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1 | =head1 NAME |
2 | |
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3 | perlfaq3 - Programming Tools ($Revision: 1.29 $, $Date: 1998/08/05 11:57:04 $) |
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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 man pages? 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 | Regexps perlre, perlfunc, perlop, perllocale |
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23 | Moving to perl5 perltrap, perl |
24 | Linking w/C perlxstut, perlxs, perlcall, perlguts, perlembed |
25 | Various http://www.perl.com/CPAN/doc/FMTEYEWTK/index.html |
26 | (not a man-page but still useful) |
27 | |
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28 | L<perltoc> provides a crude table of contents for the perl man page set. |
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29 | |
30 | =head2 How can I use Perl interactively? |
31 | |
32 | The typical approach uses the Perl debugger, described in the |
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33 | perldebug(1) man page, on an ``empty'' program, like this: |
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34 | |
35 | perl -de 42 |
36 | |
37 | Now just type in any legal Perl code, and it will be immediately |
38 | evaluated. You can also examine the symbol table, get stack |
39 | backtraces, check variable values, set breakpoints, and other |
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40 | operations typically found in symbolic debuggers. |
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41 | |
42 | =head2 Is there a Perl shell? |
43 | |
44 | In general, no. The Shell.pm module (distributed with perl) makes |
45 | perl try commands which aren't part of the Perl language as shell |
46 | commands. perlsh from the source distribution is simplistic and |
47 | uninteresting, but may still be what you want. |
48 | |
49 | =head2 How do I debug my Perl programs? |
50 | |
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51 | Have you used C<-w>? It enables warnings for dubious practices. |
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52 | |
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53 | Have you tried C<use strict>? It prevents you from using symbolic |
54 | references, makes you predeclare any subroutines that you call as bare |
55 | words, and (probably most importantly) forces you to predeclare your |
56 | variables with C<my> or C<use vars>. |
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57 | |
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58 | Did you check the returns of each and every system call? The operating |
59 | system (and thus Perl) tells you whether they worked or not, and if not |
60 | why. |
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61 | |
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62 | open(FH, "> /etc/cantwrite") |
63 | or die "Couldn't write to /etc/cantwrite: $!\n"; |
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64 | |
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65 | Did you read L<perltrap>? It's full of gotchas for old and new Perl |
66 | programmers, and even has sections for those of you who are upgrading |
67 | from languages like I<awk> and I<C>. |
68 | |
69 | Have you tried the Perl debugger, described in L<perldebug>? You can |
70 | step through your program and see what it's doing and thus work out |
71 | why what it's doing isn't what it should be doing. |
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72 | |
73 | =head2 How do I profile my Perl programs? |
74 | |
75 | You should get the Devel::DProf module from CPAN, and also use |
76 | Benchmark.pm from the standard distribution. Benchmark lets you time |
77 | specific portions of your code, while Devel::DProf gives detailed |
78 | breakdowns of where your code spends its time. |
79 | |
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80 | Here's a sample use of Benchmark: |
81 | |
82 | use Benchmark; |
83 | |
84 | @junk = `cat /etc/motd`; |
85 | $count = 10_000; |
86 | |
87 | timethese($count, { |
88 | 'map' => sub { my @a = @junk; |
89 | map { s/a/b/ } @a; |
90 | return @a |
91 | }, |
92 | 'for' => sub { my @a = @junk; |
93 | local $_; |
94 | for (@a) { s/a/b/ }; |
95 | return @a }, |
96 | }); |
97 | |
98 | This is what it prints (on one machine--your results will be dependent |
99 | on your hardware, operating system, and the load on your machine): |
100 | |
101 | Benchmark: timing 10000 iterations of for, map... |
102 | for: 4 secs ( 3.97 usr 0.01 sys = 3.98 cpu) |
103 | map: 6 secs ( 4.97 usr 0.00 sys = 4.97 cpu) |
104 | |
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105 | =head2 How do I cross-reference my Perl programs? |
106 | |
107 | The B::Xref module, shipped with the new, alpha-release Perl compiler |
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108 | (not the general distribution prior to the 5.005 release), can be used |
109 | to generate cross-reference reports for Perl programs. |
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110 | |
