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1 | =head1 NAME |
2 | |
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3 | perlfaq3 - Programming Tools ($Revision: 1.37 $, $Date: 2003/11/24 19:55:50 $) |
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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. |
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14 | Have you read the appropriate manpages? Here's a brief index: |
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15 | |
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16 | Basics perldata, perlvar, perlsyn, perlop, perlsub |
17 | Execution perlrun, perldebug |
18 | Functions perlfunc |
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19 | Objects perlref, perlmod, perlobj, perltie |
20 | Data Structures perlref, perllol, perldsc |
f102b883 |
21 | Modules perlmod, perlmodlib, perlsub |
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22 | Regexes perlre, perlfunc, perlop, perllocale |
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23 | Moving to perl5 perltrap, perl |
24 | Linking w/C perlxstut, perlxs, perlcall, perlguts, perlembed |
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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) |
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28 | |
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29 | A crude table of contents for the Perl manpage set is found in L<perltoc>. |
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30 | |
31 | =head2 How can I use Perl interactively? |
32 | |
33 | The typical approach uses the Perl debugger, described in the |
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34 | perldebug(1) manpage, on an ``empty'' program, like this: |
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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 |
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41 | operations typically found in symbolic debuggers. |
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42 | |
43 | =head2 Is there a Perl shell? |
44 | |
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45 | The psh (Perl sh) is currently at version 1.8. The Perl Shell is a |
46 | shell that combines the interactive nature of a Unix shell with the |
47 | power of Perl. The goal is a full featured shell that behaves as |
48 | expected for normal shell activity and uses Perl syntax and |
49 | functionality for control-flow statements and other things. |
50 | You can get psh at http://www.focusresearch.com/gregor/psh/ . |
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51 | |
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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 | |
55e174a4 |
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 |
59 | from the source distribution is simplistic and uninteresting, but |
60 | may still be what you want. |
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61 | |
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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 |
65 | installed distributions, although it can take awhile to do |
66 | its magic. The standard library which comes with Perl just |
67 | shows up as "Perl" (although you can get those with |
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68 | Module::CoreList). |
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69 | |
70 | use ExtUtils::Installed; |
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71 | |
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72 | my $inst = ExtUtils::Installed->new(); |
73 | my @modules = $inst->modules(); |
74 | |
75 | If you want a list of all of the Perl module filenames, you |
76 | can use File::Find::Rule. |
77 | |
78 | use File::Find::Rule; |
197aec24 |
79 | |
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80 | my @files = File::Find::Rule->file()->name( '*.pm' )->in( @INC ); |
81 | |
82 | If you do not have that module, you can do the same thing |
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83 | with File::Find which is part of the standard library. |
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84 | |
85 | use File::Find; |
86 | my @files; |
87 | |
88 | find sub { push @files, $File::Find::name if -f _ && /\.pm$/ }, |
89 | @INC; |
90 | |
91 | print join "\n", @files; |
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92 | |
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93 | If you simply need to quickly check to see if a module is |
94 | available, you can check for its documentation. If you can |
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95 | read the documentation the module is most likely installed. |
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96 | If you cannot read the documentation, the module might not |
97 | have any (in rare cases). |
98 | |
99 | prompt% perldoc Module::Name |
100 | |
101 | You can also try to include the module in a one-liner to see if |
102 | perl finds it. |
103 | |
104 | perl -MModule::Name -e1 |
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105 | |
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106 | =head2 How do I debug my Perl programs? |
107 | |
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108 | Have you tried C<use warnings> or used C<-w>? They enable warnings |
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109 | to detect dubious practices. |
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110 | |
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111 | Have you tried C<use strict>? It prevents you from using symbolic |
112 | references, makes you predeclare any subroutines that you call as bare |
113 | words, and (probably most importantly) forces you to predeclare your |
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114 | variables with C<my>, C<our>, or C<use vars>. |
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115 | |
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116 | Did you check the return values of each and every system call? The operating |
117 | system (and thus Perl) tells you whether they worked, and if not |
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118 | why. |
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119 | |
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120 | open(FH, "> /etc/cantwrite") |
121 | or die "Couldn't write to /etc/cantwrite: $!\n"; |
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122 | |
