=head1 NAME
-perlfaq - frequently asked questions about Perl ($Date: 1999/05/23 20:38:02 $)
+perlfaq - frequently asked questions about Perl ($Date: 2003/01/31 17:37:17 $)
=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.
+
+=head2 Where to get the perlfaq
+
+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/
+
+=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: Structural overview of the FAQ.
+=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
-This document.
+=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 *
-=item * Who supports Perl? Who develops it? Why is it free?
+What are perl4 and perl5?
-=item * Which version of Perl should I use?
+=item *
-=item * What are perl4 and perl5?
+What is perl6?
-=item * What is perl6?
+=item *
-=item * How stable is Perl?
+How stable is Perl?
-=item * Is Perl difficult to learn?
+=item *
-=item * How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl?
+Is Perl difficult to learn?
-=item * Can I do [task] in Perl?
+=item *
-=item * When shouldn't I program in Perl?
+How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl?
-=item * What's the difference between "perl" and "Perl"?
+=item *
-=item * Is it a Perl program or a Perl script?
+Can I do [task] in Perl?
-=item * What is a JAPH?
+=item *
-=item * Where can I get a list of Larry Wall witticisms?
+When shouldn't I program in Perl?
-=item * How can I convince my sysadmin/supervisor/employees to use version 5/5.005/Perl instead of some other language?
+=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 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,
+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 *
-=item * I don't have a C compiler on my system. How can I compile perl?
+How can I get a binary version of Perl?
-=item * I copied the Perl binary from one machine to another, but scripts don't work.
+=item *
-=item * I grabbed the sources and tried to compile but gdbm/dynamic loading/malloc/linking/... failed. How do I make it work?
+I don't have a C compiler on my system. How can I compile perl?
-=item * What modules and extensions are available for Perl? What is CPAN? What does CPAN/src/... mean?
+=item *
-=item * Is there an ISO or ANSI certified version of Perl?
+I copied the Perl binary from one machine to another, but scripts don't work.
-=item * Where can I get information on Perl?
+=item *
-=item * What are the Perl newsgroups on Usenet? Where do I post questions?
+I grabbed the sources and tried to compile but gdbm/dynamic loading/malloc/linking/... failed. How do I make it work?
-=item * Where should I post source code?
+=item *
-=item * Perl Books
+What modules and extensions are available for Perl? What is CPAN? What does CPAN/src/... mean?
-=item * Perl in Magazines
+=item *
-=item * Perl on the Net: FTP and WWW Access
+Is there an ISO or ANSI certified version of Perl?
-=item * What mailing lists are there for Perl?
+=item *
-=item * Archives of comp.lang.perl.misc
+Where can I get information on Perl?
-=item * Where can I buy a commercial version of Perl?
+=item *
-=item * Where do I send bug reports?
+What are the Perl newsgroups on Usenet? Where do I post questions?
-=item * What is perl.com? Perl Mongers? pm.org? perl.org?
+=item *
+
+Where should I post source code?
+
+=item *
+
+Perl Books
+
+=item *
+
+Perl in Magazines
+
+=item *
+
+Perl on the Net: FTP and WWW Access
+
+=item *
+
+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 *
+
+How can I use Perl interactively?
+
+=item *
-=item * How can I use Perl interactively?
+Is there a Perl shell?
-=item * Is there a Perl shell?
+=item *
-=item * How do I debug my Perl programs?
+How do I find which modules are installed on my system?
-=item * How do I profile my Perl programs?
+=item *
-=item * How do I cross-reference my Perl programs?
+How do I debug my Perl programs?
-=item * Is there a pretty-printer (formatter) for Perl?
+=item *
-=item * Is there a ctags for Perl?
+How do I profile 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 cross-reference my Perl programs?
-=item * Where can I get perl-mode for emacs?
+=item *
-=item * How can I use curses with Perl?
+Is there a pretty-printer (formatter) for Perl?
-=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 ctags for Perl?
-=item * What is undump?
+=item *
-=item * How can I make my Perl program run faster?
+Is there an IDE or Windows Perl Editor?
-=item * How can I make my Perl program take less memory?
+=item *
-=item * Is it unsafe to return a pointer to local data?
+Where can I get Perl macros for vi?
-=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-mode for emacs?
-=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?
+How can I use curses with Perl?
