Utility of "use lib qw{ . }" ?

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

I saw in a recent node of Juerd's (it isn't really relevant where) the following code:

use lib '.';
[download]

Now, at one point I used to do this myself. However, on accident one day I noticed that it wasn't necessary. Observe:

[scorch:~/monks] alex% ./testlib.pl
bar
bletch
[scorch:~/monks] alex% find .
.
./Demo
./Demo/SubDemo.pm
./Demo.pm
./testlib.pl
[scorch:~/monks] alex% find . -name '*p[ml]' -exec cat {} \;
package Demo::SubDemo;

$baz = "bletch";

1;
package Demo;

$foo = "bar";

1;
#!/usr/bin/perl -wl
use Demo;
use Demo::SubDemo;
print $Demo::foo;
print $Demo::SubDemo::baz;
[scorch:~/monks] alex% echo $PERL5LIB
PERL5LIB: Undefined variable.
[download]

Note that nowhere am I asking perl to use "." in @INC. Yet, perl still sees it. I think this is pretty sensible behaviour. Additionally, were I to have POD in any of the Demo modules, I could use perldoc, and it would DTRT as regards '.'.

Am I missing something that coders are using lib this way? I guess with the exception of CGI applications (although I suspect it isn't necessary there, either).

Cheers
dep.

--
Laziness, Impatience, Hubris, and Generosity.

minor reword edit on first line.

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Re: Utility of "use lib qw{ . }" ?
by Lachesis (Friar) on Jun 23, 2003 at 14:00 UTC

use lib '.';
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(jeffa) 2Re: Utility of "use lib qw{ . }" ?

by jeffa (Bishop) on Jun 23, 2003 at 14:30 UTC

perl -le"print for @INC"

perl -Mlib=. -le"print for @INC"
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jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

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Re: Utility of "use lib qw{ . }" ?
by broquaint (Abbot) on Jun 23, 2003 at 13:58 UTC

Note that nowhere am I asking perl to use "." in @INC. Yet, perl still sees it.

perl

'.'

@INC

'.'

taint mode

@INC

perlvar

_________ broquaint

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Re: Utility of "use lib qw{ . }" ?
by gellyfish (Monsignor) on Jun 23, 2003 at 14:18 UTC

The only time that you might want to use use lib '.' (and with extreme caution) is when running your program with taint mode (the -T switch) on, when the current directory is removed from @INC - this should be done with caution because it is not alway possible for a program to control what it's current working directory is before requiring or using any modules and in a less secure environment (such as a web server) there is a risk of malicious code in the current directory being substituted for that of a real module. At the very least one should assure oneself that the directories that are likely to be the working directory for your program are not world writeable - of course if it is necessary to add the (assumed) current working directory (probably the directory in which the program resides) to @INC when using '-T' then it is probably best to supply the absolute path rather than '.', which whilst having some postential impact on portability is actually more likely to work under some conditions as well as being more secure.

/J\

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Re: Utility of "use lib qw{ . }" ?
by crouchingpenguin (Priest) on Jun 23, 2003 at 14:19 UTC

Just a small comment on the utility of modifying @INC under apache/mod_perl. I often include directories in the startup file (often named startup.pl) via use libs like:

use lib qw( /var/www/perl_lib ); ### for example
[download]

This is especially handy when you have a dev apache instance that includes dev copies of your local libs.

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Re: Utility of "use lib qw{ . }" ?
by PodMaster (Abbot) on Jun 23, 2003 at 14:45 UTC

#!$var/bin/perl

MJD says "you can't just make shit up and expect the computer to know what you mean, retardo!"
I run a Win32 PPM repository for perl 5.6.x and 5.8.x -- I take requests (README).
** The third rule of perl club is a statement of fact: pod is sexy.

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