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123 | Did you read L<perltrap>? It's full of gotchas for old and new Perl |
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124 | programmers and even has sections for those of you who are upgrading |
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125 | from languages like I<awk> and I<C>. |
126 | |
127 | Have you tried the Perl debugger, described in L<perldebug>? You can |
128 | step through your program and see what it's doing and thus work out |
129 | why what it's doing isn't what it should be doing. |
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130 | |
131 | =head2 How do I profile my Perl programs? |
132 | |
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133 | You should get the Devel::DProf module from the standard distribution |
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134 | (or separately on CPAN) and also use Benchmark.pm from the standard |
135 | distribution. The Benchmark module lets you time specific portions of |
136 | your code, while Devel::DProf gives detailed breakdowns of where your |
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137 | code spends its time. |
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138 | |
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139 | Here's a sample use of Benchmark: |
140 | |
141 | use Benchmark; |
142 | |
143 | @junk = `cat /etc/motd`; |
144 | $count = 10_000; |
145 | |
146 | timethese($count, { |
147 | 'map' => sub { my @a = @junk; |
148 | map { s/a/b/ } @a; |
6c43ef16 |
149 | return @a }, |
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150 | 'for' => sub { my @a = @junk; |
92c2ed05 |
151 | for (@a) { s/a/b/ }; |
152 | return @a }, |
153 | }); |
154 | |
155 | This is what it prints (on one machine--your results will be dependent |
156 | on your hardware, operating system, and the load on your machine): |
157 | |
158 | Benchmark: timing 10000 iterations of for, map... |
159 | for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu) |
160 | map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu) |
161 | |
65acb1b1 |
162 | Be aware that a good benchmark is very hard to write. It only tests the |
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163 | data you give it and proves little about the differing complexities |
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164 | of contrasting algorithms. |
165 | |
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166 | =head2 How do I cross-reference my Perl programs? |
167 | |
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168 | The B::Xref module can be used to generate cross-reference reports |
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169 | for Perl programs. |
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170 | |
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171 | perl -MO=Xref[,OPTIONS] scriptname.plx |
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172 | |
173 | =head2 Is there a pretty-printer (formatter) for Perl? |
174 | |
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175 | Perltidy is a Perl script which indents and reformats Perl scripts |
176 | to make them easier to read by trying to follow the rules of the |
177 | L<perlstyle>. If you write Perl scripts, or spend much time reading |
178 | them, you will probably find it useful. It is available at |
179 | http://perltidy.sourceforge.net |
180 | |
181 | Of course, if you simply follow the guidelines in L<perlstyle>, |
182 | you shouldn't need to reformat. The habit of formatting your code |
183 | as you write it will help prevent bugs. Your editor can and should |
184 | help you with this. The perl-mode or newer cperl-mode for emacs |
185 | can provide remarkable amounts of help with most (but not all) |
186 | code, and even less programmable editors can provide significant |
187 | assistance. Tom Christiansen and many other VI users swear by |
188 | the following settings in vi and its clones: |
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189 | |
190 | set ai sw=4 |
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191 | map! ^O {^M}^[O^T |
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192 | |
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193 | Put that in your F<.exrc> file (replacing the caret characters |
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194 | with control characters) and away you go. In insert mode, ^T is |
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195 | for indenting, ^D is for undenting, and ^O is for blockdenting-- |
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196 | as it were. A more complete example, with comments, can be found at |
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197 | http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz |
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198 | |
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199 | The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps.gz does |
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200 | lots of things related to generating nicely printed output of |
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201 | documents, as does enscript at http://people.ssh.fi/mtr/genscript/ . |
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202 | |
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203 | =head2 Is there a ctags for Perl? |
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204 | |
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205 | Recent versions of ctags do much more than older versions did. |
206 | EXUBERANT CTAGS is available from http://ctags.sourceforge.net/ |
207 | and does a good job of making tags files for perl code. |
208 | |
209 | There is also a simple one at |
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210 | http://www.cpan.org/authors/id/TOMC/scripts/ptags.gz which may do |
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211 | the trick. It can be easy to hack this into what you want. |
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212 | |
213 | =head2 Is there an IDE or Windows Perl Editor? |
214 | |
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215 | Perl programs are just plain text, so any editor will do. |
216 | |
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217 | If you're on Unix, you already have an IDE--Unix itself. The UNIX |
218 | philosophy is the philosophy of several small tools that each do one |
