=head1 NAME
-perlfaq - frequently asked questions about Perl ($Date: 1999/05/23 20:38:02 $)
+perlfaq - frequently asked questions about Perl ($Revision: 3606 $)
=head1 DESCRIPTION
-This document is structured into the following sections:
+The perlfaq comprises several documents that answer the most commonly
+asked questions about Perl and Perl programming. It's divided by topic
+into nine major sections outlined in this document.
+
+=head2 Where to get the perlfaq
+
+The perlfaq comes with the standard Perl distribution, so if you have Perl
+you should have the perlfaq. You should also have the C<perldoc> tool
+that let's you read the L<perlfaq>:
+
+ $ perldoc perlfaq
+
+Besides your local system, you can find the perlfaq on the web, including
+at http://perldoc.perl.org/ .
+
+The perlfaq is an evolving document and you can read the latest version
+at http://faq.perl.org/ . The perlfaq-workers periodically post extracts
+of the latest perlfaq to comp.lang.perl.misc.
+
+You can view the source tree at
+https://svn.perl.org/modules/perlfaq/trunk/ (which is outside of the
+main Perl source tree). The SVN repository notes all changes to the FAQ
+and holds the latest version of the working documents and may vary
+significantly from the version distributed with the latest version of
+Perl. Check the repository before sending your corrections.
+
+=head2 How to contribute to the perlfaq
+
+You can mail corrections, additions, and suggestions to
+C<< <perlfaq-workers AT perl DOT org> >>. The perlfaq volunteers use this
+address to coordinate their efforts and track the perlfaq development.
+They appreciate your contributions to the FAQ but do not have time to
+provide individual help, so don't use this address to ask FAQs.
+
+The perlfaq server posts extracts of the perlfaq to that newsgroup every
+6 hours (or so), and the community of volunteers reviews and updates the
+answers. If you'd like to help review and update the answers, check out
+comp.lang.perl.misc.
+
+=head2 What will happen if you mail your Perl programming problems to the authors?
+
+The perlfaq-workers like to keep all traffic on the perlfaq-workers list
+so that everyone can see the work being done (and the work that needs to
+be done). The mailing list serves as an official record. If you email the
+authors or maintainers directly, you'll probably get a reply asking you
+to post to the mailing list. If you don't get a reply, it probably means
+that the person never saw the message or didn't have time to deal with
+it. Posting to the list allows the volunteers with time to deal with it
+when others are busy.
+
+If you have a question that isn't in the FAQ and you would like help with
+it, try the resources in L<perlfaq2>.
+
+=head1 CREDITS
+
+Tom Christiansen wrote the original perlfaq then expanded it with the
+help of Nat Torkington. The perlfaq-workers maintain current document
+and the dezinens of comp.lang.perl.misc regularly review and update the
+FAQ. Several people have contributed answers, corrections, and comments,
+and the perlfaq notes those contributions wherever appropriate.
+
+=head1 AUTHOR AND COPYRIGHT
+
+Tom Christainsen wrote the original version of this document.
+brian d foy C<< <bdfoy@cpan.org> >> wrote this version. See the
+individual perlfaq documents for additional copyright information.
+
+This document is available under the same terms as Perl itself. Code
+examples in all the perlfaq documents are in the public domain. Use
+them as you see fit (and at your own risk with no warranty from anyone).
+
+=head1 Table of Contents
=over 4
-=item perlfaq: Structural overview of the FAQ.
+=item perlfaq - this document
+
+=item perlfaq1 - General Questions About Perl
-This document.
+=item perlfaq2 - Obtaining and Learning about Perl
-=item L<perlfaq1>: General Questions About Perl
+=item perlfaq3 - Programming Tools
-Very general, high-level information about Perl.
+=item perlfaq4 - Data Manipulation
+
+=item perlfaq5 - Files and Formats
+
+=item perlfaq6 - Regular Expressions
+
+=item perlfaq7 - General Perl Language Issues
+
+=item perlfaq8 - System Interaction
+
+=item perlfaq9 - Networking
+
+=back
+
+=head1 The Questions
+
+=head2 L<perlfaq1>: General Questions About 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, perl5, or perl6?
+
+=item *
+
+What is Ponie?
-=item * Who supports Perl? Who develops it? Why is it free?
+=item *
-=item * Which version of Perl should I use?
+What is perl6?
-=item * What are perl4 and perl5?
