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1 | =head1 NAME |
2 | |
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3 | perlfaq3 - Programming Tools ($Revision: 1.54 $, $Date: 2005/11/17 17:22:02 $) |
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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 |
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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 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/ . |
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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 | |
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57 | The Shell.pm module (distributed with Perl) makes Perl try commands |
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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. |
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61 | |
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62 | =head2 How do I find which modules are installed on my system? |
63 | |
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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). |
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68 | |
69 | use ExtUtils::Installed; |
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70 | |
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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; |
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78 | |
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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 |
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82 | with File::Find which is part of the standard library. |
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83 | |
84 | use File::Find; |
85 | my @files; |
86 | |
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87 | find( |
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88 | sub { |
89 | push @files, $File::Find::name |
90 | if -f $File::Find::name && /\.pm$/ |
91 | }, |
92 | |
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93 | @INC |
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94 | ); |
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95 | |
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96 | print join "\n", @files; |
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97 | |
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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 |
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100 | read the documentation the module is most likely installed. |
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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 |
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110 | |
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111 | =head2 How do I debug my Perl programs? |
112 | |
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113 | Have you tried C<use warnings> or used C<-w>? They enable warnings |
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114 | to detect dubious practices. |
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115 | |
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116 | Have you tried C<use strict>? It prevents you from using symbolic |
117 | references, makes you predeclare any subroutines that you call as bare |
118 | words, and (probably most importantly) forces you to predeclare your |
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119 | variables with C<my>, C<our>, or C<use vars>. |
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120 | |
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121 | Did you check the return values of each and every system call? The operating |
122 | system (and thus Perl) tells you whether they worked, and if not |
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123 | why. |
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124 | |
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125 | open(FH, "> /etc/cantwrite") |
126 | or die "Couldn't write to /etc/cantwrite: $!\n"; |
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127 | |
92c2ed05 |
128 | Did you read L<perltrap>? It's full of gotchas for old and new Perl |
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129 | programmers and even has sections for those of you who are upgrading |
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130 | from languages like I<awk> and I<C>. |
131 | |
132 | Have you tried the Perl debugger, described in L<perldebug>? You can |
133 | step through your program and see what it's doing and thus work out |
134 | why what it's doing isn't what it should be doing. |
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135 | |
136 | =head2 How do I profile my Perl programs? |
137 | |
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138 | You should get the Devel::DProf module from the standard distribution |
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139 | (or separately on CPAN) and also use Benchmark.pm from the standard |
140 | distribution. The Benchmark module lets you time specific portions of |
141 | your code, while Devel::DProf gives detailed breakdowns of where your |
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142 | code spends its time. |
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143 | |
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144 | Here's a sample use of Benchmark: |
145 | |
146 | use Benchmark; |
147 | |
148 | @junk = `cat /etc/motd`; |
149 | $count = 10_000; |
150 | |
151 | timethese($count, { |
152 | 'map' => sub { my @a = @junk; |
153 | map { s/a/b/ } @a; |
6c43ef16 |
154 | return @a }, |
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155 | 'for' => sub { my @a = @junk; |
92c2ed05 |
156 | for (@a) { s/a/b/ }; |
157 | return @a }, |
158 | }); |
159 | |
160 | This is what it prints (on one machine--your results will be dependent |
161 | on your hardware, operating system, and the load on your machine): |
162 | |
163 | Benchmark: timing 10000 iterations of for, map... |
164 | for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu) |