219 | thing and do it well. It's like a carpenter's toolbox. |
220 | |
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221 | If you want an IDE, check the following: |
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222 | |
223 | =over 4 |
224 | |
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225 | =item Komodo |
226 | |
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227 | ActiveState's cross-platform (as of April 2001 Windows and Linux), |
228 | multi-language IDE has Perl support, including a regular expression |
229 | debugger and remote debugging |
f224927c |
230 | ( http://www.ActiveState.com/Products/Komodo/index.html ). (Visual |
5ca69f12 |
231 | Perl, a Visual Studio.NET plug-in is currently (early 2001) in beta |
1577cd80 |
232 | ( http://www.ActiveState.com/Products/VisualPerl/index.html )). |
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233 | |
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234 | =item The Object System |
235 | |
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236 | ( http://www.castlelink.co.uk/object_system/ ) is a Perl web |
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237 | applications development IDE, apparently for any platform |
238 | that runs Perl. |
239 | |
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240 | =item Open Perl IDE |
241 | |
242 | ( http://open-perl-ide.sourceforge.net/ ) |
243 | Open Perl IDE is an integrated development environment for writing |
244 | and debugging Perl scripts with ActiveState's ActivePerl distribution |
245 | under Windows 95/98/NT/2000. |
246 | |
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247 | =item PerlBuilder |
248 | |
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249 | ( http://www.solutionsoft.com/perl.htm ) is an integrated development |
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250 | environment for Windows that supports Perl development. |
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251 | |
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252 | =item visiPerl+ |
253 | |
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254 | ( http://helpconsulting.net/visiperl/ ) |
255 | From Help Consulting, for Windows. |
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256 | |
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257 | =item OptiPerl |
258 | |
259 | ( http://www.optiperl.com/ ) is a Windows IDE with simulated CGI |
260 | environment, including debugger and syntax highlighting editor. |
261 | |
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262 | =back |
263 | |
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264 | For editors: if you're on Unix you probably have vi or a vi clone already, |
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265 | and possibly an emacs too, so you may not need to download anything. |
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266 | In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the |
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267 | best available Perl editing mode in any editor. |
268 | |
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269 | If you are using Windows, you can use any editor that lets |
270 | you work with plain text, such as NotePad or WordPad. Word |
271 | processors, such as Microsoft Word or WordPerfect, typically |
272 | do not work since they insert all sorts of behind-the-scenes |
273 | information, although some allow you to save files as "Text |
274 | Only". You can also download text editors designed |
275 | specifically for programming, such as Textpad |
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276 | ( http://www.textpad.com/ ) and UltraEdit |
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277 | ( http://www.ultraedit.com/ ), among others. |
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278 | |
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279 | If you are using MacOS, the same concerns apply. MacPerl |
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280 | (for Classic environments) comes with a simple editor. |
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281 | Popular external editors are BBEdit ( http://www.bbedit.com/ ) |
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282 | or Alpha ( http://www.kelehers.org/alpha/ ). MacOS X users can |
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283 | use Unix editors as well. |
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284 | |
285 | =over 4 |
286 | |
287 | =item GNU Emacs |
288 | |
289 | http://www.gnu.org/software/emacs/windows/ntemacs.html |
290 | |
291 | =item MicroEMACS |
292 | |
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293 | http://www.microemacs.de/ |
68fbfbd7 |
294 | |
295 | =item XEmacs |
296 | |
297 | http://www.xemacs.org/Download/index.html |
298 | |
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299 | =item Jed |
300 | |
301 | http://space.mit.edu/~davis/jed/ |
302 | |
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303 | =back |
304 | |
305 | or a vi clone such as |
306 | |
307 | =over 4 |
308 | |
309 | =item Elvis |
310 | |
311 | ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/ |
312 | |
313 | =item Vile |
314 | |
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315 | http://dickey.his.com/vile/vile.html |
68fbfbd7 |
316 | |
317 | =item Vim |
318 | |
319 | http://www.vim.org/ |
320 | |
68fbfbd7 |
321 | =back |
322 | |
5a13f98a |
323 | For vi lovers in general, Windows or elsewhere: |
f05bbc40 |
324 | |
325 | http://www.thomer.com/thomer/vi/vi.html |
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326 | |
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327 | nvi ( http://www.bostic.com/vi/ , available from CPAN in src/misc/) is |
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328 | yet another vi clone, unfortunately not available for Windows, but in |
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329 | UNIX platforms you might be interested in trying it out, firstly because |
330 | strictly speaking it is not a vi clone, it is the real vi, or the new |
331 | incarnation of it, and secondly because you can embed Perl inside it |
332 | to use Perl as the scripting language. nvi is not alone in this, |
7c82de66 |
333 | though: at least also vim and vile offer an embedded Perl. |
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334 | |
68fbfbd7 |
