| 1 | =head1 NAME |
| 2 | |
| 3 | perlfaq3 - Programming Tools ($Revision: 10127 $) |
| 4 | |
| 5 | =head1 DESCRIPTION |
| 6 | |
| 7 | This section of the FAQ answers questions related to programmer tools |
| 8 | and programming support. |
| 9 | |
| 10 | =head2 How do I do (anything)? |
| 11 | |
| 12 | Have you looked at CPAN (see L<perlfaq2>)? The chances are that |
| 13 | someone has already written a module that can solve your problem. |
| 14 | Have you read the appropriate manpages? Here's a brief index: |
| 15 | |
| 16 | Basics perldata, perlvar, perlsyn, perlop, perlsub |
| 17 | Execution perlrun, perldebug |
| 18 | Functions perlfunc |
| 19 | Objects perlref, perlmod, perlobj, perltie |
| 20 | Data Structures perlref, perllol, perldsc |
| 21 | Modules perlmod, perlmodlib, perlsub |
| 22 | Regexes perlre, perlfunc, perlop, perllocale |
| 23 | Moving to perl5 perltrap, perl |
| 24 | Linking w/C perlxstut, perlxs, perlcall, perlguts, perlembed |
| 25 | Various http://www.cpan.org/misc/olddoc/FMTEYEWTK.tgz |
| 26 | (not a man-page but still useful, a collection |
| 27 | of various essays on Perl techniques) |
| 28 | |
| 29 | A crude table of contents for the Perl manpage set is found in L<perltoc>. |
| 30 | |
| 31 | =head2 How can I use Perl interactively? |
| 32 | |
| 33 | The typical approach uses the Perl debugger, described in the |
| 34 | perldebug(1) manpage, on an "empty" program, like this: |
| 35 | |
| 36 | perl -de 42 |
| 37 | |
| 38 | Now just type in any legal Perl code, and it will be immediately |
| 39 | evaluated. You can also examine the symbol table, get stack |
| 40 | backtraces, check variable values, set breakpoints, and other |
| 41 | operations typically found in symbolic debuggers. |
| 42 | |
| 43 | =head2 Is there a Perl shell? |
| 44 | |
| 45 | The psh (Perl sh) is currently at version 1.8. The Perl Shell is a shell |
| 46 | that combines the interactive nature of a Unix shell with the power of |
| 47 | Perl. The goal is a full featured shell that behaves as expected for |
| 48 | normal shell activity and uses Perl syntax and functionality for |
| 49 | control-flow statements and other things. You can get psh at |
| 50 | http://sourceforge.net/projects/psh/ . |
| 51 | |
| 52 | Zoidberg is a similar project and provides a shell written in perl, |
| 53 | configured in perl and operated in perl. It is intended as a login shell |
| 54 | and development environment. It can be found at http://zoidberg.sf.net/ |
| 55 | or your local CPAN mirror. |
| 56 | |
| 57 | The Shell.pm module (distributed with Perl) makes Perl try commands |
| 58 | which aren't part of the Perl language as shell commands. perlsh from |
| 59 | the source distribution is simplistic and uninteresting, but may still |
| 60 | be what you want. |
| 61 | |
| 62 | =head2 How do I find which modules are installed on my system? |
| 63 | |
| 64 | You can use the ExtUtils::Installed module to show all installed |
| 65 | distributions, although it can take awhile to do its magic. The |
| 66 | standard library which comes with Perl just shows up as "Perl" (although |
| 67 | you can get those with Module::CoreList). |
| 68 | |
| 69 | use ExtUtils::Installed; |
| 70 | |
| 71 | my $inst = ExtUtils::Installed->new(); |
| 72 | my @modules = $inst->modules(); |
| 73 | |
| 74 | If you want a list of all of the Perl module filenames, you |
| 75 | can use File::Find::Rule. |
| 76 | |
| 77 | use File::Find::Rule; |
| 78 | |
| 79 | my @files = File::Find::Rule->file()->name( '*.pm' )->in( @INC ); |
| 80 | |
| 81 | If you do not have that module, you can do the same thing |
| 82 | with File::Find which is part of the standard library. |
| 83 | |
| 84 | use File::Find; |
| 85 | my @files; |
| 86 | |
| 87 | find( |
| 88 | sub { |
| 89 | push @files, $File::Find::name |
| 90 | if -f $File::Find::name && /\.pm$/ |
| 91 | }, |
| 92 | |
| 93 | @INC |
| 94 | ); |
| 95 | |
| 96 | print join "\n", @files; |
| 97 | |
| 98 | If you simply need to quickly check to see if a module is |
| 99 | available, you can check for its documentation. If you can |
| 100 | read the documentation the module is most likely installed. |
| 101 | If you cannot read the documentation, the module might not |
| 102 | have any (in rare cases). |
| 103 | |
| 104 | prompt% perldoc Module::Name |
| 105 | |
| 106 | You can also try to include the module in a one-liner to see if |
| 107 | perl finds it. |
| 108 | |
| 109 | perl -MModule::Name -e1 |
| 110 | |
| 111 | =head2 How do I debug my Perl programs? |
| 112 | |
| 113 | (contributed by brian d foy) |
| 114 | |
| 115 | Before you do anything else, you can help yourself by ensuring that |
| 116 | you let Perl tell you about problem areas in your code. By turning |
| 117 | on warnings and strictures, you can head off many problems before |
| 118 | they get too big. You can find out more about these in L<strict> |
| 119 | and L<warnings>. |
| 120 | |
| 121 | #!/usr/bin/perl |
| 122 | use strict; |
| 123 | use warnings; |
| 124 | |
| 125 | Beyond that, the simplest debugger is the C<print> function. Use it |
| 126 | to look at values as you run your program: |
| 127 | |
| 128 | print STDERR "The value is [$value]\n"; |
| 129 | |
| 130 | The C<Data::Dumper> module can pretty-print Perl data structures: |
| 131 | |
| 132 | use Data::Dumper qw( Dumper ); |
| 133 | print STDERR "The hash is " . Dumper( \%hash ) . "\n"; |
| 134 | |
| 135 | Perl comes with an interactive debugger, which you can start with the |
| 136 | C<-d> switch. It's fully explained in L<perldebug>. |
| 137 | |
| 138 | If you'd like a graphical user interface and you have Tk, you can use |
| 139 | C<ptkdb>. It's on CPAN and available for free. |
| 140 | |
| 141 | If you need something much more sophisticated and controllable, Leon |
