I am really a very beginner. I saw "use 5.014002;" in perl script. What does it mean? Thanks!
It means perl version at least 5.14.2 is required to run the script. See use.
It also enables all the features (like say, state etc.) that come with the version, see feature or even Syntax::Construct.
There are several ways how to write the version number, but this one is the most portable one, working in older versions of Perl.
Related
For example, I want to compress log files a script generates. I'm using version 5.8.8 so there isn't anything built into the core to do it. The script is cross-platform, Linux, Solaris, AIX, HPUX, and Windows.
Right now I'm thinking of using IO::Compress::Gzip. Are there any known bugs with that module? Will it work across all platforms?
To generalize a little more, how can I find out if a certain module has any known bugs, and what platforms that module will run on?
CPAN offers an array of tools you can use to determine the usefulness of a module before installing it. Unfortunately, IO::Compress::Gzip is a suboptimal example of how this can go.
When you visit the metacpan page of a module, there is a list of tools in the left column. The interesting points are
Test Results: This takes you to a page where the results of the test suite on different OSes and different perl versions are shown. Unfortunately, this service doesn't respond to my requests at the time of writing.
Bugs: This is a link to the bugtracker for this module. You can browse the list of open bugs to find possible dealbrakers. And if you find an issue, you can report it here.
Reviews: Some modules have short reviews and ratings by the Perl community. The module you mentioned doesn't have any ratings yet, so as an example, here are the ratings for List::MoreUtils.
Dependencies are listed on the right column. If you click the “dependencies” link, you can get a summary of test results for the required non-core modules for a given perl version. Unfortunately, there don't seem to be any results available currently.
Many modules also have a “bugs and limitations” section in the documentation.
Note: according to the corelist program, IO::Compress::Gzip is a core module since perl5, v9.4. This doesn't mean much: Core modules are in Core because they are needed to install other modules (or because they have historical significance … CGI, *cough*). However, this is an indication that it is reasonably stable and thoroughly cross-platform.
ANSWERED: Basically, it can be done with no major side-effects if you compiled your own perl and you did it the same way your OS did. While it isn't a recommended practice, I've been able to run like this for more then a month. I would conclude it is relatively safe to do if you know what you are doing.
We came to the conclusion at work today that we needed to upgrade perl to 5.10.0
CentOS 5.x comes with perl 5.8.8.
We determined that the effort involved in maintaining scripts with #!/usr/bin/perl was futile.
According to some install stuff on CPAN and other places, it isn't a 'good' idea to replace the OS's version of perl. I already updated the link in /usr/bin/. So my question is, how bad is it really to replace /usr/bin/perl?
I've not noticed any adverse effects in our systems yet, but I'm prepared to correct the link (back to 5.8.8) as soon as there is a problem.
I'm worried that there may be some modules in the CentOS standard distro that aren't included in CPAN's source 5.10.0. I'm still trying to figure out what those modules might be.
Thanks in advance.
In my experience, the best practice is to compile your entire stack (Perl, Apache, ImageMagick, ...) from source yourself. That gives you complete control over which versions of everything are used and when everything gets upgraded.
Replacing /usr/bin/perl with one you compiled is a crap shoot. The OS might be using /usr/bin/perl as part of its maintenance or init scripts so changing it could brick your server or cause strange failures.
So ignore the system Perl, build your own, and fix your scripts to refer to your version of Perl.
Generally newer versions of Perl5 attempt to maintain backward compatibility with older versions. But that's not 100% assured. For example, a script that depends on an undefined behavior in Perl 5.8.8 (which shouldn't happen but sometimes does), that behavior may be different under 5.10.0. Nevertheless, it's usually fairly safe to assume that a script written for Perl 5.8.8 will run under 5.10.0 assuming there are no other factors involved.
But there usually are other factors (modules, byte compatibility for XS code, and so on). The list of possible gotchas is huge. That doesn't mean that any one of them will snag you on this go-around, but there is potential for problems.
If you've already got an upgraded Perl in /usr/local/bin, go ahead and use it. But don't dismantle or upgrade the old /usr/bin/ version. It's only a small chunk of hard drive (very small by today's standards).
By the way, a lot of people speak highly of perlbrew (App::Perlbrew on CPAN) as a tool to help maintain multiple versions of Perl.
Well, if you do decide to change the location of where Perl is installed, that is completely up to you and where you prefer it to be. But, keep in mind that any scripts that exist with a shebang line pointing to #!/usr/bin/perl will possibly break.