335 | The following are Win32 multilanguage editor/IDESs that support Perl: |
336 | |
337 | =over 4 |
338 | |
339 | =item Codewright |
340 | |
341 | http://www.starbase.com/ |
342 | |
343 | =item MultiEdit |
344 | |
345 | http://www.MultiEdit.com/ |
346 | |
347 | =item SlickEdit |
348 | |
349 | http://www.slickedit.com/ |
350 | |
351 | =back |
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352 | |
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353 | There is also a toyedit Text widget based editor written in Perl |
354 | that is distributed with the Tk module on CPAN. The ptkdb |
f224927c |
355 | ( http://world.std.com/~aep/ptkdb/ ) is a Perl/tk based debugger that |
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356 | acts as a development environment of sorts. Perl Composer |
49d635f9 |
357 | ( http://perlcomposer.sourceforge.net/ ) is an IDE for Perl/Tk |
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358 | GUI creation. |
359 | |
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360 | In addition to an editor/IDE you might be interested in a more |
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361 | powerful shell environment for Win32. Your options include |
362 | |
363 | =over 4 |
364 | |
365 | =item Bash |
366 | |
1577cd80 |
367 | from the Cygwin package ( http://sources.redhat.com/cygwin/ ) |
68fbfbd7 |
368 | |
369 | =item Ksh |
370 | |
f224927c |
371 | from the MKS Toolkit ( http://www.mks.com/ ), or the Bourne shell of |
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372 | the U/WIN environment ( http://www.research.att.com/sw/tools/uwin/ ) |
68fbfbd7 |
373 | |
374 | =item Tcsh |
375 | |
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376 | ftp://ftp.astron.com/pub/tcsh/ , see also |
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377 | http://www.primate.wisc.edu/software/csh-tcsh-book/ |
378 | |
379 | =item Zsh |
380 | |
f224927c |
381 | ftp://ftp.blarg.net/users/amol/zsh/ , see also http://www.zsh.org/ |
68fbfbd7 |
382 | |
383 | =back |
384 | |
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385 | MKS and U/WIN are commercial (U/WIN is free for educational and |
386 | research purposes), Cygwin is covered by the GNU Public License (but |
387 | that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all |
388 | contain (in addition to the shells) a comprehensive set of standard |
389 | UNIX toolkit utilities. |
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390 | |
5a13f98a |
391 | If you're transferring text files between Unix and Windows using FTP |
392 | be sure to transfer them in ASCII mode so the ends of lines are |
393 | appropriately converted. |
394 | |
e083a89c |
395 | On Mac OS the MacPerl Application comes with a simple 32k text editor |
396 | that behaves like a rudimentary IDE. In contrast to the MacPerl Application |
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397 | the MPW Perl tool can make use of the MPW Shell itself as an editor (with |
68fbfbd7 |
398 | no 32k limit). |
399 | |
400 | =over 4 |
401 | |
402 | =item BBEdit and BBEdit Lite |
403 | |
404 | are text editors for Mac OS that have a Perl sensitivity mode |
1577cd80 |
405 | ( http://web.barebones.com/ ). |
68fbfbd7 |
406 | |
407 | =item Alpha |
408 | |
409 | is an editor, written and extensible in Tcl, that nonetheless has |
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410 | built in support for several popular markup and programming languages |
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411 | including Perl and HTML ( http://alpha.olm.net/ ). |
68fbfbd7 |
412 | |
413 | =back |
414 | |
415 | Pepper and Pe are programming language sensitive text editors for Mac |
1577cd80 |
416 | OS X and BeOS respectively ( http://www.hekkelman.com/ ). |
68dc0745 |
417 | |
418 | =head2 Where can I get Perl macros for vi? |
419 | |
420 | For a complete version of Tom Christiansen's vi configuration file, |
a93751fa |
421 | see http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz , |
a6dd486b |
422 | the standard benchmark file for vi emulators. The file runs best with nvi, |
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423 | the current version of vi out of Berkeley, which incidentally can be built |
bfeeaf1b |
424 | with an embedded Perl interpreter--see http://www.cpan.org/src/misc/ . |
68dc0745 |
425 | |
426 | =head2 Where can I get perl-mode for emacs? |
427 | |
428 | Since Emacs version 19 patchlevel 22 or so, there have been both a |
87275199 |
429 | perl-mode.el and support for the Perl debugger built in. These should |
68dc0745 |
430 | come with the standard Emacs 19 distribution. |
431 | |
87275199 |
432 | In the Perl source directory, you'll find a directory called "emacs", |
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433 | which contains a cperl-mode that color-codes keywords, provides |
434 | context-sensitive help, and other nifty things. |
435 | |
92c2ed05 |
436 | Note that the perl-mode of emacs will have fits with C<"main'foo"> |
d92eb7b0 |
437 | (single quote), and mess up the indentation and highlighting. You |
65acb1b1 |
438 | are probably using C<"main::foo"> in new Perl code anyway, so this |
92c2ed05 |
439 | shouldn't be an issue. |
68dc0745 |
440 | |
441 | =head2 How can I use curses with Perl? |
442 | |
443 | The Curses module from CPAN provides a dynamically loadable object |
5a964f20 |
444 | module interface to a curses library. A small demo can be found at the |
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445 | directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep.gz ; |
5a964f20 |
446 | this program repeats a command and updates the screen as needed, rendering |
447 | B<rep ps axu> similar to B<top>. |
68dc0745 |
448 | |
449 | =head2 How can I use X or Tk with Perl? |
450 | |
5a964f20 |
451 | Tk is a completely Perl-based, object-oriented interface to the Tk toolkit |
452 | that doesn't force you to use Tcl just to get at Tk. Sx is an interface |
453 | to the Athena Widget set. Both are available from CPAN. See the |
a93751fa |
454 | directory http://www.cpan.org/modules/by-category/08_User_Interfaces/ |
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455 | |
a6dd486b |
456 | Invaluable for Perl/Tk programming are the Perl/Tk FAQ at |
87275199 |
457 | http://w4.lns.cornell.edu/%7Epvhp/ptk/ptkTOC.html , the Perl/Tk Reference |
92c2ed05 |
458 | Guide available at |
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459 | http://www.cpan.org/authors/Stephen_O_Lidie/ , and the |
