X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlfaq.pod;h=7acdf613d041bfa49bb01cc45d8e7e5509cd57c3;hb=80b46460027bf2bee58a37ec48620576b7519f26;hp=cb354931ccc90f134cb675438d7a6722b2417685;hpb=65acb1b1d672587d3a0d073613a475584830e38e;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlfaq.pod b/pod/perlfaq.pod index cb35493..7acdf61 100644 --- a/pod/perlfaq.pod +++ b/pod/perlfaq.pod @@ -1,819 +1,1402 @@ =head1 NAME -perlfaq - frequently asked questions about Perl ($Date: 1999/01/08 05:54:52 $) +perlfaq - frequently asked questions about Perl ($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. -=over +=head2 Where to get the perlfaq -=item perlfaq: Structural overview of the FAQ. +Extracts of the perlfaq are posted regularly to +comp.lang.perl.misc. It is available on many web sites: +http://www.perldoc.com/ and http://faq.perl.org/ -This document. +=head2 How to contribute to the perlfaq + +You may mail corrections, additions, and suggestions to +perlfaq-workers@perl.org . This alias should not be used to +I FAQs. It's for fixing the current FAQ. Send +questions to the comp.lang.perl.misc newsgroup. You can +view the source tree at http://cvs.perl.org/cvsweb/perlfaq/ +(which is outside of the main Perl source tree). The CVS +repository notes all changes to the FAQ. + +=head2 What will happen if you mail your Perl programming problems to the authors + +Your questions will probably go unread, unless they're +suggestions of new questions to add to the FAQ, in which +case they should have gone to the perlfaq-workers@perl.org +instead. + +You should have read section 2 of this faq. There you would +have learned that comp.lang.perl.misc is the appropriate +place to go for free advice. If your question is really +important and you require a prompt and correct answer, you +should hire a consultant. + +=head1 Credits + +The original perlfaq was written by Tom Christiansen, then expanded +by collaboration between Tom and Nathan Torkington. The current +document is maintained by the perlfaq-workers (perlfaq-workers@perl.org). +Several people have contributed answers, corrections, and comments. + +=head1 Author and Copyright Information + +Copyright (c) 1997-2003 Tom Christiansen, Nathan Torkington, and +other contributors noted in the answers. + +All rights reserved. + +=head2 Bundled Distributions + +This documentation is free; you can redistribute it and/or modify it +under the same terms as Perl itself. + +Irrespective of its distribution, all code examples in these files +are hereby placed into the public domain. You are permitted and +encouraged to use this code in your own programs for fun +or for profit as you see fit. A simple comment in the code giving +credit would be courteous but is not required. + +=head2 Disclaimer + +This information is offered in good faith and in the hope that it may +be of use, but is not guaranteed to be correct, up to date, or suitable +for any particular purpose whatsoever. The authors accept no liability +in respect of this information or its use. + +=head1 Table of Contents + +=over 4 + +=item perlfaq - this document + +=item perlfaq1 - General Questions About Perl + +=item perlfaq2 - Obtaining and Learning about Perl + +=item perlfaq3 - Programming Tools + +=item perlfaq4 - Data Manipulation + +=item perlfaq5 - Files and Formats + +=item perlfaq6 - Regular Expressions + +=item perlfaq7 - General Perl Language Issues + +=item perlfaq8 - System Interaction + +=item perlfaq9 - Networking -=item L: General Questions About Perl -Very general, high-level information about Perl. +=back + + +=head1 The Questions + +=head2 L: 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: Obtaining and Learning about Perl +=head2 L: 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 * -=item * How can I get a binary version of Perl? +How can I get a binary version of Perl? -=item * I don't have a C compiler on my system. How can I compile perl? +=item * -=item * I copied the Perl binary from one machine to another, but scripts don't work. +I don't have a C compiler on my system. How can I compile perl? -=item * I grabbed the sources and tried to compile but gdbm/dynamic loading/malloc/linking/... failed. How do I make it work? +=item * -=item * What modules and extensions are available for Perl? What is CPAN? What does CPAN/src/... mean? +I copied the Perl binary from one machine to another, but scripts don't work. -=item * Is there an ISO or ANSI certified version of Perl? +=item * -=item * Where can I get information on Perl? +I grabbed the sources and tried to compile but gdbm/dynamic loading/malloc/linking/... failed. How do I make it work? -=item * What are the Perl newsgroups on USENET? Where do I post questions? +=item * -=item * Where should I post source code? +What modules and extensions are available for Perl? What is CPAN? What does CPAN/src/... mean? -=item * Perl Books +=item * -=item * Perl in Magazines +Is there an ISO or ANSI certified version of Perl? -=item * Perl on the Net: FTP and WWW Access +=item * -=item * What mailing lists are there for perl? +Where can I get information on Perl? -=item * Archives of comp.lang.perl.misc +=item * -=item * Where can I buy a commercial version of Perl? +What are the Perl newsgroups on Usenet? Where do I post questions? -=item * Where do I send bug reports? +=item * -=item * What is perl.com? +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: Programming Tools +=head2 L: 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 can I use Perl interactively? +=item * -=item * Is there a Perl shell? +How do I find which modules are installed on my system? -=item * How do I debug my Perl programs? +=item * -=item * How do I profile my Perl programs? +How do I debug my Perl programs? -=item * How do I cross-reference my Perl programs? +=item * -=item * Is there a pretty-printer (formatter) for Perl? +How do I profile my Perl programs? -=item * Is there a ctags for Perl? +=item * -=item * Is there an IDE or Windows Perl Editor? +How do I cross-reference my Perl programs? -=item * Where can I get Perl macros for vi? +=item * -=item * Where can I get perl-mode for emacs? +Is there a pretty-printer (formatter) for Perl? -=item * How can I use curses with Perl? +=item * -=item * How can I use X or Tk with Perl? +Is there a ctags for Perl? -=item * How can I generate simple menus without using CGI or Tk? +=item * -=item * What is undump? +Is there an IDE or Windows Perl Editor? -=item * How can I make my Perl program run faster? +=item * -=item * How can I make my Perl program take less memory? +Where can I get Perl macros for vi? -=item * Is it unsafe to return a pointer to local data? +=item * -=item * How can I free an array or hash so my program shrinks? +Where can I get perl-mode for emacs? -=item * How can I make my CGI script more efficient? +=item * -=item * How can I hide the source for my Perl program? +How can I use curses with Perl? -=item * How can I compile my Perl program into byte code or C? +=item * -=item * How can I compile Perl into Java? +How can I use X or Tk with Perl? -=item * How can I get C<#!perl> to work on [MS-DOS,NT,...]? +=item * -=item * Can I write useful perl programs on the command line? +How can I generate simple menus without using CGI or Tk? -=item * Why don't perl one-liners work on my DOS/Mac/VMS system? +=item * -=item * Where can I learn about CGI or Web programming in Perl? +How can I make my Perl program run faster? -=item * Where can I learn about object-oriented Perl programming? +=item * -=item * Where can I learn about linking C with Perl? [h2xs, xsubpp] +How can I make my Perl program take less memory? -=item * I've read perlembed, perlguts, etc., but I can't embed perl in -my C program, what am I doing wrong? +=item * -=item * When I tried to run my script, I got this message. What does it -mean? +Is it safe to return a reference to local or lexical data? -=item * What's MakeMaker? +=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 * + +What's MakeMaker? =back -=item L: Data Manipulation +=head2 L: 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 * + +How do I capitalize all the words on one line? + +=item * -=item * Why isn't my octal data interpreted correctly? +How can I split a [character] delimited string except when inside [character]? -=item * Does Perl have a round() function? What about ceil() and floor()? Trig functions? +=item * -=item * How do I convert bits into ints? +How do I strip blank space from the beginning/end of a string? -=item * Why doesn't & work the way I want it to? +=item * -=item * How do I multiply matrices? +How do I pad a string with blanks or pad a number with zeroes? -=item * How do I perform an operation on a series of integers? +=item * -=item * How can I output Roman numerals? +How do I extract selected columns from a string? -=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 find the soundex value of 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 can I expand variables in text strings? -=item * How can I find the Julian Day? +=item * -=item * How do I find yesterday's date? +What's wrong with always quoting "$vars"? -=item * Does Perl have a year 2000 problem? Is Perl Y2K compliant? +=item * -=item * How do I validate input? +Why don't my EEHERE documents work? -=item * How do I unescape a string? +=item * -=item * How do I remove consecutive pairs of characters? +What is the difference between a list and an array? -=item * How do I expand function calls in a string? +=item * -=item * How do I find matching/nesting anything? +What is the difference between $array[1] and @array[1]? -=item * How do I reverse a string? +=item * -=item * How do I expand tabs in a string? +How can I remove duplicate elements from a list or array? -=item * How do I reformat a paragraph? +=item * -=item * How can I access/change the first N letters of a string? +How can I tell whether a certain element is contained in a list or array? -=item * How do I change the Nth occurrence of something? +=item * -=item * How can I count the number of occurrences of a substring within a string? +How do I compute the difference of two arrays? How do I compute the intersection of two arrays? -=item * How do I capitalize all the words on one line? +=item * -=item * How can I split a [character] delimited string except when inside -[character]? (Comma-separated files) +How do I test whether two arrays or hashes are equal? -=item * How do I strip blank space from the beginning/end of a string? +=item * -=item * How do I pad a string with blanks or pad a number with zeroes? +How do I find the first array element for which a condition is true? -=item * How do I extract selected columns from a string? +=item * -=item * How do I find the soundex value of a string? +How do I handle linked lists? -=item * How can I expand variables in text strings? +=item * -=item * What's wrong with always quoting "$vars"? +How do I handle circular lists? -=item * Why don't my EEHERE documents work? +=item * -=item * What is the difference between a list and an array? +How do I shuffle an array randomly? -=item * What is the difference between $array[1] and @array[1]? +=item * -=item * How can I extract just the unique elements of an array? +How do I process/modify each element of an array? -=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 select a random element from 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 permute N elements of a list? -=item * How do I handle linked lists? +=item * -=item * How do I handle circular lists? +How do I sort an array by (anything)? -=item * How do I shuffle an array randomly? +=item * -=item * How do I process/modify each element of an array? +How do I manipulate arrays of bits? -=item * How do I select a random element from an array? +=item * -=item * How do I permute N elements of a list? +Why does defined() return true on empty arrays and hashes? -=item * How do I sort an array by (anything)? +=item * -=item * How do I manipulate arrays of bits? +How do I process an entire hash? -=item * Why does defined() return true on empty arrays and hashes? +=item * -=item * How do I process an entire hash? +What happens if I add or remove keys from a hash while iterating over it? -=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? +How do I look up a hash element by value? -=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 can I know how many entries are in a hash? -=item * How can I always keep my hash sorted? +=item * -=item * What's the difference between "delete" and "undef" with hashes? +How do I sort a hash (optionally by value instead of key)? -=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 can I always keep my hash sorted? -=item * How can I get the unique keys from two hashes? +=item * -=item * How can I store a multidimensional array in a DBM file? +What's the difference between "delete" and "undef" with hashes? -=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? +Why don't my tied hashes make the defined/exists distinction? -=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? +How do I reset an each() operation part-way through? -=item * How do I handle binary data correctly? +=item * -=item * How do I determine whether a scalar is a number/whole/integer/float? +How can I get the unique keys from two hashes? -=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 store a multidimensional array in a DBM file? -=item * How do I define methods for every class/object? +=item * -=item * How do I verify a credit card checksum? +How can I make my hash remember the order I put elements into it? -=item * How do I pack arrays of doubles or floats for XS code? +=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: Files and Formats +=head2 L: 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 can I translate tildes (~) in a filename? + +=item * -=item * How do I change one line in a file/delete a line in a file/insert a line in the middle of a file/append to the beginning of a file? +How come when I open a file read-write it wipes it out? -=item * How do I count the number of lines in a file? +=item * -=item * How do I make a temporary file name? +Why do I sometimes