My recommendation would be that after you have installed it, create a soft link in /usr/bin/perl pointing to the executable for the new version of Perl that you installed. Just a thought. Its a work around to avoid breaking anything.
Creating the link above would certainly help to avoid the possibility of 'bricking your server' as #Mu pointed out.
Regards,
Jeff
Is Perl a good option for writing (possibly and partially) platform independent desktop applications? I know there are interesting widget libraries like GTK2 Perl and wxWidgets but I'm not familiar with development on Windows.
Is it possible to write a good application with Perl and those tools, maybe embedding everything needed to avoid asking the user to install external (and probably non conventional for many) libraries? Are there examples of this kind of apps around?
Sort of. You can certainly write Perl scripts that provide a Tk GUI that will work on any platform, and you can even package the libraries they need to work with PAR to put together an application that will run anywhere with an appropriate version of perl installed without requiring the end use to install a bunch of stuff from CPAN to get it to work.
However, an application that will run anywhere without requiring an existing perl installation (and it's probably not safe to assume the average Windows user will have perl) isn't really viable. One solution would be to distribute an "everywhere but Windows" version that simply uses PAR to include the necessary libraries, and a PAR::Packer-built version for Windows, which would be a fully-functional .exe including the perl interpreter and the libraries.
EDIT: following daotoad's response, it does appear that ActiveState's PerlApp can build cross-platform binaries for for Windows, Mac OS X, Linux, Solaris, and AIX; I haven't tried this but if it works as advertised it would seem to meet your requirements.
My employer uses ActiveState's PerlApp to produce executable versions of our apps with great success.
We tested PAR and PerlApp before selecting our packaging method. At that time, PerlApp had faster load times. Several versions of each tool have come and gone since then, so I would recommend testing with each before selecting a tool.
Executable packaging has been very effective for us.
There are a few portability issues issues with Perl, but if you pay attention to perlport, it's easy to avoid most issues. Our biggest problems are always with Win32. From time to time, some simple thing will require stupid, bizarre work-arounds or digging into Win32 API for a platform specific hack.
We have used both Wx and Tk guis.
Frozen Bubble is a well known and widely available app you can look at.
Check out PAR (available via CPAN) with respect to your bundling requirement.
Consider having a look at Padre for an example of a complex application written in perl using Wx.
So yes. All of your requirements are achievable, including portability.
I am working on the module XUL::Gui on CPAN, which uses Firefox to display cross platform gui apps from Perl. It is under development, but stable, and may be complete enough for your needs. You can build your gui in HTML and/or XUL (the Mozilla gui language that Firefox itself is written in), and then style everything with CSS. Let me know if you have any feature requests.
I'm new to Object-Oriented programming and the perldoc page on CPAN.pm confuses the hell out of me. My program needs to download a couple of modules if they don't already exist. Is this basically just:
CPAN::Shell->install("Module::Name::Here");
or is there more to it? Does that download the package, unarchive it, and install it, or just one or two of those steps? If it's not all three, how do I do the other one (or two)? I would like it to make sure it doesn't try to re-install anything if the package is already there - is this the default behavior of the function or no?
And how can I tell if Perl couldn't connect to CPAN to get the package?
No one else has mentioned it, but you have to load the CPAN config first:
use CPAN;
CPAN::HandleConfig->load;
CPAN::Shell::setup_output;
CPAN::Index->reload;
# now do your stuff
You can also look at the cpan(1) script that comes with CPAN.pm to see a lot of the programmer's interface in action. I also wrote on article for the latest issue of The Perl Review showing examples of the programmer's interface to CPAN.pm.
However, you might not need to do any of this. Why is your program downloading modules on its own? Are you trying to create a distribution that has dependencies? There are better ways to handle that so you don't have to repeat the work that's already done in other tools. For instance, see my article Creating Perl Application Distributions. You treat your program as if it's a module and get the benefit of all the cool module tools so you don't have to reinvent something.
If you tell us more about the problem that you're actually trying to solve, we might have other good answers too. :)
Good luck,
the perldoc page on CPAN.pm confuses the hell out of me.
Yes, documentation of the CPAN API is still a bit lacking. It wasn't every really designed for programmatic use by others. You might have better luck with CPANPLUS, if that's available to you.
