In Perl, how can I find out if my file is being used as a module or run as a script?

Question

Let's say I have a Perl file in which there are parts I need to run only when I'm called as a script. I remember reading sometime back about including those parts in a main() method and doing a

main() unless(<some condition which tests if I'm being used as a module>);

But I forgot what the condition was. Searching Google hasn't turned out anything fruitful. Can someone point out the right place to look for this?

Answer 1

If the file is invoked as a script, there will be no caller so you can use:

main() unless caller;

See brian d foy's explanation.

#!/usr/bin/perl

use strict;
use warnings;

main() unless caller;

sub main {
    my $obj = MyClass->new;
    $obj->hello;
}

package MyClass;

use strict;
use warnings;

sub new { bless {} => shift };

sub hello { print "Hello World\n" }

no warnings 'void';
"MyClass"

Output:

C:\Temp> perl MyClass.pm
Hello World

Using from another script:

C:\Temp\> cat mytest.pl
#!/usr/bin/perl

use strict;
use warnings;

use MyClass;

my $obj = MyClass->new;
$obj->hello;

Output:

C:\Temp> mytest.pl
Hello World