165 | map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu) |
166 | |
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167 | Be aware that a good benchmark is very hard to write. It only tests the |
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168 | data you give it and proves little about the differing complexities |
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169 | of contrasting algorithms. |
170 | |
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171 | =head2 How do I cross-reference my Perl programs? |
172 | |
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173 | The B::Xref module can be used to generate cross-reference reports |
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174 | for Perl programs. |
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175 | |
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176 | perl -MO=Xref[,OPTIONS] scriptname.plx |
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177 | |
178 | =head2 Is there a pretty-printer (formatter) for Perl? |
179 | |
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180 | Perltidy is a Perl script which indents and reformats Perl scripts |
181 | to make them easier to read by trying to follow the rules of the |
182 | L<perlstyle>. If you write Perl scripts, or spend much time reading |
183 | them, you will probably find it useful. It is available at |
184 | http://perltidy.sourceforge.net |
185 | |
186 | Of course, if you simply follow the guidelines in L<perlstyle>, |
187 | you shouldn't need to reformat. The habit of formatting your code |
188 | as you write it will help prevent bugs. Your editor can and should |
189 | help you with this. The perl-mode or newer cperl-mode for emacs |
190 | can provide remarkable amounts of help with most (but not all) |
191 | code, and even less programmable editors can provide significant |
192 | assistance. Tom Christiansen and many other VI users swear by |
193 | the following settings in vi and its clones: |
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194 | |
195 | set ai sw=4 |
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196 | map! ^O {^M}^[O^T |
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197 | |
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198 | Put that in your F<.exrc> file (replacing the caret characters |
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199 | with control characters) and away you go. In insert mode, ^T is |
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200 | for indenting, ^D is for undenting, and ^O is for blockdenting-- |
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201 | as it were. A more complete example, with comments, can be found at |
213329dd |
202 | http://www.cpan.org/authors/id/TOMC/scripts/toms.exrc.gz |
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203 | |
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204 | The a2ps http://www-inf.enst.fr/%7Edemaille/a2ps/black+white.ps.gz does |
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205 | lots of things related to generating nicely printed output of |
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206 | documents, as does enscript at http://people.ssh.fi/mtr/genscript/ . |
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207 | |
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208 | =head2 Is there a ctags for Perl? |
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209 | |
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210 | (contributed by brian d foy) |
211 | |
212 | Exuberent ctags supports Perl: http://ctags.sourceforge.net/ |
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213 | |
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214 | You might also try pltags: http://www.mscha.com/pltags.zip |
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215 | |
216 | =head2 Is there an IDE or Windows Perl Editor? |
217 | |
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218 | Perl programs are just plain text, so any editor will do. |
219 | |
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220 | If you're on Unix, you already have an IDE--Unix itself. The UNIX |
221 | philosophy is the philosophy of several small tools that each do one |
222 | thing and do it well. It's like a carpenter's toolbox. |
223 | |
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224 | If you want an IDE, check the following (in alphabetical order, not |
225 | order of preference): |
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226 | |
227 | =over 4 |
228 | |
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229 | =item Eclipse |
230 | |
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231 | http://e-p-i-c.sf.net/ |
232 | |
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233 | The Eclipse Perl Integration Project integrates Perl |
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234 | editing/debugging with Eclipse. |
235 | |
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236 | =item Enginsite |
237 | |
238 | http://www.enginsite.com/ |
239 | |
240 | Perl Editor by EngInSite is a complete integrated development |
241 | environment (IDE) for creating, testing, and debugging Perl scripts; |
242 | the tool runs on Windows 9x/NT/2000/XP or later. |
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243 | |
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244 | =item Komodo |
245 | |
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246 | http://www.ActiveState.com/Products/Komodo/ |
247 | |
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248 | ActiveState's cross-platform (as of October 2004, that's Windows, Linux, |
249 | and Solaris), multi-language IDE has Perl support, including a regular expression |
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250 | debugger and remote debugging. |
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251 | |
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252 | =item Open Perl IDE |
253 | |
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254 | http://open-perl-ide.sourceforge.net/ |
