/IronPython_Main/Runtime/Tests/LinqDlrTests/testenv/perl/lib/pod/perlfaq3.pod

=head1 NAME



perlfaq3 - Programming Tools ($Revision: 1.38 $, $Date: 1999/05/23 16:08:30 $)



=head1 DESCRIPTION



This section of the FAQ answers questions related to programmer tools

and programming support.



=head2 How do I do (anything)?



Have you looked at CPAN (see L<perlfaq2>)?  The chances are that

someone has already written a module that can solve your problem.

Have you read the appropriate man pages?  Here's a brief index:



	Basics	        perldata, perlvar, perlsyn, perlop, perlsub

	Execution	perlrun, perldebug

	Functions	perlfunc

	Objects		perlref, perlmod, perlobj, perltie

	Data Structures	perlref, perllol, perldsc

	Modules		perlmod, perlmodlib, perlsub

	Regexes		perlre, perlfunc, perlop, perllocale

	Moving to perl5	perltrap, perl

	Linking w/C	perlxstut, perlxs, perlcall, perlguts, perlembed

	Various 	http://www.perl.com/CPAN/doc/FMTEYEWTK/index.html

			(not a man-page but still useful)



A crude table of contents for the Perl man page set is found in L<perltoc>.



=head2 How can I use Perl interactively?



The typical approach uses the Perl debugger, described in the

perldebug(1) man page, on an ``empty'' program, like this:



    perl -de 42



Now just type in any legal Perl code, and it will be immediately

evaluated.  You can also examine the symbol table, get stack

backtraces, check variable values, set breakpoints, and other

operations typically found in symbolic debuggers.



=head2 Is there a Perl shell?



In general, no.  The Shell.pm module (distributed with Perl) makes

Perl try commands which aren't part of the Perl language as shell

commands.  perlsh from the source distribution is simplistic and

uninteresting, but may still be what you want.



=head2 How do I debug my Perl programs?



Have you tried C<use warnings> or used C<-w>?  They enable warnings 

to detect dubious practices.



Have you tried C<use strict>?  It prevents you from using symbolic

references, makes you predeclare any subroutines that you call as bare

words, and (probably most importantly) forces you to predeclare your

variables with C<my>, C<our>, or C<use vars>.



Did you check the return values of each and every system call?  The operating

system (and thus Perl) tells you whether they worked, and if not

why.



  open(FH, "> /etc/cantwrite")

    or die "Couldn't write to /etc/cantwrite: $!\n";



Did you read L<perltrap>?  It's full of gotchas for old and new Perl

programmers and even has sections for those of you who are upgrading

from languages like I<awk> and I<C>.



Have you tried the Perl debugger, described in L<perldebug>?  You can

step through your program and see what it's doing and thus work out

why what it's doing isn't what it should be doing.



=head2 How do I profile my Perl programs?



You should get the Devel::DProf module from the standard distribution

(or separately on CPAN) and also use Benchmark.pm from the standard 

distribution.  The Benchmark module lets you time specific portions of 

your code, while Devel::DProf gives detailed breakdowns of where your 

code spends its time.



Here's a sample use of Benchmark:



  use Benchmark;



  @junk = `cat /etc/motd`;

  $count = 10_000;



  timethese($count, {

            'map' => sub { my @a = @junk;

			   map { s/a/b/ } @a;

			   return @a

			 },

            'for' => sub { my @a = @junk;

			   local $_;

			   for (@a) { s/a/b/ };

			   return @a },

           });



This is what it prints (on one machine--your results will be dependent

on your hardware, operating system, and the load on your machine):



  Benchmark: timing 10000 iterations of for, map...

         for:  4 secs ( 3.97 usr  0.01 sys =  3.98 cpu)

         map:  6 secs ( 4.97 usr  0.00 sys =  4.97 cpu)



Be aware that a good benchmark is very hard to write.  It only tests the

data you give it and proves little about the differing complexities

of contrasting algorithms.



=head2 How do I cross-reference my Perl programs?