get an "Argument list too long" when I use E*E? -=item * How can I manipulate fixed-record-length files? +=item * -=item * How can I make a filehandle local to a subroutine? How do I pass filehandles between subroutines? How do I make an array of filehandles? +Is there a leak/bug in glob()? -=item * How can I use a filehandle indirectly? +=item * -=item * How can I set up a footer format to be used with write()? +How can I open a file with a leading ">" or trailing blanks? -=item * How can I write() into a string? +=item * -=item * How can I output my numbers with commas added? +How can I reliably rename a file? -=item * How can I translate tildes (~) in a filename? +=item * -=item * How come when I open a file read-write it wipes it out? +How can I lock a file? -=item * Why do I sometimes get an "Argument list too long" when I use E*E? +=item * -=item * Is there a leak/bug in glob()? +Why can't I just open(FH, "Efile.lock")? -=item * How can I open a file with a leading "E" or trailing blanks? +=item * -=item * How can I reliably rename a file? +I still don't get locking. I just want to increment the number in the file. How can I do this? -=item * How can I lock a file? +=item * -=item * Why can't I just open(FH, ">file.lock")? +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 * I still don't get locking. I just want to increment the number in the file. How can I do this? +=item * -=item * How do I randomly update a binary file? +How do I randomly update a binary file? -=item * How do I get a file's timestamp in perl? +=item * -=item * How do I set a file's timestamp in perl? +How do I get a file's timestamp in perl? -=item * How do I print to more than one file at once? +=item * -=item * How can I read in a file by paragraphs? +How do I set 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 print to more than one file at once? -=item * How do I do a C in perl? +=item * -=item * How do I dup() a filehandle in Perl? +How can I read in an entire file all 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 a file by paragraphs? -=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 a single character from a file? From the keyboard? -=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 tell whether there's a character waiting on a filehandle? + +=item * + +How do I do a C 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: Regexps +=head2 L: 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 * + +How can I pull out lines between two patterns that are themselves on different lines? + +=item * -=item * I'm having trouble matching over more than one line. What's wrong? +I put a regular expression into $/ but it didn't work. What's wrong? -=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 do I substitute case insensitively on the LHS while preserving case on the RHS? -=item * How do I substitute case insensitively on the LHS, but preserving case on the RHS? +=item * -=item * How can I make C<\w> match national character sets? +How can I make C<\w> match national character sets? -=item * How can I match a locale-smart version of C? +=item * -=item * How can I quote a variable to use in a regexp? +How can I match a locale-smart version of C? -=item * What is C really for? +=item * -=item * How do I use a regular expression to strip C style comments from a file? +How can I quote a variable to use in a regex? -=item * Can I use Perl regular expressions to match balanced text? +=item * -=item * What does it mean that regexps are greedy? How can I get around it? +What is C really for? -=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 do I use a regular expression to strip C style comments from a file? -=item * How can I do approximate matching? +=item * -=item * How do I efficiently match many regular expressions at once? +Can I use Perl regular expressions to match balanced text? -=item * Why don't word-boundary searches with C<\b> work for me? +=item * -=item * Why does using $&, $`, or $' slow my program down? +What does it mean that regexes are greedy? How can I get around it? -=item * What good is C<\G> in a regular expression? +=item * -=item * Are Perl regexps DFAs or NFAs? Are they POSIX compliant? +How do I process each word on each line? -=item * What's wrong with using grep or map in a void context? +=item * -=item * How can I match strings with multibyte characters? +How can I print out a word-frequency or line-frequency summary? -=item * How do I match a pattern that is supplied by the user? +=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: General Perl Language Issues +=head2 L: 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 * What are all these $@%* punctuation signs, and how do I know when to use them? +Do