Perl problem 'require' the same file - perl

Question

I have a shared module in perl. The main program needs two files, first, a shared file (let's call it 'X'), and, second, a 'package' file. File 'X' is also included in the 'package' file using 'require'. When I compile this program it gives me the following error:
Undefined subroutine &main::trim called at testing.pl line 8.
My understanding is that perl couldn't find the trim() module. If I don't include the package file, then this will run without any problem.
Can anyone shed light on this problem?
These are my codes:
Main program: testing.pl
#!/usr/bin/perl -w
use strict;
use postgres;
require "shared.pl";
trim("als");
Package File: postgres.pm
#!/usr/bin/perl
package postgres;
use strict;
use DBI;
require "shared.pl";
1;
shared file: shared.pl
#!/usr/bin/perl
# =============
# shared module
# =============
use strict;
sub trim($)
{
}
1;

Answer 1

If the module doesn't use package, you want do instead of require. See What is the difference between library files and modules?.
do "shared.pl" or die $#;
You really should create a proper module, one with a package statement.
package Shared;
use strict;
use warnings;
our #EXPORT = qw( trim );
use Exporter qw( import );
sub trim { ... }
1;
Name the file Shared.pm and load it using use Shared;.

Answer 2

By default, require will only load a file one time. In this case, that one time is from the file postgres.pm, in the postgres package. So the trim subroutine gets defined in the postgres namespace as &postgres::trim.
One workaround would be to use the fully qualified subroutine name in the testing.pl file:
postgres::trim("als"); # not trim("als")
Another workaround is to hack the %INC table (the variable that keeps track of what modules/files have already been use'd and require'd) so you can reload shared.pl into the main package:
use postgres;
delete $INC{"shared.pl"};
require "shared.pl";
A third workaround would be to export the trim function from the postgres package to the main package. The docs for the Exporter module are a good introduction to why and how this is done.
# in postgres.pm
*main::trim = *trim;
# or in testing.pl
*trim = *postgres::trim;
trim("als");