My program needs to download a couple of modules if they don't already exist. Is this basically just: CPAN::Shell->install("Module::Name::Here");
Yes, that's pretty much it for the simplest possible thing. In fact, that's pretty much all the 'cpan' command line program does when you type "cpan Module::Name::Here". However, you will need to have CPAN.pm configured in advance.
Does that download the package, unarchive it, and install it?
Yes, all three.
I would like it to make sure it doesn't try to re-install anything if the package is already there - is this the default behavior of the function or no?
Yes, the default behavior is not to install anything if the module is up to date. You can actually check that yourself with the "uptodate()" method like this:
my $mod = CPAN::Shell->expand("Module", "Module::Name::Here");
$mod->install unless $mod->uptodate;
And how can I tell if Perl couldn't connect to CPAN to get the package?
That's hard to do programmatically in a way that would be simple to explain. You either need to look at the output or else just check $mod->uptodate afterwards;
my $mod = CPAN::Shell->expand("Module", "Module::Name::Here");
if ( ! $mod->uptodate ) {
$mod->install;
die "Problems installing" unless $mod->uptodate;
}
Best of luck!
Basically using CPAN is the following:
perl -MCPAN -e shell
if this is the first time you are running it, it will ask you a few questions and save the results in a configuration file.
then to install PGP::Sign just type:
install PGP::Sign
and you're set.
As for you last question, don't worry, it will say to you whether it can connect or not.
As you can tell, most of us use only use CPAN.pm in the interactive mode, however, you're on the right track.
Things I can point out for the moment:
Yes, calling CPAN::Shell->install() will download, compile, test and install a package. It should also do the same for any dependencies the package has, recursively.
The default behaviour is to not install anything which is already installed (unless a newer version is available).
I'm not strictly sure how the error handling works - I'll look into it, and report back.
It might prompt your user, though.
Keltia has it right. I'll add that his first instruction is done from the command prompt, usually as root, but not necessarily so. The second command is done from the CPAN prompt. You can also do it all on the command line, but I usually don't.
If you're using windows, your best bet is to use PPM, but its repositories are annoyingly out of date most times.
I need to create a Zip archive after filtering the list of files I want to include. Preferably I'd like the module to work in both Windows and Linux.
Since I need to filter the list of files, I don't really want to to use an external program. I'd rather not introduce external dependencies either so I can compile the script into a single executable on Windows (using ActiveState PDK).
What I already tried
Until now I've used Archive::Zip found on CPAN but it has a major bug on Windows machine that use non-ASCII filenames: the filenames get corrupted in the archive as they don't get translated into unicode.
There is a bug report filed for that but it hasn't been updated in over 10 months and in the module documentation the developer is rather unhelpful (of the "fix your computer or get rid of Windows" kind).
Update:
Thanks to the clarifications from brian and Alan Haggai Alavi it seems that enough love is being put in Archive::Zip to get these bugs out soon and finally have a fully functioning zip module in Windows.
Although the module documentation says some stupid things about Windows, the current maintainer is Adam Kennedy, the same guy who brought you Strawberry Perl. He's definitely not anti-Windows. He released a version October, so they are working on it. There's also an open grant from The Perl Foundation to fix Archive::Extract bugs.The bug you mention, RT 35334: Filename Encoding by Archive::Zip, maybe just needs someone to show it some love. That could be you. People solve the problems that bother them, so maybe nobody interested in the module needs this just yet.
The module has had problems, and I've been following its progress since I use it in a couple projects. It has gotten a lot better recently and can certainly use some love. Sometimes open source means helping to fix the problems that you encounter. I know this doesn't help you solve your problem immediately, but that's how I think you're going to get this done aside from system() calls.
The above said bug has been solved very lately by the addition of Unicode filename support under Windows. A release featuring the fix will be available in CPAN within a week.
You could try the standard-distribution Archive::Extract. It may not be any better than Archive::Zip, but the documentation says that, if there are problems, it goes under the hood to try to use command-line tools on your system to unzip the file. This is probably most robust on Unix, but Windows has a zip archive utility, and it should be accessible via the command line. Plus, Archive::Extract can handle many other types of compression (theoretically).
Of course, it may turn out that Archive::Extract simply figures out what kind of compression the file uses and then passes it to the appropriate other library, which might be Archive::Zip.
You might also try IO::Uncompress::Unzip and it's counterpart, IO::Compress::Zip, for just unzipping, reading, and rezipping. If absolutely necessary. Again, I don't know how much better these will work, but they are all part of the standard library.