$ echo 'print "Included a.pm\n";' > a.pm
$ perl -e 'require a' # Included a.pm

##</code><code>##

$ perl -e 'require a; require a' # Included a.pm
$ perl -e 'do "a.pm"; do "a.pm"' # Included a.pm\
                                 # Included a.pm