perl newsgroups on Usenet? Where do I post questions?
-=item * What are the Perl newsgroups on USENET? Where do I post questions?
+=item *
-=item * Where should I post source code?
+Where should I post source code?
-=item * Perl Books
+=item *
-=item * Perl in Magazines
+Perl Books
-=item * Perl on the Net: FTP and WWW Access
+=item *
-=item * What mailing lists are there for perl?
+Perl in Magazines
-=item * Archives of comp.lang.perl.misc
+=item *
-=item * Where can I buy a commercial version of Perl?
+Perl on the Net: FTP and WWW Access
-=item * Where do I send bug reports?
+=item *
-=item * What is perl.com?
+What mailing lists are there for Perl?
+
+=item *
+
+Archives of 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
-=
item L<perlfaq3>: Programming Tools
+=
head2 L<perlfaq3>: Programming Tools
Programmer tools and programming support.
=over 4
-=item * How do I do (anything)?
+=item *
+
+How do I do (anything)?
+
+=item *
-=item * How can I use Perl interactively?
+How can I use Perl interactively?
-=item * Is there a Perl shell?
+=item *
-=item * How do I debug my Perl programs?
+Is there a Perl shell?
-=item * How do I profile my Perl programs?
+=item *
-=item * How do I cross-reference my Perl programs?
+How do I find which modules are installed on my system?
-=item * Is there a pretty-printer (formatter) for Perl?
+=item *
-=item * Is there a ctags for Perl?
+How do I debug my Perl programs?
-=item * Is there an IDE or Windows Perl Editor?
+=item *
-=item * Where can I get Perl macros for vi?
+How do I profile my Perl programs?
-=item * Where can I get perl-mode for emacs?
+=item *
-=item * How can I use curses with Perl?
+How do I cross-reference my Perl programs?
-=item * How can I use X or Tk with Perl?
+=item *
-=item * How can I generate simple menus without using CGI or Tk?
+Is there a pretty-printer (formatter) for Perl?
-=item * What is undump?
+=item *
-=item * How can I make my Perl program run faster?
+Is there a ctags for Perl?
-=item * How can I make my Perl program take less memory?
+=item *
-=item * Is it unsafe to return a pointer to local data?
+Is there an IDE or Windows Perl Editor?
-=item * How can I free an array or hash so my program shrinks?
+=item *
-=item * How can I make my CGI script more efficient?
+Where can I get Perl macros for vi?
-=item * How can I hide the source for my Perl program?
+=item *
-=item * How can I compile my Perl program into byte code or C?
+Where can I get perl-mode for emacs?
-=item * How can I compile Perl into Java?
+=item *
-=item * How can I get C<#!perl> to work on [MS-DOS,NT,...]?
+How can I use curses with Perl?
-=item * Can I write useful perl programs on the command line?
+=item *
-=item * Why don't perl one-liners work on my DOS/Mac/VMS system?
+How can I use X or Tk with Perl?
-=item * Where can I learn about CGI or Web programming in Perl?
+=item *
-=item * Where can I learn about object-oriented Perl programming?
+How can I generate simple menus without using CGI or Tk?
-=item * Where can I learn about linking C with Perl? [h2xs, xsubpp]
+=item *
-=item * I've read perlembed, perlguts, etc., but I can't embed perl in
-my C program, what am I doing wrong?
+How can I make my Perl program run faster?
-=item * When I tried to run my script, I got this message. What does it
-mean?
+=item *
-=item * What's MakeMaker?
+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 compile Perl into Java?
+
+=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? [h2xs, xsubpp]
+
+=item *
+
+I've read perlembed, perlguts, etc., but I can't embed perl in
+
+=item *
+
+When I tried to run my script, I got this message. What does it mean?
+
+=item *
+
+What's MakeMaker?
=back
-=
item L<perlfaq4>: Data Manipulation
+=
head2 L<perlfaq4>: Data Manipulation
-Manipulating numbers, dates, strings, arrays, hashes, and
-miscellaneous data issues.
+Manipulating 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 *
-=item * Why isn't my octal data interpreted correctly?
+Why am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?
-=item * Does Perl have a round() function? What about ceil() and floor()? Trig functions?