92c2ed05 |
460 | online manpages at |
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461 | http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html . |
92c2ed05 |
462 | |
68dc0745 |
463 | =head2 How can I generate simple menus without using CGI or Tk? |
464 | |
a93751fa |
465 | The http://www.cpan.org/authors/id/SKUNZ/perlmenu.v4.0.tar.gz |
68dc0745 |
466 | module, which is curses-based, can help with this. |
467 | |
68dc0745 |
468 | =head2 How can I make my Perl program run faster? |
469 | |
92c2ed05 |
470 | The best way to do this is to come up with a better algorithm. This |
b73a15ae |
471 | can often make a dramatic difference. Jon Bentley's book |
5cd0b561 |
472 | I<Programming Pearls> (that's not a misspelling!) has some good tips |
92c2ed05 |
473 | on optimization, too. Advice on benchmarking boils down to: benchmark |
474 | and profile to make sure you're optimizing the right part, look for |
475 | better algorithms instead of microtuning your code, and when all else |
57b19278 |
476 | fails consider just buying faster hardware. You will probably want to |
5cd0b561 |
477 | read the answer to the earlier question ``How do I profile my Perl |
478 | programs?'' if you haven't done so already. |
68dc0745 |
479 | |
92c2ed05 |
480 | A different approach is to autoload seldom-used Perl code. See the |
68dc0745 |
481 | AutoSplit and AutoLoader modules in the standard distribution for |
482 | that. Or you could locate the bottleneck and think about writing just |
483 | that part in C, the way we used to take bottlenecks in C code and |
5cd0b561 |
484 | write them in assembler. Similar to rewriting in C, modules that have |
485 | critical sections can be written in C (for instance, the PDL module |
486 | from CPAN). |
487 | |
488 | If you're currently linking your perl executable to a shared |
489 | I<libc.so>, you can often gain a 10-25% performance benefit by |
490 | rebuilding it to link with a static libc.a instead. This will make a |
491 | bigger perl executable, but your Perl programs (and programmers) may |
492 | thank you for it. See the F<INSTALL> file in the source distribution |
493 | for more information. |
494 | |
495 | The undump program was an ancient attempt to speed up Perl program by |
496 | storing the already-compiled form to disk. This is no longer a viable |
497 | option, as it only worked on a few architectures, and wasn't a good |
498 | solution anyway. |
68dc0745 |
499 | |
500 | =head2 How can I make my Perl program take less memory? |
501 | |
502 | When it comes to time-space tradeoffs, Perl nearly always prefers to |
503 | throw memory at a problem. Scalars in Perl use more memory than |
65acb1b1 |
504 | strings in C, arrays take more than that, and hashes use even more. While |
68dc0745 |
505 | there's still a lot to be done, recent releases have been addressing |
506 | these issues. For example, as of 5.004, duplicate hash keys are |
507 | shared amongst all hashes using them, so require no reallocation. |
508 | |
509 | In some cases, using substr() or vec() to simulate arrays can be |
510 | highly beneficial. For example, an array of a thousand booleans will |
511 | take at least 20,000 bytes of space, but it can be turned into one |
a6dd486b |
512 | 125-byte bit vector--a considerable memory savings. The standard |
68dc0745 |
513 | Tie::SubstrHash module can also help for certain types of data |
514 | structure. If you're working with specialist data structures |
515 | (matrices, for instance) modules that implement these in C may use |
516 | less memory than equivalent Perl modules. |
517 | |
518 | Another thing to try is learning whether your Perl was compiled with |
54310121 |
519 | the system malloc or with Perl's builtin malloc. Whichever one it |
68dc0745 |
520 | is, try using the other one and see whether this makes a difference. |
521 | Information about malloc is in the F<INSTALL> file in the source |
522 | distribution. You can find out whether you are using perl's malloc by |
523 | typing C<perl -V:usemymalloc>. |
524 | |
24f1ba9b |
525 | Of course, the best way to save memory is to not do anything to waste |
526 | it in the first place. Good programming practices can go a long way |
527 | toward this: |
528 | |
529 | =over 4 |
530 | |
531 | =item * Don't slurp! |
532 | |
533 | Don't read an entire file into memory if you can process it line |
534 | by line. Or more concretely, use a loop like this: |
535 | |
536 | # |
537 | # Good Idea |
538 | # |
539 | while (<FILE>) { |
540 | # ... |
541 | } |
542 | |
543 | instead of this: |
544 | |
545 | # |
546 | # Bad Idea |
547 | # |
548 | @data = <FILE>; |
549 | foreach (@data) { |
550 | # ... |
551 | } |
552 | |
553 | When the files you're processing are small, it doesn't much matter which |
554 | way you do it, but it makes a huge difference when they start getting |
197aec24 |
555 | larger. |
24f1ba9b |
556 | |
bc06af74 |
557 | =item * Use map and grep selectively |
558 | |
559 | Remember that both map and grep expect a LIST argument, so doing this: |
560 | |
561 | @wanted = grep {/pattern/} <FILE>; |
562 | |
563 | will cause the entire file to be slurped. For large files, it's better |
564 | to loop: |
565 | |
566 | while (<FILE>) { |
567 | push(@wanted, $_) if /pattern/; |
568 | } |
569 | |
570 | =item * Avoid unnecessary quotes and stringification |
571 | |
572 | Don't quote large strings unless absolutely necessary: |
573 | |
574 | my $copy = "$large_string"; |
575 | |
576 | makes 2 copies of $large_string (one for $copy and another for the |
577 | quotes), whereas |
578 | |
579 | my $copy = $large_string; |
580 | |
581 | only makes one copy. |
582 | |
583 | Ditto for stringifying large arrays: |
584 | |
585 | { |
586 | local $, = "\n"; |
587 | print @big_array; |
588 | } |
589 | |
590 | is much more memory-efficient than either |
591 | |
592 | print join "\n", @big_array; |
593 | |
594 | or |
595 | |
596 | { |
597 | local $" = "\n"; |
598 | print "@big_array"; |
599 | } |
600 | |
601 | |
24f1ba9b |
602 | =item * Pass by reference |
603 | |
604 | Pass arrays and hashes by reference, not by value. For one thing, it's |
605 | the only way to pass multiple lists or hashes (or both) in a single |
606 | call/return. It also avoids creating a copy of all the contents. This |
607 | requires some judgment, however, because any changes will be propagated |
608 | back to the original data. If you really want to mangle (er, modify) a |