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111 | perl -MO=Xref[,OPTIONS] scriptname.plx |
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112 | |
113 | =head2 Is there a pretty-printer (formatter) for Perl? |
114 | |
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115 | There is no program that will reformat Perl as much as indent(1) does |
116 | for C. The complex feedback between the scanner and the parser (this |
117 | feedback is what confuses the vgrind and emacs programs) makes it |
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118 | challenging at best to write a stand-alone Perl parser. |
119 | |
120 | Of course, if you simply follow the guidelines in L<perlstyle>, you |
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121 | shouldn't need to reformat. The habit of formatting your code as you |
122 | write it will help prevent bugs. Your editor can and should help you |
123 | with this. The perl-mode for emacs can provide a remarkable amount of |
124 | help with most (but not all) code, and even less programmable editors |
125 | can provide significant assistance. |
126 | |
127 | If you are used to using I<vgrind> program for printing out nice code |
128 | to a laser printer, you can take a stab at this using |
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129 | http://www.perl.com/CPAN/doc/misc/tips/working.vgrind.entry, but the |
130 | results are not particularly satisfying for sophisticated code. |
131 | |
132 | =head2 Is there a ctags for Perl? |
133 | |
134 | There's a simple one at |
135 | http://www.perl.com/CPAN/authors/id/TOMC/scripts/ptags.gz which may do |
136 | the trick. |
137 | |
138 | =head2 Where can I get Perl macros for vi? |
139 | |
140 | For a complete version of Tom Christiansen's vi configuration file, |
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141 | see http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/toms.exrc, |
142 | the standard benchmark file for vi emulators. This runs best with nvi, |
143 | the current version of vi out of Berkeley, which incidentally can be built |
144 | with an embedded Perl interpreter -- see http://www.perl.com/CPAN/src/misc. |
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145 | |
146 | =head2 Where can I get perl-mode for emacs? |
147 | |
148 | Since Emacs version 19 patchlevel 22 or so, there have been both a |
149 | perl-mode.el and support for the perl debugger built in. These should |
150 | come with the standard Emacs 19 distribution. |
151 | |
152 | In the perl source directory, you'll find a directory called "emacs", |
153 | which contains a cperl-mode that color-codes keywords, provides |
154 | context-sensitive help, and other nifty things. |
155 | |
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156 | Note that the perl-mode of emacs will have fits with C<"main'foo"> |
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157 | (single quote), and mess up the indentation and hilighting. You |
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158 | should be using C<"main::foo"> in new Perl code anyway, so this |
159 | shouldn't be an issue. |
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160 | |
161 | =head2 How can I use curses with Perl? |
162 | |
163 | The Curses module from CPAN provides a dynamically loadable object |
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164 | module interface to a curses library. A small demo can be found at the |
165 | directory http://www.perl.com/CPAN/authors/Tom_Christiansen/scripts/rep; |
166 | this program repeats a command and updates the screen as needed, rendering |
167 | B<rep ps axu> similar to B<top>. |
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168 | |
169 | =head2 How can I use X or Tk with Perl? |
170 | |
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171 | Tk is a completely Perl-based, object-oriented interface to the Tk toolkit |
172 | that doesn't force you to use Tcl just to get at Tk. Sx is an interface |
173 | to the Athena Widget set. Both are available from CPAN. See the |
174 | directory http://www.perl.com/CPAN/modules/by-category/08_User_Interfaces/ |
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175 | |
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176 | Invaluable for Perl/Tk programming are: the Perl/Tk FAQ at |
177 | http://w4.lns.cornell.edu/~pvhp/ptk/ptkTOC.html , the Perl/Tk Reference |
178 | Guide available at |
179 | http://www.perl.com/CPAN-local/authors/Stephen_O_Lidie/ , and the |
180 | online manpages at |
181 | http://www-users.cs.umn.edu/~amundson/perl/perltk/toc.html . |
182 | |
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183 | =head2 How can I generate simple menus without using CGI or Tk? |
184 | |
185 | The http://www.perl.com/CPAN/authors/id/SKUNZ/perlmenu.v4.0.tar.gz |
186 | module, which is curses-based, can help with this. |
187 | |
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188 | =head2 What is undump? |
189 | |
190 | See the next questions. |
191 | |
192 | =head2 How can I make my Perl program run faster? |
193 | |
