How to change @INC lib contents by using no lib command in PERL

Question

if (@arr =~ /env1/) #checking enviroment  
{
   # Want to flush the @INC contents using below no lib
   # --> Command before the perl get the libraries of my choice at the time of compilation 

   no lib "//First/lib/"; #flush INC  
   no lib "//Second/lib/"; #flush INC  
   print log1 "INC before current- @INC\n";

   #set library of my choice with either syntax
   BEGIN{ unshift @INC, "//Third/lib/" };                                    
   # or                                      
   use lib "//third/lib/";

   print log1 "INC after- @INC\n";  
   print log2 "INC after- %INC\n";  
   print log3 map {"$_ => $INC{$_}\n"} keys %INC; 

   use DirHandle;  
   use File::Find;  
   use File::Copy;  

   print map {"$_ => $INC{$_}\n"} keys %INC;
}

I want to know the above thing can be achieved in a simpler way. Do I need to include any Perl modules to use the (no lib and use lib commands). This is a requirement due to script running in multiple enviroment and when one of the enviroments is down the script stops running. I want to achieve this by passing the libraries of my choice to be used by perl.

Suggestions are welcome.

---

Edit: Here's the actual code.

if (@temp[arr_index]=~ /env1/) #enviroment 1
                      {              

                     BEGIN{ unshift @INC, "//server1/lib/" }; #server 1 for same app lower enviroment 1
                     BEGIN{ unshift @INC, "//server2/lib/" }; #server 2 for same app lower enviroment 1

                                    use File::Copy; 

                    }

    elsif (@temp[arr_index]=~ /env2/) #enviroment 2

    {
                    BEGIN{ unshift @INC, "//server1/lib/" }; #server 1 for same app lower enviroment 2
                    BEGIN{ unshift @INC, "//server2/lib/" }; #server 2 for same app lower enviroment 2

                                    use File::Copy;
    }


    elsif (@temp[arr_index]=~ /env3/) #enviroment 3

    {
                    BEGIN{ unshift @INC, "//server1/lib/" }; #server 1 for same app lower enviroment 3
                    BEGIN{ unshift @INC, "//server2/lib/" }; #server 2 for same app lower enviroment 3

                                    use File::Copy;
    }

@INC - Having @INC the values same for all enviroments which is causing issue. Hope the above adds some clarity to your understanding . THANKS.

Answer 1

I would suggest just pushing all of them into @INC in the order of your preferred environments. Perl will look at the contents of @INC. Perlvar says about it:

The array @INC contains the list of places that the do EXPR , require, or use constructs look for their library files.

That means it will look at the list of paths from left to right, as described here. Thus, you can just push your library paths into @INC one after another:

@!/usr/bin/perl
use strict;
use warnings;

BEGIN {
  use lib 'first/lib', 'second/lib', 'third/lib';
}

If you now go and require Some::Module, Perl will look in first/lib first. If it cannot find it there, maybe because the path doesn't exist in your environment (it won't complain about that), Perl will proceed to look in second/lib and third/lib one after the other. You don't have to do anything else.

-- On another note, you have mixed compile time and run time a lot in your above code. The three use parts and the BEGIN block will be called at compile time regardless of the if construct they are in. Everything else, including the no lib calls will only be called at run time if the match is true. See perlmod for a more detailed explanation of how this works.