609 | copy, you'll have to sacrifice the memory needed to make one. |
610 | |
611 | =item * Tie large variables to disk. |
612 | |
613 | For "big" data stores (i.e. ones that exceed available memory) consider |
614 | using one of the DB modules to store it on disk instead of in RAM. This |
ed8cf1fe |
615 | will incur a penalty in access time, but that's probably better than |
24f1ba9b |
616 | causing your hard disk to thrash due to massive swapping. |
617 | |
618 | =back |
619 | |
49d635f9 |
620 | =head2 Is it safe to return a reference to local or lexical data? |
68dc0745 |
621 | |
49d635f9 |
622 | Yes. Perl's garbage collection system takes care of this so |
623 | everything works out right. |
68dc0745 |
624 | |
625 | sub makeone { |
626 | my @a = ( 1 .. 10 ); |
627 | return \@a; |
628 | } |
629 | |
197aec24 |
630 | for ( 1 .. 10 ) { |
68dc0745 |
631 | push @many, makeone(); |
632 | } |
633 | |
634 | print $many[4][5], "\n"; |
635 | |
636 | print "@many\n"; |
637 | |
638 | =head2 How can I free an array or hash so my program shrinks? |
639 | |
2c646907 |
640 | You usually can't. On most operating systems, memory |
641 | allocated to a program can never be returned to the system. |
642 | That's why long-running programs sometimes re-exec |
643 | themselves. Some operating systems (notably, systems that |
644 | use mmap(2) for allocating large chunks of memory) can |
645 | reclaim memory that is no longer used, but on such systems, |
646 | perl must be configured and compiled to use the OS's malloc, |
647 | not perl's. |
68dc0745 |
648 | |
649 | However, judicious use of my() on your variables will help make sure |
a6dd486b |
650 | that they go out of scope so that Perl can free up that space for |
92c2ed05 |
651 | use in other parts of your program. A global variable, of course, never |
68dc0745 |
652 | goes out of scope, so you can't get its space automatically reclaimed, |
653 | although undef()ing and/or delete()ing it will achieve the same effect. |
46fc3d4c |
654 | In general, memory allocation and de-allocation isn't something you can |
68dc0745 |
655 | or should be worrying about much in Perl, but even this capability |
656 | (preallocation of data types) is in the works. |
657 | |
658 | =head2 How can I make my CGI script more efficient? |
659 | |
660 | Beyond the normal measures described to make general Perl programs |
661 | faster or smaller, a CGI program has additional issues. It may be run |
662 | several times per second. Given that each time it runs it will need |
46fc3d4c |
663 | to be re-compiled and will often allocate a megabyte or more of system |
68dc0745 |
664 | memory, this can be a killer. Compiling into C B<isn't going to help |
46fc3d4c |
665 | you> because the process start-up overhead is where the bottleneck is. |
68dc0745 |
666 | |
92c2ed05 |
667 | There are two popular ways to avoid this overhead. One solution |
668 | involves running the Apache HTTP server (available from |
f224927c |
669 | http://www.apache.org/ ) with either of the mod_perl or mod_fastcgi |
92c2ed05 |
670 | plugin modules. |
671 | |
672 | With mod_perl and the Apache::Registry module (distributed with |
673 | mod_perl), httpd will run with an embedded Perl interpreter which |
674 | pre-compiles your script and then executes it within the same address |
675 | space without forking. The Apache extension also gives Perl access to |
676 | the internal server API, so modules written in Perl can do just about |
677 | anything a module written in C can. For more on mod_perl, see |
678 | http://perl.apache.org/ |
679 | |
65acb1b1 |
680 | With the FCGI module (from CPAN) and the mod_fastcgi |
bfeeaf1b |
681 | module (available from http://www.fastcgi.com/ ) each of your Perl |
87275199 |
682 | programs becomes a permanent CGI daemon process. |
68dc0745 |
683 | |
684 | Both of these solutions can have far-reaching effects on your system |
87275199 |
685 | and on the way you write your CGI programs, so investigate them with |
68dc0745 |
686 | care. |
687 | |
a93751fa |
688 | See http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ . |
5a964f20 |
689 | |
65acb1b1 |
690 | A non-free, commercial product, ``The Velocity Engine for Perl'', |
a6dd486b |
691 | (http://www.binevolve.com/ or http://www.binevolve.com/velocigen/ ) |
692 | might also be worth looking at. It will allow you to increase the |
693 | performance of your Perl programs, running programs up to 25 times |
694 | faster than normal CGI Perl when running in persistent Perl mode or 4 |
695 | to 5 times faster without any modification to your existing CGI |
696 | programs. Fully functional evaluation copies are available from the |
697 | web site. |
c8db1d39 |
698 | |
68dc0745 |
699 | =head2 How can I hide the source for my Perl program? |
700 | |
701 | Delete it. :-) Seriously, there are a number of (mostly |
92c2ed05 |
702 | unsatisfactory) solutions with varying levels of ``security''. |
68dc0745 |
703 | |
704 | First of all, however, you I<can't> take away read permission, because |
705 | the source code has to be readable in order to be compiled and |
706 | interpreted. (That doesn't mean that a CGI script's source is |
a6dd486b |
707 | readable by people on the web, though--only by people with access to |
708 | the filesystem.) So you have to leave the permissions at the socially |
92c2ed05 |
709 | friendly 0755 level. |
68dc0745 |
710 | |
711 | Some people regard this as a security problem. If your program does |
a6dd486b |
712 | insecure things and relies on people not knowing how to exploit those |
68dc0745 |
713 | insecurities, it is not secure. It is often possible for someone to |
714 | determine the insecure things and exploit them without viewing the |
715 | source. Security through obscurity, the name for hiding your bugs |
716 | instead of fixing them, is little security indeed. |
717 | |
83df6a1d |
718 | You can try using encryption via source filters (Starting from Perl |
719 | 5.8 the Filter::Simple and Filter::Util::Call modules are included in |
720 | the standard distribution), but any decent programmer will be able to |
721 | decrypt it. You can try using the byte code compiler and interpreter |
722 | described below, but the curious might still be able to de-compile it. |
723 | You can try using the native-code compiler described below, but |
724 | crackers might be able to disassemble it. These pose varying degrees |
725 | of difficulty to people wanting to get at your code, but none can |