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194 | The best way to do this is to come up with a better algorithm. This |
195 | can often make a dramatic difference. Chapter 8 in the Camel has some |
196 | efficiency tips in it you might want to look at. Jon Bentley's book |
197 | ``Programming Pearls'' (that's not a misspelling!) has some good tips |
198 | on optimization, too. Advice on benchmarking boils down to: benchmark |
199 | and profile to make sure you're optimizing the right part, look for |
200 | better algorithms instead of microtuning your code, and when all else |
201 | fails consider just buying faster hardware. |
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202 | |
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203 | A different approach is to autoload seldom-used Perl code. See the |
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204 | AutoSplit and AutoLoader modules in the standard distribution for |
205 | that. Or you could locate the bottleneck and think about writing just |
206 | that part in C, the way we used to take bottlenecks in C code and |
207 | write them in assembler. Similar to rewriting in C is the use of |
208 | modules that have critical sections written in C (for instance, the |
209 | PDL module from CPAN). |
210 | |
211 | In some cases, it may be worth it to use the backend compiler to |
212 | produce byte code (saving compilation time) or compile into C, which |
213 | will certainly save compilation time and sometimes a small amount (but |
214 | not much) execution time. See the question about compiling your Perl |
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215 | programs for more on the compiler--the wins aren't as obvious as you'd |
216 | hope. |
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217 | |
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218 | If you're currently linking your perl executable to a shared I<libc.so>, |
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219 | you can often gain a 10-25% performance benefit by rebuilding it to |
220 | link with a static libc.a instead. This will make a bigger perl |
221 | executable, but your Perl programs (and programmers) may thank you for |
222 | it. See the F<INSTALL> file in the source distribution for more |
223 | information. |
224 | |
225 | Unsubstantiated reports allege that Perl interpreters that use sfio |
226 | outperform those that don't (for IO intensive applications). To try |
227 | this, see the F<INSTALL> file in the source distribution, especially |
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228 | the ``Selecting File IO mechanisms'' section. |
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229 | |
230 | The undump program was an old attempt to speed up your Perl program |
231 | by storing the already-compiled form to disk. This is no longer |
232 | a viable option, as it only worked on a few architectures, and |
233 | wasn't a good solution anyway. |
234 | |
235 | =head2 How can I make my Perl program take less memory? |
236 | |
237 | When it comes to time-space tradeoffs, Perl nearly always prefers to |
238 | throw memory at a problem. Scalars in Perl use more memory than |
239 | strings in C, arrays take more that, and hashes use even more. While |
240 | there's still a lot to be done, recent releases have been addressing |
241 | these issues. For example, as of 5.004, duplicate hash keys are |
242 | shared amongst all hashes using them, so require no reallocation. |
243 | |
244 | In some cases, using substr() or vec() to simulate arrays can be |
245 | highly beneficial. For example, an array of a thousand booleans will |
246 | take at least 20,000 bytes of space, but it can be turned into one |
247 | 125-byte bit vector for a considerable memory savings. The standard |
248 | Tie::SubstrHash module can also help for certain types of data |
249 | structure. If you're working with specialist data structures |
250 | (matrices, for instance) modules that implement these in C may use |
251 | less memory than equivalent Perl modules. |
252 | |
253 | Another thing to try is learning whether your Perl was compiled with |
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254 | the system malloc or with Perl's builtin malloc. Whichever one it |
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255 | is, try using the other one and see whether this makes a difference. |
256 | Information about malloc is in the F<INSTALL> file in the source |
257 | distribution. You can find out whether you are using perl's malloc by |
258 | typing C<perl -V:usemymalloc>. |
259 | |
260 | =head2 Is it unsafe to return a pointer to local data? |
261 | |
262 | No, Perl's garbage collection system takes care of this. |
263 | |
264 | sub makeone { |
265 | my @a = ( 1 .. 10 ); |
266 | return \@a; |
267 | } |
268 | |
269 | for $i ( 1 .. 10 ) { |
270 | push @many, makeone(); |
271 | } |
272 | |
273 | print $many[4][5], "\n"; |
274 | |
275 | print "@many\n"; |
276 | |
277 | =head2 How can I free an array or hash so my program shrinks? |
278 | |
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279 | You can't. On most operating systems, memory allocated to a program |
