Strange issues with mod_perl and use lib

Farenji has asked for the wisdom of the Perl Monks concerning the following question:

I'm building a web application using perl, apache2 and mod_perl2. I'm experiencing some weird stuff. When I run the app from the console, it works fine. Also using perl cgi instead of mod_perl it works fine.

When I use mod_perl I get a not found error, on the first "use"d module. All the modules are in the same dir as the .pl script, /www/domain/cgi-bin/.

When I insert "use lib '/www/domain/cgi-bin';" in the script, the app works fine. But I rather not have hardcoded paths in my script, that's what config files are for.

I tried to overcome this issue by using FindBin and FindBin::Real, and using the $0 var. But without success. The bizarre thing is that the following works:

use lib "/www/domain/cgi-bin";

but the following does NOT work:

my $path = "/www/domain/cgi-bin";
use lib $path;

and that freaks me out.

Could anyone shed some light on this please?

Comment on Strange issues with mod_perl and use lib

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Re: Strange issues with mod_perl and use lib by Joost (Canon) on May 12, 2007 at 22:49 UTC
but the following does NOT work: my $path = "/www/domain/cgi-bin"; use lib $path; use() is executed at compile time, while assignment is executed at runtime. That means that "use $path;" is run when $path is still undefined. Try this: `BEGIN { my $path = "/www/domain/cgi-bin"; use lib $path; }` [download] See use. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l]
Re^2: Strange issues with mod_perl and use lib by ikegami (Patriarch) on May 13, 2007 at 01:44 UTC
That doesn't fix the problem. The assignment is done earlier than it would have without the `BEGIN`, but it still happens after the `use` statement is executed. While the `BEGIN` block is executed as soon as it finishes compiling, the same goes for the `use` statement. Since the `use` statement is fully compiled before the BEGIN block is fully compiled (i.e. it ends first), the `use` statement is executed before the BEGIN block is executed, and therefore before the assignment is executed. Solutions: `my $path; BEGIN { # Code that determines the path and stores it in $path. $path = "/www/domain/cgi-bin"; } use lib $path;` [download] or `use lib do { # Code that determines the path and returns it. "/www/domain/cgi-bin" };` [download] or `sub get_lib_path { # Code that determines the path and returns it. return "/www/domain/cgi-bin"; } use lib get_lib_path();` [download] or `# Hardcoded use lib "/www/domain/cgi-bin";` [download] Update: Clarified the wording.	[reply] [d/l] [select]
Re^3: Strange issues with mod_perl and use lib by Joost (Canon) on May 17, 2007 at 22:08 UTC
Thanks for that correction. I didn't know nested BEGIN blocks execute in "reverse order". It seems completely unintuitive, illogical, and I don't like it but at least now I know :-) update: `perl -e 'print "a"; BEGIN { print "b"; BEGIN { print "c" }}'` [download] "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l]
Re^4: Strange issues with mod_perl and use lib by ikegami (Patriarch) on May 18, 2007 at 14:17 UTC
Re^2: Strange issues with mod_perl and use lib by Farenji (Novice) on May 12, 2007 at 23:38 UTC
Unfortunately, that doesn't work either...	[reply]
Re: Strange issues with mod_perl and use lib by perrin (Chancellor) on May 13, 2007 at 02:58 UTC
It sounds like you need ModPerl::RegistryPrefork, as explained here.	[reply]
Re^2: Strange issues with mod_perl and use lib by Farenji (Novice) on May 13, 2007 at 10:39 UTC
Thank you for this excellent advice. PerlRunPrefork was indeed the solution. It works now, without hard coded directories in my code! :)	[reply]
Re: Strange issues with mod_perl and use lib by RL (Monk) on May 13, 2007 at 06:09 UTC
That's because @INC is reset to the contents valid on Apache startup on each run. The use..bla statement is only executed the first time the script is run. On subsequent runs of the same script in the same Apache process (or it's children) the use statements are not executed again. At least this is my understanding from what I read. What I did was adding the following line to the end of /etc/apache2/apache2.conf: `PerlRequire "/etc/apache2/modperl_startup.pl"` [download] The file modperl_startup.pl reads: `#!/usr/bin/perl use lib "/htdocs/perl5lib"; 1;` [download] Hope this helps RL	[reply] [d/l] [select]
Re: Strange issues with mod_perl and use lib by Errto (Vicar) on May 13, 2007 at 05:28 UTC
that's what config files are for. Then go ahead and put it in the config file: `PerlSwitches -I/www/domain/cgi` [download] The above cribbed from the mod_perl 2.0 docs	[reply] [d/l]
Re: Strange issues with mod_perl and use lib by Bro. Doug (Monk) on May 14, 2007 at 02:20 UTC
Farenji, I have a large perl app with several years worth of a few dozen coder's work in it. I often see this in the code: `my $package = "Some::Package" ; eval "require $package" ;` [download] It drives me ape when I see this. They forgot a key part. It should look like this: `my $package = "Some::Package" ; eval "require $package" ; warn $@ if $@ ;` [download] The point is: this will work for you to include your libs at runtime. Peace, monks. Bro. Doug :wq	[reply] [d/l] [select]