I always/never have to quote my strings or use semicolons and commas? -=item * Do I always/never have to quote my strings or use semicolons and commas? +=item * -=item * How do I skip some return values? +How do I skip some return values? -=item * How do I temporarily block warnings? +=item * -=item * What's an extension? +How do I temporarily block warnings? -=item * Why do Perl operators have different precedence than C operators? +=item * -=item * How do I declare/create a structure? +What's an extension? -=item * How do I create a module? +=item * -=item * How do I create a class? +Why do Perl operators have different precedence than C operators? -=item * How can I tell if a variable is tainted? +=item * -=item * What's a closure? +How do I declare/create a structure? -=item * What is variable suicide and how can I prevent it? +=item * -=item * How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regexp}? +How do I create a module? -=item * How do I create a static variable? +=item * -=item * What's the difference between dynamic and lexical (static) scoping? Between local() and my()? +How do I create a class? -=item * How can I access a dynamic variable while a similarly named lexical is in scope? +=item * -=item * What's the difference between deep and shallow binding? +How can I tell if a variable is tainted? -=item * Why doesn't "my($foo) = EFILEE;" work right? +=item * -=item * How do I redefine a builtin function, operator, or method? +What's a closure? -=item * What's the difference between calling a function as &foo and foo()? +=item * -=item * How do I create a switch or case statement? +What is variable suicide and how can I prevent it? -=item * How can I catch accesses to undefined variables/functions/methods? +=item * -=item * Why can't a method included in this same file be found? +How can I pass/return a {Function, FileHandle, Array, Hash, Method, Regex}? -=item * How can I find out my current package? +=item * -=item * How can I comment out a large block of perl code? +How do I create a static variable? -=item * How do I clear a package? +=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) = EFILEE;" 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: System Interaction +=head2 L: 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 make my program run with sh and csh? +=item * -=item * How do I find out if I'm running interactively or not? +Why doesn't my sockets program work under System V (Solaris)? What does the error message "Protocol not supported" mean? -=item * How do I timeout a slow event? +=item * -=item * How do I set CPU limits? +How can I call my system's unique C functions from Perl? -=item * How do I avoid zombies on a Unix system? +=item * -=item * How do I use an SQL database? +Where do I get the include files to do ioctl() or syscall()? -=item * How do I make a system() exit on control-C? +=item * -=item * How do I open a file without blocking? +Why do setuid perl scripts complain about kernel problems? -=item * How do I install a CPAN module? +=item * -=item * What's the difference between require and use? +How can I open a pipe both to and from a command? -=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? +Why can't I get the output of a command with system()? -=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 capture STDERR from an external command? -=back +=item * +Why doesn't open() return an error when a pipe open fails? -=item L: Networking +=item * -Networking, the Internet, and a few on the web. +What's wrong with using backticks in a void context? -=over 4 +=item * -=item * My CGI script runs from the command line but not the browser. (500 Server Error) +How can I call backticks without shell processing? -=item * How can I get better error messages from a CGI program? +=item * -=item * How do I remove HTML from a string? +Why can't my script read from STDIN after I gave it EOF (^D on Unix, ^Z on MS-DOS)? -=item * How do I extract URLs? +=item * -=item * How do I download a file from the user's machine? How do I open a file on another machine? +How can I convert my shell script to perl? -=item * How do I make a pop-up menu in HTML? +=item * -=item * How do I fetch an HTML file? +Can I use perl to run a telnet or ftp session? -=item * How do I automate an HTML form submission? +=item * -=item * How do I decode or create those %-encodings on the web? +How can I write expect in Perl? -=item * How do I redirect to another page? +=item * -=item * How do I put a password on my web pages? +Is there a way to hide perl's command line from programs such as "ps"? -=item * How do I edit my .htpasswd and .htgroup files with Perl? +=item * -=item * How do I make sure users can't enter values into a