The B::Xref module, shipped with the new, alpha-release Perl compiler

(not the general distribution prior to the 5.005 release), can be used

to generate cross-reference reports for Perl programs.



    perl -MO=Xref[,OPTIONS] scriptname.plx



=head2 Is there a pretty-printer (formatter) for Perl?



There is no program that will reformat Perl as much as indent(1) does

for C.  The complex feedback between the scanner and the parser (this

feedback is what confuses the vgrind and emacs programs) makes it

challenging at best to write a stand-alone Perl parser.



Of course, if you simply follow the guidelines in L<perlstyle>, you

shouldn't need to reformat.  The habit of formatting your code as you

write it will help prevent bugs.  Your editor can and should help you

with this.  The perl-mode or newer cperl-mode for emacs can provide

remarkable amounts of help with most (but not all) code, and even less

programmable editors can provide significant assistance.  Tom swears

by the following settings in vi and its clones:



    set ai sw=4

    map! ^O {^M}^[O^T



Now put that in your F<.exrc> file (replacing the caret characters

with control characters) and away you go.  In insert mode, ^T is

for indenting, ^D is for undenting, and ^O is for blockdenting--

as it were.  If you haven't used the last one, you're missing

a lot.  A more complete example, with comments, can be found at

http://www.perl.com/CPAN-local/authors/id/TOMC/scripts/toms.exrc.gz



If you are used to using the I<vgrind> program for printing out nice code

to a laser printer, you can take a stab at this using

http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the

results are not particularly satisfying for sophisticated code.



The a2ps at http://www.infres.enst.fr/%7Edemaille/a2ps/ does lots of things

related to generating nicely printed output of documents.



=head2 Is there a ctags for Perl?



There's a simple one at

http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do

the trick.  And if not, it's easy to hack into what you want.



=head2 Is there an IDE or Windows Perl Editor?



Perl programs are just plain text, so any editor will do.



If you're on Unix, you already have an IDE--Unix itself.  The UNIX

philosophy is the philosophy of several small tools that each do one

thing and do it well.  It's like a carpenter's toolbox.



If you want a Windows IDE, check the following:



=over 4



=item CodeMagicCD



http://www.codemagiccd.com/



=item Komodo



ActiveState's cross-platform, multi-language IDE has Perl support,

including a regular expression debugger and remote debugging

(http://www.ActiveState.com/Products/Komodo/index.html).

(Visual Perl, a Visual Studio.NET plug-in is currently (early 2001)

in beta (http://www.ActiveState.com/Products/VisualPerl/index.html)).



=item The Object System



(http://www.castlelink.co.uk/object_system/) is a Perl web

applications development IDE.



=item PerlBuilder



(http://www.solutionsoft.com/perl.htm) is an integrated development

environment for Windows that supports Perl development.



=item Perl code magic



(http://www.petes-place.com/codemagic.html).



=item visiPerl+



http://helpconsulting.net/visiperl/, from Help Consulting.



=back



For editors: if you're on Unix you probably have vi or a vi clone already,

and possibly an emacs too, so you may not need to download anything.

In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the

best available Perl editing mode in any editor.



For Windows editors: you can download an Emacs



=over 4



=item GNU Emacs



http://www.gnu.org/software/emacs/windows/ntemacs.html



=item MicroEMACS



http://members.nbci.com/uemacs/



=item XEmacs



http://www.xemacs.org/Download/index.html



=back



or a vi clone such as



=over 4



=item Elvis



ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/



=item Vile



http://vile.cx/



=item Vim



http://www.vim.org/



win32: http://www.cs.vu.nl/%7Etmgil/vi.html



=back



For vi lovers in general, Windows or elsewhere:

http://www.thomer.com/thomer/vi/vi.html.



nvi (http://www.bostic.com/vi/, available from CPAN in src/misc/) is

yet another vi clone, unfortunately not available for Windows, but in

UNIX platforms you might be interested in trying it out, firstly because

strictly speaking it is not a vi clone, it is the real vi, or the new

incarnation of it, and secondly because you can embed Perl inside it

to use Perl as the scripting language.  nvi is not alone in this,

though: at least also vim and vile offer an embedded Perl.



