my $logger = sub {
    $log->message(@_);
}

# now you can call $logger like this:
$logger->('This is a logging message');
# or like that:
&$logger('This is a logging message');
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Don't know if that answers your question, though.

Update: on second reading I think your problem is a different one: you want to print $log. But what do you want the output to be? An object doesn't have a nice default string representation.

use strict;
use warnings;

package MyModule;

use overload q{""} => q{printObject};

sub new
{
...
}
...
sub printObject
{
    # print your attributes here
}

package main;

my $obj = MyModule->new(some => q{args});
...
print qq{$obj};
...
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I'm not sure either from your post whether this is what you want but here's hoping.

Cheers,

JohnGG

... print $log ; gives HASH(0x1e2ec5c)

It should print "Test_logger=HASH(0x1e2ec5c)", i.e. the stringified representation of an object reference would normally include the package name.  The fact that it doesn't, in your case, makes me think that maybe you forgot to bless the hash in the constructor?

Here's a simple example that should work the way (I think) you're expecting:

___ Test_logger.pm ___

package Test_logger;

sub new {
    my $pkg = shift;
    my $self = {
        logfile => "/tmp/test_logger.log",  # default
        @_   # merge in user-specified attributes
    };
    open my $fh, ">", $self->{logfile} or die "Cannot open logfile '$s
+elf->{logfile}': $!";
    $self->{logfh} = $fh;
    return bless $self, $pkg;
}

sub message {
    my $self = shift;
    my $msg  = shift;
    my $fh = $self->{logfh};
    print $fh "$msg\n";
}

1;
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___ main program ___

#!/usr/bin/perl

use strict;
use warnings;

use Test_logger;

sub test_addition {
    my $log = shift;
    $log->message("Inside the subroutine test_addition");
}

my $log = Test_logger->new( logfile => "my.log" );

$log->message("Start of program");

test_addition($log);
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Of course, you can similarly pass $log to any subroutine defined in other modules as well...