280 | can never be returned to the system. That's why long-running programs |
281 | sometimes re-exec themselves. Some operating systems (notably, FreeBSD) |
282 | allegedly reclaim large chunks of memory that is no longer used, but |
283 | it doesn't appear to happen with Perl (yet). The Mac appears to be the |
284 | only platform that will reliably (albeit, slowly) return memory to the OS. |
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285 | |
286 | However, judicious use of my() on your variables will help make sure |
287 | that they go out of scope so that Perl can free up their storage for |
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288 | use in other parts of your program. A global variable, of course, never |
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289 | goes out of scope, so you can't get its space automatically reclaimed, |
290 | although undef()ing and/or delete()ing it will achieve the same effect. |
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291 | In general, memory allocation and de-allocation isn't something you can |
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292 | or should be worrying about much in Perl, but even this capability |
293 | (preallocation of data types) is in the works. |
294 | |
295 | =head2 How can I make my CGI script more efficient? |
296 | |
297 | Beyond the normal measures described to make general Perl programs |
298 | faster or smaller, a CGI program has additional issues. It may be run |
299 | several times per second. Given that each time it runs it will need |
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300 | to be re-compiled and will often allocate a megabyte or more of system |
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301 | memory, this can be a killer. Compiling into C B<isn't going to help |
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302 | you> because the process start-up overhead is where the bottleneck is. |
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303 | |
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304 | There are two popular ways to avoid this overhead. One solution |
305 | involves running the Apache HTTP server (available from |
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306 | http://www.apache.org/) with either of the mod_perl or mod_fastcgi |
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307 | plugin modules. |
308 | |
309 | With mod_perl and the Apache::Registry module (distributed with |
310 | mod_perl), httpd will run with an embedded Perl interpreter which |
311 | pre-compiles your script and then executes it within the same address |
312 | space without forking. The Apache extension also gives Perl access to |
313 | the internal server API, so modules written in Perl can do just about |
314 | anything a module written in C can. For more on mod_perl, see |
315 | http://perl.apache.org/ |
316 | |
317 | With the FCGI module (from CPAN), a Perl executable compiled with sfio |
318 | (see the F<INSTALL> file in the distribution) and the mod_fastcgi |
319 | module (available from http://www.fastcgi.com/) each of your perl |
320 | scripts becomes a permanent CGI daemon process. |
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321 | |
322 | Both of these solutions can have far-reaching effects on your system |
323 | and on the way you write your CGI scripts, so investigate them with |
324 | care. |
325 | |
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326 | See http://www.perl.com/CPAN/modules/by-category/15_World_Wide_Web_HTML_HTTP_CGI/ . |
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327 | |
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328 | A non-free, commerical product, ``The Velocity Engine for Perl'', |
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329 | (http://www.binevolve.com/ or http://www.binevolve.com/bine/vep) might |
330 | also be worth looking at. It will allow you to increase the performance |
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331 | of your perl scripts, upto 25 times faster than normal CGI perl by |
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332 | running in persistent perl mode, or 4 to 5 times faster without any |
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333 | modification to your existing CGI scripts. Fully functional evaluation |
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334 | copies are available from the web site. |
335 | |
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336 | =head2 How can I hide the source for my Perl program? |
337 | |
338 | Delete it. :-) Seriously, there are a number of (mostly |
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339 | unsatisfactory) solutions with varying levels of ``security''. |
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340 | |
341 | First of all, however, you I<can't> take away read permission, because |
342 | the source code has to be readable in order to be compiled and |
343 | interpreted. (That doesn't mean that a CGI script's source is |