| 142 | Brocard's Devel::ebug (which you can call with the -D switch as -Debug) |
| 143 | gives you the programmatic hooks into everything you need to write your |
| 144 | own (without too much pain and suffering). |
| 145 | |
| 146 | You can also use a commercial debugger such as Affrus (Mac OS X), Komodo |
| 147 | from Activestate (Windows and Mac OS X), or EPIC (most platforms). |
| 148 | |
| 149 | =head2 How do I profile my Perl programs? |
| 150 | |
| 151 | You should get the Devel::DProf module from the standard distribution |
| 152 | (or separately on CPAN) and also use Benchmark.pm from the standard |
| 153 | distribution. The Benchmark module lets you time specific portions of |
| 154 | your code, while Devel::DProf gives detailed breakdowns of where your |
| 155 | code spends its time. |
| 156 | |
| 157 | Here's a sample use of Benchmark: |
| 158 | |
| 159 | use Benchmark; |
| 160 | |
| 161 | @junk = `cat /etc/motd`; |
| 162 | $count = 10_000; |
| 163 | |
| 164 | timethese($count, { |
| 165 | 'map' => sub { my @a = @junk; |
| 166 | map { s/a/b/ } @a; |
| 167 | return @a }, |
| 168 | 'for' => sub { my @a = @junk; |
| 169 | for (@a) { s/a/b/ }; |
| 170 | return @a }, |
| 171 | }); |
| 172 | |
| 173 | This is what it prints (on one machine--your results will be dependent |
| 174 | on your hardware, operating system, and the load on your machine): |
| 175 | |
| 176 | Benchmark: timing 10000 iterations of for, map... |
| 177 | for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu) |
| 178 | map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu) |
| 179 | |
| 180 | Be aware that a good benchmark is very hard to write. It only tests the |
| 181 | data you give it and proves little about the differing complexities |
| 182 | of contrasting algorithms. |
| 183 | |
| 184 | =head2 How do I cross-reference my Perl programs? |
| 185 | |
| 186 | The B::Xref module can be used to generate cross-reference reports |
| 187 | for Perl programs. |
| 188 | |
| 189 | perl -MO=Xref[,OPTIONS] scriptname.plx |
| 190 | |
| 191 | =head2 Is there a pretty-printer (formatter) for Perl? |
| 192 | |
| 193 | Perltidy is a Perl script which indents and reformats Perl scripts |
| 194 | to make them easier to read by trying to follow the rules of the |
| 195 | L<perlstyle>. If you write Perl scripts, or spend much time reading |
| 196 | them, you will probably find it useful. It is available at |
| 197 | http://perltidy.sourceforge.net |
| 198 | |
| 199 | Of course, if you simply follow the guidelines in L<perlstyle>, |
| 200 | you shouldn't need to reformat. The habit of formatting your code |
| 201 | as you write it will help prevent bugs. Your editor can and should |
| 202 | help you with this. The perl-mode or newer cperl-mode for emacs |
| 203 | can provide remarkable amounts of help with most (but not all) |
| 204 | code, and even less programmable editors can provide significant |
| 205 | assistance. Tom Christiansen and many other VI users swear by |
| 206 | the following settings in vi and its clones: |
| 207 | |
| 208 | set ai sw=4 |
| 209 | map! ^O {^M}^[O^T |
| 210 | |
| 211 | Put that in your F<.exrc> file (replacing the caret characters |
| 212 | with control characters) and away you go. In insert mode, ^T is |
| 213 | for indenting, ^D is for undenting, and ^O is for blockdenting--as |
| 214 | it were. A more complete example, with comments, can be found at |
| 215 | http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz |
| 216 | |
| 217 | The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps.gz does |
| 218 | lots of things related to generating nicely printed output of |
| 219 | documents. |
| 220 | |
| 221 | =head2 Is there a ctags for Perl? |
| 222 | |
| 223 | (contributed by brian d foy) |
| 224 | |
| 225 | Ctags uses an index to quickly find things in source code, and many |
| 226 | popular editors support ctags for several different languages, |
| 227 | including Perl. |
| 228 | |
| 229 | Exuberent ctags supports Perl: http://ctags.sourceforge.net/ |
| 230 | |
| 231 | You might also try pltags: http://www.mscha.com/pltags.zip |
| 232 | |
| 233 | =head2 Is there an IDE or Windows Perl Editor? |
| 234 | |
| 235 | Perl programs are just plain text, so any editor will do. |
| 236 | |
| 237 | If you're on Unix, you already have an IDE--Unix itself. The UNIX |
| 238 | philosophy is the philosophy of several small tools that each do one |
| 239 | thing and do it well. It's like a carpenter's toolbox. |
| 240 | |
| 241 | If you want an IDE, check the following (in alphabetical order, not |
| 242 | order of preference): |
| 243 | |
| 244 | =over 4 |
| 245 | |
| 246 | =item Eclipse |
| 247 | |
| 248 | http://e-p-i-c.sf.net/ |
| 249 | |
| 250 | The Eclipse Perl Integration Project integrates Perl |
| 251 | editing/debugging with Eclipse. |
| 252 | |
| 253 | =item Enginsite |
| 254 | |
| 255 | http://www.enginsite.com/ |
| 256 | |
| 257 | Perl Editor by EngInSite is a complete integrated development |
| 258 | environment (IDE) for creating, testing, and debugging Perl scripts; |
| 259 | the tool runs on Windows 9x/NT/2000/XP or later. |
| 260 | |
| 261 | =item Komodo |
| 262 | |
| 263 | http://www.ActiveState.com/Products/Komodo/ |
| 264 | |
| 265 | ActiveState's cross-platform (as of October 2004, that's Windows, Linux, |
| 266 | and Solaris), multi-language IDE has Perl support, including a regular expression |
| 267 | debugger and remote debugging. |
| 268 | |
| 269 | =item Open Perl IDE |
| 270 | |
| 271 | http://open-perl-ide.sourceforge.net/ |
| 272 | |
| 273 | Open Perl IDE is an integrated development environment for writing |
| 274 | and debugging Perl scripts with ActiveState's ActivePerl distribution |
| 275 | under Windows 95/98/NT/2000. |
| 276 | |
| 277 | =item OptiPerl |
| 278 | |
| 279 | http://www.optiperl.com/ |
| 280 | |