255 | |
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256 | Open Perl IDE is an integrated development environment for writing |
257 | and debugging Perl scripts with ActiveState's ActivePerl distribution |
258 | under Windows 95/98/NT/2000. |
259 | |
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260 | =item OptiPerl |
261 | |
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262 | http://www.optiperl.com/ |
263 | |
264 | OptiPerl is a Windows IDE with simulated CGI environment, including |
265 | debugger and syntax highlighting editor. |
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266 | |
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267 | =item PerlBuilder |
268 | |
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269 | http://www.solutionsoft.com/perl.htm |
270 | |
271 | PerlBuidler is an integrated development environment for Windows that |
272 | supports Perl development. |
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273 | |
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274 | =item visiPerl+ |
275 | |
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276 | http://helpconsulting.net/visiperl/ |
277 | |
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278 | From Help Consulting, for Windows. |
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279 | |
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280 | =item Visual Perl |
281 | |
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282 | http://www.activestate.com/Products/Visual_Perl/ |
283 | |
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284 | Visual Perl is a Visual Studio.NET plug-in from ActiveState. |
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285 | |
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286 | =item Zeus |
287 | |
288 | http://www.zeusedit.com/lookmain.html |
289 | |
290 | Zeus for Window is another Win32 multi-language editor/IDE |
291 | that comes with support for Perl: |
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292 | |
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293 | =back |
294 | |
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295 | For editors: if you're on Unix you probably have vi or a vi clone |
296 | already, and possibly an emacs too, so you may not need to download |
297 | anything. In any emacs the cperl-mode (M-x cperl-mode) gives you |
298 | perhaps the best available Perl editing mode in any editor. |
299 | |
300 | If you are using Windows, you can use any editor that lets you work |
301 | with plain text, such as NotePad or WordPad. Word processors, such as |
302 | Microsoft Word or WordPerfect, typically do not work since they insert |
303 | all sorts of behind-the-scenes information, although some allow you to |
304 | save files as "Text Only". You can also download text editors designed |
305 | specifically for programming, such as Textpad ( |
306 | http://www.textpad.com/ ) and UltraEdit ( http://www.ultraedit.com/ ), |
307 | among others. |
308 | |
309 | If you are using MacOS, the same concerns apply. MacPerl (for Classic |
310 | environments) comes with a simple editor. Popular external editors are |
311 | BBEdit ( http://www.bbedit.com/ ) or Alpha ( |
312 | http://www.his.com/~jguyer/Alpha/Alpha8.html ). MacOS X users can use |
313 | Unix editors as well. Neil Bowers (the man behind Geekcruises) has a |
314 | list of Mac editors that can handle Perl ( |
315 | http://www.neilbowers.org/macperleditors.html ). |
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316 | |
317 | =over 4 |
318 | |
319 | =item GNU Emacs |
320 | |
321 | http://www.gnu.org/software/emacs/windows/ntemacs.html |
322 | |
323 | =item MicroEMACS |
324 | |
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325 | http://www.microemacs.de/ |
68fbfbd7 |
326 | |
327 | =item XEmacs |
328 | |
329 | http://www.xemacs.org/Download/index.html |
330 | |
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331 | =item Jed |
332 | |
333 | http://space.mit.edu/~davis/jed/ |
334 | |
68fbfbd7 |
335 | =back |
336 | |
337 | or a vi clone such as |
338 | |
339 | =over 4 |
340 | |
341 | =item Elvis |
342 | |
343 | ftp://ftp.cs.pdx.edu/pub/elvis/ http://www.fh-wedel.de/elvis/ |
344 | |
345 | =item Vile |
346 | |
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347 | http://dickey.his.com/vile/vile.html |
68fbfbd7 |
348 | |
349 | =item Vim |
350 | |
351 | http://www.vim.org/ |
352 | |
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353 | =back |
354 | |
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355 | For vi lovers in general, Windows or elsewhere: |
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356 | |
357 | http://www.thomer.com/thomer/vi/vi.html |
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358 | |
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359 | nvi ( http://www.bostic.com/vi/ , available from CPAN in src/misc/) is |
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360 | yet another vi clone, unfortunately not available for Windows, but in |
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361 | UNIX platforms you might be interested in trying it out, firstly because |
362 | strictly speaking it is not a vi clone, it is the real vi, or the new |
363 | incarnation of it, and secondly because you can embed Perl inside it |
364 | to use Perl as the scripting language. nvi is not alone in this, |
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365 | though: at least also vim and vile offer an embedded Perl. |
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366 | |
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367 | The following are Win32 multilanguage editor/IDESs that support Perl: |
368 | |
369 | =over 4 |
370 | |
371 | =item Codewright |
372 | |
c98c5709 |
373 | http://www.borland.com/codewright/ |
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374 | |
375 | =item MultiEdit |
376 | |
377 | http://www.MultiEdit.com/ |
378 | |
379 | =item SlickEdit |
380 | |
381 | http://www.slickedit.com/ |
382 | |
383 | =back |
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384 | |
