Calling a Perl Module which is Installed in different path/directory

Question

I am writing a Perl script which does -

• SSH to one of the server and do some operation using Net::OpenSSH Perl Module.
• I want to have entire log of the script to be stored in certain log file using Log::Log4perl Perl Module.
• I want to write some data to CSV file using Text::CSV Perl Module.

Actually these three Perl Modules have been installed in different directories.

Lets say -

• Net::OpenSSH is installed in /path/to/lib1
• Log::Log4perl is installed in /path/to/lib2
• Text::CSV is installed in /path/to/lib3

Since these Perl Modules has been installed in different locations, I am mentioning the respective paths in Shebang line like below:

Method1:

#!/usr/bin/perl -I/path/to/lib1 -I/path/to/lib2 -I/path/to/lib3

use strict;
use warnings;

use Net::OpenSSH;
use Log::Log4perl;
use Text::CSV;

#continue flow of the script
..

This works perfectly fine for me.

I found one more method to call these Perl modules like below:

Method 2:

#!/usr/bin/perl

use strict;
use warnings;

use lib '/path/to/lib1';
use lib '/path/to/lib2';
use lib '/path/to/lib3';
...

Above method also works fine for me.

I found the standard way to call these Perl modules by the use of FindBin.

I am confused with its syntax. How can I achieve same using FindBin Perl Module.

Method 3:

#!/usr/bin/perl

use strict;
use warnings;

use FindBin qw($Bin);
use lib "$Bin/path/to/lib1";
use lib "$Bin/path/to/lib2";
use lib "$Bin/path/to/lib3";
...

This throws me following error which doesn't appears when I use first two methods (Method1, Method2).

unable to load Perl module IO::Pty: Can't locate IO/Pty.pm in @INC ...

Where I am doing wrong in Method 3?

Answer 1

$RealBin is the directory in which the script is located. ($Bin is a broken version of the same thing.)

If there's no relationship between the directory in which the script is located and the directory in which a module is located, it doesn't make sense to use $RealBin. In fact, it usually makes more sense to use the PERL5LIB env var than use lib in such cases.

On the other hand, if the script was located in /path/to/bin, it might make sense to use a path relative to $RealBin.

use lib                 # In /path/to/bin/script,
   "$RealBin/../lib1",  #    This is /path/to/bin/../lib1, or /path/to/lib1
   "$RealBin/../lib2",  #    This is /path/to/bin/../lib2, or /path/to/lib2
   "$RealBin/../lib3";  #    This is /path/to/bin/../lib3, or /path/to/lib3

$RealBin is usually used when the script and modules are packaged together (part of the same project). Same for use lib, really.