perl/dir_handler.pl: Code is not tidy at line 1, column 1.  See page 33 of PBP.  (Severity: 1)
perl/system.pl: Code before warnings are enabled at line 10, column 1.  See page 431 of PBP.  (Severity: 4)
perl/ch1/hello: Backtick operator used at line 7, column 10.  Use IPC::Open3 instead.  (Severity: 3)