+=item *
-=item * How do I convert bits into ints?
+Why is int() broken?
-=item * Why doesn't & work the way I want it to?
+=item *
-=item * How do I multiply matrices?
+Why isn't my octal data interpreted correctly?
-=item * How do I perform an operation on a series of integers?
+=item *
-=item * How can I output Roman numerals?
+Does Perl have a round() function? What about ceil() and floor()? Trig functions?
-=item * Why aren't my random numbers random?
+=item *
-=item * How do I find the week-of-the-year/day-of-the-year?
+How do I convert between numeric representations/bases/radixes?
-=item * How do I find the current century or millennium?
+=item *
-=item * How can I compare two dates and find the difference?
+Why doesn't & work the way I want it to?
-=item * How can I take a string and turn it into epoch seconds?
+=item *
-=item * How can I find the Julian Day?
+How do I multiply matrices?
-=item * How do I find yesterday's date?
+=item *
-=item * Does Perl have a year 2000 problem? Is Perl Y2K compliant?
+How do I perform an operation on a series of integers?
-=item * How do I validate input?
+=item *
-=item * How do I unescape a string?
+How can I output Roman numerals?
-=item * How do I remove consecutive pairs of characters?
+=item *
-=item * How do I expand function calls in a string?
+Why aren't my random numbers random?
-=item * How do I find matching/nesting anything?
+=item *
-=item * How do I reverse a string?
+How do I get a random number between X and Y?
-=item * How do I expand tabs in a string?
+=item *
-=item * How do I reformat a paragraph?
+How do I find the day or week of the year?
-=item * How can I access/change the first N letters of a string?
+=item *
-=item * How do I change the Nth occurrence of something?
+How do I find the current century or millennium?
-=item * How can I count the number of occurrences of a substring within a string?
+=item *
-=item * How do I capitalize all the words on one line?
+How can I compare two dates and find the difference?
-=item * How can I split a [character] delimited string except when inside
-[character]? (Comma-separated files)
+=item *
-=item * How do I strip blank space from the beginning/end of a string?
+How can I take a string and turn it into epoch seconds?
-=item * How do I pad a string with blanks or pad a number with zeroes?
+=item *
-=item * How do I extract selected columns from a string?
+How can I find the Julian Day?
-=item * How do I find the soundex value of a string?
+=item *
-=item * How can I expand variables in text strings?
+How do I find yesterday's date?
-=item * What's wrong with always quoting "$vars"?
+=item *
-=item * Why don't my <<HERE documents work?
+Does Perl have a Year 2000 problem? Is Perl Y2K compliant?
-=item * What is the difference between a list and an array?
+=item *
-=item * What is the difference between $array[1] and @array[1]?
+How do I validate input?
-=item * How can I remove duplicate elements from a list or array?
+=item *
-=item * How can I tell whether a list or array contains a certain element?
+How do I unescape a string?
-=item * How do I compute the difference of two arrays? How do I compute the intersection of two arrays?
+=item *
-=item * How do I test whether two arrays or hashes are equal?
+How do I remove consecutive pairs of characters?
-=item * How do I find the first array element for which a condition is true?
+=item *
-=item * How do I handle linked lists?
+How do I expand function calls in a string?
-=item * How do I handle circular lists?
+=item *
-=item * How do I shuffle an array randomly?
+How do I find matching/nesting anything?
-=item * How do I process/modify each element of an array?
+=item *
-=item * How do I select a random element from an array?
+How do I reverse a string?
-=item * How do I permute N elements of a list?
+=item *
-=item * How do I sort an array by (anything)?
+How do I expand tabs in a string?
-=item * How do I manipulate arrays of bits?
+=item *
-=item * Why does defined() return true on empty arrays and hashes?
+How do I reformat a paragraph?
-=item * How do I process an entire hash?
+=item *
-=item * What happens if I add or remove keys from a hash while iterating over it?
+How can I access or change N characters of a string?
-=item * How do I look up a hash element by value?
+=item *
-=item * How can I know how many entries are in a hash?
+How do I change the Nth occurrence of something?
-=item * How do I sort a hash (optionally by value instead of key)?
+=item *
-=item * How can I always keep my hash sorted?
+How can I count the number of occurrences of a substring within a string?