The following are Win32 multilanguage editor/IDESs that support Perl:



=over 4



=item Codewright



http://www.starbase.com/



=item MultiEdit



http://www.MultiEdit.com/



=item SlickEdit



http://www.slickedit.com/



=back



There is also a toyedit Text widget based editor written in Perl

that is distributed with the Tk module on CPAN.  The ptkdb

(http://world.std.com/~aep/ptkdb/) is a Perl/tk based debugger that

acts as a development environment of sorts.  Perl Composer

(http://perlcomposer.sourceforge.net/vperl.html) is an IDE for Perl/Tk

GUI creation.



In addition to an editor/IDE you might be interested in a more

powerful shell environment for Win32.  Your options include



=over 4



=item Bash



from the Cygwin package (http://sources.redhat.com/cygwin/)



=item Ksh



from the MKS Toolkit (http://www.mks.com/), or the Bourne shell of

the U/WIN environment (http://www.research.att.com/sw/tools/uwin/)



=item Tcsh



ftp://ftp.astron.com/pub/tcsh/, see also

http://www.primate.wisc.edu/software/csh-tcsh-book/



=item Zsh



ftp://ftp.blarg.net/users/amol/zsh/, see also http://www.zsh.org/



=back



MKS and U/WIN are commercial (U/WIN is free for educational and

research purposes), Cygwin is covered by the GNU Public License (but

that shouldn't matter for Perl use).  The Cygwin, MKS, and U/WIN all

contain (in addition to the shells) a comprehensive set of standard

UNIX toolkit utilities.



If you're transferring text files between Unix and Windows using FTP

be sure to transfer them in ASCII mode so the ends of lines are

appropriately converted.



On Mac OS the MacPerl Application comes with a simple 32k text editor

that behaves like a rudimentary IDE.  In contrast to the MacPerl Application

the MPW Perl tool can make use of the MPW Shell itself as an editor (with

no 32k limit).



=over 4



=item BBEdit and BBEdit Lite



are text editors for Mac OS that have a Perl sensitivity mode

(http://web.barebones.com/).



=item Alpha



is an editor, written and extensible in Tcl, that nonetheless has

built in support for several popular markup and programming languages

including Perl and HTML (http://alpha.olm.net/).



=back



Pepper and Pe are programming language sensitive text editors for Mac

OS X and BeOS respectively (http://www.hekkelman.com/).



=head2 Where can I get Perl macros for vi?



For a complete version of Tom Christiansen's vi configuration file,

see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc.gz ,

the standard benchmark file for vi emulators.  The file runs best with nvi,

the current version of vi out of Berkeley, which incidentally can be built

with an embedded Perl interpreter--see http://www.perl.com/CPAN/src/misc.



=head2 Where can I get perl-mode for emacs?



Since Emacs version 19 patchlevel 22 or so, there have been both a

perl-mode.el and support for the Perl debugger built in.  These should

come with the standard Emacs 19 distribution.



In the Perl source directory, you'll find a directory called "emacs",

which contains a cperl-mode that color-codes keywords, provides

context-sensitive help, and other nifty things.



Note that the perl-mode of emacs will have fits with C<"main'foo">

(single quote), and mess up the indentation and highlighting.  You

are probably using C<"main::foo"> in new Perl code anyway, so this

shouldn't be an issue.



=head2 How can I use curses with Perl?



The Curses module from CPAN provides a dynamically loadable object

module interface to a curses library.  A small demo can be found at the

directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep;

this program repeats a command and updates the screen as needed, rendering

B<rep ps axu> similar to B<top>.



=head2 How can I use X or Tk with Perl?



Tk is a completely Perl-based, object-oriented interface to the Tk toolkit

that doesn't force you to use Tcl just to get at Tk.  Sx is an interface

to the Athena Widget set.  Both are available from CPAN.  See the

directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/



Invaluable for Perl/Tk programming are the Perl/Tk FAQ at

http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference

Guide available at

http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the

online manpages at

http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html .



