[ Index ]

PHP Cross Reference of Unnamed Project

title

Body

[close]

/se3-unattended/var/se3/unattended/install/linuxaux/opt/perl/lib/5.10.0/pod/ -> perlfaq3.pod (source)

   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.


Generated: Tue Mar 17 22:47:18 2015 Cross-referenced by PHPXref 0.7.1