-=item * What's the difference between "delete" and "undef" with hashes?
+=item *
-=item * Why don't my tied hashes make the defined/exists distinction?
+How do I capitalize all the words on one line?
-=item * How do I reset an each() operation part-way through?
+=item *
-=item * How can I get the unique keys from two hashes?
+How can I split a [character] delimited string except when inside [character]?
-=item * How can I store a multidimensional array in a DBM file?
+=item *
-=item * How can I make my hash remember the order I put elements into it?
+How do I strip blank space from the beginning/end of a string?
-=item * Why does passing a subroutine an undefined element in a hash create it?
+=item *
-=item * How can I make the Perl equivalent of a C structure/C++ class/hash or array of hashes or arrays?
+How do I pad a string with blanks or pad a number with zeroes?
-=item * How can I use a reference as a hash key?
+=item *
-=item * How do I handle binary data correctly?
+How do I extract selected columns from a string?
-=item * How do I determine whether a scalar is a number/whole/integer/float?
+=item *
-=item * How do I keep persistent data across program calls?
+How do I find the soundex value of a string?
-=item * How do I print out or copy a recursive data structure?
+=item *
-=item * How do I define methods for every class/object?
+How can I expand variables in text strings?
-=item * How do I verify a credit card checksum?
+=item *
-=item * How do I pack arrays of doubles or floats for XS code?
+What's wrong with always quoting "$vars"?
-=back
+=item *
+Why don't my E<lt>E<lt>HERE documents work?
-=item L<perlfaq5>: Files and Formats
+=item *
-I/O and the "f" issues: filehandles, flushing, formats and footers.
+What is the difference between a list and an array?
-=over 4
+=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 flush/unbuffer an output filehandle? Why must I do this?
+=item *
-=item * 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?
+How do I handle linked lists?
-=item * How do I count the number of lines in a file?
+=item *
-=item * How do I make a temporary file name?
+How do I handle circular lists?
-=item * How can I manipulate fixed-record-length files?
+=item *
-=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?
+How do I shuffle an array randomly?
-=item * How can I use a filehandle indirectly?
+=item *
-=item * How can I set up a footer format to be used with write()?
+How do I process/modify each element of an array?
-=item * How can I write() into a string?
+=item *
-=item * How can I output my numbers with commas added?
+How do I select a random element from an array?
-=item * How can I translate tildes (~) in a filename?
+=item *
-=item * How come when I open a file read-write it wipes it out?
+How do I permute N elements of a list?
-=item * Why do I sometimes get an "Argument list too long" when I use <*>?
+=item *
-=item * Is there a leak/bug in glob()?
+How do I sort an array by (anything)?
-=item * How can I open a file with a leading ">" or trailing blanks?
+=item *
-=item * How can I reliably rename a file?
+How do I manipulate arrays of bits?
-=item * How can I lock a file?
+=item *
-=item * Why can't I just open(FH, ">file.lock")?
+Why does defined() return true on empty arrays and hashes?
-=item * I still don't get locking. I just want to increment the number in the file. How can I do this?
+=item *
-=item * How do I randomly update a binary file?
+How do I process an entire hash?
-=item * How do I get a file's timestamp in perl?
+=item *
-=item * How do I set a file's timestamp in perl?
+What happens if I add or remove keys from a hash while iterating over it?
-=item * How do I print to more than one file at once?
+=item *
-=item * How can I read in an entire file all at once?
+How do I look up a hash element by value?
-=item * How can I read in a file by paragraphs?
+=item *
-=item * How can I read a single character from a file? From the keyboard?
+How can I know how many entries are in a hash?
-=item * How can I tell whether there's a character waiting on a filehandle?
+=item *
-=item * How do I do a C<tail -f> in perl?
+How do I sort a hash (optionally by value instead of key)?
-=item * How do I dup() a filehandle in Perl?
+=item *
-=item * How do I close a file descriptor by number?
+How can I always keep my hash sorted?
-=item * Why can't I use "C:\temp\foo" in DOS paths? What doesn't `C:\temp\foo.exe` work?
+=item *
-=item * Why doesn't glob("*.*") get all the files?
+What's the difference between "delete" and "undef" with hashes?