| 281 | OptiPerl is a Windows IDE with simulated CGI environment, including |
| 282 | debugger and syntax highlighting editor. |
| 283 | |
| 284 | =item PerlBuilder |
| 285 | |
| 286 | http://www.solutionsoft.com/perl.htm |
| 287 | |
| 288 | PerlBuidler is an integrated development environment for Windows that |
| 289 | supports Perl development. |
| 290 | |
| 291 | =item visiPerl+ |
| 292 | |
| 293 | http://helpconsulting.net/visiperl/ |
| 294 | |
| 295 | From Help Consulting, for Windows. |
| 296 | |
| 297 | =item Visual Perl |
| 298 | |
| 299 | http://www.activestate.com/Products/Visual_Perl/ |
| 300 | |
| 301 | Visual Perl is a Visual Studio.NET plug-in from ActiveState. |
| 302 | |
| 303 | =item Zeus |
| 304 | |
| 305 | http://www.zeusedit.com/lookmain.html |
| 306 | |
| 307 | Zeus for Window is another Win32 multi-language editor/IDE |
| 308 | that comes with support for Perl: |
| 309 | |
| 310 | =back |
| 311 | |
| 312 | For editors: if you're on Unix you probably have vi or a vi clone |
| 313 | already, and possibly an emacs too, so you may not need to download |
| 314 | anything. In any emacs the cperl-mode (M-x cperl-mode) gives you |
| 315 | perhaps the best available Perl editing mode in any editor. |
| 316 | |
| 317 | If you are using Windows, you can use any editor that lets you work |
| 318 | with plain text, such as NotePad or WordPad. Word processors, such as |
| 319 | Microsoft Word or WordPerfect, typically do not work since they insert |
| 320 | all sorts of behind-the-scenes information, although some allow you to |
| 321 | save files as "Text Only". You can also download text editors designed |
| 322 | specifically for programming, such as Textpad ( |
| 323 | http://www.textpad.com/ ) and UltraEdit ( http://www.ultraedit.com/ ), |
| 324 | among others. |
| 325 | |
| 326 | If you are using MacOS, the same concerns apply. MacPerl (for Classic |
| 327 | environments) comes with a simple editor. Popular external editors are |
| 328 | BBEdit ( http://www.bbedit.com/ ) or Alpha ( |
| 329 | http://www.his.com/~jguyer/Alpha/Alpha8.html ). MacOS X users can use |
| 330 | Unix editors as well. |
| 331 | |
| 332 | =over 4 |
| 333 | |
| 334 | =item GNU Emacs |
| 335 | |
| 336 | http://www.gnu.org/software/emacs/windows/ntemacs.html |
| 337 | |
| 338 | =item MicroEMACS |
| 339 | |
| 340 | http://www.microemacs.de/ |
| 341 | |
| 342 | =item XEmacs |
| 343 | |
| 344 | http://www.xemacs.org/Download/index.html |
| 345 | |
| 346 | =item Jed |
| 347 | |
| 348 | http://space.mit.edu/~davis/jed/ |
| 349 | |
| 350 | =back |
| 351 | |
| 352 | or a vi clone such as |
| 353 | |
| 354 | =over 4 |
| 355 | |
| 356 | =item Elvis |
| 357 | |
| 358 | ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/ |
| 359 | |
| 360 | =item Vile |
| 361 | |
| 362 | http://dickey.his.com/vile/vile.html |
| 363 | |
| 364 | =item Vim |
| 365 | |
| 366 | http://www.vim.org/ |
| 367 | |
| 368 | =back |
| 369 | |
| 370 | For vi lovers in general, Windows or elsewhere: |
| 371 | |
| 372 | http://www.thomer.com/thomer/vi/vi.html |
| 373 | |
| 374 | nvi ( http://www.bostic.com/vi/ , available from CPAN in src/misc/) is |
| 375 | yet another vi clone, unfortunately not available for Windows, but in |
| 376 | UNIX platforms you might be interested in trying it out, firstly because |
| 377 | strictly speaking it is not a vi clone, it is the real vi, or the new |
| 378 | incarnation of it, and secondly because you can embed Perl inside it |
| 379 | to use Perl as the scripting language. nvi is not alone in this, |
| 380 | though: at least also vim and vile offer an embedded Perl. |
| 381 | |
| 382 | The following are Win32 multilanguage editor/IDESs that support Perl: |
| 383 | |
| 384 | =over 4 |
| 385 | |
| 386 | =item Codewright |
| 387 | |
| 388 | http://www.borland.com/codewright/ |
| 389 | |
| 390 | =item MultiEdit |
| 391 | |
| 392 | http://www.MultiEdit.com/ |
| 393 | |
| 394 | =item SlickEdit |
| 395 | |
| 396 | http://www.slickedit.com/ |
| 397 | |
| 398 | =back |
| 399 | |
| 400 | There is also a toyedit Text widget based editor written in Perl |
| 401 | that is distributed with the Tk module on CPAN. The ptkdb |
| 402 | ( http://ptkdb.sourceforge.net/ ) is a Perl/tk based debugger that |
| 403 | acts as a development environment of sorts. Perl Composer |
| 404 | ( http://perlcomposer.sourceforge.net/ ) is an IDE for Perl/Tk |
| 405 | GUI creation. |
| 406 | |
| 407 | In addition to an editor/IDE you might be interested in a more |
| 408 | powerful shell environment for Win32. Your options include |
| 409 | |
| 410 | =over 4 |
| 411 | |
| 412 | =item Bash |
| 413 | |
| 414 | from the Cygwin package ( http://sources.redhat.com/cygwin/ ) |
| 415 | |
| 416 | =item Ksh |
| 417 | |
| 418 | from the MKS Toolkit ( http://www.mks.com/ ), or the Bourne shell of |
| 419 | the U/WIN environment ( http://www.research.att.com/sw/tools/uwin/ ) |
| 420 | |
| 421 | =item Tcsh |
| 422 | |
| 423 | ftp://ftp.astron.com/pub/tcsh/ , see also |
| 424 | http://www.primate.wisc.edu/software/csh-tcsh-book/ |
| 425 | |
| 426 | =item Zsh |
| 427 | |
| 428 | http://www.zsh.org/ |
| 429 | |
| 430 | =back |
| 431 | |
| 432 | MKS and U/WIN are commercial (U/WIN is free for educational and |
| 433 | research purposes), Cygwin is covered by the GNU Public License (but |
| 434 | that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all |
| 435 | contain (in addition to the shells) a comprehensive set of standard |
| 436 | UNIX toolkit utilities. |
| 437 | |
| 438 | If you're transferring text files between Unix and Windows using FTP |
| 439 | be sure to transfer them in ASCII mode so the ends of lines are |
| 440 | appropriately converted. |
| 441 | |
| 442 | On Mac OS the MacPerl Application comes with a simple 32k text editor |