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385 | There is also a toyedit Text widget based editor written in Perl |
386 | that is distributed with the Tk module on CPAN. The ptkdb |
f224927c |
387 | ( http://world.std.com/~aep/ptkdb/ ) is a Perl/tk based debugger that |
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388 | acts as a development environment of sorts. Perl Composer |
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389 | ( http://perlcomposer.sourceforge.net/ ) is an IDE for Perl/Tk |
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390 | GUI creation. |
391 | |
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392 | In addition to an editor/IDE you might be interested in a more |
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393 | powerful shell environment for Win32. Your options include |
394 | |
395 | =over 4 |
396 | |
397 | =item Bash |
398 | |
1577cd80 |
399 | from the Cygwin package ( http://sources.redhat.com/cygwin/ ) |
68fbfbd7 |
400 | |
401 | =item Ksh |
402 | |
f224927c |
403 | from the MKS Toolkit ( http://www.mks.com/ ), or the Bourne shell of |
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404 | the U/WIN environment ( http://www.research.att.com/sw/tools/uwin/ ) |
68fbfbd7 |
405 | |
406 | =item Tcsh |
407 | |
f224927c |
408 | ftp://ftp.astron.com/pub/tcsh/ , see also |
68fbfbd7 |
409 | http://www.primate.wisc.edu/software/csh-tcsh-book/ |
410 | |
411 | =item Zsh |
412 | |
f224927c |
413 | ftp://ftp.blarg.net/users/amol/zsh/ , see also http://www.zsh.org/ |
68fbfbd7 |
414 | |
415 | =back |
416 | |
614a1598 |
417 | MKS and U/WIN are commercial (U/WIN is free for educational and |
418 | research purposes), Cygwin is covered by the GNU Public License (but |
419 | that shouldn't matter for Perl use). The Cygwin, MKS, and U/WIN all |
420 | contain (in addition to the shells) a comprehensive set of standard |
421 | UNIX toolkit utilities. |
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422 | |
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423 | If you're transferring text files between Unix and Windows using FTP |
424 | be sure to transfer them in ASCII mode so the ends of lines are |
425 | appropriately converted. |
426 | |
e083a89c |
427 | On Mac OS the MacPerl Application comes with a simple 32k text editor |
428 | that behaves like a rudimentary IDE. In contrast to the MacPerl Application |
733271b5 |
429 | the MPW Perl tool can make use of the MPW Shell itself as an editor (with |
68fbfbd7 |
430 | no 32k limit). |
431 | |
432 | =over 4 |
433 | |
c98c5709 |
434 | =item Affrus |
68fbfbd7 |
435 | |
d7f8936a |
436 | is a full Perl development environment with full debugger support |
7678cced |
437 | ( http://www.latenightsw.com ). |
68fbfbd7 |
438 | |
439 | =item Alpha |
440 | |
441 | is an editor, written and extensible in Tcl, that nonetheless has |
733271b5 |
442 | built in support for several popular markup and programming languages |
c98c5709 |
443 | including Perl and HTML ( http://www.his.com/~jguyer/Alpha/Alpha8.html ). |
444 | |
445 | =item BBEdit and BBEdit Lite |
446 | |
447 | are text editors for Mac OS that have a Perl sensitivity mode |
448 | ( http://web.barebones.com/ ). |
449 | |
68fbfbd7 |
450 | |
451 | =back |
452 | |
453 | Pepper and Pe are programming language sensitive text editors for Mac |
1577cd80 |
454 | OS X and BeOS respectively ( http://www.hekkelman.com/ ). |
68dc0745 |
455 | |
456 | =head2 Where can I get Perl macros for vi? |
457 | |
458 | For a complete version of Tom Christiansen's vi configuration file, |
a93751fa |
459 | see http://www.cpan.org/authors/Tom_Christiansen/scripts/toms.exrc.gz , |
a6dd486b |
460 | the standard benchmark file for vi emulators. The file runs best with nvi, |
5a964f20 |
461 | the current version of vi out of Berkeley, which incidentally can be built |
bfeeaf1b |
462 | with an embedded Perl interpreter--see http://www.cpan.org/src/misc/ . |
68dc0745 |
463 | |
464 | =head2 Where can I get perl-mode for emacs? |
465 | |
466 | Since Emacs version 19 patchlevel 22 or so, there have been both a |
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467 | perl-mode.el and support for the Perl debugger built in. These should |
68dc0745 |
468 | come with the standard Emacs 19 distribution. |
469 | |
87275199 |
470 | In the Perl source directory, you'll find a directory called "emacs", |
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471 | which contains a cperl-mode that color-codes keywords, provides |
472 | context-sensitive help, and other nifty things. |
473 | |
92c2ed05 |
474 | Note that the perl-mode of emacs will have fits with C<"main'foo"> |
d92eb7b0 |
475 | (single quote), and mess up the indentation and highlighting. You |
65acb1b1 |
476 | are probably using C<"main::foo"> in new Perl code anyway, so this |
92c2ed05 |
477 | shouldn't be an issue. |
68dc0745 |
478 | |
479 | =head2 How can I use curses with Perl? |
480 | |
481 | The Curses module from CPAN provides a dynamically loadable object |
5a964f20 |
482 | module interface to a curses library. A small demo can be found at the |
49d635f9 |
483 | directory http://www.cpan.org/authors/Tom_Christiansen/scripts/rep.gz ; |
5a964f20 |
484 | this program repeats a command and updates the screen as needed, rendering |
485 | B<rep ps axu> similar to B<top>. |
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486 | |
487 | =head2 How can I use X or Tk with Perl? |
488 | |
5a964f20 |
489 | Tk is a completely Perl-based, object-oriented interface to the Tk toolkit |
490 | that doesn't force you to use Tcl just to get at Tk. Sx is an interface |
491 | to the Athena Widget set. Both are available from CPAN. See the |
a93751fa |
492 | directory http://www.cpan.org/modules/by-category/08_User_Interfaces/ |
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493 | |
a6dd486b |
494 | Invaluable for Perl/Tk programming are the Perl/Tk FAQ at |
c98c5709 |
495 | http://phaseit.net/claird/comp.lang.perl.tk/ptkFAQ.html , the Perl/Tk Reference |
92c2ed05 |
496 | Guide available at |
213329dd |
497 | http://www.cpan.org/authors/Stephen_O_Lidie/ , and the |