726 | definitively conceal it (true of every language, not just Perl). |
68dc0745 |
727 | |
49d635f9 |
728 | It is very easy to recover the source of Perl programs. You simply |
729 | feed the program to the perl interpreter and use the modules in |
730 | the B:: hierarchy. The B::Deparse module should be able to |
731 | defeat most attempts to hide source. Again, this is not |
732 | unique to Perl. |
733 | |
68dc0745 |
734 | If you're concerned about people profiting from your code, then the |
d92eb7b0 |
735 | bottom line is that nothing but a restrictive license will give you |
68dc0745 |
736 | legal security. License your software and pepper it with threatening |
92c2ed05 |
737 | statements like ``This is unpublished proprietary software of XYZ Corp. |
68dc0745 |
738 | Your access to it does not give you permission to use it blah blah |
92c2ed05 |
739 | blah.'' We are not lawyers, of course, so you should see a lawyer if |
d92eb7b0 |
740 | you want to be sure your license's wording will stand up in court. |
68dc0745 |
741 | |
54310121 |
742 | =head2 How can I compile my Perl program into byte code or C? |
68dc0745 |
743 | |
744 | Malcolm Beattie has written a multifunction backend compiler, |
5e3006a4 |
745 | available from CPAN, that can do both these things. It is included |
746 | in the perl5.005 release, but is still considered experimental. |
747 | This means it's fun to play with if you're a programmer but not |
748 | really for people looking for turn-key solutions. |
68dc0745 |
749 | |
92c2ed05 |
750 | Merely compiling into C does not in and of itself guarantee that your |
751 | code will run very much faster. That's because except for lucky cases |
752 | where a lot of native type inferencing is possible, the normal Perl |
a6dd486b |
753 | run-time system is still present and so your program will take just as |
92c2ed05 |
754 | long to run and be just as big. Most programs save little more than |
755 | compilation time, leaving execution no more than 10-30% faster. A few |
a6dd486b |
756 | rare programs actually benefit significantly (even running several times |
92c2ed05 |
757 | faster), but this takes some tweaking of your code. |
68dc0745 |
758 | |
68dc0745 |
759 | You'll probably be astonished to learn that the current version of the |
760 | compiler generates a compiled form of your script whose executable is |
761 | just as big as the original perl executable, and then some. That's |
762 | because as currently written, all programs are prepared for a full |
763 | eval() statement. You can tremendously reduce this cost by building a |
92c2ed05 |
764 | shared I<libperl.so> library and linking against that. See the |
87275199 |
765 | F<INSTALL> podfile in the Perl source distribution for details. If |
d92eb7b0 |
766 | you link your main perl binary with this, it will make it minuscule. |
92c2ed05 |
767 | For example, on one author's system, F</usr/bin/perl> is only 11k in |
68dc0745 |
768 | size! |
769 | |
5a964f20 |
770 | In general, the compiler will do nothing to make a Perl program smaller, |
a6dd486b |
771 | faster, more portable, or more secure. In fact, it can make your |
772 | situation worse. The executable will be bigger, your VM system may take |
5a964f20 |
773 | longer to load the whole thing, the binary is fragile and hard to fix, |
774 | and compilation never stopped software piracy in the form of crackers, |
775 | viruses, or bootleggers. The real advantage of the compiler is merely |
776 | packaging, and once you see the size of what it makes (well, unless |
777 | you use a shared I<libperl.so>), you'll probably want a complete |
5e3006a4 |
778 | Perl install anyway. |
5a964f20 |
779 | |
65acb1b1 |
780 | =head2 How can I compile Perl into Java? |
781 | |
a6dd486b |
782 | You can also integrate Java and Perl with the |
65acb1b1 |
783 | Perl Resource Kit from O'Reilly and Associates. See |
a6dd486b |
784 | http://www.oreilly.com/catalog/prkunix/ . |
785 | |
786 | Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in |
787 | development, allows Perl code to be called from Java. See jpl/README |
788 | in the Perl source tree. |
65acb1b1 |
789 | |
92c2ed05 |
790 | =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]? |
68dc0745 |
791 | |
792 | For OS/2 just use |
793 | |
794 | extproc perl -S -your_switches |
795 | |
796 | as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's |
46fc3d4c |
797 | `extproc' handling). For DOS one should first invent a corresponding |
fd1adc71 |
798 | batch file and codify it in C<ALTERNATE_SHEBANG> (see the |
799 | F<dosish.h> file in the source distribution for more information). |
68dc0745 |
800 | |
92c2ed05 |
801 | The Win95/NT installation, when using the ActiveState port of Perl, |
802 | will modify the Registry to associate the C<.pl> extension with the |
d92eb7b0 |
803 | perl interpreter. If you install another port, perhaps even building |
804 | your own Win95/NT Perl from the standard sources by using a Windows port |
d702ae42 |
805 | of gcc (e.g., with cygwin or mingw32), then you'll have to modify |
d92eb7b0 |
806 | the Registry yourself. In addition to associating C<.pl> with the |
807 | interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them |
808 | run the program C<install-linux.pl> merely by typing C<install-linux>. |
68dc0745 |
809 | |
87275199 |
810 | Macintosh Perl programs will have the appropriate Creator and |
811 | Type, so that double-clicking them will invoke the Perl application. |
68dc0745 |
812 | |
813 | I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just |
814 | throw the perl interpreter into your cgi-bin directory, in order to |
87275199 |
815 | get your programs working for a web server. This is an EXTREMELY big |
68dc0745 |
816 | security risk. Take the time to figure out how to do it correctly. |
817 | |
87275199 |
818 | =head2 Can I write useful Perl programs on the command line? |
68dc0745 |
819 | |
820 | Yes. Read L<perlrun> for more information. Some examples follow. |
821 | (These assume standard Unix shell quoting rules.) |
822 | |
823 | # sum first and last fields |
5a964f20 |
824 | perl -lane 'print $F[0] + $F[-1]' * |
68dc0745 |
825 | |
826 | # identify text files |
827 | perl -le 'for(@ARGV) {print if -f && -T _}' * |
828 | |
5a964f20 |
829 | # remove (most) comments from C program |
68dc0745 |
830 | perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c |
831 | |
832 | # make file a month younger than today, defeating reaper daemons |