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344 | readable by people on the web, though, only by people with access to |
345 | the filesystem) So you have to leave the permissions at the socially |
346 | friendly 0755 level. |
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347 | |
348 | Some people regard this as a security problem. If your program does |
349 | insecure things, and relies on people not knowing how to exploit those |
350 | insecurities, it is not secure. It is often possible for someone to |
351 | determine the insecure things and exploit them without viewing the |
352 | source. Security through obscurity, the name for hiding your bugs |
353 | instead of fixing them, is little security indeed. |
354 | |
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355 | You can try using encryption via source filters (Filter::* from CPAN), |
356 | but crackers might be able to decrypt it. You can try using the byte |
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357 | code compiler and interpreter described below, but crackers might be |
358 | able to de-compile it. You can try using the native-code compiler |
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359 | described below, but crackers might be able to disassemble it. These |
360 | pose varying degrees of difficulty to people wanting to get at your |
361 | code, but none can definitively conceal it (this is true of every |
362 | language, not just Perl). |
363 | |
364 | If you're concerned about people profiting from your code, then the |
365 | bottom line is that nothing but a restrictive licence will give you |
366 | legal security. License your software and pepper it with threatening |
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367 | statements like ``This is unpublished proprietary software of XYZ Corp. |
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368 | Your access to it does not give you permission to use it blah blah |
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369 | blah.'' We are not lawyers, of course, so you should see a lawyer if |
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370 | you want to be sure your licence's wording will stand up in court. |
371 | |
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372 | =head2 How can I compile my Perl program into byte code or C? |
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373 | |
374 | Malcolm Beattie has written a multifunction backend compiler, |
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375 | available from CPAN, that can do both these things. It is included |
376 | in the perl5.005 release, but is still considered experimental. |
377 | This means it's fun to play with if you're a programmer but not |
378 | really for people looking for turn-key solutions. |
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379 | |
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380 | Merely compiling into C does not in and of itself guarantee that your |
381 | code will run very much faster. That's because except for lucky cases |
382 | where a lot of native type inferencing is possible, the normal Perl |
383 | run time system is still present and so your program will take just as |
384 | long to run and be just as big. Most programs save little more than |
385 | compilation time, leaving execution no more than 10-30% faster. A few |
386 | rare programs actually benefit significantly (like several times |
387 | faster), but this takes some tweaking of your code. |
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388 | |
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389 | You'll probably be astonished to learn that the current version of the |
390 | compiler generates a compiled form of your script whose executable is |
391 | just as big as the original perl executable, and then some. That's |
392 | because as currently written, all programs are prepared for a full |
393 | eval() statement. You can tremendously reduce this cost by building a |
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394 | shared I<libperl.so> library and linking against that. See the |
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395 | F<INSTALL> podfile in the perl source distribution for details. If |
396 | you link your main perl binary with this, it will make it miniscule. |
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397 | For example, on one author's system, F</usr/bin/perl> is only 11k in |
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398 | size! |
399 | |
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400 | In general, the compiler will do nothing to make a Perl program smaller, |
401 | faster, more portable, or more secure. In fact, it will usually hurt |
402 | all of those. The executable will be bigger, your VM system may take |
403 | longer to load the whole thing, the binary is fragile and hard to fix, |
404 | and compilation never stopped software piracy in the form of crackers, |
405 | viruses, or bootleggers. The real advantage of the compiler is merely |
406 | packaging, and once you see the size of what it makes (well, unless |