92c2ed05 |
498 | online manpages at |
87275199 |
499 | http://www-users.cs.umn.edu/%7Eamundson/perl/perltk/toc.html . |
92c2ed05 |
500 | |
68dc0745 |
501 | =head2 How can I make my Perl program run faster? |
502 | |
92c2ed05 |
503 | The best way to do this is to come up with a better algorithm. This |
b73a15ae |
504 | can often make a dramatic difference. Jon Bentley's book |
5cd0b561 |
505 | I<Programming Pearls> (that's not a misspelling!) has some good tips |
92c2ed05 |
506 | on optimization, too. Advice on benchmarking boils down to: benchmark |
507 | and profile to make sure you're optimizing the right part, look for |
508 | better algorithms instead of microtuning your code, and when all else |
57b19278 |
509 | fails consider just buying faster hardware. You will probably want to |
b432a672 |
510 | read the answer to the earlier question "How do I profile my Perl |
511 | programs?" if you haven't done so already. |
68dc0745 |
512 | |
92c2ed05 |
513 | A different approach is to autoload seldom-used Perl code. See the |
68dc0745 |
514 | AutoSplit and AutoLoader modules in the standard distribution for |
515 | that. Or you could locate the bottleneck and think about writing just |
516 | that part in C, the way we used to take bottlenecks in C code and |
5cd0b561 |
517 | write them in assembler. Similar to rewriting in C, modules that have |
518 | critical sections can be written in C (for instance, the PDL module |
519 | from CPAN). |
520 | |
521 | If you're currently linking your perl executable to a shared |
522 | I<libc.so>, you can often gain a 10-25% performance benefit by |
523 | rebuilding it to link with a static libc.a instead. This will make a |
524 | bigger perl executable, but your Perl programs (and programmers) may |
525 | thank you for it. See the F<INSTALL> file in the source distribution |
526 | for more information. |
527 | |
528 | The undump program was an ancient attempt to speed up Perl program by |
529 | storing the already-compiled form to disk. This is no longer a viable |
530 | option, as it only worked on a few architectures, and wasn't a good |
531 | solution anyway. |
68dc0745 |
532 | |
533 | =head2 How can I make my Perl program take less memory? |
534 | |
535 | When it comes to time-space tradeoffs, Perl nearly always prefers to |
536 | throw memory at a problem. Scalars in Perl use more memory than |
65acb1b1 |
537 | strings in C, arrays take more than that, and hashes use even more. While |
68dc0745 |
538 | there's still a lot to be done, recent releases have been addressing |
539 | these issues. For example, as of 5.004, duplicate hash keys are |
540 | shared amongst all hashes using them, so require no reallocation. |
541 | |
542 | In some cases, using substr() or vec() to simulate arrays can be |
543 | highly beneficial. For example, an array of a thousand booleans will |
544 | take at least 20,000 bytes of space, but it can be turned into one |
a6dd486b |
545 | 125-byte bit vector--a considerable memory savings. The standard |
68dc0745 |
546 | Tie::SubstrHash module can also help for certain types of data |
547 | structure. If you're working with specialist data structures |
548 | (matrices, for instance) modules that implement these in C may use |
549 | less memory than equivalent Perl modules. |
550 | |
551 | Another thing to try is learning whether your Perl was compiled with |
54310121 |
552 | the system malloc or with Perl's builtin malloc. Whichever one it |
68dc0745 |
553 | is, try using the other one and see whether this makes a difference. |
554 | Information about malloc is in the F<INSTALL> file in the source |
555 | distribution. You can find out whether you are using perl's malloc by |
556 | typing C<perl -V:usemymalloc>. |
557 | |
24f1ba9b |
558 | Of course, the best way to save memory is to not do anything to waste |
559 | it in the first place. Good programming practices can go a long way |
560 | toward this: |
561 | |
562 | =over 4 |
563 | |
564 | =item * Don't slurp! |
565 | |
566 | Don't read an entire file into memory if you can process it line |
567 | by line. Or more concretely, use a loop like this: |
568 | |
569 | # |
570 | # Good Idea |
571 | # |
572 | while (<FILE>) { |
573 | # ... |
574 | } |
575 | |
576 | instead of this: |
577 | |
578 | # |
579 | # Bad Idea |
580 | # |
581 | @data = <FILE>; |
582 | foreach (@data) { |
583 | # ... |
584 | } |
585 | |
586 | When the files you're processing are small, it doesn't much matter which |
587 | way you do it, but it makes a huge difference when they start getting |
197aec24 |
588 | larger. |
24f1ba9b |
589 | |
bc06af74 |
590 | =item * Use map and grep selectively |
591 | |
592 | Remember that both map and grep expect a LIST argument, so doing this: |
593 | |
594 | @wanted = grep {/pattern/} <FILE>; |
595 | |
596 | will cause the entire file to be slurped. For large files, it's better |
597 | to loop: |
598 | |
599 | while (<FILE>) { |
600 | push(@wanted, $_) if /pattern/; |
601 | } |
602 | |
603 | =item * Avoid unnecessary quotes and stringification |
604 | |
605 | Don't quote large strings unless absolutely necessary: |
606 | |
607 | my $copy = "$large_string"; |
608 | |
609 | makes 2 copies of $large_string (one for $copy and another for the |
610 | quotes), whereas |
611 | |
612 | my $copy = $large_string; |
613 | |
614 | only makes one copy. |
615 | |
616 | Ditto for stringifying large arrays: |
617 | |
618 | { |
619 | local $, = "\n"; |
620 | print @big_array; |
621 | } |
622 | |
623 | is much more memory-efficient than either |
624 | |
625 | print join "\n", @big_array; |
626 | |
627 | or |
628 | |
629 | { |
630 | local $" = "\n"; |
631 | print "@big_array"; |
632 | } |
633 | |
634 | |
24f1ba9b |
635 | =item * Pass by reference |
636 | |
637 | Pass arrays and hashes by reference, not by value. For one thing, it's |
638 | the only way to pass multiple lists or hashes (or both) in a single |
639 | call/return. It also avoids creating a copy of all the contents. This |
640 | requires some judgment, however, because any changes will be propagated |