| 443 | that behaves like a rudimentary IDE. In contrast to the MacPerl Application |
| 444 | the MPW Perl tool can make use of the MPW Shell itself as an editor (with |
| 445 | no 32k limit). |
| 446 | |
| 447 | =over 4 |
| 448 | |
| 449 | =item Affrus |
| 450 | |
| 451 | is a full Perl development environment with full debugger support |
| 452 | ( http://www.latenightsw.com ). |
| 453 | |
| 454 | =item Alpha |
| 455 | |
| 456 | is an editor, written and extensible in Tcl, that nonetheless has |
| 457 | built in support for several popular markup and programming languages |
| 458 | including Perl and HTML ( http://www.his.com/~jguyer/Alpha/Alpha8.html ). |
| 459 | |
| 460 | =item BBEdit and BBEdit Lite |
| 461 | |
| 462 | are text editors for Mac OS that have a Perl sensitivity mode |
| 463 | ( http://web.barebones.com/ ). |
| 464 | |
| 465 | |
| 466 | =back |
| 467 | |
| 468 | Pepper and Pe are programming language sensitive text editors for Mac |
| 469 | OS X and BeOS respectively ( http://www.hekkelman.com/ ). |
| 470 | |
| 471 | =head2 Where can I get Perl macros for vi? |
| 472 | |
| 473 | For a complete version of Tom Christiansen's vi configuration file, |
| 474 | see http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz , |
| 475 | the standard benchmark file for vi emulators. The file runs best with nvi, |
| 476 | the current version of vi out of Berkeley, which incidentally can be built |
| 477 | with an embedded Perl interpreter--see http://www.cpan.org/src/misc/ . |
| 478 | |
| 479 | =head2 Where can I get perl-mode for emacs? |
| 480 | |
| 481 | Since Emacs version 19 patchlevel 22 or so, there have been both a |
| 482 | perl-mode.el and support for the Perl debugger built in. These should |
| 483 | come with the standard Emacs 19 distribution. |
| 484 | |
| 485 | In the Perl source directory, you'll find a directory called "emacs", |
| 486 | which contains a cperl-mode that color-codes keywords, provides |
| 487 | context-sensitive help, and other nifty things. |
| 488 | |
| 489 | Note that the perl-mode of emacs will have fits with C<"main'foo"> |
| 490 | (single quote), and mess up the indentation and highlighting. You |
| 491 | are probably using C<"main::foo"> in new Perl code anyway, so this |
| 492 | shouldn't be an issue. |
| 493 | |
| 494 | =head2 How can I use curses with Perl? |
| 495 | |
| 496 | The Curses module from CPAN provides a dynamically loadable object |
| 497 | module interface to a curses library. A small demo can be found at the |
| 498 | directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep.gz ; |
| 499 | this program repeats a command and updates the screen as needed, rendering |
| 500 | B<rep ps axu> similar to B<top>. |
| 501 | |
| 502 | =head2 How can I write a GUI (X, Tk, Gtk, etc.) in Perl? |
| 503 | X<GUI> X<Tk> X<Wx> X<WxWidgets> X<Gtk> X<Gtk2> X<CamelBones> X<Qt> |
| 504 | |
| 505 | (contributed by Ben Morrow) |
| 506 | |
| 507 | There are a number of modules which let you write GUIs in Perl. Most |
| 508 | GUI toolkits have a perl interface: an incomplete list follows. |
| 509 | |
| 510 | =over 4 |
| 511 | |
| 512 | =item Tk |
| 513 | |
| 514 | This works under Unix and Windows, and the current version doesn't |
| 515 | look half as bad under Windows as it used to. Some of the gui elements |
| 516 | still don't 'feel' quite right, though. The interface is very natural |
| 517 | and 'perlish', making it easy to use in small scripts that just need a |
| 518 | simple gui. It hasn't been updated in a while. |
| 519 | |
| 520 | =item Wx |
| 521 | |
| 522 | This is a Perl binding for the cross-platform wxWidgets toolkit |
| 523 | L<http://www.wxwidgets.org>. It works under Unix, Win32 and Mac OS X, |
| 524 | using native widgets (Gtk under Unix). The interface follows the C++ |
| 525 | interface closely, but the documentation is a little sparse for someone |
| 526 | who doesn't know the library, mostly just referring you to the C++ |
| 527 | documentation. |
| 528 | |
| 529 | =item Gtk and Gtk2 |
| 530 | |
| 531 | These are Perl bindings for the Gtk toolkit L<http://www.gtk.org>. The |
| 532 | interface changed significantly between versions 1 and 2 so they have |
| 533 | separate Perl modules. It runs under Unix, Win32 and Mac OS X (currently |
| 534 | it requires an X server on Mac OS, but a 'native' port is underway), and |
| 535 | the widgets look the same on every plaform: i.e., they don't match the |
| 536 | native widgets. As with Wx, the Perl bindings follow the C API closely, |
| 537 | and the documentation requires you to read the C documentation to |
| 538 | understand it. |
| 539 | |
| 540 | =item Win32::GUI |
| 541 | |
| 542 | This provides access to most of the Win32 GUI widgets from Perl. |
| 543 | Obviously, it only runs under Win32, and uses native widgets. The Perl |
| 544 | interface doesn't really follow the C interface: it's been made more |
| 545 | Perlish, and the documentation is pretty good. More advanced stuff may |
| 546 | require familiarity with the C Win32 APIs, or reference to MSDN. |
| 547 | |
| 548 | =item CamelBones |
| 549 | |
| 550 | CamelBones L<http://camelbones.sourceforge.net> is a Perl interface to |
| 551 | Mac OS X's Cocoa GUI toolkit, and as such can be used to produce native |
| 552 | GUIs on Mac OS X. It's not on CPAN, as it requires frameworks that |
| 553 | CPAN.pm doesn't know how to install, but installation is via the |
| 554 | standard OSX package installer. The Perl API is, again, very close to |
| 555 | the ObjC API it's wrapping, and the documentation just tells you how to |
| 556 | translate from one to the other. |
| 557 | |
| 558 | =item Qt |
| 559 | |
| 560 | There is a Perl interface to TrollTech's Qt toolkit, but it does not |
| 561 | appear to be maintained. |
| 562 | |
| 563 | =item Athena |
| 564 | |