=head2 How can I generate simple menus without using CGI or Tk?



The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz

module, which is curses-based, can help with this.



=head2 What is undump?



See the next question on ``How can I make my Perl program run faster?''



=head2 How can I make my Perl program run faster?



The best way to do this is to come up with a better algorithm.  This

can often make a dramatic difference.  Jon Bentley's book

``Programming Pearls'' (that's not a misspelling!)  has some good tips

on optimization, too.  Advice on benchmarking boils down to: benchmark

and profile to make sure you're optimizing the right part, look for

better algorithms instead of microtuning your code, and when all else

fails consider just buying faster hardware.



A different approach is to autoload seldom-used Perl code.  See the

AutoSplit and AutoLoader modules in the standard distribution for

that.  Or you could locate the bottleneck and think about writing just

that part in C, the way we used to take bottlenecks in C code and

write them in assembler.  Similar to rewriting in C,

modules that have critical sections can be written in C (for instance, the

PDL module from CPAN).



In some cases, it may be worth it to use the backend compiler to

produce byte code (saving compilation time) or compile into C, which

will certainly save compilation time and sometimes a small amount (but

not much) execution time.  See the question about compiling your Perl

programs for more on the compiler--the wins aren't as obvious as you'd

hope.



If you're currently linking your perl executable to a shared I<libc.so>,

you can often gain a 10-25% performance benefit by rebuilding it to

link with a static libc.a instead.  This will make a bigger perl

executable, but your Perl programs (and programmers) may thank you for

it.  See the F<INSTALL> file in the source distribution for more

information.



Unsubstantiated reports allege that Perl interpreters that use sfio

outperform those that don't (for I/O intensive applications).  To try

this, see the F<INSTALL> file in the source distribution, especially

the ``Selecting File I/O mechanisms'' section.



The undump program was an old attempt to speed up your Perl program

by storing the already-compiled form to disk.  This is no longer

a viable option, as it only worked on a few architectures, and

wasn't a good solution anyway.



=head2 How can I make my Perl program take less memory?



When it comes to time-space tradeoffs, Perl nearly always prefers to

throw memory at a problem.  Scalars in Perl use more memory than

strings in C, arrays take more than that, and hashes use even more.  While

there's still a lot to be done, recent releases have been addressing

these issues.  For example, as of 5.004, duplicate hash keys are

shared amongst all hashes using them, so require no reallocation.



In some cases, using substr() or vec() to simulate arrays can be

highly beneficial.  For example, an array of a thousand booleans will

take at least 20,000 bytes of space, but it can be turned into one

125-byte bit vector--a considerable memory savings.  The standard

Tie::SubstrHash module can also help for certain types of data

structure.  If you're working with specialist data structures

(matrices, for instance) modules that implement these in C may use

less memory than equivalent Perl modules.



Another thing to try is learning whether your Perl was compiled with

the system malloc or with Perl's builtin malloc.  Whichever one it

is, try using the other one and see whether this makes a difference.

Information about malloc is in the F<INSTALL> file in the source

distribution.  You can find out whether you are using perl's malloc by

typing C<perl -V:usemymalloc>.



=head2 Is it unsafe to return a pointer to local data?



No, Perl's garbage collection system takes care of this.



    sub makeone {

	my @a = ( 1 .. 10 );

	return \@a;

    }



    for $i ( 1 .. 10 ) {

        push @many, makeone();

    }



    print $many[4][5], "\n";



    print "@many\n";



=head2 How can I free an array or hash so my program shrinks?



You can't.  On most operating systems, memory allocated to a program

can never be returned to the system.  That's why long-running programs

sometimes re-exec themselves.  Some operating systems (notably,

FreeBSD and Linux) allegedly reclaim large chunks of memory that is no

longer used, but it doesn't appear to happen with Perl (yet).  The Mac

appears to be the only platform that will reliably (albeit, slowly)

return memory to the OS.



