Setting PERL5LIB - perl

Question

Can I set PERL5LIB in a separate script and call that script in other scripts? How do I do it? And how would it affect the script in which it is used?

Answer 1

Setting PERL5LIB at runtime will not affect Perl's search path. You need to export the variable before executing the interpreter.
Alternatively you can modify #INC at compile time (also possible to do in a separate script/module):
BEGIN { unshift #INC, "/path/to/dir" }
This is what the lib pragma does.

Answer 2

You'd do this via 'use lib' rather than manipulating the environment:
use lib '/home/perl5';
That could be in a separate file that you 'require' in.

Answer 3

PERL5INC is a shell environment variable, so you wouldn't set it inside your Perl program (normally) but instead specify it before invoking Perl. The below is a shell command where I've used PERL5LIB to instruct prove to find a Perl module residing in ~/OnePop:
$ PERL5LIB=~/OnePop prove -l t
... PERL5LIB is unset here ....
When a command is preceded by a variable assignment like this, the shell sets and exports the variable (PERL5LIB) to that command, but after that the variable will be unset again. You can also set the variable in the shell, so that all subsequent commands will inherit it.
$ export PERL5LIB=~/OnePop
...
$ prove -l t
... PERL5LIB continues to be set here ...
If you forget the export keyword in the above example (i.e. assigns the value using PERL5LIB=~/OnePop on a separate line) the variable will be set in the shell, but it will not be inherited by any commands you run (meaning that prove will not be able to see it).
Finally, if you wanted to set the environment PERL5LIB variable from inside a Perl program you'd have to write it like this:
$ENV{PERL5LIB} = glob("~/OnePop"); # glob() expands the tilde
system(qw( prove -l t ));
Though, as other have pointed out, if you want to specify the include path from inside Perl it is easier/better to use use lib $PATH.

Answer 4

PERL5INC is an environment variable. Environment variables are only inherited from parents to their children and can't (easily) be set the other way around. If you want to store extra search paths in an external file I suggest you make it a simple list of paths and write a simple loop to read each path from the file and manipulate #INC in the current process. If you want this to be done early at compile time you'll have to use a BEGIN {} block.
For example
BEGIN{
open(INCFILE,"<","my.inc.file") or die($!);
foreach(<INCFILE>){
push #INC,$_;
}
close(INCFILE);
}

Answer 5

Alternative to PERL5LIB:
You could instead install the latest version of Perl 5 available (in a non-system location, of course). After you have used a module file or done whatever is necessary to make the new perl and cpan executables visible to your shell, you can use cpan to install all the modules you need. I have sometimes done this for individual applications in a similar vein to using Python Virtual Environments.