833 | perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' * |
834 | |
835 | # find first unused uid |
836 | perl -le '$i++ while getpwuid($i); print $i' |
837 | |
838 | # display reasonable manpath |
839 | echo $PATH | perl -nl -072 -e ' |
840 | s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}' |
841 | |
87275199 |
842 | OK, the last one was actually an Obfuscated Perl Contest entry. :-) |
68dc0745 |
843 | |
87275199 |
844 | =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system? |
68dc0745 |
845 | |
846 | The problem is usually that the command interpreters on those systems |
847 | have rather different ideas about quoting than the Unix shells under |
848 | which the one-liners were created. On some systems, you may have to |
849 | change single-quotes to double ones, which you must I<NOT> do on Unix |
850 | or Plan9 systems. You might also have to change a single % to a %%. |
851 | |
852 | For example: |
853 | |
854 | # Unix |
855 | perl -e 'print "Hello world\n"' |
856 | |
46fc3d4c |
857 | # DOS, etc. |
68dc0745 |
858 | perl -e "print \"Hello world\n\"" |
859 | |
46fc3d4c |
860 | # Mac |
68dc0745 |
861 | print "Hello world\n" |
862 | (then Run "Myscript" or Shift-Command-R) |
863 | |
d2321c93 |
864 | # MPW |
865 | perl -e 'print "Hello world\n"' |
866 | |
68dc0745 |
867 | # VMS |
868 | perl -e "print ""Hello world\n""" |
869 | |
a6dd486b |
870 | The problem is that none of these examples are reliable: they depend on the |
92c2ed05 |
871 | command interpreter. Under Unix, the first two often work. Under DOS, |
a6dd486b |
872 | it's entirely possible that neither works. If 4DOS was the command shell, |
92c2ed05 |
873 | you'd probably have better luck like this: |
68dc0745 |
874 | |
875 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" |
876 | |
46fc3d4c |
877 | Under the Mac, it depends which environment you are using. The MacPerl |
68dc0745 |
878 | shell, or MPW, is much like Unix shells in its support for several |
46fc3d4c |
879 | quoting variants, except that it makes free use of the Mac's non-ASCII |
68dc0745 |
880 | characters as control characters. |
881 | |
65acb1b1 |
882 | Using qq(), q(), and qx(), instead of "double quotes", 'single |
883 | quotes', and `backticks`, may make one-liners easier to write. |
884 | |
d2321c93 |
885 | There is no general solution to all of this. It is a mess. |
68dc0745 |
886 | |
887 | [Some of this answer was contributed by Kenneth Albanowski.] |
888 | |
889 | =head2 Where can I learn about CGI or Web programming in Perl? |
890 | |
891 | For modules, get the CGI or LWP modules from CPAN. For textbooks, |
892 | see the two especially dedicated to web stuff in the question on |
92c2ed05 |
893 | books. For problems and questions related to the web, like ``Why |
894 | do I get 500 Errors'' or ``Why doesn't it run from the browser right |
8305e449 |
895 | when it runs fine on the command line'', see the troubleshooting |
896 | guides and references in L<perlfaq9> or in the CGI MetaFAQ: |
68dc0745 |
897 | |
8305e449 |
898 | http://www.perl.org/CGI_MetaFAQ.html |
0f542199 |
899 | |
68dc0745 |
900 | =head2 Where can I learn about object-oriented Perl programming? |
901 | |
a6dd486b |
902 | A good place to start is L<perltoot>, and you can use L<perlobj>, |
06a5f41f |
903 | L<perlboot>, L<perltoot>, L<perltooc>, and L<perlbot> for reference. |
904 | (If you are using really old Perl, you may not have all of these, |
905 | try http://www.perldoc.com/ , but consider upgrading your perl.) |
906 | |
907 | A good book on OO on Perl is the "Object-Oriented Perl" |
197aec24 |
908 | by Damian Conway from Manning Publications, |
06a5f41f |
909 | http://www.manning.com/Conway/index.html |
68dc0745 |
910 | |
911 | =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp] |
912 | |
913 | If you want to call C from Perl, start with L<perlxstut>, |
914 | moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to |
915 | call Perl from C, then read L<perlembed>, L<perlcall>, and |
916 | L<perlguts>. Don't forget that you can learn a lot from looking at |
917 | how the authors of existing extension modules wrote their code and |
918 | solved their problems. |
919 | |
920 | =head2 I've read perlembed, perlguts, etc., but I can't embed perl in |
a6dd486b |
921 | my C program; what am I doing wrong? |
68dc0745 |
922 | |
923 | Download the ExtUtils::Embed kit from CPAN and run `make test'. If |
924 | the tests pass, read the pods again and again and again. If they |
87275199 |
925 | fail, see L<perlbug> and send a bug report with the output of |
68dc0745 |
926 | C<make test TEST_VERBOSE=1> along with C<perl -V>. |
927 | |
83ded9ee |
928 | =head2 When I tried to run my script, I got this message. What does it mean? |
68dc0745 |
929 | |
87275199 |
930 | A complete list of Perl's error messages and warnings with explanatory |
931 | text can be found in L<perldiag>. You can also use the splain program |
932 | (distributed with Perl) to explain the error messages: |
68dc0745 |
933 | |
934 | perl program 2>diag.out |
935 | splain [-v] [-p] diag.out |
936 | |
937 | or change your program to explain the messages for you: |
938 | |
939 | use diagnostics; |
940 | |
941 | or |
942 | |
943 | use diagnostics -verbose; |
944 | |
945 | =head2 What's MakeMaker? |
946 | |
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947 | This module (part of the standard Perl distribution) is designed to |
68dc0745 |
948 | write a Makefile for an extension module from a Makefile.PL. For more |
949 | information, see L<ExtUtils::MakeMaker>. |
950 | |
951 | =head1 AUTHOR AND COPYRIGHT |
952 | |
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953 | Copyright (c) 1997-2002 Tom Christiansen and Nathan Torkington. |
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954 | All rights reserved. |
955 | |
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956 | This documentation is free; you can redistribute it and/or modify it |
957 | under the same terms as Perl itself. |
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958 | |
87275199 |
959 | Irrespective of its distribution, all code examples here are in the public |
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960 | domain. You are permitted and encouraged to use this code and any |
961 | derivatives thereof in your own programs for fun or for profit as you |
962 | see fit. A simple comment in the code giving credit to the FAQ would |
963 | be courteous but is not required. |