| 565 | Sx is an interface to the Athena widget set which comes with X, but |
| 566 | again it appears not to be much used nowadays. |
| 567 | |
| 568 | =back |
| 569 | |
| 570 | =head2 How can I make my Perl program run faster? |
| 571 | |
| 572 | The best way to do this is to come up with a better algorithm. This |
| 573 | can often make a dramatic difference. Jon Bentley's book |
| 574 | I<Programming Pearls> (that's not a misspelling!) has some good tips |
| 575 | on optimization, too. Advice on benchmarking boils down to: benchmark |
| 576 | and profile to make sure you're optimizing the right part, look for |
| 577 | better algorithms instead of microtuning your code, and when all else |
| 578 | fails consider just buying faster hardware. You will probably want to |
| 579 | read the answer to the earlier question "How do I profile my Perl |
| 580 | programs?" if you haven't done so already. |
| 581 | |
| 582 | A different approach is to autoload seldom-used Perl code. See the |
| 583 | AutoSplit and AutoLoader modules in the standard distribution for |
| 584 | that. Or you could locate the bottleneck and think about writing just |
| 585 | that part in C, the way we used to take bottlenecks in C code and |
| 586 | write them in assembler. Similar to rewriting in C, modules that have |
| 587 | critical sections can be written in C (for instance, the PDL module |
| 588 | from CPAN). |
| 589 | |
| 590 | If you're currently linking your perl executable to a shared |
| 591 | I<libc.so>, you can often gain a 10-25% performance benefit by |
| 592 | rebuilding it to link with a static libc.a instead. This will make a |
| 593 | bigger perl executable, but your Perl programs (and programmers) may |
| 594 | thank you for it. See the F<INSTALL> file in the source distribution |
| 595 | for more information. |
| 596 | |
| 597 | The undump program was an ancient attempt to speed up Perl program by |
| 598 | storing the already-compiled form to disk. This is no longer a viable |
| 599 | option, as it only worked on a few architectures, and wasn't a good |
| 600 | solution anyway. |
| 601 | |
| 602 | =head2 How can I make my Perl program take less memory? |
| 603 | |
| 604 | When it comes to time-space tradeoffs, Perl nearly always prefers to |
| 605 | throw memory at a problem. Scalars in Perl use more memory than |
| 606 | strings in C, arrays take more than that, and hashes use even more. While |
| 607 | there's still a lot to be done, recent releases have been addressing |
| 608 | these issues. For example, as of 5.004, duplicate hash keys are |
| 609 | shared amongst all hashes using them, so require no reallocation. |
| 610 | |
| 611 | In some cases, using substr() or vec() to simulate arrays can be |
| 612 | highly beneficial. For example, an array of a thousand booleans will |
| 613 | take at least 20,000 bytes of space, but it can be turned into one |
| 614 | 125-byte bit vector--a considerable memory savings. The standard |
| 615 | Tie::SubstrHash module can also help for certain types of data |
| 616 | structure. If you're working with specialist data structures |
| 617 | (matrices, for instance) modules that implement these in C may use |
| 618 | less memory than equivalent Perl modules. |
| 619 | |
| 620 | Another thing to try is learning whether your Perl was compiled with |
| 621 | the system malloc or with Perl's builtin malloc. Whichever one it |
| 622 | is, try using the other one and see whether this makes a difference. |
| 623 | Information about malloc is in the F<INSTALL> file in the source |
| 624 | distribution. You can find out whether you are using perl's malloc by |
| 625 | typing C<perl -V:usemymalloc>. |
| 626 | |
| 627 | Of course, the best way to save memory is to not do anything to waste |
| 628 | it in the first place. Good programming practices can go a long way |
| 629 | toward this: |
| 630 | |
| 631 | =over 4 |
| 632 | |
| 633 | =item * Don't slurp! |
| 634 | |
| 635 | Don't read an entire file into memory if you can process it line |
| 636 | by line. Or more concretely, use a loop like this: |
| 637 | |
| 638 | # |
| 639 | # Good Idea |
| 640 | # |
| 641 | while (<FILE>) { |
| 642 | # ... |
| 643 | } |
| 644 | |
| 645 | instead of this: |
| 646 | |
| 647 | # |
| 648 | # Bad Idea |
| 649 | # |
| 650 | @data = <FILE>; |
| 651 | foreach (@data) { |
| 652 | # ... |
| 653 | } |
| 654 | |
| 655 | When the files you're processing are small, it doesn't much matter which |
| 656 | way you do it, but it makes a huge difference when they start getting |
| 657 | larger. |
| 658 | |
| 659 | =item * Use map and grep selectively |
| 660 | |
| 661 | Remember that both map and grep expect a LIST argument, so doing this: |
| 662 | |
| 663 | @wanted = grep {/pattern/} <FILE>; |
| 664 | |
| 665 | will cause the entire file to be slurped. For large files, it's better |
| 666 | to loop: |
| 667 | |
| 668 | while (<FILE>) { |
| 669 | push(@wanted, $_) if /pattern/; |
| 670 | } |
| 671 | |
| 672 | =item * Avoid unnecessary quotes and stringification |
| 673 | |
| 674 | Don't quote large strings unless absolutely necessary: |
| 675 | |
| 676 | my $copy = "$large_string"; |
| 677 | |
| 678 | makes 2 copies of $large_string (one for $copy and another for the |
| 679 | quotes), whereas |
| 680 | |
| 681 | my $copy = $large_string; |
| 682 | |
| 683 | only makes one copy. |
| 684 | |
| 685 | Ditto for stringifying large arrays: |
| 686 | |
| 687 | { |
| 688 | local $, = "\n"; |
| 689 | print @big_array; |
| 690 | } |
| 691 | |
| 692 | is much more memory-efficient than either |
| 693 | |
| 694 | print join "\n", @big_array; |
| 695 | |
| 696 | or |
| 697 | |
| 698 | { |
| 699 | local $" = "\n"; |
| 700 | print "@big_array"; |
| 701 | } |
| 702 | |
| 703 | |
| 704 | =item * Pass by reference |
| 705 | |
| 706 | Pass arrays and hashes by reference, not by value. For one thing, it's |
