>type script.pl
use M1 qw( );
sub test2 { M1::test3(); }
sub test1 { test2(); }
test1();

>type M1.pm
package M1;
use M2 qw( );
sub test4 { M2::test5(); }
sub test3 { test4(); }
1;

>type M2.pm
package M2;
use Carp qw( croak );
sub test5 { croak("ribbit"); }
1;

>perl script.pl
ribbit at M1.pm line 3

##</code><code>##

>perl -MCarp=verbose script.pl
ribbit at M2.pm line 3
        M2::test5() called at M1.pm line 3
        M1::test4() called at M1.pm line 4
        M1::test3() called at script.pl line 2
        main::test2() called at script.pl line 3
        main::test1() called at script.pl line 4