+=item *
-=item * What is perl6?
+How stable is Perl?
-=item * How stable is Perl?
+=item *
-=item * Is Perl difficult to learn?
+Is Perl difficult to learn?
-=item * How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl?
+=item *
-=item * Can I do [task] in Perl?
+How does Perl compare with other languages like Java, Python, REXX, Scheme, or Tcl?
-=item * When shouldn't I program in Perl?
+=item *
-=item * What's the difference between "perl" and "Perl"?
+Can I do [task] in Perl?
-=item * Is it a Perl program or a Perl script?
+=item *
-=item * What is a JAPH?
+When shouldn't I program in Perl?
-=item * Where can I get a list of Larry Wall witticisms?
+=item *
-=item * How can I convince my sysadmin/supervisor/employees to use (version 5/5.005/Perl) instead of some other language?
+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,
-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. How can I build my own Perl interpreter?
+
+=item *
+
+I copied the perl binary from one machine to another, but scripts don't work.
+
+=item *
+
+I grabbed the sources and tried to compile but gdbm/dynamic loading/malloc/linking/... failed. How do I make it work?
+
+=item *
+
+What modules and extensions are available for Perl? What is CPAN? What does CPAN/src/... mean?
-=item * 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?
+Is there an ISO or ANSI certified 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?
+Where can I get information on 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?
+What are the Perl newsgroups on Usenet? Where do I post questions?
-=item * Where can I get information on Perl?
+=item *
-=item * What are the Perl newsgroups on USENET? Where do I post questions?
+Where should I post source code?
-=item * Where should I post source code?
+=item *
-=item * Perl Books
+Perl Books
-=item * Perl in Magazines
+=item *
-=item * Perl on the Net: FTP and WWW Access
+Which magazines have Perl content?
-=item * What mailing lists are there for perl?
+=item *
-=item * Archives of comp.lang.perl.misc
+What mailing lists are there for Perl?
-=item * Where can I buy a commercial version of Perl?
+=item *
-=item * Where do I send bug reports?
+Where are the archives for comp.lang.perl.misc?
-=item * What is perl.com?
+=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 *
+
+Is there a Perl shell?
+
+=item *
+
+How do I find which modules are installed on my system?
+
+=item *
+
+How do I debug my Perl programs?
+
+=item *
+
+How do I profile my Perl programs?
+
+=item *
+
+How do I cross-reference my Perl programs?
+
+=item *
-=item * How can I use Perl interactively?
+Is there a pretty-printer (formatter) for Perl?
-=item * Is there a Perl shell?
+=item *
-=item * How do I debug my Perl programs?
+Is there a ctags for Perl?
-=item * How do I profile my Perl programs?
+=item *
-=item * How do I cross-reference my Perl programs?
+Is there an IDE or Windows Perl Editor?
-=item * Is there a pretty-printer (formatter) for Perl?
+=item *
-=item * Is there a ctags for Perl?
+Where can I get Perl macros for vi?
-=item * Is there an IDE or Windows Perl Editor?
+=item *
-=item * Where can I get Perl macros for vi?
+Where can I get perl-mode for emacs?
-=item * Where can I get perl-mode for emacs?
+=item *
-=item * How can I use curses with Perl?
+How can I use curses with Perl?
-=item * How can I use X or Tk with Perl?
+=item *
-=item * How can I generate simple menus without using CGI or Tk?
+How can I use X or Tk with Perl?
-=item * What is undump?
+=item *
-=item * How can I make my Perl program run faster?
+How can I make my Perl program run faster?
-=item * How can I make my Perl program take less memory?
+=item *
-=item * Is it unsafe to return a pointer to local data?
+How can I make my Perl program take less memory?
-=item * How can I free an array or hash so my program shrinks?
+=item *
-=item * How can I make my CGI script more efficient?
+Is it safe to return a reference to local or lexical data?
-=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 free an array or hash so my program shrinks?
-=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 make my CGI script more efficient?
-=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 hide the source for my Perl program?
-=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 compile my Perl program into byte code or C?
-=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 compile Perl into Java?
-=item * When I tried to run my script, I got this message. What does it
-mean?
+=item *
-=item * What's MakeMaker?
+How can I get C<#!perl> to work on [MS-DOS,NT,...]?
+
+=item *
+
+Can I write useful Perl programs on the command line?