641 | back to the original data. If you really want to mangle (er, modify) a |
642 | copy, you'll have to sacrifice the memory needed to make one. |
643 | |
644 | =item * Tie large variables to disk. |
645 | |
646 | For "big" data stores (i.e. ones that exceed available memory) consider |
647 | using one of the DB modules to store it on disk instead of in RAM. This |
ed8cf1fe |
648 | will incur a penalty in access time, but that's probably better than |
24f1ba9b |
649 | causing your hard disk to thrash due to massive swapping. |
650 | |
651 | =back |
652 | |
49d635f9 |
653 | =head2 Is it safe to return a reference to local or lexical data? |
68dc0745 |
654 | |
49d635f9 |
655 | Yes. Perl's garbage collection system takes care of this so |
656 | everything works out right. |
68dc0745 |
657 | |
658 | sub makeone { |
659 | my @a = ( 1 .. 10 ); |
660 | return \@a; |
661 | } |
662 | |
197aec24 |
663 | for ( 1 .. 10 ) { |
68dc0745 |
664 | push @many, makeone(); |
665 | } |
666 | |
667 | print $many[4][5], "\n"; |
668 | |
669 | print "@many\n"; |
670 | |
671 | =head2 How can I free an array or hash so my program shrinks? |
672 | |
7678cced |
673 | (contributed by Michael Carman) |
674 | |
675 | You usually can't. Memory allocated to lexicals (i.e. my() variables) |
676 | cannot be reclaimed or reused even if they go out of scope. It is |
677 | reserved in case the variables come back into scope. Memory allocated |
678 | to global variables can be reused (within your program) by using |
679 | undef()ing and/or delete(). |
680 | |
681 | On most operating systems, memory allocated to a program can never be |
682 | returned to the system. That's why long-running programs sometimes re- |
683 | exec themselves. Some operating systems (notably, systems that use |
684 | mmap(2) for allocating large chunks of memory) can reclaim memory that |
685 | is no longer used, but on such systems, perl must be configured and |
686 | compiled to use the OS's malloc, not perl's. |
687 | |
46fc3d4c |
688 | In general, memory allocation and de-allocation isn't something you can |
7678cced |
689 | or should be worrying about much in Perl. |
690 | |
691 | See also "How can I make my Perl program take less memory?" |
68dc0745 |
692 | |
693 | =head2 How can I make my CGI script more efficient? |
694 | |
695 | Beyond the normal measures described to make general Perl programs |
696 | faster or smaller, a CGI program has additional issues. It may be run |
697 | several times per second. Given that each time it runs it will need |
46fc3d4c |
698 | to be re-compiled and will often allocate a megabyte or more of system |
68dc0745 |
699 | memory, this can be a killer. Compiling into C B<isn't going to help |
46fc3d4c |
700 | you> because the process start-up overhead is where the bottleneck is. |
68dc0745 |
701 | |
92c2ed05 |
702 | There are two popular ways to avoid this overhead. One solution |
703 | involves running the Apache HTTP server (available from |
f224927c |
704 | http://www.apache.org/ ) with either of the mod_perl or mod_fastcgi |
92c2ed05 |
705 | plugin modules. |
706 | |
707 | With mod_perl and the Apache::Registry module (distributed with |
708 | mod_perl), httpd will run with an embedded Perl interpreter which |
709 | pre-compiles your script and then executes it within the same address |
710 | space without forking. The Apache extension also gives Perl access to |
711 | the internal server API, so modules written in Perl can do just about |
712 | anything a module written in C can. For more on mod_perl, see |
713 | http://perl.apache.org/ |
714 | |
65acb1b1 |
715 | With the FCGI module (from CPAN) and the mod_fastcgi |
bfeeaf1b |
716 | module (available from http://www.fastcgi.com/ ) each of your Perl |
87275199 |
717 | programs becomes a permanent CGI daemon process. |
68dc0745 |
718 | |
719 | Both of these solutions can have far-reaching effects on your system |
87275199 |
720 | and on the way you write your CGI programs, so investigate them with |
68dc0745 |
721 | care. |
722 | |
a93751fa |
723 | See http://www.cpan.org/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ . |
5a964f20 |
724 | |
68dc0745 |
725 | =head2 How can I hide the source for my Perl program? |
726 | |
727 | Delete it. :-) Seriously, there are a number of (mostly |
b432a672 |
728 | unsatisfactory) solutions with varying levels of "security". |
68dc0745 |
729 | |
730 | First of all, however, you I<can't> take away read permission, because |
731 | the source code has to be readable in order to be compiled and |
732 | interpreted. (That doesn't mean that a CGI script's source is |
a6dd486b |
733 | readable by people on the web, though--only by people with access to |
734 | the filesystem.) So you have to leave the permissions at the socially |
92c2ed05 |
735 | friendly 0755 level. |
68dc0745 |
736 | |
737 | Some people regard this as a security problem. If your program does |
a6dd486b |
738 | insecure things and relies on people not knowing how to exploit those |
68dc0745 |
739 | insecurities, it is not secure. It is often possible for someone to |
740 | determine the insecure things and exploit them without viewing the |
741 | source. Security through obscurity, the name for hiding your bugs |
742 | instead of fixing them, is little security indeed. |
743 | |
83df6a1d |
744 | You can try using encryption via source filters (Starting from Perl |
745 | 5.8 the Filter::Simple and Filter::Util::Call modules are included in |
746 | the standard distribution), but any decent programmer will be able to |
747 | decrypt it. You can try using the byte code compiler and interpreter |
748 | described below, but the curious might still be able to de-compile it. |
749 | You can try using the native-code compiler described below, but |
750 | crackers might be able to disassemble it. These pose varying degrees |
751 | of difficulty to people wanting to get at your code, but none can |
752 | definitively conceal it (true of every language, not just Perl). |
68dc0745 |
753 | |
49d635f9 |
754 | It is very easy to recover the source of Perl programs. You simply |
755 | feed the program to the perl interpreter and use the modules in |