We've had reports that on Linux (Redhat 5.1) on Intel, C<undef

$scalar> will return memory to the system, while on Solaris 2.6 it

won't.  In general, try it yourself and see.



However, judicious use of my() on your variables will help make sure

that they go out of scope so that Perl can free up that space for

use in other parts of your program.  A global variable, of course, never

goes out of scope, so you can't get its space automatically reclaimed,

although undef()ing and/or delete()ing it will achieve the same effect.

In general, memory allocation and de-allocation isn't something you can

or should be worrying about much in Perl, but even this capability

(preallocation of data types) is in the works.



=head2 How can I make my CGI script more efficient?



Beyond the normal measures described to make general Perl programs

faster or smaller, a CGI program has additional issues.  It may be run

several times per second.  Given that each time it runs it will need

to be re-compiled and will often allocate a megabyte or more of system

memory, this can be a killer.  Compiling into C B<isn't going to help

you> because the process start-up overhead is where the bottleneck is.



There are two popular ways to avoid this overhead.  One solution

involves running the Apache HTTP server (available from

http://www.apache.org/) with either of the mod_perl or mod_fastcgi

plugin modules.



With mod_perl and the Apache::Registry module (distributed with

mod_perl), httpd will run with an embedded Perl interpreter which

pre-compiles your script and then executes it within the same address

space without forking.  The Apache extension also gives Perl access to

the internal server API, so modules written in Perl can do just about

anything a module written in C can.  For more on mod_perl, see

http://perl.apache.org/



With the FCGI module (from CPAN) and the mod_fastcgi

module (available from http://www.fastcgi.com/) each of your Perl

programs becomes a permanent CGI daemon process.



Both of these solutions can have far-reaching effects on your system

and on the way you write your CGI programs, so investigate them with

care.



See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ .



A non-free, commercial product, ``The Velocity Engine for Perl'',

(http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ )

might also be worth looking at.  It will allow you to increase the

performance of your Perl programs, running programs up to 25 times

faster than normal CGI Perl when running in persistent Perl mode or 4

to 5 times faster without any modification to your existing CGI

programs. Fully functional evaluation copies are available from the

web site.



=head2 How can I hide the source for my Perl program?



Delete it. :-) Seriously, there are a number of (mostly

unsatisfactory) solutions with varying levels of ``security''.



First of all, however, you I<can't> take away read permission, because

the source code has to be readable in order to be compiled and

interpreted.  (That doesn't mean that a CGI script's source is

readable by people on the web, though--only by people with access to

the filesystem.)  So you have to leave the permissions at the socially

friendly 0755 level.



Some people regard this as a security problem.  If your program does

insecure things and relies on people not knowing how to exploit those

insecurities, it is not secure.  It is often possible for someone to

determine the insecure things and exploit them without viewing the

source.  Security through obscurity, the name for hiding your bugs

instead of fixing them, is little security indeed.



You can try using encryption via source filters (Filter::* from CPAN),

but any decent programmer will be able to decrypt it.  You can try using

the byte code compiler and interpreter described below, but the curious

might still be able to de-compile it.  You can try using the native-code

compiler described below, but crackers might be able to disassemble it.

These pose varying degrees of difficulty to people wanting to get at

your code, but none can definitively conceal it (true of every

language, not just Perl).



If you're concerned about people profiting from your code, then the

bottom line is that nothing but a restrictive license will give you

legal security.  License your software and pepper it with threatening

statements like ``This is unpublished proprietary software of XYZ Corp.

Your access to it does not give you permission to use it blah blah

blah.''  We are not lawyers, of course, so you should see a lawyer if

you want to be sure your license's wording will stand up in court.



=head2 How can I compile my Perl program into byte code or C?



Malcolm Beattie has written a multifunction backend compiler,

available from CPAN, that can do both these things.  It is included

in the perl5.005 release, but is still considered experimental.

This means it's fun to play with if you're a programmer but not

really for people looking for turn-key solutions.