-=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 X or Tk 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 generate simple menus without using CGI or Tk?
-=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 make my Perl program run faster?
-=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
+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
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 *
+
+When I tried to run my script, I got this message. What does it mean?
-=item * What's MakeMaker?
+=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.
=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 am I getting long decimals (eg, 19.9499999999999) instead of the numbers I should be getting (eg, 19.95)?
+
+=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?
+
+=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 * Why isn't my octal data interpreted correctly?
+=item *
-=item * Does Perl have a round() function? What about ceil() and floor()? Trig functions?
+How do I capitalize all the words on one line?
-=item * How do I convert bits into ints?
+=item *
-=item * Why doesn't & work the way I want it to?
+How can I split a [character] delimited string except when inside [character]?
-=item * How do I multiply matrices?
+=item *
-=item * How do I perform an operation on a series of integers?
+How do I strip blank space from the beginning/end of a string?
-=item * How can I output Roman numerals?
+=item *
-=item * Why aren't my random numbers random?
+How do I pad a string with blanks or pad a number with zeroes?
-=item * How do I find the week-of-the-year/day-of-the-year?
+=item *
-=item * How do I find the current century or millennium?
+How do I extract selected columns from a string?
-=item * How can I compare two dates and find the difference?
+=item *
-=item * How can I take a string and turn it into epoch seconds?
+How do I find the soundex value of a string?
-=item * How can I find the Julian Day?
+=item *
-=item * How do I find yesterday's date?
+How can I expand variables in text strings?
-=item * Does Perl have a Year 2000 problem? Is Perl Y2K compliant?
+=item *
-=item * How do I validate input?
+What's wrong with always quoting "$vars"?
-=item * How do I unescape a string?
+=item *
-=item * How do I remove consecutive pairs of characters?
+Why don't my E<lt>E<lt>HERE documents work?
-=item * How do I expand function calls in a string?
+=item *
-=item * How do I find matching/nesting anything?
+What is the difference between a list and an array?
-=item * How do I reverse a string?
+=item *
-=item * How do I expand tabs in a string?
+What is the difference between $array[1] and @array[1]?
-=item * How do I reformat a paragraph?
+=item *
-=item * How can I access/change the first N letters of a string?
+How can I remove duplicate elements from a list or array?
-=item * How do I change the Nth occurrence of something?
+=item *
-=item * How can I count the number of occurrences of a substring within a string?
+How can I tell whether a certain element is contained in a list or array?
-=item * How do I capitalize all the words on one line?
+=item *
-=item * How can I split a [character] delimited string except when inside
-[character]? (Comma-separated files)
+How do I compute the difference of two arrays? How do I compute the intersection of two arrays?
-=item * How do I strip blank space from the beginning/end of a string?
+=item *
-=item * How do I pad a string with blanks or pad a number with zeroes?
+How do I test whether two arrays or hashes are equal?
-=item * How do I extract selected columns from a string?
+=item *
-=item * How do I find the soundex value of a string?
+How do I find the first array element for which a condition is true?
-=item * How can I expand variables in text strings?
+=item *
-=item * What's wrong with always quoting "$vars"?
+How do I handle linked lists?
-=item * Why don't my <<HERE documents work?
+=item *
-=item * What is the difference between a list and an array?
+How do I handle circular lists?
-=item * What is the difference between $array[1] and @array[1]?
+=item *
-=item * How can I remove duplicate elements from a list or array?
+How do I shuffle an array randomly?
-=item * How can I tell whether a list or array contains a certain element?
+=item *
-=item * How do I compute the difference of two arrays? How do I compute the intersection of two arrays?
+How do I process/modify each element of an array?
-=item * How do I test whether two arrays or hashes are equal?
+=item *
-=item * How do I find the first array element for which a condition is true?
+How do I select a random element from an array?
-=item * How do I handle linked lists?
+=item *
-=item * How do I handle circular lists?
+How do I permute N elements of a list?
-=item * How do I shuffle an array randomly?
+=item *
-=item * How do I process/modify each element of an array?
+How do I sort an array by (anything)?
-=item * How do I select a random element from an array?
+=item *
-=item * How do I permute N elements of a list?
+How do I manipulate arrays of bits?
-=item * How do I sort an array by (anything)?
+=item *
-=item * How do I manipulate arrays of bits?
+Why does defined() return true on empty arrays and hashes?