-=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 *
-=item * How do I select a random line from a file?
+Why don't my tied hashes make the defined/exists distinction?
-=item * Why do I get weird spaces when I print an array of lines?
+=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
-=item L<perlfaq6>: Regexps
+=head2 L<perlfaq5>: Files and Formats
-Pattern matching and regular expressions.
+I/O and the "f" issues: filehandles, flushing, formats, and footers.
=over 4
-=item * How can I hope to use regular expressions without creating illegible and unmaintainable code?
+=item *
+
+How do I flush/unbuffer an output filehandle? Why must I do this?
+
+=item *
+
+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?
+
+=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 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 *
-=item * I'm having trouble matching over more than one line. What's wrong?
+How can I set up a footer format to be used with write()?
-=item * How can I pull out lines between two patterns that are themselves on different lines?
+=item *
-=item * I put a regular expression into $/ but it didn't work. What's wrong?
+How can I write() into a string?
-=item * How do I substitute case insensitively on the LHS, but preserving case on the RHS?
+=item *
-=item * How can I make C<\w> match national character sets?
+How can I output my numbers with commas added?
-=item * How can I match a locale-smart version of C</[a-zA-Z]/>?
+=item *
-=item * How can I quote a variable to use in a regex?
+How can I translate tildes (~) in a filename?
-=item * What is C</o> really for?
+=item *
-=item * How do I use a regular expression to strip C style comments from a file?
+How come when I open a file read-write it wipes it out?
-=item * Can I use Perl regular expressions to match balanced text?
+=item *
-=item * What does it mean that regexes are greedy? How can I get around it?
+Why do I sometimes get an "Argument list too long" when I use E<lt>*E<gt>?
-=item * How do I process each word on each line?
+=item *
-=item * How can I print out a word-frequency or line-frequency summary?
+Is there a leak/bug in glob()?
-=item * How can I do approximate matching?
+=item *
-=item * How do I efficiently match many regular expressions at once?
+How can I open a file with a leading ">" or trailing blanks?
-=item * Why don't word-boundary searches with C<\b> work for me?
+=item *
-=item * Why does using $&, $`, or $' slow my program down?
+How can I reliably rename a file?
-=item * What good is C<\G> in a regular expression?
+=item *
-=item * Are Perl regexes DFAs or NFAs? Are they POSIX compliant?
+How can I lock a file?
-=item * What's wrong with using grep or map in a void context?
+=item *
-=item * How can I match strings with multibyte characters?
+Why can't I just open(FH, "E<gt>file.lock")?
-=item * How do I match a pattern that is supplied by the user?
+=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
-=item L<perlfaq7>: General Perl Language Issues
+=head2 L<perlfaq6>: Regular Expressions
-General Perl language issues that don't clearly fit into any of the
-other sections.
+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).
=over 4
-=item * Can I get a BNF/yacc/RE for the Perl language?
+=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 *
-=item * What are all these $@%&* punctuation signs, and how do I know when to use them?
+How do I substitute case insensitively on the LHS while preserving case on the RHS?
-=item * Do I always/never have to quote my strings or use semicolons and commas?
+=item *
-=item * How do I skip some return values?
+How can I make C<\w> match national character sets?
-=item * How do I temporarily block warnings?
+=item *
-=item * What's an extension?
+How can I match a locale-smart version of C</[a-zA-Z]/>?
-=item * Why do Perl operators have different precedence than C operators?
+=item *
-=item * How do I declare/create a structure?
+How can I quote a variable to use in a regex?
-=item * How do I create a module?
+=item *
-=item * How do I create a class?
+What is C</o> really for?
-=item * How can I tell if a variable is tainted?
+=item *
-=item * What's a closure?
+How do I use a regular expression to strip C style comments from a file?
-=item * What is variable suicide and how can I prevent it?
+=item *
-=item * How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}?
+Can I use Perl regular expressions to match balanced text?
-=item * How do I create a static variable?
+=item *
-=item * What's the difference between dynamic and lexical (static) scoping? Between local() and my()?
+What does it mean that regexes are greedy? How can I get around it?
-=item * How can I access a dynamic variable while a similarly named lexical is in scope?
+=item *
-=item * What's the difference between deep and shallow binding?