407 | you use a shared I<libperl.so>), you'll probably want a complete |
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408 | Perl install anyway. |
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409 | |
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410 | =head2 How can I get C<#!perl> to work on [MS-DOS,NT,...]? |
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411 | |
412 | For OS/2 just use |
413 | |
414 | extproc perl -S -your_switches |
415 | |
416 | as the first line in C<*.cmd> file (C<-S> due to a bug in cmd.exe's |
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417 | `extproc' handling). For DOS one should first invent a corresponding |
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418 | batch file, and codify it in C<ALTERNATIVE_SHEBANG> (see the |
419 | F<INSTALL> file in the source distribution for more information). |
420 | |
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421 | The Win95/NT installation, when using the ActiveState port of Perl, |
422 | will modify the Registry to associate the C<.pl> extension with the |
423 | perl interpreter. If you install another port (Gurusaramy Sarathy's |
424 | is the recommended Win95/NT port), or (eventually) build your own |
425 | Win95/NT Perl using WinGCC, then you'll have to modify the Registry |
426 | yourself. |
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427 | |
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428 | Macintosh perl scripts will have the appropriate Creator and |
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429 | Type, so that double-clicking them will invoke the perl application. |
430 | |
431 | I<IMPORTANT!>: Whatever you do, PLEASE don't get frustrated, and just |
432 | throw the perl interpreter into your cgi-bin directory, in order to |
433 | get your scripts working for a web server. This is an EXTREMELY big |
434 | security risk. Take the time to figure out how to do it correctly. |
435 | |
436 | =head2 Can I write useful perl programs on the command line? |
437 | |
438 | Yes. Read L<perlrun> for more information. Some examples follow. |
439 | (These assume standard Unix shell quoting rules.) |
440 | |
441 | # sum first and last fields |
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442 | perl -lane 'print $F[0] + $F[-1]' * |
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443 | |
444 | # identify text files |
445 | perl -le 'for(@ARGV) {print if -f && -T _}' * |
446 | |
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447 | # remove (most) comments from C program |
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448 | perl -0777 -pe 's{/\*.*?\*/}{}gs' foo.c |
449 | |
450 | # make file a month younger than today, defeating reaper daemons |
451 | perl -e '$X=24*60*60; utime(time(),time() + 30 * $X,@ARGV)' * |
452 | |
453 | # find first unused uid |
454 | perl -le '$i++ while getpwuid($i); print $i' |
455 | |
456 | # display reasonable manpath |
457 | echo $PATH | perl -nl -072 -e ' |
458 | s![^/+]*$!man!&&-d&&!$s{$_}++&&push@m,$_;END{print"@m"}' |
459 | |
460 | Ok, the last one was actually an obfuscated perl entry. :-) |
461 | |
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462 | =head2 Why don't perl one-liners work on my DOS/Mac/VMS system? |
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463 | |
464 | The problem is usually that the command interpreters on those systems |
465 | have rather different ideas about quoting than the Unix shells under |
466 | which the one-liners were created. On some systems, you may have to |
467 | change single-quotes to double ones, which you must I<NOT> do on Unix |
468 | or Plan9 systems. You might also have to change a single % to a %%. |
469 | |
470 | For example: |
471 | |
472 | # Unix |
473 | perl -e 'print "Hello world\n"' |
474 | |
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475 | # DOS, etc. |
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476 | perl -e "print \"Hello world\n\"" |
477 | |
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478 | # Mac |
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479 | print "Hello world\n" |
480 | (then Run "Myscript" or Shift-Command-R) |
481 | |
482 | # VMS |
483 | perl -e "print ""Hello world\n""" |
484 | |
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485 | The problem is that none of this is reliable: it depends on the |
486 | command interpreter. Under Unix, the first two often work. Under DOS, |
487 | it's entirely possible neither works. If 4DOS was the command shell, |
488 | you'd probably have better luck like this: |
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489 | |
490 | perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>"" |
491 | |
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492 | Under the Mac, it depends which environment you are using. The MacPerl |
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493 | shell, or MPW, is much like Unix shells in its support for several |
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494 | quoting variants, except that it makes free use of the Mac's non-ASCII |