Merely compiling into C does not in and of itself guarantee that your

code will run very much faster.  That's because except for lucky cases

where a lot of native type inferencing is possible, the normal Perl

run-time system is still present and so your program will take just as

long to run and be just as big.  Most programs save little more than

compilation time, leaving execution no more than 10-30% faster.  A few

rare programs actually benefit significantly (even running several times

faster), but this takes some tweaking of your code.



You'll probably be astonished to learn that the current version of the

compiler generates a compiled form of your script whose executable is

just as big as the original perl executable, and then some.  That's

because as currently written, all programs are prepared for a full

eval() statement.  You can tremendously reduce this cost by building a

shared I<libperl.so> library and linking against that.  See the

F<INSTALL> podfile in the Perl source distribution for details.  If

you link your main perl binary with this, it will make it minuscule.

For example, on one author's system, F</usr/bin/perl> is only 11k in

size!



In general, the compiler will do nothing to make a Perl program smaller,

faster, more portable, or more secure.  In fact, it can make your

situation worse.  The executable will be bigger, your VM system may take

longer to load the whole thing, the binary is fragile and hard to fix,

and compilation never stopped software piracy in the form of crackers,

viruses, or bootleggers.  The real advantage of the compiler is merely

packaging, and once you see the size of what it makes (well, unless

you use a shared I<libperl.so>), you'll probably want a complete

Perl install anyway.



=head2 How can I compile Perl into Java?



You can also integrate Java and Perl with the

Perl Resource Kit from O'Reilly and Associates.  See

http://www.oreilly.com/catalog/prkunix/ .



Perl 5.6 comes with Java Perl Lingo, or JPL.  JPL, still in

development, allows Perl code to be called from Java.  See jpl/README

in the Perl source tree.



=head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]?



For OS/2 just use



    extproc perl -S -your_switches



as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's

`extproc' handling).  For DOS one should first invent a corresponding

batch file and codify it in C<ALTERNATIVE_SHEBANG> (see the

F<INSTALL> file in the source distribution for more information).



The Win95/NT installation, when using the ActiveState port of Perl,

will modify the Registry to associate the C<.pl> extension with the

perl interpreter.  If you install another port, perhaps even building

your own Win95/NT Perl from the standard sources by using a Windows port

of gcc (e.g., with cygwin or mingw32), then you'll have to modify

the Registry yourself.  In addition to associating C<.pl> with the

interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them

run the program C<install-linux.pl> merely by typing C<install-linux>.



Macintosh Perl programs will have the appropriate Creator and

Type, so that double-clicking them will invoke the Perl application.



I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just

throw the perl interpreter into your cgi-bin directory, in order to

get your programs working for a web server.  This is an EXTREMELY big

security risk.  Take the time to figure out how to do it correctly.



=head2 Can I write useful Perl programs on the command line?



Yes.  Read L<perlrun> for more information.  Some examples follow.

(These assume standard Unix shell quoting rules.)



    # sum first and last fields

    perl -lane 'print $F[0] + $F[-1]' *



    # identify text files

    perl -le 'for(@ARGV) {print if -f && -T _}' *



    # remove (most) comments from C program

    perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c



    # make file a month younger than today, defeating reaper daemons

    perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' *



    # find first unused uid

    perl -le '$i++ while getpwuid($i); print $i'



    # display reasonable manpath

    echo $PATH | perl -nl -072 -e '

	s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}'



OK, the last one was actually an Obfuscated Perl Contest entry. :-)



=head2 Why don't Perl one-liners work on my DOS/Mac/VMS system?



The problem is usually that the command interpreters on those systems

have rather different ideas about quoting than the Unix shells under

which the one-liners were created.  On some systems, you may have to

change single-quotes to double ones, which you must I<NOT> do on Unix

or Plan9 systems.  You might also have to change a single % to a %%.



