$ perl -MCSV -e'dcsv (in => "formula.csv")'
[
    [   'a',
        'b',
        'c'
        ],
    [   '1',
        '=2+3',
        '4'
        ],
    [   '6',
        '',
        '7',
        '=8+9',
        ''
        ]
    ]

$ perl -MCSV -e'dcsv (in => "formula.csv", formula => "none")'
[
    [   'a',
        'b',
        'c'
        ],
    [   '1',
        '=2+3',
        '4'
        ],
    [   '6',
        '',
        '7',
        '=8+9',
        ''
        ]
    ]

$ perl -MCSV -e'dcsv (in => "formula.csv", formula => "die")'
Formulas are forbidden

$ perl -MCSV -e'dcsv (in => "formula.csv", formula => "croak")'
Formulas are forbidden

$ perl -MCSV -e'dcsv (in => "formula.csv", formula => "diag")'
Field 2 in record 1 contains formula '=2+3'
Field 4 in record 2 contains formula '=8+9'
[
    [   'a',
        'b',
        'c'
        ],
    [   '1',
        '=2+3',
        '4'
        ],
    [   '6',
        '',
        '7',
        '=8+9',
        ''
        ]
    ]

$ perl -MCSV -e'dcsv (in => "formula.csv", formula => "empty")'
[
    [   'a',
        'b',
        'c'
        ],
    [   '1',
        '',
        '4'
        ],
    [   '6',
        '',
        '7',
        '',
        ''
        ]
    ]

$ perl -MCSV -e'dcsv (in => "formula.csv", formula => "undef")'
[
    [   'a',
        'b',
        'c'
        ],
    [   '1',
        undef,
        '4'
        ],
    [   '6',
        '',
        '7',
        undef,
        ''
        ]
    ]