+How do I process each word on each line?
-=item * Why doesn't "my($foo) = <FILE>;" work right?
+=item *
-=item * How do I redefine a builtin function, operator, or method?
+How can I print out a word-frequency or line-frequency summary?
-=item * What's the difference between calling a function as &foo and foo()?
+=item *
-=item * How do I create a switch or case statement?
+How can I do approximate matching?
-=item * How can I catch accesses to undefined variables/functions/methods?
+=item *
-=item * Why can't a method included in this same file be found?
+How do I efficiently match many regular expressions at once?
-=item * How can I find out my current package?
+=item *
-=item * How can I comment out a large block of perl code?
+Why don't word-boundary searches with C<\b> work for me?
-=item * How do I clear a package?
+=item *
-=item * How can I use a variable as a variable name?
+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 pattern that is supplied by the user?
=back
-=item L<perlfaq8>: System Interaction
+=head2 L<perlfaq7>: General Perl Language Issues
-Interprocess communication (IPC), control over the user-interface
-(keyboard, screen and pointing devices).
+General Perl language issues that don't clearly fit into any of the other sections.
=over 4
-=item * How do I find out which operating system I'm running under?
+=item *
+
+Can I get a BNF/yacc/RE for the Perl language?
-=item * How come exec() doesn't return?
+=item *
-=item * How do I do fancy stuff with the keyboard/screen/mouse?
+What are all these $@%&* punctuation signs, and how do I know when to use them?
-=item * How do I print something out in color?
+=item *
-=item * How do I read just one key without waiting for a return key?
+Do I always/never have to quote my strings or use semicolons and commas?
-=item * How do I check whether input is ready on the keyboard?
+=item *
-=item * How do I clear the screen?
+How do I skip some return values?
-=item * How do I get the screen size?
+=item *
-=item * How do I ask the user for a password?
+How do I temporarily block warnings?
-=item * How do I read and write the serial port?
+=item *
-=item * How do I decode encrypted password files?
+What's an extension?
-=item * How do I start a process in the background?
+=item *
-=item * How do I trap control characters/signals?
+Why do Perl operators have different precedence than C operators?
-=item * How do I modify the shadow password file on a Unix system?
+=item *
-=item * How do I set the time and date?
+How do I declare/create a structure?
-=item * How can I sleep() or alarm() for under a second?
+=item *
-=item * How can I measure time under a second?
+How do I create a module?
-=item * How can I do an atexit() or setjmp()/longjmp()? (Exception handling)
+=item *
-=item * Why doesn't my sockets program work under System V (Solaris)? What does the error message "Protocol not supported" mean?
+How do I create a class?
-=item * How can I call my system's unique C functions from Perl?
+=item *
-=item * Where do I get the include files to do ioctl() or syscall()?
+How can I tell if a variable is tainted?
-=item * Why do setuid perl scripts complain about kernel problems?
+=item *
-=item * How can I open a pipe both to and from a command?
+What's a closure?
-=item * Why can't I get the output of a command with system()?
+=item *
-=item * How can I capture STDERR from an external command?
+What is variable suicide and how can I prevent it?
-=item * Why doesn't open() return an error when a pipe open fails?
+=item *
-=item * What's wrong with using backticks in a void context?
+How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}?
-=item * How can I call backticks without shell processing?
+=item *
-=item * Why can't my script read from STDIN after I gave it EOF (^D on Unix, ^Z on MS-DOS)?
+How do I create a static variable?
-=item * How can I convert my shell script to perl?
+=item *
-=item * Can I use perl to run a telnet or ftp session?
+What's the difference between dynamic and lexical (static) scoping? Between local() and my()?
-=item * How can I write expect in Perl?
+=item *
-=item * Is there a way to hide perl's command line from programs such as "ps"?
+How can I access a dynamic variable while a similarly named lexical is in scope?
-=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 *
-=item * How do I close a process's filehandle without waiting for it to complete?
+What's the difference between deep and shallow binding?
-=item * How do I fork a daemon process?
+=item *
-=item * How do I make my program run with sh and csh?
+Why doesn't "my($foo) = E<lt>FILEE<gt>;" work right?
-=item * How do I find out if I'm running interactively or not?