756 | the B:: hierarchy. The B::Deparse module should be able to |
757 | defeat most attempts to hide source. Again, this is not |
758 | unique to Perl. |
759 | |
68dc0745 |
760 | If you're concerned about people profiting from your code, then the |
d92eb7b0 |
761 | bottom line is that nothing but a restrictive license will give you |
68dc0745 |
762 | legal security. License your software and pepper it with threatening |
b432a672 |
763 | statements like "This is unpublished proprietary software of XYZ Corp. |
68dc0745 |
764 | Your access to it does not give you permission to use it blah blah |
b432a672 |
765 | blah." We are not lawyers, of course, so you should see a lawyer if |
d92eb7b0 |
766 | you want to be sure your license's wording will stand up in court. |
68dc0745 |
767 | |
54310121 |
768 | =head2 How can I compile my Perl program into byte code or C? |
68dc0745 |
769 | |
7678cced |
770 | (contributed by brian d foy) |
771 | |
772 | In general, you can't do this. There are some things that may work |
773 | for your situation though. People usually ask this question |
6670e5e7 |
774 | because they want to distribute their works without giving away |
7678cced |
775 | the source code, and most solutions trade disk space for convenience. |
776 | You probably won't see much of a speed increase either, since most |
6670e5e7 |
777 | solutions simply bundle a Perl interpreter in the final product |
7678cced |
778 | (but see L<How can I make my Perl program run faster?>). |
779 | |
9e72e4c6 |
780 | The Perl Archive Toolkit ( http://par.perl.org/index.cgi ) is Perl's |
781 | analog to Java's JAR. It's freely available and on CPAN ( |
782 | http://search.cpan.org/dist/PAR/ ). |
7678cced |
783 | |
9e72e4c6 |
784 | The B::* namespace, often called "the Perl compiler", but is really a way |
785 | for Perl programs to peek at its innards rather than create pre-compiled |
786 | versions of your program. However. the B::Bytecode module can turn your |
787 | script into a bytecode format that could be loaded later by the |
788 | ByteLoader module and executed as a regular Perl script. |
7678cced |
789 | |
9e72e4c6 |
790 | There are also some commercial products that may work for you, although |
791 | you have to buy a license for them. |
7678cced |
792 | |
9e72e4c6 |
793 | The Perl Dev Kit ( http://www.activestate.com/Products/Perl_Dev_Kit/ ) |
794 | from ActiveState can "Turn your Perl programs into ready-to-run |
7678cced |
795 | executables for HP-UX, Linux, Solaris and Windows." |
796 | |
9e72e4c6 |
797 | Perl2Exe ( http://www.indigostar.com/perl2exe.htm ) is a command line |
798 | program for converting perl scripts to executable files. It targets both |
799 | Windows and unix platforms. |
5a964f20 |
800 | |
65acb1b1 |
801 | =head2 How can I compile Perl into Java? |
802 | |
a6dd486b |
803 | You can also integrate Java and Perl with the |
c98c5709 |
804 | Perl Resource Kit from O'Reilly Media. See |
a6dd486b |
805 | http://www.oreilly.com/catalog/prkunix/ . |
806 | |
807 | Perl 5.6 comes with Java Perl Lingo, or JPL. JPL, still in |
808 | development, allows Perl code to be called from Java. See jpl/README |
809 | in the Perl source tree. |
65acb1b1 |
810 | |
92c2ed05 |
811 | =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]? |
68dc0745 |
812 | |
813 | For OS/2 just use |
814 | |
815 | extproc perl -S -your_switches |
816 | |
817 | as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's |
b432a672 |
818 | "extproc" handling). For DOS one should first invent a corresponding |
fd1adc71 |
819 | batch file and codify it in C<ALTERNATE_SHEBANG> (see the |
820 | F<dosish.h> file in the source distribution for more information). |
68dc0745 |
821 | |
92c2ed05 |
822 | The Win95/NT installation, when using the ActiveState port of Perl, |
823 | will modify the Registry to associate the C<.pl> extension with the |
d92eb7b0 |
824 | perl interpreter. If you install another port, perhaps even building |
825 | your own Win95/NT Perl from the standard sources by using a Windows port |
d702ae42 |
826 | of gcc (e.g., with cygwin or mingw32), then you'll have to modify |
d92eb7b0 |
827 | the Registry yourself. In addition to associating C<.pl> with the |
828 | interpreter, NT people can use: C<SET PATHEXT=%PATHEXT%;.PL> to let them |
829 | run the program C<install-linux.pl> merely by typing C<install-linux>. |
68dc0745 |
830 | |
8e30f651 |
831 | Under "Classic" MacOS, a perl program will have the appropriate Creator and |
832 | Type, so that double-clicking them will invoke the MacPerl application. |
833 | Under Mac OS X, clickable apps can be made from any C<#!> script using Wil |
834 | Sanchez' DropScript utility: http://www.wsanchez.net/software/ . |
68dc0745 |
835 | |
836 | I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just |
837 | throw the perl interpreter into your cgi-bin directory, in order to |
87275199 |
838 | get your programs working for a web server. This is an EXTREMELY big |
68dc0745 |
839 | security risk. Take the time to figure out how to do it correctly. |
840 | |
87275199 |
841 | =head2 Can I write useful Perl programs on the command line? |
68dc0745 |
842 | |
843 | Yes. Read L<perlrun> for more information. Some examples follow. |
844 | (These assume standard Unix shell quoting rules.) |
845 | |
846 | # sum first and last fields |
5a964f20 |
847 | perl -lane 'print $F[0] + $F[-1]' * |
68dc0745 |
848 | |
849 | # identify text files |
850 | perl -le 'for(@ARGV) {print if -f && -T _}' * |
851 | |
5a964f20 |
852 | # remove (most) comments from C program |
68dc0745 |
853 | perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c |
854 | |
855 | # make file a month younger than today, defeating reaper daemons |
856 | perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' * |
857 | |
858 | # find first unused uid |
859 | perl -le '$i++ while getpwuid($i); print $i' |
860 | |
861 | # display reasonable manpath |
862 | echo $PATH | perl -nl -072 -e ' |
863 | s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}' |
864 | |
87275199 |
865 | OK, the last one was actually an Obfuscated Perl Contest entry. :-) |
