UT theoretical chemistry code forum

hello: I'm a new user from china, now I come across a problem. When I input the order chgsum.pl AECCAR0 AECCAR2 it say: chgsum.pl: command not found I chmod the chgsum.pl before input the order. I download the chgsum.pl script from this website. who can tell me why! thanks! PS:forgive my poor English.