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495 | characters as control characters. |
496 | |
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497 | There is no general solution to all of this. It is a mess, pure and |
498 | simple. Sucks to be away from Unix, huh? :-) |
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499 | |
500 | [Some of this answer was contributed by Kenneth Albanowski.] |
501 | |
502 | =head2 Where can I learn about CGI or Web programming in Perl? |
503 | |
504 | For modules, get the CGI or LWP modules from CPAN. For textbooks, |
505 | see the two especially dedicated to web stuff in the question on |
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506 | books. For problems and questions related to the web, like ``Why |
507 | do I get 500 Errors'' or ``Why doesn't it run from the browser right |
508 | when it runs fine on the command line'', see these sources: |
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509 | |
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510 | WWW Security FAQ |
511 | http://www.w3.org/Security/Faq/ |
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512 | |
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513 | Web FAQ |
514 | http://www.boutell.com/faq/ |
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515 | |
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516 | CGI FAQ |
517 | http://www.webthing.com/page.cgi/cgifaq |
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518 | |
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519 | HTTP Spec |
520 | http://www.w3.org/pub/WWW/Protocols/HTTP/ |
521 | |
522 | HTML Spec |
523 | http://www.w3.org/TR/REC-html40/ |
524 | http://www.w3.org/pub/WWW/MarkUp/ |
525 | |
526 | CGI Spec |
527 | http://www.w3.org/CGI/ |
528 | |
529 | CGI Security FAQ |
530 | http://www.go2net.com/people/paulp/cgi-security/safe-cgi.txt |
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531 | |
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532 | |
533 | =head2 Where can I learn about object-oriented Perl programming? |
534 | |
535 | L<perltoot> is a good place to start, and you can use L<perlobj> and |
536 | L<perlbot> for reference. Perltoot didn't come out until the 5.004 |
537 | release, but you can get a copy (in pod, html, or postscript) from |
538 | http://www.perl.com/CPAN/doc/FMTEYEWTK/ . |
539 | |
540 | =head2 Where can I learn about linking C with Perl? [h2xs, xsubpp] |
541 | |
542 | If you want to call C from Perl, start with L<perlxstut>, |
543 | moving on to L<perlxs>, L<xsubpp>, and L<perlguts>. If you want to |
544 | call Perl from C, then read L<perlembed>, L<perlcall>, and |
545 | L<perlguts>. Don't forget that you can learn a lot from looking at |
546 | how the authors of existing extension modules wrote their code and |
547 | solved their problems. |
548 | |
549 | =head2 I've read perlembed, perlguts, etc., but I can't embed perl in |
550 | my C program, what am I doing wrong? |
551 | |
552 | Download the ExtUtils::Embed kit from CPAN and run `make test'. If |
553 | the tests pass, read the pods again and again and again. If they |
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554 | fail, see L<perlbug> and send a bugreport with the output of |
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555 | C<make test TEST_VERBOSE=1> along with C<perl -V>. |
556 | |
557 | =head2 When I tried to run my script, I got this message. What does it |
558 | mean? |
559 | |
560 | L<perldiag> has a complete list of perl's error messages and warnings, |
561 | with explanatory text. You can also use the splain program (distributed |
562 | with perl) to explain the error messages: |
563 | |
564 | perl program 2>diag.out |
565 | splain [-v] [-p] diag.out |
566 | |
567 | or change your program to explain the messages for you: |
568 | |
569 | use diagnostics; |
570 | |
571 | or |
572 | |
573 | use diagnostics -verbose; |
574 | |
575 | =head2 What's MakeMaker? |
576 | |
577 | This module (part of the standard perl distribution) is designed to |
578 | write a Makefile for an extension module from a Makefile.PL. For more |
579 | information, see L<ExtUtils::MakeMaker>. |
580 | |
581 | =head1 AUTHOR AND COPYRIGHT |
582 | |
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583 | Copyright (c) 1997, 1998 Tom Christiansen and Nathan Torkington. |
584 | All rights reserved. |
585 | |
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586 | When included as an integrated part of the Standard Distribution |
587 | of Perl or of its documentation (printed or otherwise), this works is |
588 | covered under Perl's Artistic Licence. For separate distributions of |
589 | all or part of this FAQ outside of that, see L<perlfaq>. |
590 | |
591 | Irrespective of its distribution, all code examples here are public |
592 | domain. You are permitted and encouraged to use this code and any |
593 | derivatives thereof in your own programs for fun or for profit as you |
594 | see fit. A simple comment in the code giving credit to the FAQ would |
595 | be courteous but is not required. |