+
+=item *
+
+Why don't Perl one-liners work on my DOS/Mac/VMS system?
+
+=item *
+
+Where can I learn about CGI or Web programming in Perl?
+
+=item *
+
+Where can I learn about object-oriented Perl programming?
+
+=item *
+
+Where can I learn about linking C with Perl?
+
+=item *
+
+I've read perlembed, perlguts, etc., but I can't embed perl in my C program; what am I doing wrong?
+
+=item *
+
+When I tried to run my script, I got this message. What does it mean?
+
+=item *
+
+What's MakeMaker?
=back
-=
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 handle linked lists?
+
+=item *
+
+How do I handle circular lists?
+
+=item *
+
+How do I shuffle an array randomly?
+
+=item *
+
+How do I process/modify each element of an array?
+
+=item *
-=item * How do I flush/unbuffer an output filehandle? Why must I do this?
+How do I select a random element from an array?
-=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 do I permute N elements of a list?
-=item * How do I make a temporary file name?
+=item *
-=item * How can I manipulate fixed-record-length files?
+How do I sort an array by (anything)?
-=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?
+How do I manipulate arrays of bits?
-=item * How can I set up a footer format to be used with write()?
+=item *
-=item * How can I write() into a string?
+Why does defined() return true on empty arrays and hashes?
-=item * How can I output my numbers with commas added?
+=item *
-=item * How can I translate tildes (~) in a filename?
+How do I process an entire hash?
-=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 <*>?
+What happens if I add or remove keys from a hash while iterating over it?
-=item * Is there a leak/bug in glob()?
+=item *
-=item * How can I open a file with a leading ">" or trailing blanks?
+How do I look up a hash element by value?
-=item * How can I reliably rename a file?
+=item *
-=item * How can I lock a file?
+How can I know how many entries are in a hash?
-=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?
+How do I sort a hash (optionally by value instead of key)?
-=item * How do I randomly update a binary file?
+=item *
-=item * How do I get a file's timestamp in perl?
+How can I always keep my hash sorted?
-=item * How do I set a file's timestamp in perl?
+=item *
-=item * How do I print to more than one file at once?
+What's the difference between "delete" and "undef" with hashes?
-=item * How can I read in an entire file all at once?
+=item *
-=item * How can I read in a file by paragraphs?
+Why don't my tied hashes make the defined/exists distinction?
-=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 reset an each() operation part-way through?
-=item * How do I do a C<tail -f> in perl?
+=item *
-=item * How do I dup() a filehandle in Perl?
+How can I get the unique keys from two hashes?
-=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 store a multidimensional array in a DBM file?
-=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 make my hash remember the order I put elements into it?
-=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?
+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 can I copy a file?
+
+=item *
+
+How do I make a temporary file name?
+
+=item *
+
+How can I manipulate fixed-record-length files?
+
+=item *
+
+How can I make a filehandle local to a subroutine? How do I pass filehandles between subroutines? How do I make an array of filehandles?
+
+=item *
+
+How can I use a filehandle indirectly?
+
+=item *
+
+How can I set up a footer format to be used with write()?
+
+=item *
-=item * I'm having trouble matching over more than one line. What's wrong?
+How can I write() into a string?
-=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 output my numbers with commas added?
-=item * How do I substitute case insensitively on the LHS while preserving case on the RHS?
+=item *
-=item * How can I make C<\w> match national character sets?
+How can I translate tildes (~) in a filename?
-=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 come when I open a file read-write it wipes it out?
-=item * What is C</o> really for?
+=item *
-=item * How do I use a regular expression to strip C style comments from a file?
+Why do I sometimes get an "Argument list too long" when I use E<lt>*E<gt>?
-=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?
+Is there a leak/bug in glob()?
-=item * How do I process each word on each line?
+=item *
-=item * How can I print out a word-frequency or line-frequency summary?
+How can I open a file with a leading ">" or trailing blanks?
-=item * How can I do approximate matching?
+=item *
-=item * How do I efficiently match many regular expressions at once?
+How can I reliably rename a file?
-=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 lock a file?
-=item * What good is C<\G> in a regular expression?
+=item *
-=item * Are Perl regexes DFAs or NFAs? Are they POSIX compliant?
+Why can't I just open(FH, "E<gt>file.lock")?
-=item * What's wrong with using grep or map in a void context?
+=item *
-=item * How can I match strings with multibyte characters?