-=item * Why does defined() return true on empty arrays and hashes?
+=item *
-=item * How do I process an entire hash?
+How do I process an entire hash?
-=item * What happens if I add or remove keys from a hash while iterating over it?
+=item *
-=item * How do I look up a hash element by value?
+What happens if I add or remove keys from a hash while iterating over it?
-=item * How can I know how many entries are in a hash?
+=item *
-=item * How do I sort a hash (optionally by value instead of key)?
+How do I look up a hash element by value?
-=item * How can I always keep my hash sorted?
+=item *
-=item * What's the difference between "delete" and "undef" with hashes?
+How can I know how many entries are in a hash?
-=item * Why don't my tied hashes make the defined/exists distinction?
+=item *
-=item * How do I reset an each() operation part-way through?
+How do I sort a hash (optionally by value instead of key)?
-=item * How can I get the unique keys from two hashes?
+=item *
-=item * How can I store a multidimensional array in a DBM file?
+How can I always keep my hash sorted?
-=item * How can I make my hash remember the order I put elements into it?
+=item *
-=item * Why does passing a subroutine an undefined element in a hash create it?
+What's the difference between "delete" and "undef" with hashes?
-=item * How can I make the Perl equivalent of a C structure/C++ class/hash or array of hashes or arrays?
+=item *
-=item * How can I use a reference as a hash key?
+Why don't my tied hashes make the defined/exists distinction?
-=item * How do I handle binary data correctly?
+=item *
-=item * How do I determine whether a scalar is a number/whole/integer/float?
+How do I reset an each() operation part-way through?
-=item * How do I keep persistent data across program calls?
+=item *
-=item * How do I print out or copy a recursive data structure?
+How can I get the unique keys from two hashes?
-=item * How do I define methods for every class/object?
+=item *
-=item * How do I verify a credit card checksum?
+How can I store a multidimensional array in a DBM file?
-=item * How do I pack arrays of doubles or floats for XS code?
+=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<perlfaq5>: Files and Formats
+=head2 L<perlfaq5>: Files and Formats
-I/O and the "f" issues: filehandles, flushing, formats and footers.
+I/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 *
+
+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 *
+
+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 output my numbers with commas added?
-=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 *
-=item * How do I count the number of lines in a file?
+How can I translate tildes (~) in a filename?
-=item * How do I make a temporary file name?
+=item *
-=item * How can I manipulate fixed-record-length files?
+How come when I open a file read-write it wipes it out?
-=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 *
-=item * How can I use a filehandle indirectly?
+Why do I sometimes get an "Argument list too long" when I use E<lt>*E<gt>?
-=item * How can I set up a footer format to be used with write()?
+=item *
-=item * How can I write() into a string?
+Is there a leak/bug in glob()?
-=item * How can I output my numbers with commas added?
+=item *
-=item * How can I translate tildes (~) in a filename?
+How can I open a file with a leading ">" or trailing blanks?
-=item * How come when I open a file read-write it wipes it out?
+=item *
-=item * Why do I sometimes get an "Argument list too long" when I use <*>?
+How can I reliably rename a file?
-=item * Is there a leak/bug in glob()?
+=item *
-=item * How can I open a file with a leading ">" or trailing blanks?
+How can I lock a file?
-=item * How can I reliably rename a file?
+=item *
-=item * How can I lock a file?
+Why can't I just open(FH, "E<gt>file.lock")?
-=item * Why can't I just open(FH, ">file.lock")?
+=item *
-=item * I still don't get locking. I just want to increment the number in the file. How can I do this?
+I still don't get locking. I just want to increment the number in the file. How can I do this?
-=item * How do I randomly update a binary file?
+=item *
-=item * How do I get a file's timestamp in perl?
+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 set a file's timestamp in perl?
+=item *
-=item * How do I print to more than one file at once?
+How do I randomly update a binary file?
-=item * How can I read in an entire file all at once?
+=item *
-=item * How can I read in a file by paragraphs?
+How do I get a file's timestamp in perl?
-=item * How can I read a single character from a file? From the keyboard?
+=item *
-=item * How can I tell whether there's a character waiting on a filehandle?
+How do I set a file's timestamp in perl?
-=item * How do I do a C<tail -f> in perl?
+=item *
-=item * How do I dup() a filehandle in Perl?