| 707 | the only way to pass multiple lists or hashes (or both) in a single |
| 708 | call/return. It also avoids creating a copy of all the contents. This |
| 709 | requires some judgement, however, because any changes will be propagated |
| 710 | back to the original data. If you really want to mangle (er, modify) a |
| 711 | copy, you'll have to sacrifice the memory needed to make one. |
| 712 | |
| 713 | =item * Tie large variables to disk. |
| 714 | |
| 715 | For "big" data stores (i.e. ones that exceed available memory) consider |
| 716 | using one of the DB modules to store it on disk instead of in RAM. This |
| 717 | will incur a penalty in access time, but that's probably better than |
| 718 | causing your hard disk to thrash due to massive swapping. |
| 719 | |
| 720 | =back |
| 721 | |
| 722 | =head2 Is it safe to return a reference to local or lexical data? |
| 723 | |
| 724 | Yes. Perl's garbage collection system takes care of this so |
| 725 | everything works out right. |
| 726 | |
| 727 | sub makeone { |
| 728 | my @a = ( 1 .. 10 ); |
| 729 | return \@a; |
| 730 | } |
| 731 | |
| 732 | for ( 1 .. 10 ) { |
| 733 | push @many, makeone(); |
| 734 | } |
| 735 | |
| 736 | print $many[4][5], "\n"; |
| 737 | |
| 738 | print "@many\n"; |
| 739 | |
| 740 | =head2 How can I free an array or hash so my program shrinks? |
| 741 | |
| 742 | (contributed by Michael Carman) |
| 743 | |
| 744 | You usually can't. Memory allocated to lexicals (i.e. my() variables) |
| 745 | cannot be reclaimed or reused even if they go out of scope. It is |
| 746 | reserved in case the variables come back into scope. Memory allocated |
| 747 | to global variables can be reused (within your program) by using |
| 748 | undef()ing and/or delete(). |
| 749 | |
| 750 | On most operating systems, memory allocated to a program can never be |
| 751 | returned to the system. That's why long-running programs sometimes re- |
| 752 | exec themselves. Some operating systems (notably, systems that use |
| 753 | mmap(2) for allocating large chunks of memory) can reclaim memory that |
| 754 | is no longer used, but on such systems, perl must be configured and |
| 755 | compiled to use the OS's malloc, not perl's. |
| 756 | |
| 757 | In general, memory allocation and de-allocation isn't something you can |
| 758 | or should be worrying about much in Perl. |
| 759 | |
| 760 | See also "How can I make my Perl program take less memory?" |
| 761 | |
| 762 | =head2 How can I make my CGI script more efficient? |
| 763 | |
| 764 | Beyond the normal measures described to make general Perl programs |
| 765 | faster or smaller, a CGI program has additional issues. It may be run |
| 766 | several times per second. Given that each time it runs it will need |
| 767 | to be re-compiled and will often allocate a megabyte or more of system |
| 768 | memory, this can be a killer. Compiling into C B<isn't going to help |
| 769 | you> because the process start-up overhead is where the bottleneck is. |
| 770 | |
| 771 | There are two popular ways to avoid this overhead. One solution |
| 772 | involves running the Apache HTTP server (available from |
| 773 | http://www.apache.org/ ) with either of the mod_perl or mod_fastcgi |
| 774 | plugin modules. |
| 775 | |
| 776 | With mod_perl and the Apache::Registry module (distributed with |
| 777 | mod_perl), httpd will run with an embedded Perl interpreter which |
| 778 | pre-compiles your script and then executes it within the same address |
| 779 | space without forking. The Apache extension also gives Perl access to |
| 780 | the internal server API, so modules written in Perl can do just about |
| 781 | anything a module written in C can. For more on mod_perl, see |
| 782 | http://perl.apache.org/ |
| 783 | |
| 784 | With the FCGI module (from CPAN) and the mod_fastcgi |
| 785 | module (available from http://www.fastcgi.com/ ) each of your Perl |
| 786 | programs becomes a permanent CGI daemon process. |
| 787 | |
| 788 | Both of these solutions can have far-reaching effects on your system |
| 789 | and on the way you write your CGI programs, so investigate them with |
| 790 | care. |
| 791 | |
| 792 | See http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ . |
| 793 | |
| 794 | =head2 How can I hide the source for my Perl program? |
| 795 | |
| 796 | Delete it. :-) Seriously, there are a number of (mostly |
| 797 | unsatisfactory) solutions with varying levels of "security". |
| 798 | |
| 799 | First of all, however, you I<can't> take away read permission, because |
| 800 | the source code has to be readable in order to be compiled and |
| 801 | interpreted. (That doesn't mean that a CGI script's source is |
| 802 | readable by people on the web, though--only by people with access to |
| 803 | the filesystem.) So you have to leave the permissions at the socially |
| 804 | friendly 0755 level. |
| 805 | |
| 806 | Some people regard this as a security problem. If your program does |
| 807 | insecure things and relies on people not knowing how to exploit those |
| 808 | insecurities, it is not secure. It is often possible for someone to |
| 809 | determine the insecure things and exploit them without viewing the |
| 810 | source. Security through obscurity, the name for hiding your bugs |
| 811 | instead of fixing them, is little security indeed. |
| 812 | |
| 813 | You can try using encryption via source filters (Starting from Perl |
| 814 | 5.8 the Filter::Simple and Filter::Util::Call modules are included in |
| 815 | the standard distribution), but any decent programmer will be able to |
| 816 | decrypt it. You can try using the byte code compiler and interpreter |
| 817 | described later in L<perlfaq3>, but the curious might still be able to |