+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 match a pattern that is supplied by the user?
+=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 * 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?
+I put a regular expression into $/ but it didn't work. What's wrong?
-=item * How do I skip some return values?
+=item *
-=item * How do I temporarily block warnings?
+How do I substitute case insensitively on the LHS while preserving case on the RHS?
-=item * What's an extension?
+=item *
-=item * Why do Perl operators have different precedence than C operators?
+How can I make C<\w> match national character sets?
-=item * How do I declare/create a structure?
+=item *
-=item * How do I create a module?
+How can I match a locale-smart version of C</[a-zA-Z]/>?
-=item * How do I create a class?
+=item *
-=item * How can I tell if a variable is tainted?
+How can I quote a variable to use in a regex?
-=item * What's a closure?
+=item *
-=item * What is variable suicide and how can I prevent it?
+What is C</o> really for?
-=item * How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}?
+=item *
-=item * How do I create a static variable?
+How do I use a regular expression to strip C style comments from a file?
-=item * What's the difference between dynamic and lexical (static) scoping? Between local() and my()?
+=item *
-=item * How can I access a dynamic variable while a similarly named lexical is in scope?
+Can I use Perl regular expressions to match balanced text?
-=item * What's the difference between deep and shallow binding?
+=item *
-=item * Why doesn't "my($foo) = <FILE>;" work right?
+What does it mean that regexes are greedy? How can I get around it?
-=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 do I process each word on each line?
-=item * How do I create a switch or case statement?
+=item *
-=item * How can I catch accesses to undefined variables/functions/methods?
+How can I print out a word-frequency or line-frequency summary?
-=item * Why can't a method included in this same file be found?
+=item *
-=item * How can I find out my current package?
+How can I do approximate matching?
-=item * How can I comment out a large block of perl code?
+=item *
-=item * How do I clear a package?
+How do I efficiently match many regular expressions at once?
-=item * How can I use a variable as a variable name?
+=item *
+
+Why don't word-boundary searches with C<\b> work for me?
+
+=item *
+
+Why does using $&, $`, or $' slow my program down?
+
+=item *
+
+What good is C<\G> in a regular expression?
+
+=item *
+
+Are Perl regexes DFAs or NFAs? Are they POSIX compliant?
+
+=item *
+
+What's wrong with using grep in a void context?
+
+=item *
+
+How can I match strings with multibyte characters?
+
+=item *
+
+How do I match a 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 *
+
+What are all these $@%&* punctuation signs, and how do I know when to use them?
+
+=item *
+
+Do I always/never have to quote my strings or use semicolons and commas?
+
+=item *
-=item * How come exec() doesn't return?
+How do I skip some return values?
-=item * How do I do fancy stuff with the keyboard/screen/mouse?
+=item *
-=item * How do I print something out in color?
+How do I temporarily block warnings?
-=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?
+What's an extension?
-=item * How do I clear the screen?
+=item *
-=item * How do I get the screen size?
+Why do Perl operators have different precedence than C operators?
-=item * How do I ask the user for a password?
+=item *
-=item * How do I read and write the serial port?
+How do I declare/create a structure?
-=item * How do I decode encrypted password files?
+=item *
-=item * How do I start a process in the background?
+How do I create a module?
-=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 create a class?
-=item * How do I set the time and date?
+=item *
-=item * How can I sleep() or alarm() for under a second?
+How can I tell if a variable is tainted?
-=item * How can I measure time under a second?
+=item *
-=item * How can I do an atexit() or setjmp()/longjmp()? (Exception handling)
+What's a closure?
-=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?
+What is variable suicide and how can I prevent it?
-=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 can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}?
-=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 create a static variable?
-=item * How can I capture STDERR from an external command?
+=item *
-=item * Why doesn't open() return an error when a pipe open fails?
+What's the difference between dynamic and lexical (static) scoping? Between local() and my()?
-=item * What's wrong with using backticks in a void context?
+=item *
-=item * How can I call backticks without shell processing?
+How can I access a dynamic variable while a similarly named lexical is in scope?
-=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?
+What's the difference between deep and shallow binding?
-=item * Can I use perl to run a telnet or ftp session?
+=item *
-=item * How can I write expect in Perl?
+Why doesn't "my($foo) = E<lt>FILEE<gt>;" work right?
-=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 do I redefine a builtin function, operator, or method?