+How do I print to more than one file at once?
-=item * How do I close a file descriptor by number?
+=item *
-=item * Why can't I use "C:\temp\foo" in DOS paths? What doesn't `C:\temp\foo.exe` work?
+How can I read in an entire file all at once?
-=item * Why doesn't glob("*.*") get all the files?
+=item *
-=item * Why does Perl let me delete read-only files? Why does C<-i> clobber protected files? Isn't this a bug in Perl?
+How can I read in a file by paragraphs?
-=item * How do I select a random line from a file?
+=item *
-=item * Why do I get weird spaces when I print an array of lines?
+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
-=item L<perlfaq6>: Regexps
+=head2 L<perlfaq6>: Regular Expressions
Pattern matching and regular expressions.
=over 4
-=item * How can I hope to use regular expressions without creating illegible and unmaintainable code?
+=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 * I'm having trouble matching over more than one line. What's wrong?
+=item *
-=item * How can I pull out lines between two patterns that are themselves on different lines?
+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 * How do I substitute case insensitively on the LHS while preserving case on the RHS?
+I put a regular expression into $/ but it didn't work. What's wrong?
-=item * How can I make C<\w> match national character sets?
+=item *
-=item * How can I match a locale-smart version of C</[a-zA-Z]/>?
+How do I substitute case insensitively on the LHS while preserving case on the RHS?
-=item * How can I quote a variable to use in a regex?
+=item *
-=item * What is C</o> really for?
+How can I make C<\w> match national character sets?
-=item * How do I use a regular expression to strip C style comments from a file?
+=item *
-=item * Can I use Perl regular expressions to match balanced text?
+How can I match a locale-smart version of C</[a-zA-Z]/>?
-=item * What does it mean that regexes are greedy? How can I get around it?
+=item *
-=item * How do I process each word on each line?
+How can I quote a variable to use in a regex?
-=item * How can I print out a word-frequency or line-frequency summary?
+=item *
-=item * How can I do approximate matching?
+What is C</o> really for?
-=item * How do I efficiently match many regular expressions at once?
+=item *
-=item * Why don't word-boundary searches with C<\b> work for me?
+How do I use a regular expression to strip C style comments from a file?
-=item * Why does using $&, $`, or $' slow my program down?
+=item *
-=item * What good is C<\G> in a regular expression?
+Can I use Perl regular expressions to match balanced text?
-=item * Are Perl regexes DFAs or NFAs? Are they POSIX compliant?
+=item *
-=item * What's wrong with using grep or map in a void context?
+What does it mean that regexes are greedy? How can I get around it?
-=item * How can I match strings with multibyte characters?
+=item *
-=item * How do I match a pattern that is supplied by the user?
+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
-=item L<perlfaq7>: General Perl Language Issues
+=head2 L<perlfaq7>: General Perl Language Issues
General 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 *
+
+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 *
-=item * Do I always/never have to quote my strings or use semicolons and commas?
+What are all these $@%&* punctuation signs, and how do I know when to use them?
-=item * How do I skip some return values?
+=item *
-=item * How do I temporarily block warnings?
+Do I always/never have to quote my strings or use semicolons and commas?
-=item * What's an extension?
+=item *
-=item * Why do Perl operators have different precedence than C operators?
+How do I skip some return values?
-=item * How do I declare/create a structure?
+=item *
-=item * How do I create a module?
+How do I temporarily block warnings?
-=item * How do I create a class?
+=item *
-=item * How can I tell if a variable is tainted?
+What's an extension?
-=item * What's a closure?
+=item *
-=item * What is variable suicide and how can I prevent it?
+Why do Perl operators have different precedence than C operators?
-=item * How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}?
+=item *
-=item * How do I create a static variable?
+How do I declare/create a structure?
-=item * What's the difference between dynamic and lexical (static) scoping? Between local() and my()?
+=item *
-=item * How can I access a dynamic variable while a similarly named lexical is in scope?
+How do I create a module?
-=item * What's the difference between deep and shallow binding?
+=item *
-=item * Why doesn't "my($foo) = <FILE>;" work right?
+How do I create a class?
-=item * How do I redefine a builtin function, operator, or method?
+=item *
-=item * What's the difference between calling a function as &foo and foo()?
+How can I tell if a variable is tainted?
-=item * How do I create a switch or case statement?