form that cause my CGI script to do bad things? +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 parse a mail header? +=item * -=item * How do I decode a CGI form? +How do I close a process's filehandle without waiting for it to complete? -=item * How do I check a valid mail address? +=item * -=item * How do I decode a MIME/BASE64 string? +How do I fork a daemon process? -=item * How do I return the user's mail address? +=item * -=item * How do I send mail? +How do I find out if I'm running interactively or not? -=item * How do I read mail? +=item * -=item * How do I find out my hostname/domainname/IP address? +How do I timeout a slow event? -=item * How do I fetch a news article or the active newsgroups? +=item * -=item * How do I fetch/put an FTP file? +How do I set CPU limits? -=item * How can I do RPC in Perl? +=item * -=back +How do I avoid zombies on a Unix system? +=item * -=back +How do I use an SQL database? -=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/ . +How do I make a system() exit on control-C? -=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 FAQs. It's for fixing the current FAQ. -Send questions to the comp.lang.perl.misc newsgroup. +How do I open a file without blocking? -=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. +How do I install a module from CPAN? -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 +What's the difference between require and use? -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 +How do I keep my own module/library directory? -Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington. -All rights reserved. +=item * -=head2 Bundled Distributions +How do I add the directory my program lives in to the module/library search path? -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 -of that package require 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 do I add a directory to my include path at runtime? -=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. +What is socket.ph and where do I get it? + +=back -=head1 Changes + +=head2 L: Networking + +Networking, the internet, and a few on the web. =over 4 -=item 7/January/99 +=item * + +What is the correct form of response from a CGI script? + +=item * + +My CGI script runs from the command line but not the browser. (500 Server Error) + +=item * + +How can I get better error messages from a CGI program? + +=item * + +How do I remove HTML from a string? + +=item * + +How do I extract URLs? + +=item * + +How do I download a file from the user's machine? How do I open a file on another machine? + +=item * + +How do I make a pop-up menu in HTML? -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 fetch an HTML file? -Significant changes throughout in preparation for the 5.005 -release. +=item * -=item 24/April/97 +How do I automate an HTML form submission? -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 decode or create those %-encodings on the web? -Added http://www.oasis.leo.org/perl/ to L. Style fix to -L. 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. Added example of passing and storing -filehandles, added commify to L. Restored variable suicide, -and added mass commenting to L. Added Net::Telnet, fixed -backticks, added reader/writer pair to telnet question, added FindBin, -grouped module questions together in L. Expanded caveats -for the simple URL extractor, gave LWP example, added CGI security -question, expanded on the mail address answer in L. +=item * -=item 25/March/97 +How do I redirect to another page? -Added more info to the binary distribution section of L. -Added Net::Telnet to L. Fixed typos in L. Added -mail sending example to L. Added Merlyn's columns to -L. +=item * -=item 18/March/97 +How do I put a password on my web pages? -Added the DATE to the NAME section, indicating which sections have -changed. +=item * -Mentioned SIGPIPE and L in the forking open answer in -L. +How do I edit my .htpasswd and .htgroup files with Perl? -Fixed description of a regular expression in L. +=item * -=item 17/March/97 Version +How do I make sure users can't enter values into a form that cause my CGI script to do bad things? -Various typos fixed throughout. +=item * -Added new question on Perl BNF on L. +How do I parse a mail header? -=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 CGI form? + +=item * + +How do I check a valid mail address? + +=item * + +How do I decode a MIME/BASE64 string? + +=item * + +How do I return the user's mail address? + +=item * + +How do I send mail? + +=item * + +How do I use MIME to make an attachment to a mail message? + +=item * + +How do I read mail? + +=item * + +How do I find out my hostname/domainname/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 +