-=item * How do I close a process's filehandle without waiting for it to complete?
+=item *
-=item * How do I fork a daemon process?
+What's the difference between calling a function as &foo and foo()?
-=item * How do I make my program run with sh and csh?
+=item *
-=item * How do I find out if I'm running interactively or not?
+How do I create a switch or case statement?
-=item * How do I timeout a slow event?
+=item *
-=item * How do I set CPU limits?
+How can I catch accesses to undefined variables, functions, or methods?
-=item * How do I avoid zombies on a Unix system?
+=item *
-=item * How do I use an SQL database?
+Why can't a method included in this same file be found?
-=item * How do I make a system() exit on control-C?
+=item *
-=item * How do I open a file without blocking?
+How can I find out my current package?
-=item * How do I install a module from CPAN?
+=item *
-=item * What's the difference between require and use?
+How can I comment out a large block of perl code?
-=item * How do I keep my own module/library directory?
+=item *
-=item * How do I add the directory my program lives in to the module/library search path?
+How do I clear a package?
-=item * How do I add a directory to my include path at runtime?
+=item *
-=item * What is socket.ph and where do I get it?
+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 *
+
+How do I modify the shadow password file on a Unix system?
+
+=item *
+
+How do I set the time and date?
+
+=item *
+
+How can I sleep() or alarm() for under a second?
+
+=item *
+
+How can I measure time under a second?
+
+=item *
+
+How can I do an atexit() or setjmp()/longjmp()? (Exception handling)
+
+=item *
+
+Why doesn't my sockets program work under System V (Solaris)? What does the error message "Protocol not supported" mean?
+
+=item *
+
+How can I call my system's unique C functions from Perl?
+
+=item *
+
+Where do I get the include files to do ioctl() or syscall()?
-=head2 Where to get this document
+=item *
-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/ .
+Why do setuid perl scripts complain about kernel problems?
-=head2 How to contribute to this document
+=item *
-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.
+How can I open a pipe both to and from a command?
-=head2 What will happen if you mail your Perl programming problems to the authors
+=item *
-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.
+Why can't I get the output of a command with system()?
-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.
+=item *
-=head1 Credits
+How can I capture STDERR from an external command?
-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.
+=item *
-=head1 Author and Copyright Information
+Why doesn't open() return an error when a pipe open fails?
-Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.
-All rights reserved.
+=item *
-=head2 Bundled Distributions
+What's wrong with using backticks in a void context?
-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.
+=item *
-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.
+How can I call backticks without shell processing?
-=head2 Disclaimer
+=item *
-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.
+Why can't my script read from STDIN after I gave it EOF (^D on Unix, ^Z on MS-DOS)?
-=head1 Changes
+=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 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?
+
+=item *
+
+How do I download a file from the user's machine? How do I open a file on another machine?
-A few grammatical fixes and updates implemented by John Borwick.
+=item *
-=item 23/May/99
+How do I make a pop-up menu in HTML?
-Extensive updates from the net in preparation for 5.6 release.
+=item *
-=item 13/April/99
+How do I fetch an HTML file?
-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 automate an HTML form submission?
-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 decode or create those %-encodings on the web?
-Significant changes throughout in preparation for the 5.005
-release.
+=item *
-=item 24/April/97
+How do I redirect to another page?
-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 put a password on my web pages?
-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 edit my .htpasswd and .htgroup files with Perl?
-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 make sure users can't enter values into a form that cause my CGI script to do bad things?
-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 parse a mail header?
-Fixed description of a regular expression in L<perlfaq4>.
+=item *
-=item 17/March/97 Version
+How do I decode a CGI form?
-Various typos fixed throughout.
+=item *
-Added new question on Perl BNF on L<perlfaq7>.
+How do I check a valid mail address?
-=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 decode a MIME/BASE64 string?
+
+=item *
+
+How do I return the user's mail address?
+
+=item *
+
+How do I send mail?
+
+=item *
+
+How do I use MIME to make an attachment to a mail message?
+
+=item *
+
+How do I read mail?
+
+=item *
+
+How do I find out my hostname, domainname, or IP address?
+
+=item *
+
+How do I fetch a news article or the active newsgroups?
+
+=item *
+
+How do I fetch/put an FTP file?
+
+=item *
+
+How can I do RPC in Perl?
=back
+
+
https://perl5.git.perl.org / perl5.git / blobdiff