+=item *
-=item * How do I timeout a slow event?
+How do I redefine a builtin function, operator, or method?
-=item * How do I set CPU limits?
+=item *
-=item * How do I avoid zombies on a Unix system?
+What's the difference between calling a function as &foo and foo()?
-=item * How do I use an SQL database?
+=item *
-=item * How do I make a system() exit on control-C?
+How do I create a switch or case statement?
-=item * How do I open a file without blocking?
+=item *
-=item * How do I install a module from CPAN?
+How can I catch accesses to undefined variables, functions, or methods?
-=item * What's the difference between require and use?
+=item *
-=item * How do I keep my own module/library directory?
+Why can't a method included in this same file be found?
-=item * How do I add the directory my program lives in to the module/library search path?
+=item *
-=item * How do I add a directory to my include path at runtime?
+How can I find out my current package?
-=item * What is socket.ph and where do I get it?
+=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
-=item L<perlfaq9>: Networking
+=head2 L<perlfaq8>: System Interaction
-Networking, the Internet, and a few on the web.
+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.
=over 4
-=item * My CGI script runs from the command line but not the browser. (500 Server Error)
+=item *
-=item * How can I get better error messages from a CGI program?
+How do I find out which operating system I'm running under?
-=item * How do I remove HTML from a string?
+=item *
-=item * How do I extract URLs?
+How come exec() doesn't return?
-=item * How do I download a file from the user's machine? How do I open a file on another machine?
+=item *
-=item * How do I make a pop-up menu in HTML?
+How do I do fancy stuff with the keyboard/screen/mouse?
-=item * How do I fetch an HTML file?
+=item *
-=item * How do I automate an HTML form submission?
+How do I print something out in color?
-=item * How do I decode or create those %-encodings on the web?
+=item *
-=item * How do I redirect to another page?
+How do I read just one key without waiting for a return key?
-=item * How do I put a password on my web pages?
+=item *
-=item * How do I edit my .htpasswd and .htgroup files with Perl?
+How do I check whether input is ready on the keyboard?
-=item * How do I make sure users can't enter values into a form that cause my CGI script to do bad things?
+=item *
-=item * How do I parse a mail header?
+How do I clear the screen?
-=item * How do I decode a CGI form?
+=item *
-=item * How do I check a valid mail address?
+How do I get the screen size?
-=item * How do I decode a MIME/BASE64 string?
+=item *
-=item * How do I return the user's mail address?
+How do I ask the user for a password?
-=item * How do I send mail?
+=item *
-=item * How do I read mail?
+How do I read and write the serial port?
-=item * How do I find out my hostname/domainname/IP address?
+=item *
-=item * How do I fetch a news article or the active newsgroups?
+How do I decode encrypted password files?
-=item * How do I fetch/put an FTP file?
+=item *
-=item * How can I do RPC in Perl?
+How do I start a process in the background?
-=back
+=item *
+How do I trap control characters/signals?
-=back
+=item *
-=head2 Where to get this document
+How do I modify the shadow password file on a Unix system?
-This document is posted regularly to comp.lang.perl.announce and
-several other related newsgroups. It is available in a variety of
-formats from CPAN in the /CPAN/doc/FAQs/FAQ/ directory, or on the web
-at http://www.perl.com/perl/faq/ .
+=item *
-=head2 How to contribute to this document
+How do I set the time and date?
-You may mail corrections, additions, and suggestions to
-perlfaq-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.
+=item *
-=head2 What will happen if you mail your Perl programming problems to the authors
+How can I sleep() or alarm() for under a second?
-Your questions will probably go unread, unless they're suggestions of
-new questions to add to the FAQ, in which case they should have gone
-to the perlfaq-suggestions@perl.com instead.
+=item *
-You should have read section 2 of this faq. There you would have
-learned that comp.lang.perl.misc is the appropriate place to go for
-free advice. If your question is really important and you require a
-prompt and correct answer, you should hire a consultant.
+How can I measure time under a second?
-=head1 Credits
+=item *
-When I first began the Perl FAQ in the late 80s, I never realized it
-would have grown to over a hundred pages, nor that Perl would ever become
-so popular and widespread. This document could not have been written
-without the tremendous help provided by Larry Wall and the rest of the
-Perl Porters.