For example:



    # Unix

    perl -e 'print "Hello world\n"'



    # DOS, etc.

    perl -e "print \"Hello world\n\""



    # Mac

    print "Hello world\n"

     (then Run "Myscript" or Shift-Command-R)



    # VMS

    perl -e "print ""Hello world\n"""



The problem is that none of these examples are reliable: they depend on the

command interpreter.  Under Unix, the first two often work. Under DOS,

it's entirely possible that neither works.  If 4DOS was the command shell,

you'd probably have better luck like this:



  perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""



Under the Mac, it depends which environment you are using.  The MacPerl

shell, or MPW, is much like Unix shells in its support for several

quoting variants, except that it makes free use of the Mac's non-ASCII

characters as control characters.



Using qq(), q(), and qx(), instead of "double quotes", 'single

quotes', and `backticks`, may make one-liners easier to write.



There is no general solution to all of this.  It is a mess, pure and

simple.  Sucks to be away from Unix, huh? :-)



[Some of this answer was contributed by Kenneth Albanowski.]



=head2 Where can I learn about CGI or Web programming in Perl?



For modules, get the CGI or LWP modules from CPAN.  For textbooks,

see the two especially dedicated to web stuff in the question on

books.  For problems and questions related to the web, like ``Why

do I get 500 Errors'' or ``Why doesn't it run from the browser right

when it runs fine on the command line'', see these sources:



    WWW Security FAQ

        http://www.w3.org/Security/Faq/



    Web FAQ

        http://www.boutell.com/faq/



    CGI FAQ

        http://www.webthing.com/tutorials/cgifaq.html



    HTTP Spec

        http://www.w3.org/pub/WWW/Protocols/HTTP/



    HTML Spec

        http://www.w3.org/TR/REC-html40/

        http://www.w3.org/pub/WWW/MarkUp/



    CGI Spec

        http://www.w3.org/CGI/



    CGI Security FAQ

        http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt



=head2 Where can I learn about object-oriented Perl programming?



A good place to start is L<perltoot>, and you can use L<perlobj>,

L<perlboot>, and L<perlbot> for reference.  Perltoot didn't come out

until the 5.004 release; you can get a copy (in pod, html, or

postscript) from http://www.perl.com/CPAN/doc/FMTEYEWTK/ .



=head2 Where can I learn about linking C with Perl? [h2xs, xsubpp]



If you want to call C from Perl, start with L<perlxstut>,

moving on to L<perlxs>, L<xsubpp>, and L<perlguts>.  If you want to

call Perl from C, then read L<perlembed>, L<perlcall>, and

L<perlguts>.  Don't forget that you can learn a lot from looking at

how the authors of existing extension modules wrote their code and

solved their problems.



=head2 I've read perlembed, perlguts, etc., but I can't embed perl in

my C program; what am I doing wrong?



Download the ExtUtils::Embed kit from CPAN and run `make test'.  If

the tests pass, read the pods again and again and again.  If they

fail, see L<perlbug> and send a bug report with the output of

C<make test TEST_VERBOSE=1> along with C<perl -V>.



=head2 When I tried to run my script, I got this message. What does it

mean?



A complete list of Perl's error messages and warnings with explanatory

text can be found in L<perldiag>. You can also use the splain program

(distributed with Perl) to explain the error messages:



    perl program 2>diag.out

    splain [-v] [-p] diag.out



or change your program to explain the messages for you:



    use diagnostics;



or



    use diagnostics -verbose;



=head2 What's MakeMaker?



This module (part of the standard Perl distribution) is designed to

write a Makefile for an extension module from a Makefile.PL.  For more

information, see L<ExtUtils::MakeMaker>.



=head1 AUTHOR AND COPYRIGHT



Copyright (c) 1997-1999 Tom Christiansen and Nathan Torkington.

All rights reserved.



When included as an integrated part of the Standard Distribution

of Perl or of its documentation (printed or otherwise), this works is

covered under Perl's Artistic License.  For separate distributions of

all or part of this FAQ outside of that, see L<perlfaq>.



Irrespective of its distribution, all code examples here are in the public

domain.  You are permitted and encouraged to use this code and any

derivatives thereof in your own programs for fun or for profit as you

see fit.  A simple comment in the code giving credit to the FAQ would

be courteous but is not required.