68dc0745 |
866 | |
87275199 |
867 | =head2 Why don't Perl one-liners work on my DOS/Mac/VMS system? |
68dc0745 |
868 | |
869 | The problem is usually that the command interpreters on those systems |
870 | have rather different ideas about quoting than the Unix shells under |
871 | which the one-liners were created. On some systems, you may have to |
872 | change single-quotes to double ones, which you must I<NOT> do on Unix |
873 | or Plan9 systems. You might also have to change a single % to a %%. |
874 | |
875 | For example: |
876 | |
877 | # Unix |
878 | perl -e 'print "Hello world\n"' |
879 | |
46fc3d4c |
880 | # DOS, etc. |
68dc0745 |
881 | perl -e "print \"Hello world\n\"" |
882 | |
46fc3d4c |
883 | # Mac |
68dc0745 |
884 | print "Hello world\n" |
885 | (then Run "Myscript" or Shift-Command-R) |
886 | |
d2321c93 |
887 | # MPW |
888 | perl -e 'print "Hello world\n"' |
889 | |
68dc0745 |
890 | # VMS |
891 | perl -e "print ""Hello world\n""" |
892 | |
a6dd486b |
893 | The problem is that none of these examples are reliable: they depend on the |
92c2ed05 |
894 | command interpreter. Under Unix, the first two often work. Under DOS, |
a6dd486b |
895 | it's entirely possible that neither works. If 4DOS was the command shell, |
92c2ed05 |
896 | you'd probably have better luck like this: |
68dc0745 |
897 | |
898 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" |
899 | |
46fc3d4c |
900 | Under the Mac, it depends which environment you are using. The MacPerl |
68dc0745 |
901 | shell, or MPW, is much like Unix shells in its support for several |
46fc3d4c |
902 | quoting variants, except that it makes free use of the Mac's non-ASCII |
68dc0745 |
903 | characters as control characters. |
904 | |
65acb1b1 |
905 | Using qq(), q(), and qx(), instead of "double quotes", 'single |
906 | quotes', and `backticks`, may make one-liners easier to write. |
907 | |
d2321c93 |
908 | There is no general solution to all of this. It is a mess. |
68dc0745 |
909 | |
910 | [Some of this answer was contributed by Kenneth Albanowski.] |
911 | |
912 | =head2 Where can I learn about CGI or Web programming in Perl? |
913 | |
914 | For modules, get the CGI or LWP modules from CPAN. For textbooks, |
915 | see the two especially dedicated to web stuff in the question on |
b432a672 |
916 | books. For problems and questions related to the web, like "Why |
917 | do I get 500 Errors" or "Why doesn't it run from the browser right |
918 | when it runs fine on the command line", see the troubleshooting |
8305e449 |
919 | guides and references in L<perlfaq9> or in the CGI MetaFAQ: |
68dc0745 |
920 | |
8305e449 |
921 | http://www.perl.org/CGI_MetaFAQ.html |
0f542199 |
922 | |
68dc0745 |
923 | =head2 Where can I learn about object-oriented Perl programming? |
924 | |
a6dd486b |
925 | A good place to start is L<perltoot>, and you can use L<perlobj>, |
06a5f41f |
926 | L<perlboot>, L<perltoot>, L<perltooc>, and L<perlbot> for reference. |
06a5f41f |
927 | |
928 | A good book on OO on Perl is the "Object-Oriented Perl" |
9e72e4c6 |
929 | by Damian Conway from Manning Publications, or "Learning Perl |
930 | References, Objects, & Modules" by Randal Schwartz and Tom |
931 | Phoenix from O'Reilly Media. |
68dc0745 |
932 | |
b68463f7 |
933 | =head2 Where can I learn about linking C with Perl? |
68dc0745 |
934 | |
935 | If you want to call C from Perl, start with L<perlxstut>, |
936 | moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to |
937 | call Perl from C, then read L<perlembed>, L<perlcall>, and |
938 | L<perlguts>. Don't forget that you can learn a lot from looking at |
939 | how the authors of existing extension modules wrote their code and |
940 | solved their problems. |
941 | |
b68463f7 |
942 | You might not need all the power of XS. The Inline::C module lets |
943 | you put C code directly in your Perl source. It handles all the |
944 | magic to make it work. You still have to learn at least some of |
945 | the perl API but you won't have to deal with the complexity of the |
946 | XS support files. |
947 | |
7678cced |
948 | =head2 I've read perlembed, perlguts, etc., but I can't embed perl in my C program; what am I doing wrong? |
68dc0745 |
949 | |
950 | Download the ExtUtils::Embed kit from CPAN and run `make test'. If |
951 | the tests pass, read the pods again and again and again. If they |
87275199 |
952 | fail, see L<perlbug> and send a bug report with the output of |
68dc0745 |
953 | C<make test TEST_VERBOSE=1> along with C<perl -V>. |
954 | |
83ded9ee |
955 | =head2 When I tried to run my script, I got this message. What does it mean? |
68dc0745 |
956 | |
87275199 |
957 | A complete list of Perl's error messages and warnings with explanatory |
958 | text can be found in L<perldiag>. You can also use the splain program |
959 | (distributed with Perl) to explain the error messages: |
68dc0745 |
960 | |
961 | perl program 2>diag.out |
962 | splain [-v] [-p] diag.out |
963 | |
964 | or change your program to explain the messages for you: |
965 | |
966 | use diagnostics; |
967 | |
968 | or |
969 | |
970 | use diagnostics -verbose; |
971 | |
972 | =head2 What's MakeMaker? |
973 | |
87275199 |
974 | This module (part of the standard Perl distribution) is designed to |
68dc0745 |
975 | write a Makefile for an extension module from a Makefile.PL. For more |
976 | information, see L<ExtUtils::MakeMaker>. |
977 | |
978 | =head1 AUTHOR AND COPYRIGHT |
979 | |
7678cced |
980 | Copyright (c) 1997-2005 Tom Christiansen, Nathan Torkington, and |
981 | other authors as noted. All rights reserved. |
5a964f20 |
982 | |
5a7beb56 |
983 | This documentation is free; you can redistribute it and/or modify it |
984 | under the same terms as Perl itself. |
c8db1d39 |
985 | |
87275199 |
986 | Irrespective of its distribution, all code examples here are in the public |
c8db1d39 |
987 | domain. You are permitted and encouraged to use this code and any |
988 | derivatives thereof in your own programs for fun or for profit as you |
989 | see fit. A simple comment in the code giving credit to the FAQ would |
990 | be courteous but is not required. |