| 818 | de-compile it. You can try using the native-code compiler described |
| 819 | later, but crackers might be able to disassemble it. These pose |
| 820 | varying degrees of difficulty to people wanting to get at your code, |
| 821 | but none can definitively conceal it (true of every language, not just |
| 822 | Perl). |
| 823 | |
| 824 | It is very easy to recover the source of Perl programs. You simply |
| 825 | feed the program to the perl interpreter and use the modules in |
| 826 | the B:: hierarchy. The B::Deparse module should be able to |
| 827 | defeat most attempts to hide source. Again, this is not |
| 828 | unique to Perl. |
| 829 | |
| 830 | If you're concerned about people profiting from your code, then the |
| 831 | bottom line is that nothing but a restrictive license will give you |
| 832 | legal security. License your software and pepper it with threatening |
| 833 | statements like "This is unpublished proprietary software of XYZ Corp. |
| 834 | Your access to it does not give you permission to use it blah blah |
| 835 | blah." We are not lawyers, of course, so you should see a lawyer if |
| 836 | you want to be sure your license's wording will stand up in court. |
| 837 | |
| 838 | =head2 How can I compile my Perl program into byte code or C? |
| 839 | |
| 840 | (contributed by brian d foy) |
| 841 | |
| 842 | In general, you can't do this. There are some things that may work |
| 843 | for your situation though. People usually ask this question |
| 844 | because they want to distribute their works without giving away |
| 845 | the source code, and most solutions trade disk space for convenience. |
| 846 | You probably won't see much of a speed increase either, since most |
| 847 | solutions simply bundle a Perl interpreter in the final product |
| 848 | (but see L<How can I make my Perl program run faster?>). |
| 849 | |
| 850 | The Perl Archive Toolkit ( http://par.perl.org/ ) is Perl's |
| 851 | analog to Java's JAR. It's freely available and on CPAN ( |
| 852 | http://search.cpan.org/dist/PAR/ ). |
| 853 | |
| 854 | There are also some commercial products that may work for you, although |
| 855 | you have to buy a license for them. |
| 856 | |
| 857 | The Perl Dev Kit ( http://www.activestate.com/Products/Perl_Dev_Kit/ ) |
| 858 | from ActiveState can "Turn your Perl programs into ready-to-run |
| 859 | executables for HP-UX, Linux, Solaris and Windows." |
| 860 | |
| 861 | Perl2Exe ( http://www.indigostar.com/perl2exe.htm ) is a command line |
| 862 | program for converting perl scripts to executable files. It targets both |
| 863 | Windows and unix platforms. |
| 864 | |
| 865 | =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]? |
| 866 | |
| 867 | For OS/2 just use |
| 868 | |
| 869 | extproc perl -S -your_switches |
| 870 | |
| 871 | as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's |
| 872 | "extproc" handling). For DOS one should first invent a corresponding |
| 873 | batch file and codify it in C<ALTERNATE_SHEBANG> (see the |
| 874 | F<dosish.h> file in the source distribution for more information). |
| 875 | |
| 876 | The Win95/NT installation, when using the ActiveState port of Perl, |
| 877 | will modify the Registry to associate the C<.pl> extension with the |
| 878 | perl interpreter. If you install another port, perhaps even building |
| 879 | your own Win95/NT Perl from the standard sources by using a Windows port |
| 880 | of gcc (e.g., with cygwin or mingw32), then you'll have to modify |
| 881 | the Registry yourself. In addition to associating C<.pl> with the |
| 882 | interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them |
| 883 | run the program C<install-linux.pl> merely by typing C<install-linux>. |
| 884 | |
| 885 | Under "Classic" MacOS, a perl program will have the appropriate Creator and |
| 886 | Type, so that double-clicking them will invoke the MacPerl application. |
| 887 | Under Mac OS X, clickable apps can be made from any C<#!> script using Wil |
| 888 | Sanchez' DropScript utility: http://www.wsanchez.net/software/ . |
| 889 | |
| 890 | I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just |
| 891 | throw the perl interpreter into your cgi-bin directory, in order to |
| 892 | get your programs working for a web server. This is an EXTREMELY big |
| 893 | security risk. Take the time to figure out how to do it correctly. |
| 894 | |
| 895 | =head2 Can I write useful Perl programs on the command line? |
| 896 | |
| 897 | Yes. Read L<perlrun> for more information. Some examples follow. |
| 898 | (These assume standard Unix shell quoting rules.) |
| 899 | |
| 900 | # sum first and last fields |
| 901 | perl -lane 'print $F[0] + $F[-1]' * |
| 902 | |
| 903 | # identify text files |
| 904 | perl -le 'for(@ARGV) {print if -f && -T _}' * |
| 905 | |
| 906 | # remove (most) comments from C program |
| 907 | perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c |
| 908 | |
| 909 | # make file a month younger than today, defeating reaper daemons |
| 910 | perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' * |
| 911 | |
| 912 | # find first unused uid |
| 913 | perl -le '$i++ while getpwuid($i); print $i' |
| 914 | |
| 915 | # display reasonable manpath |
| 916 | echo $PATH | perl -nl -072 -e ' |
| 917 | s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}' |
| 918 | |
| 919 | OK, the last one was actually an Obfuscated Perl Contest entry. :-) |
| 920 | |
| 921 | =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system? |
| 922 | |
| 923 | The problem is usually that the command interpreters on those systems |
| 924 | have rather different ideas about quoting than the Unix shells under |
| 925 | which the one-liners were created. On some systems, you may have to |
| 926 | change single-quotes to double ones, which you must I<NOT> do on Unix |