+=item *
-=item * How can I catch accesses to undefined variables/functions/methods?
+What's a closure?
-=item * Why can't a method included in this same file be found?
+=item *
-=item * How can I find out my current package?
+What is variable suicide and how can I prevent it?
-=item * How can I comment out a large block of perl code?
+=item *
-=item * How do I clear a package?
+How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}?
-=item * How can I use a variable as a variable name?
+=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
-=item L<perlfaq8>: System Interaction
+=head2 L<perlfaq8>: System Interaction
Interprocess 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 *
-=item * How come exec() doesn't return?
+How do I find out which operating system I'm running under?
-=item * How do I do fancy stuff with the keyboard/screen/mouse?
+=item *
-=item * How do I print something out in color?
+How come exec() doesn't return?
-=item * How do I read just one key without waiting for a return key?
+=item *
-=item * How do I check whether input is ready on the keyboard?
+How do I do fancy stuff with the keyboard/screen/mouse?
-=item * How do I clear the screen?
+=item *
-=item * How do I get the screen size?
+How do I print something out in color?
-=item * How do I ask the user for a password?
+=item *
-=item * How do I read and write the serial port?
+How do I read just one key without waiting for a return key?
-=item * How do I decode encrypted password files?
+=item *
-=item * How do I start a process in the background?
+How do I check whether input is ready on the keyboard?
-=item * How do I trap control characters/signals?
+=item *
-=item * How do I modify the shadow password file on a Unix system?
+How do I clear the screen?
-=item * How do I set the time and date?
+=item *
-=item * How can I sleep() or alarm() for under a second?
+How do I get the screen size?
-=item * How can I measure time under a second?
+=item *
-=item * How can I do an atexit() or setjmp()/longjmp()? (Exception handling)
+How do I ask the user for a password?
-=item * Why doesn't my sockets program work under System V (Solaris)? What does the error message "Protocol not supported" mean?
+=item *
-=item * How can I call my system's unique C functions from Perl?
+How do I read and write the serial port?
-=item * Where do I get the include files to do ioctl() or syscall()?
+=item *
-=item * Why do setuid perl scripts complain about kernel problems?
+How do I decode encrypted password files?
-=item * How can I open a pipe both to and from a command?
+=item *
-=item * Why can't I get the output of a command with system()?
+How do I start a process in the background?
-=item * How can I capture STDERR from an external command?
+=item *
-=item * Why doesn't open() return an error when a pipe open fails?
+How do I trap control characters/signals?
-=item * What's wrong with using backticks in a void context?
+=item *
-=item * How can I call backticks without shell processing?
+How do I modify the shadow password file on a Unix system?
-=item * Why can't my script read from STDIN after I gave it EOF (^D on Unix, ^Z on MS-DOS)?
+=item *
-=item * How can I convert my shell script to perl?
+How do I set the time and date?
-=item * Can I use perl to run a telnet or ftp session?
+=item *
-=item * How can I write expect in Perl?
+How can I sleep() or alarm() for under a second?
-=item * Is there a way to hide perl's command line from programs such as "ps"?
+=item *
-=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?
+How can I measure time under a second?
-=item * How do I close a process's filehandle without waiting for it to complete?
+=item *
-=item * How do I fork a daemon process?
+How can I do an atexit() or setjmp()/longjmp()? (Exception handling)
-=item * How do I find out if I'm running interactively or not?
+=item *
-=item * How do I timeout a slow event?
+Why doesn't my sockets program work under System V (Solaris)? What does the error message "Protocol not supported" mean?
-=item * How do I set CPU limits?
+=item *
-=item * How do I avoid zombies on a Unix system?
+How can I call my system's unique C functions from Perl?
-=item * How do I use an SQL database?
+=item *
-=item * How do I make a system() exit on control-C?
+Where do I get the include files to do ioctl() or syscall()?
-=item * How do I open a file without blocking?
+=item *
-=item * How do I install a module from CPAN?
+Why do setuid perl scripts complain about kernel problems?
-=item * What's the difference between require and use?
+=item *
-=item * How do I keep my own module/library directory?
+How can I open a pipe both to and from a command?
-=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?
+Why can't I get the output of a command with system()?
-=item * What is socket.ph and where do I get it?
+=item *
-=back
+How can I capture STDERR from an external command?
