'Return value of "open" ignored at line 188, column 3.  Check the return value of "open" for success.  (Severity: 3)'
'Readline inside "for" loop at line 51, column 16.  See page 211 of PBP.  (Severity: 4)'
'Bareword file handle opened at line 120, column 2.  See pages 202,204 of PBP.  (Severity: 5)',
'Two-argument "open" used at line 120, column 2.  See page 207 of PBP.  (Severity: 5)',
'Two-argument "open" used at line 188, column 3.  See page 207 of PBP.  (Severity: 5)'