+How can I do an atexit() or setjmp()/longjmp()? (Exception handling)
-=head1 Author and Copyright Information
+=item *
-Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.
-All rights reserved.
+Why doesn't my sockets program work under System V (Solaris)? What does the error message "Protocol not supported" mean?
-=head2 Bundled Distributions
+=item *
-When included as part of the Standard Version of Perl, or as part of
-its complete documentation whether printed or otherwise, this work
-may be distributed only under the terms of Perl's Artistic License.
-Any distribution of this file or derivatives thereof I<outside>
-of that package require that special arrangements be made with
-copyright holder.
+How can I call my system's unique C functions from Perl?
-Irrespective of its distribution, all code examples in these files
-are hereby placed into the public domain. You are permitted and
-encouraged to use this code in your own programs for fun
-or for profit as you see fit. A simple comment in the code giving
-credit would be courteous but is not required.
+=item *
-=head2 Disclaimer
+Where do I get the include files to do ioctl() or syscall()?
-This information is offered in good faith and in the hope that it may
-be of use, but is not guaranteed to be correct, up to date, or suitable
-for any particular purpose whatsoever. The authors accept no liability
-in respect of this information or its use.
+=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?
-=head1 Changes
+=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>: Networking
+
+Networking, the internet, and a few on the web.
=over 4
-=item 23/May/99
+=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 *
-Extensive updates from the net in preparation for 5.6 release.
+How do I download a file from the user's machine? How do I open a file on another machine?
-=item 13/April/99
+=item *
-More minor touch-ups. Added new question at the end
-of perlfaq7 on variable names within variables.
+How do I make a pop-up menu in HTML?
-=item 7/January/99
+=item *
-Small touchups here and there. Added all questions in this
-document as a sort of table of contents.
+How do I fetch an HTML file?
-=item 22/June/98
+=item *
-Significant changes throughout in preparation for the 5.005
-release.
+How do I automate an HTML form submission?
-=item 24/April/97
+=item *
-Style and whitespace changes from Chip, new question on reading one
-character at a time from a terminal using POSIX from Tom.
+How do I decode or create those %-encodings on the web?
-=item 23/April/97
+=item *
-Added http://www.oasis.leo.org/perl/ to L<perlfaq2>. Style fix to
-L<perlfaq3>. Added floating point precision, fixed complex number
-arithmetic, cross-references, caveat for Text::Wrap, alternative
-answer for initial capitalizing, fixed incorrect regexp, added example
-of Tie::IxHash to L<perlfaq4>. Added example of passing and storing
-filehandles, added commify to L<perlfaq5>. Restored variable suicide,
-and added mass commenting to L<perlfaq7>. Added Net::Telnet, fixed
-backticks, added reader/writer pair to telnet question, added FindBin,
-grouped module questions together in L<perlfaq8>. Expanded caveats
-for the simple URL extractor, gave LWP example, added CGI security
-question, expanded on the mail address answer in L<perlfaq9>.
+How do I redirect to another page?
-=item 25/March/97
+=item *
-Added more info to the binary distribution section of L<perlfaq2>.
-Added Net::Telnet to L<perlfaq6>. Fixed typos in L<perlfaq8>. Added
-mail sending example to L<perlfaq9>. Added Merlyn's columns to
-L<perlfaq2>.
+How do I put a password on my web pages?
-=item 18/March/97
+=item *
-Added the DATE to the NAME section, indicating which sections have
-changed.
+How do I edit my .htpasswd and .htgroup files with Perl?
-Mentioned SIGPIPE and L<perlipc> in the forking open answer in
-L<perlfaq8>.
+=item *
-Fixed description of a regular expression in L<perlfaq4>.
+How do I make sure users can't enter values into a form that cause my CGI script to do bad things?
-=item 17/March/97 Version
+=item *
-Various typos fixed throughout.
+How do I parse a mail header?
-Added new question on Perl BNF on L<perlfaq7>.
+=item *
-=item Initial Release: 11/March/97
+How do I decode a CGI form?
-This is the initial release of version 3 of the FAQ; consequently there
-have been no changes since its initial release.
+=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/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
+
+
https://perl5.git.perl.org / perl5.git / blobdiff