| 927 | or Plan9 systems. You might also have to change a single % to a %%. |
| 928 | |
| 929 | For example: |
| 930 | |
| 931 | # Unix (including Mac OS X) |
| 932 | perl -e 'print "Hello world\n"' |
| 933 | |
| 934 | # DOS, etc. |
| 935 | perl -e "print \"Hello world\n\"" |
| 936 | |
| 937 | # Mac Classic |
| 938 | print "Hello world\n" |
| 939 | (then Run "Myscript" or Shift-Command-R) |
| 940 | |
| 941 | # MPW |
| 942 | perl -e 'print "Hello world\n"' |
| 943 | |
| 944 | # VMS |
| 945 | perl -e "print ""Hello world\n""" |
| 946 | |
| 947 | The problem is that none of these examples are reliable: they depend on the |
| 948 | command interpreter. Under Unix, the first two often work. Under DOS, |
| 949 | it's entirely possible that neither works. If 4DOS was the command shell, |
| 950 | you'd probably have better luck like this: |
| 951 | |
| 952 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" |
| 953 | |
| 954 | Under the Mac, it depends which environment you are using. The MacPerl |
| 955 | shell, or MPW, is much like Unix shells in its support for several |
| 956 | quoting variants, except that it makes free use of the Mac's non-ASCII |
| 957 | characters as control characters. |
| 958 | |
| 959 | Using qq(), q(), and qx(), instead of "double quotes", 'single |
| 960 | quotes', and `backticks`, may make one-liners easier to write. |
| 961 | |
| 962 | There is no general solution to all of this. It is a mess. |
| 963 | |
| 964 | [Some of this answer was contributed by Kenneth Albanowski.] |
| 965 | |
| 966 | =head2 Where can I learn about CGI or Web programming in Perl? |
| 967 | |
| 968 | For modules, get the CGI or LWP modules from CPAN. For textbooks, |
| 969 | see the two especially dedicated to web stuff in the question on |
| 970 | books. For problems and questions related to the web, like "Why |
| 971 | do I get 500 Errors" or "Why doesn't it run from the browser right |
| 972 | when it runs fine on the command line", see the troubleshooting |
| 973 | guides and references in L<perlfaq9> or in the CGI MetaFAQ: |
| 974 | |
| 975 | http://www.perl.org/CGI_MetaFAQ.html |
| 976 | |
| 977 | =head2 Where can I learn about object-oriented Perl programming? |
| 978 | |
| 979 | A good place to start is L<perltoot>, and you can use L<perlobj>, |
| 980 | L<perlboot>, L<perltoot>, L<perltooc>, and L<perlbot> for reference. |
| 981 | |
| 982 | A good book on OO on Perl is the "Object-Oriented Perl" |
| 983 | by Damian Conway from Manning Publications, or "Intermediate Perl" |
| 984 | by Randal Schwartz, brian d foy, and Tom Phoenix from O'Reilly Media. |
| 985 | |
| 986 | =head2 Where can I learn about linking C with Perl? |
| 987 | |
| 988 | If you want to call C from Perl, start with L<perlxstut>, |
| 989 | moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to |
| 990 | call Perl from C, then read L<perlembed>, L<perlcall>, and |
| 991 | L<perlguts>. Don't forget that you can learn a lot from looking at |
| 992 | how the authors of existing extension modules wrote their code and |
| 993 | solved their problems. |
| 994 | |
| 995 | You might not need all the power of XS. The Inline::C module lets |
| 996 | you put C code directly in your Perl source. It handles all the |
| 997 | magic to make it work. You still have to learn at least some of |
| 998 | the perl API but you won't have to deal with the complexity of the |
| 999 | XS support files. |
| 1000 | |
| 1001 | =head2 I've read perlembed, perlguts, etc., but I can't embed perl in my C program; what am I doing wrong? |
| 1002 | |
| 1003 | Download the ExtUtils::Embed kit from CPAN and run `make test'. If |
| 1004 | the tests pass, read the pods again and again and again. If they |
| 1005 | fail, see L<perlbug> and send a bug report with the output of |
| 1006 | C<make test TEST_VERBOSE=1> along with C<perl -V>. |
| 1007 | |
| 1008 | =head2 When I tried to run my script, I got this message. What does it mean? |
| 1009 | |
| 1010 | A complete list of Perl's error messages and warnings with explanatory |
| 1011 | text can be found in L<perldiag>. You can also use the splain program |
| 1012 | (distributed with Perl) to explain the error messages: |
| 1013 | |
| 1014 | perl program 2>diag.out |
| 1015 | splain [-v] [-p] diag.out |
| 1016 | |
| 1017 | or change your program to explain the messages for you: |
| 1018 | |
| 1019 | use diagnostics; |
| 1020 | |
| 1021 | or |
| 1022 | |
| 1023 | use diagnostics -verbose; |
| 1024 | |
| 1025 | =head2 What's MakeMaker? |
| 1026 | |
| 1027 | (contributed by brian d foy) |
| 1028 | |
| 1029 | The C<ExtUtils::MakeMaker> module, better known simply as "MakeMaker", |
| 1030 | turns a Perl script, typically called C<Makefile.PL>, into a Makefile. |
| 1031 | The unix tool C<make> uses this file to manage dependencies and actions |
| 1032 | to process and install a Perl distribution. |
| 1033 | |
| 1034 | =head1 REVISION |
| 1035 | |
| 1036 | Revision: $Revision: 10127 $ |
| 1037 | |
| 1038 | Date: $Date: 2007-10-27 21:40:20 +0200 (Sat, 27 Oct 2007) $ |
| 1039 | |
| 1040 | See L<perlfaq> for source control details and availability. |
| 1041 | |
| 1042 | =head1 AUTHOR AND COPYRIGHT |
| 1043 | |
| 1044 | Copyright (c) 1997-2007 Tom Christiansen, Nathan Torkington, and |
| 1045 | other authors as noted. All rights reserved. |
| 1046 | |
| 1047 | This documentation is free; you can redistribute it and/or modify it |
| 1048 | under the same terms as Perl itself. |
| 1049 | |
| 1050 | Irrespective of its distribution, all code examples here are in the public |
| 1051 | domain. You are permitted and encouraged to use this code and any |
| 1052 | derivatives thereof in your own programs for fun or for profit as you |
| 1053 | see fit. A simple comment in the code giving credit to the FAQ would |
| 1054 | be courteous but is not required. |