+=item *
-=item L<perlfaq9>: Networking
+Why doesn't open() return an error when a pipe open fails?
-Networking, the Internet, and a few on the web.
+=item *
-=over 4
+What's wrong with using backticks in a void context?
-=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 can I call backticks without shell processing?
-=item * How do I remove HTML from a string?
+=item *
-=item * How do I extract URLs?
+Why can't my script read from STDIN after I gave it EOF (^D on Unix, ^Z on MS-DOS)?
-=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 can I convert my shell script to perl?
-=item * How do I fetch an HTML file?
+=item *
-=item * How do I automate an HTML form submission?
+Can I use perl to run a telnet or ftp session?
-=item * How do I decode or create those %-encodings on the web?
+=item *
-=item * How do I redirect to another page?
+How can I write expect in Perl?
-=item * How do I put a password on my web pages?
+=item *
-=item * How do I edit my .htpasswd and .htgroup files with Perl?
+Is there a way to hide perl's command line from programs such as "ps"?
-=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?
+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 decode a CGI form?
+=item *
-=item * How do I check a valid mail address?
+How do I close a process's filehandle without waiting for it to complete?
-=item * How do I decode a MIME/BASE64 string?
+=item *
-=item * How do I return the user's mail address?
+How do I fork a daemon process?
-=item * How do I send mail?
+=item *
-=item * How do I read mail?
+How do I find out if I'm running interactively or not?
-=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 timeout a slow event?
-=item * How do I fetch/put an FTP file?
+=item *
-=item * How can I do RPC in Perl?
+How do I set CPU limits?
-=back
+=item *
+How do I avoid zombies on a Unix system?
-=back
+=item *
-=head2 Where to get this document
+How do I use an SQL database?
-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 make a system() exit on control-C?
-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 do I open a file without blocking?
-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 do I install a module from CPAN?
-=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.
+What's the difference between require and use?
-=head1 Author and Copyright Information
+=item *
-Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.
-All rights reserved.
+How do I keep my own module/library directory?
-=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 requires that special arrangements be made with
-copyright holder.
+How do I add the directory my program lives in to the module/library search path?
-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
+How do I add a directory to my include path at runtime?
+
+=item *
+
+What is socket.ph and where do I get it?
+
+=back
-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 Changes
+=head2 L<perlfaq9>: Networking
+
+Networking, the internet, and a few on the web.
=over 4
-=item 1/November/2000
+=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?
-A few grammatical fixes and updates implemented by John Borwick.
+=item *
-=item 23/May/99
+How do I download a file from the user's machine? How do I open a file on another machine?
-Extensive updates from the net in preparation for 5.6 release.
+=item *
-=item 13/April/99
+How do I make a pop-up menu in HTML?
-More minor touch-ups. Added new question at the end
-of perlfaq7 on variable names within variables.
+=item *
-=item 7/January/99
+How do I fetch an HTML file?
-Small touchups here and there. Added all questions in this
-document as a sort of table of contents.
+=item *
-=item 22/June/98
+How do I automate an HTML form submission?
-Significant changes throughout in preparation for the 5.005
-release.
+=item *
-=item 24/April/97
+How do I decode or create those %-encodings on the web?
-Style and whitespace changes from Chip, new question on reading one
-character at a time from a terminal using POSIX from Tom.
+=item *
-=item 23/April/97
+How do I redirect to another page?
-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>.
+=item *
-=item 25/March/97
+How do I put a password on my web pages?
-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>.
+=item *
-=item 18/March/97
+How do I edit my .htpasswd and .htgroup files with Perl?
-Added the DATE to the NAME section, indicating which sections have
-changed.
+=item *
-Mentioned SIGPIPE and L<perlipc> in the forking open answer in
-L<perlfaq8>.
+How do I make sure users can't enter values into a form that cause my CGI script to do bad things?
-Fixed description of a regular expression in L<perlfaq4>.
+=item *
-=item 17/March/97 Version
+How do I parse a mail header?
-Various typos fixed throughout.
+=item *
-Added new question on Perl BNF on L<perlfaq7>.
+How do I decode a CGI form?
-=item Initial Release: 11/March/97
+=item *
-This is the initial release of version 3 of the FAQ; consequently there
-have been no changes since its initial release.
+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
+
+
projects / p5sagit/p5-mst-13.2.git / blobdiff